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ASME - Citrus Waste Pumped Peel Systems

March 12, 1998


It was five years ago at this conference that Carlos Odio presented a paper on pumped peel systems in Brazil. This was the first time many of us had heard of the concept.

The key advantages claimed were a reduced initial capital investment, along with reduced maintenance and horsepower requirements. These resulted from elimination of many screw conveyors and the peel bin.

I remember many doubts being expressed in discussions following the presentation. The principal concern was in regards to handling the week-end shutdown typical of many Florida processors. Also, the absence of a peel bin meant that juice extraction would have to stop whenever anything went wrong in the feedmill.

Today four of the twenty-five citrus feedmills in Florida use pumped peel. One of these was a greenfield installation that gained the advantage of reduced capital investment. The other three converted from a traditional reaction conveyor system. At least two of these three made the change because they were facing major maintenance and rebuilding costs in aged facilities.

The first two, at Florida Juice and Caulkins Indiantown, were installed by Gumaco using the system described in Odio's presentation. The third system, designed and constructed by Cook Machinery, demonstrated remarkable innovation and advancement in the technology. The latest, at Tropicana in Ft. Pierce, includes further evolution of the pumped peel concept.

Another key development in pumped peel technology came from Cutrale in Araraquara. A paper describing this was presented by Daniel Marques at the 1995 ASME conference.

At that conference I also presented a paper on feedmill technology. In it I mentioned that Dan Vincent's 1940 patent covering peel liming said that three to five minutes reaction time was required. Later in the paper I said that normal practice is to use eighteen minutes. I was aware of this contradiction, so you can imagine my surprise when Marques gave his paper: He said that only four minutes was required and he had a feedmill to prove it.

All four of the pumped peel feedmills in Florida now operate with the short reaction time that Marques described. In fact, Florida Juice and Caulkins Indiantown converted after extended periods of operating difficulties associated with excessive reaction time.

To illustrate the technical changes that have occurred, we would like to start with the flow chart in Figure I. This system calls for using recirculating press liquor and molasses as a pumping medium. The presence of this press liquor and molasses, in the ratio of two parts liquid to one part peel, was felt necessary in order to fluidize the peel sufficiently to be pumped.

Note the metal separator tank. This was a relatively large tank that served to mix the peel, lime, press liquor, and molasses. It had a sloped bottom so that tramp metal would not enter the pumps.

The pumps used were progressive cavity pumps. It is interesting to note that today all four Florida plants use progressive cavity pumps built by either Geremia or Netzsch, the two manufacturers referred to in Odio's paper.

The reaction tank was exceptionally large, assuring a reaction time in excess of forty minutes. (The Florida Juice tank was sized for over 60 minutes!) The design called for the peel to be pumped into the bottom of the tank, overflowing from the top. This required operating with a full tank at all times, even during periods when peel flow to the feedmill was reduced.

A major departure from this system was described in Marques' paper. Since only four minutes of reaction time were required, the reaction could be completed in the pipeline running from the metal separator tank to the dewatering screens. This meant that a reaction tank was no longer required. Marques mentioned that the existing Cutrale reaction tank had been converted into a lime silo.

Note that the system requires separation of the pumping medium (press liquor and molasses) from the peel, ahead of the screw presses. The typical Brazilian system used static screens, although some preferred rotating drum screens or shaker tables. A key item is that the pumping medium, already containing d-limonene, flows into the hammermill.

Let us now take a look at the Cook system (Figure II). This design was installed at the new SunPure feedmill in Avon Park. It was also installed by FMC, under technical license from Cook, at the Parmalat feedmill in Sicily.

One very important change was that only non-recirculating molasses, with absolutely no press liquor, was used as a pumping medium. Also, despite the fact that citrus molasses is more viscous than press liquor, the ratio of molasses to peel was reduced to 1:1.

One fact about the use of molasses instead of press liquor is that improved oil recovery is made possible. This is because press liquor contains all of the d-limonene oil that is recovered in the feedmill. If recirculating liquor is used to pump the peel, there is opportunity for the oil that is present to be absorbed into the albedo of the peel. It is agreed that once oil is absorbed by albedo, it stays there; the action in the screw presses does not remove this oil.

The consequence is that oil absorbed by the albedo goes with the press cake into the peel dryer. Not only is this oil lost, but it is likely to be released, with the exhaust gasses, to the atmosphere. Thus the oil becomes a Volatile Organic Compound (VOC), a focus of the Clean Air Act.

No one disputes this theory. However there are many who do dispute the quantity of oil lost by pumping with recirculating liquor. Comparing oil recovery rates would seem to be the logical way to resolve the question. Unfortunately, conditions at feedmills vary so much that no clear answer has emerged.

There is another subtle, but important reason for pumping with molasses instead of press liquor. Molasses is warm because it comes from the Waste Heat Evaporator (WHE), while press liquor is at ambient temperature, the same as the oranges. As a result, a system pumping with molasses is noticeably warmer than one using press liquor. This difference can amount to 10º C, which does not sound like much.

However, increasing the temperature of a chemical mixture by 10º C cuts in half the time required for a reaction to occur. This is true in the case of the reaction between hydrated lime and citrus peel. Consequently a much faster and more complete reaction occurs, everything else being equal, in a system pumping with warm molasses.

The Cook system had a great many innovations, and, as can be expected with such a system, there were problems to be resolved during start up. One of these led to a change in the design of the mixing tank. It was found that the original tank at SunPure had warm spots and cold spots. These were traced to peel accumulating in the poorly agitated corners of the tank. This peel spoiled and eventually would break loose and get pumped into the screw presses. Screw presses do not operate well with old peel.

A replacement mixing tank was developed by SunPure personnel, and the fabricator, Keller Sales and Engineering, made significant contributions to the final design. (Figure III) Note that the dead spots were eliminated by going to a conical bottom. Internal baffling assured violent agitation, and a clever suction design keeps tramp metal out of the pumps.

There is an interesting detail applicable to any peel processing system. The metal separator used in the Cook plants is the simplest and most effective available. Figure IV shows this device, which is arranged so that molasses is added to the peel by pumping it into the bottom of a small tank through which the peel must pass. The peel enters at the top at one end and exits at the other. Since the molasses is flowing upward, the peel is fluidized as it passes through. The result is that heavy tramp material, including stainless steel, glass, rocks and sand, separates and falls to the bottom of the tank.

Devices similar to this have been installed, with great success, at Orange-co and Cargill Frostproof. Both of these plants have traditional reaction conveyor systems (not pumped peel) where molasses was added either ahead of the shredders or directly into the reaction conveyor. A simple piping change with the addition of a drop-out box has reduced damage to the shredder screens and screw presses at these plants.

Initially the two Cook pumped peel plants (SunPure and Parmalat) used rotary positive displacement pumps. There is a lesson in industrial marketing in what came about. At Parmalat the Italian OMAC pumps have worked fine and are likely to be used in future installations. However at SunPure there were repeated rotor failures. Not only was the pump manufacturer unable to help the situation, but high prices were charged for replacement parts. As a result the pumps were discarded after the first season and replaced with proven Brazilian progressive cavity pumps.

The Cook system uses a different reaction tank design. The peel is pumped into the side of the tank and drawn off at the bottom. This means that an extra set of pumps is required, as compared to the Brazilian system. However it also means that the tank can be operated at any desired level, which translates into any desired reaction time.

Operating at a low level in the reaction tank was found to be advantageous. Florida systems operating with full reaction tanks all had difficulty with screw press operation. After long periods of frustration, the operators at Florida Juice and Caulkins Indiantown traced the difficulty to fermentation that was occurring in the tanks. This seems to occur if there is excessive reaction time, even with good agitation. The result is that today these two plants entirely by-pass their reaction tanks; SunPure operates with a minimal 20% level.

At SunPure, the system was sized for 2,500 boxes per hour (significantly higher throughput can be achieved). At the 2,500 rating there is six minutes reaction time in the pipeline from the hammermill to the feedmill. Additional reaction time is available in the mixing tank and in the reaction tank.

The reaction tank does have an important function at SunPure. Even though the peel goes straight from extraction to the feedmill, without any delay in a peel bin, there are still periods of upsets. When these upsets occur the peel can instantly become un-pressable. At SunPure this condition is overcome by filling the reaction tank until a suitable, pressable, mixture is achieved. Thus the reaction tank is better described as a surge tank.

It is noteworthy that at SunPure there is a provision to add lime solution directly to the reaction/surge tank. This feature is useful when insufficiently limed peel reaches the feedmill.

The point needs to made that pumped peel systems are very sensitive. You will recall that our original worries were about weekly start-ups and having to shut down extraction if problems occurred in the feedmill. It is fair to say that it is the sensitivity to change that has caused far more problems to operators than the problems we anticipated.

By sensitive we mean that the presses stop working and operations become near impossible. There are many normal upsets that cause immediate problems in the pumped peel systems: a slug of CIP water, a load of cull fruit, trash water in the molasses, peel over a few hours old on a hot day, a jump in molasses pH, a skip in the limer. All of these lead to wet peel going into the dryer, which has resulted in multiple cases of smoldering peel in the dryer.

Returning to the SunPure system, another innovation is evident in how the peel and pumping medium are separated ahead of the screw presses. Instead of open screening devices, Cook chose to use closed pre-presses. These machines have limited compressive characteristics, so they perform a "soft" press on the peel. These have proven noticeably more effective than screens in separating free liquid from the peel. As a result, the screw presses that follow give better performance.

One feature of the SunPure system is the use of spent caustic as a replacement for lime. In the 1950's, working at Citrus World, R. W. Kilburn showed that spent caustic could be substituted, up to 50%, for lime. In oversimplified chemistry, in order to prepare peel so that it can be pressed it is necessary to break down the pectins and to raise the pH: the spent caustic will raise the pH, while it takes lime to break down the pectin. Cook chose to take advantage of this, using 10% to 20% caustic in the lime slurry. Lime and spent caustic are mixed, in batches, and then pumped to the hammermill.

One advantage of this is that, since less lime is used, there is less lime going to the Waste Heat Evaporator with the press liquor. As a result the formation of calcium citrate is reduced and the WHE works more efficiently for longer periods.

One aspect of this technology is difficulty of control. In a reaction conveyor system the addition of lime to the peel is set by matching the speed of the limer screw to the speed of the peel bin take-out screw. The operators adjust this system by measuring pH. In a pumped peel system it is more difficult to match the lime flow to the peel flow since the peel flow is not evident to the feedmill operators. Thus the operators are all the more dependent on pH as a means of controlling lime addition. Unfortunately, pH meters tend to be unreliable, leaving the operator uncertain about how much lime is required at any given moment.

One concern frequently voiced about pumped peel systems is that, since there is no peel bin, extraction will have to be shut down if something goes wrong in the feedmill. In fact, some of the Brazilian and most of the Florida pumped peel plants do have peel bins. The more practical solution is seen at SunPure where there is no peel bin as such. Instead as a first alternative they have provision to divert peel to a dump pad. From there the peel (both their own and peel from other processors that they run on occasion) can be put back into the feedmill flow with a front end loader. Their second alternative is to divert the peel to a small loading silo from which it can be trucked off-site. This system has worked well.

There are other innovations at the SunPure feedmill unrelated to pumped peel. The principal one is found in the WHE which is a five stage, three effect evaporator with advanced technology in the oil stripping area. This 80 WHE is matched to a 40 dryer which has resulted in excellent thermal efficiency.

Figure V shows the system that went into operation at Tropicana Ft. Pierce last year. It can be described as a progression in pumped peel technology. It is characterized by gross simplification: the mixing tank is designed to provide surge capacity; the reaction tank is eliminated; and the pre-presses or dewatering screens are also eliminated.

A key to this simple system is pumping with a low ratio of liquid to peel. At Tropicana only one part molasses is added to three parts peel. To our surprise, the progressive cavity pump handles this thick mixture with no evident difficulty.

Flow through the pipeline is mostly laminar; there is little turbulence. Therefore the mixing of the lime with the peel must be thorough and complete before the peel enters the pump. At Tropicana the dry lime is added at the peel bin take-out screw. Molasses is added shortly afterwards, ahead of the hammermills. At times the mixing tank is operated at such a low level that very little mixing occurs in the tank. We were surprised that this relatively limited and simple mixing of peel and lime has proven quite adequate for achieving a proper reaction.

Operating with the peel from 3,000 boxes per hour, there is about one minute reaction time between the limer and the hammer mill. Six minutes are available if the mixing tank is full. Finally, there is one minute reaction time in the pipeline.

The mixing tank design is worthy of note. The Keller units at SunPure and Tropicana feature vertical internal baffles that work in conjunction with three tiers of center-mounted rotating paddles. Dead spots are minimal. The suction pipe requires the fluid to make a U-turn, assuring that tramp metal is effectively separated in the bottom, ahead of the pumps.

The original Tropicana system included the Vincent pre- presses shown in Figure VI. These were hard-piped directly from the peel pump. This means that the peel, from the time it enters the pump, is totally enclosed, completely preventing the emission of any VOC's.

As the ratio of molasses to peel was reduced, it was found that the pre-presses were not necessary. The main presses alone were found capable of removing the pumped fluid as well as doing their normal job of pressing the peel. The pre-presses were removed; the system as it is today is shown in Figure VII. Note that the peel is hard-piped to the presses.

It was found necessary to protect the hard-piped system from over-pressure. This has been achieved by the addition of a pressure relief valve, shown in Figure VIII.

Under steady full-load conditions, there are few problems controlling either traditional or pumped peel systems. However with pumped peel systems operators need to be more alert and learn new tricks to handle upsets and start-ups.

The upsets have been previously enumerated: a slug of CIP water, a load of cull fruit, trash water in the molasses, peel over a few hours old on a hot day, a drop in molasses pH, a skip in the limer.

In a traditional system these present a minor inconvenience for several reasons. There is usually the opportunity to mix some fresh peel from the peel bin with the bad peel. Peel flow is easily controllable by changing the speed of the peel bin take-out screw. Reacted peel color is readily observed. Lime flow is readily adjusted, sometimes by dumping bags directly into the reaction conveyor.

These are not characteristics of a pumped peel system. As a rule, the operator can observe only pH, Brix and the discharge cake from his peel presses. Thus the operator must learn to spot what is causing the upset and know what to do about it. His choices are largely limited to adjusting the lime flow and slowing his pumps so as to fill a surge tank. Filling the surge tank allows both mixing of new material with the material causing the problem as well as slowing the input to the presses.

One change to pumped peel systems that has been proposed is the addition of a weigh belt. A weigh belt would provide the operator with an indication of the tonnage of peel entering the system. This would be helpful in situations where extractor lines are started or stopped. It would give the operator knowledge of where his limer control should be set.

Originally there were serious concerns about start-up operations. Plants that shut down each weekend face a Monday start-up with water, sour press liquor, or cold molasses. However, many plants, both in Brazil and Florida, routinely get through their "Monday bad hair day." It takes careful attention by the operators, and efficiency is less than optimal, but the difficulties have proven readily surmountable.

Despite the difficulties of start-up and control, there are strong reasons favoring the pumped peel system. The simplicity of the Tropicana system has obvious advantages of reduced maintenance, space requirement, and capital investment.

This same simplicity has important implications from the standpoint of VOC control. In a pumped peel system the peel is fully enclosed and captured from the inlet to the hammer mill all of the way through the screw presses. This eliminates a host of potential VOC emission points; the equation is simplified.

Older traditional feedmills experience a great deal of maintenance. This is reflected both in operating costs and, more importantly, downtime. Screw conveyors, and especially the reaction conveyor, are notorious for failing and interrupting feedmill operations. It is not uncommon for these situations to cause a halt in juice extraction operations. Because of this condition it becomes financially attractive to convert an older system to the pumped peel technology.

Nevertheless we should note that the presses, dryer, WHE, pellet mill, and pellet loading remain unchanged in a pumped peel feedmill. Consequently it cannot be said that fewer maintenance personnel and operators are characteristic of pumped peel feedmills.

The technical progress in Florida, in pumped peel systems, has come as much from the citrus processing community as it has from the equipment suppliers. The early adaptors were the CEO's of their organizations: Ron Grigsby at Florida Juice and Roger Beret at Caulkins Indiantown. It is notable that both men were relative newcomers at the time the key decisions were made. It was their decisions that encouraged other processors to install pumped peel systems.

At SunPure it was Hadi Lashkajani who made the choice to go with the many innovations offered by Cook Machinery. Vice President Donald Dawson and Feedmill Manager Mac Greene stand out for having spent the innumerable hours required to make the system the success it is today.

Dave Van Etten, Plant Manager, had the vision that resulted in the Tropicana system. He heard Marques' presentation, went to Araraquara to see it, and came back convinced it offered many advantages in his plant. He is quick to give credit to Chris Sutherland, Instrumentation Manager, who had the understanding of what it would take to make it work on a day-to-day basis.

To summarize the technical progression that has occurred over the last five years: The Cutrale work with short reaction time allowed improvements at Florida Juice and Caulkins Indiantown, while it led into the innovation at SunPure and Tropicana. Ralph Cook first introduced concepts that will be fundamental for years to come: the avoidance of recirculating pumping fluid; bottom discharge reaction tanks; spent caustic as a lime substitute; using pre-presses instead of dewatering screens. At Tropicana the key new features are pumping with a limited amount of molasses, eliminating the reaction tank, and hard-piping to the presses. It remains to be seen what the next system will be like.

A forecast of the future should take into consideration other technical innovations in feedmilling technology. Items of note include:

Work directed by Benedito Jorge at Citrosuco has led to the development of a single pre-press that will handle the pumped peel coming from fifty FMC extractors.

Vincent pre-presses have been added to the pumped peel systems at both Florida Juice and Caulkins Indiantown. These have improved the performance of the main presses at both plants.

At Cutrale's Leesburg feedmill, the use of twin screw superchargers, with overlapping flights, has led to improvements in press performance. This has important implications in double pressing operations. See Figure IX.

The Fiber Filter, shown in Figure X, is being developed to clean-up of press liquor. This will allow WHE's and pumps to operate with higher Brix molasses than was previously possible in many plants. This results in reduced WHE fouling and improved thermal efficiency.

The use of twin circuits in the WHE, to produce higher Brix molasses for second pressing, is likely to result in significant improvements in overall thermal efficiency. One Brazilian plant is using this principle with solid results.

Some Brazilian processors have found that eucalyptus stands are more effective for disposing of wastewater than orange groves. This can impact the demands made on the WHE.

The bagged peel system, described at the most recent Citrus Short Course, eliminates the feedmill dryer altogether. Air pollution regulations in California have led to the adoption of this bagging process. Either VOC regulations or the low price of pelleted citrus peel could bring it about in Florida.

Dreyfus in Winter Garden has now begun feedmill operations using a unique Vincent screw press. Their new press features a screw design originally developed for alcohol extraction in soybean plants. In addition, the press makes use of profile bar screens, as opposed to the standard 3/32" perforated screen material. Its performance on limed orange peel is being tested.

 Presented by Robert B. Johnston, P.E.

ASME - Screw Presses In Citrus Feedmills

View PDF of ASME Screw Presses in Citrus Feedmills

Citrus Feedmill Thermal Efficiency


Daily Load = 100,000 Boxes in 22 Hours = 4,550 boxes per hour
4,550 x 44 #/peel per box = 200,000 #/peel per hour
200,000# Peel x 82% peel moisture = 36,000# Bone Dry Solids
Which produces 40,000 #/hr of Feed @ 10% Moisture

Press Cake
% Moisture
Press Cake Dryer
Therms Waste Heat
75 216,000# 156,000# 1,754 84,000#
74 207,692# 147,692# 1,660 92,308#
73 200,000# 140,000# 1,573 100,000#
72 192,857# 132,857# 1,494 107,143#
71 186,206# 126,206# 1,418 113,794#
70 180,000# 120,000# 1,349 120,000#
69 174,193# 114,193# 1,284 125,807#
68 168,750# 108,750# 1,222 131,250#
67 163,636# 103,636# 1,165 136,364#
66 158,823# 98,823# 1,110 141,177#
65 154,285# 94,285# 1,060 145,715#
64 105,000# 90,000# 1,011 150,000#
63 145,945# 85,945# 966 154,055#
62 142,105# 82,105# 923 157,895#
61 138,461# 78,461# 882 161,539#
60 135,000# 75,000# 843 165,000#

Rotary Dryer: 1,500 BTU Required Per Pound of Water Evaporated
One Therm: 100,000 BTU
Bunker C: 145,000 BTU/Gallon
Oil House Water Not Included:
  • Brown: Assume one pound per box

  • FMC: Assume four pounds per box


Citrus Feedmills 101

October 4, 2005
Issue #165

Last month Vincent Corporation gave a presentation at the Citrus Short Course (now called the International Citrus & Beverage Conference). Entitled "Citrus Feedmills 101", the presentation reviewed the efficiencies and economics of various feedmill concepts. The important points were as follows:

1. Feedmill efficiency is measured by the therms of energy required to produce a ton of citrus animal feed. This was presented as the gallons of fuel oil required per ton of pellets. It was seen that a very efficient feedmill requires 29 gallons of fuel oil per ton of feed.

2. With the selling price of pellets being around $55 a ton, delivered to the port of Tampa, it is evident that feedmill operators face a serious cost problem. Thus variations of the California Feedmill #4 option, which does not use a dryer, are of particular interest.

3. The "dryer" ceases to be a dryer once a waste heat evaporator (WHE) is installed. Instead, it is a generator of nearly saturated, high wet bulb temperature, gasses. This point is overlooked by dryer companies, attempting to enter the market, without familiarity with the fundamentals of citrus feedmills and the WHE technology.

4. It was shown that the screw presses account for only 7% of the capital cost of a feedmill, and the dryer, 13%. The WHE accounts for 33% of the capital cost.

5. The WHE does wonders for feedmill thermal efficiency because it works under a vacuum. This allows it to evaporate water with very low heat input. Furthermore, the WHE makes its own vacuum by condensing the moisture in the gasses.

6. The Vincent presentation included a statistical industry report. It showed that the typical feedmill has an overall energy consumption of about 600 BTU's per pound of water evaporated. This is contrasted to the typical stand-alone dryer, which requires at least double that much. (A British Thermal Unit (BTU) was defined as an energy unit, 1000 of which are required to evaporate a pound of water at sea level atmospheric pressure.)

7. It was shown that it is of little use to press citrus waste to where it has less than 63% moisture. There are presses available that can do this. However it is of little value because the resulting volume of press liquor will be beyond the capability of the WHE.

8. Material balances were presented, although they are upper classman, not freshman, technology. These are expressed in simple "in equals out" equations and the concept of Brix. Reiteration of simultaneous equations in a spreadsheet gives the material balance.




Citrus Installations

1992 VP-16-P11 FMC Food Machinery Italy SPA (Iran) Citrus Peel 92015
1992 VP-22-H35 Citrus Hill (Rebuild) Cargill Citro Pure Frostproof, FL - Cargill Citrus Peel 92170
1993 VP-22-P51 Orange-co Pasco Processing Bartow, FL Citrus Peel 93102
1993 VP-22-K12 Citrus World Florida's Natural Growers Lake Wales, FL Citrus Peel 93125
1993 VP-22-K51(2) Florida Juice Lakeland, FL Citrus Peel 93152
1994 VP-22-K51(2) Cook Machinery (SunPure) Cargill Citro Pure Avon Park, FL Citrus Peel 94145
1994 VP-22-K51(2) FMC Italy (Parmalat) Palermo, Italy Citrus Peel 94095
1995 VP-22-P-11(3) Cambuhy (Citrovita) Matao, SP, Brazil Citrus Peel 95001
1995 VP-22-K11(1) Tropicana Products Ft. Pierce, FL Citrus Peel 95079
1995 VP-22-K Citrus World Florida's Natural Growers Lake Wales, FL Citrus Peel 95202
1996 VP-22-K11(1) Tropicana Products Ft. Pierce, FL Citrus Peel 96042-B
1996 VP-16-K-21(5) FMC Italy (Parmalat) Palermo, Italy Citrus Peel 96200
1996 VP-22-K32(3) SunPure Avon Park, FL Citrus Peel 96042-A
1997 KP-16 Cargill Citro Pure Frostproof, FL - Cargill Emulsion 96196
1997 VP-22-K11(2) Bascitrus Agro Mirassol, SP, Brazil Citrus Peel 97002
1997 VP-22-K11(4) Cambuhy (Citrovita) Matao, SP, Brazil Citrus Peel 97009
1997 VP-16 Laconia Citrus Amyclae Sparti, Greece Citrus Peel 97103
1997 VP-22(2) Tropicana Products Ft. Pierce, FL Citrus Peel 97120
1997 VP-22(2) Cutrale Citrus Juices Leesburg, FL Citrus Peel 97160
1997 VP-22 Louis Dreyfus Citrus Winter Garden, FL (#97235) Citrus Peel 95134-B
1997 KP-16 Caulkins Indiantown Citrus Indiantown, FL Citrus Peel 97049-C
1997 KP-16 Florida Juice Partners Lakeland, FL Citrus Peel 97233-A
1998 VP-16 Del Oro Costa Rica Pineapple s/n 915131 98129
1998 FF-12 Pasco Processing Bartow, FL Press liquor 98168-A 98168-C
1999 FF-12 Texas Citrus Exchange Mission, Texas Citrus Peel 98297-B
1999 FF-12 SunPure Avon Park, FL Citrus Cloud 98168-B
1999 KP-16 FF-12 Citrus Belle LaBelle, FL Citrus Peel Press Liquor 99081-A
1999 KP-6 Tropicana Ft. Pierce, FL Sweco Tailings 99133-A
1999 VP-6 Tropicana Bradenton, FL Tech Center 83806
1999 VP-22 Citrofrut San Rafael, Vera Cruz Mexico Citrus Peel 99302
2000 FF-12 Christodoulou Bros. Greece Juice Finishing 98033-A
2000 KP-16 Mildura Fruit Juices Victoria, Australia Pulp Wash 99081-B
2000 KP-16(2) Caulkins Indiantown Citrus Indiantown, FL Citrus Peel 00049-A,B


Citrus KP-16

December 13, 2007

One of Vincent's more popular screw presses is the Model KP-16. Since its introduction in 1996, over one hundred have been built. Originally intended for applications with high freeness and capacity requirements, the presses have grown into high-torque machines being used in tough applications. At the same time, most of the economies of the original design have been retained.

The first prototype KP-16 was used at Cargill's Frostproof citrus feedmill. It was used in the first pressing position, removing the "easy" liquid from orange peel. The press worked so well that the downstream "hard squeeze" presses tripped out on overload! Shortly afterward, two KP-16's were installed at Tropicana Ft. Pierce for first pressing duty. The generation of press liquor increased so much that their Waste Heat Evaporator (WHE), which makes the press liquor into citrus molasses, was overwhelmed. In both cases, the KP-16's had to be removed from service.

Since that time Louis Dreyfus and Citrus Belle have installed KP-16's for first pressing in their citrus feedmills. The Louis Dreyfus project, in Indiantown, Florida, has worked especially well. The dewatering capacity of their KP-16's allowed a Stord press to be removed from service, saving 250 hp.

The original prototype at Cargill was put into service dewatering pulp wash. This material is quite slippery. However the press was successful in removing pulp, thus reducing the load on downstream finishers. The finishers have finer screens, and they remove fiber from press liquor.

In recent years Vincent has quoted a number of citrus feedmill projects. We have recommended that Series KP presses be used for first pressing because of their economical construction and high capacity. At the same time, the traditional VP, or newer TSP, presses are recommended for second pressing.

With the season which has just started, a new citrus application is being developed. KP-16's have been installed in Florida for dewatering core wash. Two versions of the press are being used, and both are operating in full-time service. Changes made include adding notches to the screw to improve screen wiping characteristics. The rotating cone feature has increased capacity and reduced channeling. Also, wider screen slots have proven advantageous, although this allows more pulp into the press liquor. (Downstream finishers remove this pulp.)

Issue 194

Citrus Molasses

November 19, 1998

In the states of Florida and Sao Paulo in Brazil all citrus juice extraction plants have citrus peel feedmills that produce citrus molasses. This molasses is made from the press liquor that results from pressing orange peel. The molasses is produced in waste heat evaporators (WHE) that are driven (heated) by the exhaust gasses from the cake dryers. Typically the molasses are concentrated into the range of 40º to 50º Brix and they are either sold to a distillery or re- combined with the peel. If the molasses are to be stored for more than a few days, they are concentrated to 72º Brix as fermentation will not readily occur at this high a sugar content.

Many smaller citrus processors in other countries process their peel into animal feed without producing citrus molasses. The technology they use is to either (a) simply dry the peel from its natural 80% moisture to 12% in a rotary drum dryer, or (b) press the peel from 80% to about 72% moisture and then put the cake into the dryer.

Those processors who simply dry their fresh peel find themselves at an economic disadvantage because it takes a great deal of energy to evaporate all of the moisture. Using a WHE, larger firms will use as little as one third as much energy to produce a ton of citrus pellets.

Those processors who use a press in front of the dryer fare better. Pressing from 80% to 72% moisture separates over half of the water from the peel. (It also results in the loss of almost one third of total solids because of the dissolved sugars that are carried away with the press liquor.)

However, the processors using a screw press face a serious environmental problem. Most of these, in Greece and Panama for example, send the press liquor to the sewer. The high sugar content of the press liquor (10º to 12º Bx) puts a high load on the wastewater treatment system. Odor and pollution complaints result in government pressures.

Acquisition of a WHE is out of the question for most small processors. Typically the WHE is the single largest capital item in a citrus processing plant. Furthermore, the dryers existing at many small processors are not suitable for generating the high wet bulb temperature gasses necessary for the proper operation of a WHE.

An interesting alternative exists for these small processors. Instead of a WHE, they can use a steam evaporator to produce molasses from their press liquor. A vertical tube evaporator, using falling film heat transfer, represents less capital investment yet it can be very effective in making citrus molasses. For example, the steam ratio is approximately 5:1 for a six effect evaporator. This means that for every pound of steam used to drive the evaporator, five pounds of water are evaporated from the press liquor.

The citrus molasses produced can be used as cattle feed or sold to a distillery. As a cattle feed, the molasses can be supplied to the farm in a liquid form. It is more common to add the molasses back onto the peel. The solids are diffused into the moisture in the peel, and the moisture is ultimately evaporated in either the dryer or the evaporator.

Distilleries buy molasses in order to ferment it in the production of citrus alcohol.

An important by-product is d-limonene, an oil that comes from the citrus peel. This oil is recovered in the evaporator. d-Limonene adds to the revenue stream used to justify the acquisition of an evaporator.

Issue 86

Citrus Oils


September 12, 2015

Although unknown to most people, citrus oils are a significant industry to themselves. Historically, Vincent screw presses in citrus feedmills have been a key component in the recovery of d-limonene. That is the "lemon oil" (actually it comes from oranges) everyone has smelled in industrial hand cleaners. It is a valuable by-product produced in the WHE (waste heat evaporator) which is used in large feedmills to produce citrus molasses.

Our screw presses have found application in Mexican lime and lemon processing plants. These facilities squeeze fresh fruit or peel, without the use of hydrated lime, to separate an emulsion-like flow from the peel. This emulsion contains citrus oil which can be separated in a calandria (still). Forty years ago Vincent designed and sold calandrias. Today JBT offers a stand-alone, skid-mounted READYGo™ d-LIMONENE system to recover d-limonene from oil-rich emulsions generated in the citrus extraction process.

The Cook Machinery Company of Dunedin, Florida has pioneered and led in the development of d-limonene and citrus essence oil recovery for many decades. JBT has been a key partner in their activities. Brown International is another key player in the industry.

Major processors of citrus oils include Firmenich and Givaudan. The Coca Cola Company purchases over half of all the lemon oil produced worldwide.
An overview of citrus oils follows.

Higher quality oil is more valuable as it contains more flavor and fragrance components. Usually this oil is not heat treated and has minimal contact with the fruit and water. Globally, high quality oil is purchased by flavor and perfumer houses for further refinement. Lower quality oil is less valuable and usually sold on the secondary market.
There are several of different types of commercially produced citrus oil:

The first type is cold pressed oil, or peel oil. This oil is extracted, without heat, from citrus peel. Oil is expressed from the peel and captured in water. Usually either Brown or JBT (FMC) extractors are used to express the oil from the fruit, although other types of extractors can be used. The resulting oil and water emulsion is sent to a series of centrifuges to separate the oil and water. GEA Westfalia and Alfa Laval are usually the OEMs for this equipment.

Oil produced this way is eventually fractionated into flavor components and d-limonene, using a complex distillation column. The phase separation process is described as folding oils. The flavor fraction is the more valuable component, and usually it is between five percent of the oil for some types of non-Valencia oranges up to 45% to 55% of the oil for limes. The balance of cold pressed oil is d-limonene. D-limonene is less valuable, but it has several uses including as a solvent and as an ingredient in cleaners.

The next type is essence oil. This oil is entrained in juice extracted and finished by juice extractors and finishers. Again, JBT (FMC) and Brown are the main providers of the extraction equipment, although some smaller companies also provide machines. Essence oil is captured by essence units installed on juice evaporators. These essence units also recover a water phase essence. Both oil phase and water phase essences contain flavor components. Oil phase essence can be particularly valuable to flavor and fragrance companies. Water phase essence can also be used in flavor applications, but this phase is more unstable and can degrade rapidly.

An essence-type oil archaically known as Wheeler oil is recovered from juice after juice extraction and finishing. This oil is also called juice oil. Centrifuges are used to separate this oil from the juice. No heat is used. This type of oil is not commonly produced because there is not a lot of it, mass-fraction wise. Wheeler oil is unique and has valuable flavor components due to the oil's extended contact with the juice.

A fourth type of oil is d-limonene, which is made in citrus feed mills or in distillation processes such as JBT’s READYGo d-LIMONENE unit. D-limonene is not really an oil, but a component of oil. This product is made when liquid pressed from citrus peel is concentrated in a WHE. The d-limonene is stripped from the press liquor in the WHE. Any oil or water phase essence contained in the press liquor is flashed off in the evaporator and not recovered. D-limonene recovered in this traditional system requires a full-scale feed mill, including hammer mill, lime addition and reacting screw, screw presses, dryer, waste heat evaporator, and pellet mills.

Note that lime oils are a little different. Three types of oil can be produced from whole lime fruit crushed by a screw press. Both oil and juice are expressed from the press, and peel and membranes are expelled separately. Centrifuges are then used to separate Type A lime oil from this juice and oil slurry. No heat is used to produce Type A oil. Distilled lime oil is usually produced from the oil remaining in juice exiting the centrifuges, but juice and oil directly exiting the press can also be used. For distilled lime oil, processors use steam in a still, a condenser, and a separator. Type B lime oil is cold pressed oil, extracted and separated like other cold pressed citrus oils mentioned above.

Issue #276

Citrus Pectin


OCTOBER 15, 2015

Pectin is a food ingredient which has a great many food and commercial applications.  It gives firmness to products we consume on a daily basis:  jelly, yogurt, ice cream, gravy, salad dressing and many, many others.  Its characteristics include good palatability, and it blends without affecting the flavor of the base material.

Commercial markets include pharmaceutical gel caps, paints, toothpaste and shampoos,

Pectin can be made from apples and sugar beets, plus other minor crops.  However, most pectin comes from citrus peel.  The preferred peel is from limes (mostly Mexican and Persian), closely followed by lemons.  Citrus pectin comes 56% from lemons, 30% from limes, and 13% from orange peel.  Pectin sells for around $15 a kilo – there are many different grades.  55,000 tons a year are sold, plus more in other forms.  The market is up to a billion dollars per year.

The citrus peel from which pectin is extracted is purchased from citrus processors.  These are primarily in Argentina and Mexico, although it is also produced in Brazil, Peru, Spain, Italy, and even Bolivia.  After extracting the juice, these processors wash the peel to remove oil and dissolved sugars, dry it gently, and then bale it for transport to the facilities which produce the pectin.

The major pectin producers are CP Kelco, DuPont, Cargill, Yantai Andre Pectin, and Herbstreith & Fox.   CP Kelco has three plants, in Denmark, Germany, and Brazil.  DuPont has plants in Mexico and Europe.  Cargill's plants are in Germany, France, and, added very recently, Italy.  Andre Pectin has their plant in China, and Herbstreith and Fox operates in Germany.  This link gives a listing of these firms:

Pectin is extracted from the washed and dried citrus peel by first using acid to dissolve the pectin.  The spent peel is then removed, and the remaining solution is treated with alcohol.  The alcohol causes the pectin to precipitate.  The pectin thus formed is dried and sold in powder from.

There are three applications for Vincent's screw presses in the production of pectin.


After the acid treatment there is a residual product, spent pectin peel.  This waste material has some value as an animal feed.  The material is very hard to dewater, so it is sold with high moisture content.  CP Kelco has done the best marketing by assigning a trade name, Braspulpa, to their material.

Over the years Vincent has done development work in Sicily, seeking to dewater spent pectin peel in a screw press.  It was found that a dosing with hydrated lime and cellulose (ground wood) fiber allowed a significant amount of water to be removed.  Unfortunately, the water removed would have overloaded the wastewater treatment plant, so it became one more technical success but commercial failure.


The alcohol precipitation step involves alcohol washing.  This is done in a two stage counterflow wash, first with 60% alcohol and then 80% alcohol.  A screw press, vapor-tight of course, is used between the two wash stages.  This is a "soft squeeze" application.


Squeezing out the alcohol ahead of the pectin dryer is a "hard squeeze" application which requires a great more torque capability in the screw press. 

When presses are supplied for these applications in Europe, they are designed and built to meet the ATEX explosion-proof standards.  These are ATEX Certified presses.  In other countries, where certification is not required, a less expensive unit, meeting the same standards, is supplied.

Issue #277

Citrus Pectin Peel Preparation

One of the by-products of a citrus processing plant is known as "pectin peel".  Production of pectin peel involves washing the sugars and oils from the peel and then drying the peel at low temperature. The dried peel is shipped to companies which use an acid-alcohol precipitation process to extract the pectin.  The pectin produced in this manner is sold world-wide as a food ingredient.

This processing of pectin peel is an area of technical expertise of Vincent Corporation. For many years we designed the plants and manufactured the machinery that is required. Today we offer free technical assistance and only our applicable specialty machines, screw presses and shredders.

Pectin peel is generally made from lime or lemon peel, although it can also be made from grapefruit and orange peel.

The dried peel is sold to firms such as CP Kelco in Denmark and Brazil, Danisco in Mexico, Cargill in Germany, and ICHI (Pectine Industria) in Italy.  These firms, in turn, extract pectin from the peel, for sale as a food additive.

Pectin peel generally sells in the range of US$ 300 to $600 per short ton. [April, 2011:  It is now around $1,000 a ton!]  This can be compared to selling pelletized citrus peel, for animal feed, where the market is in the range of US$ 50 to $100 per ton (in the United States).

The process of producing pectin peel revolves around washing the peel in water so as to diffuse out the soluble sugars.  Normally about 3 kilos of fresh water are required to wash one kilo of peel.  In advanced systems, only 1.25 kilo of water is used per kilo of peel.

This contrasts to drying citrus waste to make animal feed, in which the first step is to react the peel with lime. Hydrated lime degrades the pectin, releases the bound juices, and thus permits efficient pressing and dehydrating. In contrast to this, the production of pectin peel must preserve the pectin; therefore it can not be limed.

As a consequence of the washing process, the peel is a lot more slippery and a lot more difficult to press (dehydrate).  Accordingly we de-rate the capacity of our screw presses by 50%, or more, in pectin peel applications.

Further, pectin peel must be dried very carefully at low temperatures and with carefully controlled humidity. The Vincent-design rotating drum drier was the norm for the industry; however, we withdrew from the dryer business in 2007.  That dryer permitted recirculating some of the partially dried peel and mixing it with the material coming from the screw press. The design was a triple pass dryer with a stationary outer shell, which contrasts to the single pass rotating drum dryer most commonly used in the production of animal feed.

Processing plants where Vincent, over 40 years, installed pectin operations include Ci Pro Sicilia and Cesap in Italy; Laconia, Paco Hellas, Nikopolis (ex-Esperis) and Greek Juice Processing in Greece; Citrex and San Miguel in Argentina; Quimica Hercules, Productos Esenciales, Industrial Citricola, and Industriales Limonera in Mexico; Jn-Jacques and Moscoso in Haiti; Priman Canning and Yahkin in Israel; Avante in Brazil; and Unipectin in Morocco.

Currently there are no processors producing pectin peel in the United States: Ventura Coastal and Sunkist in California and Parman Kendall in Florida have all discontinued their peel washing operations.  Environmental considerations, especially disposal of the sugar laden, used wash water, were driving factors.

Typically we look at peel coming from juice extraction in the range of four tons of peel per hour on the low side and sixteen on the high side. More recently flows of 26 MTPH have been of interest.

The following equipment is key to the process:

Vincent VS-180 Shredder. This machine slices the peel in order to permit proper washing and pressing without creating excessive fines. It is of the thin, rigid blade design, as contrasted to the hammer mill concept.

Pulp Wash Conveyors or Tanks. These are used for diffusing the sugar from the peel. We recommend either three or four counterflow wash stages, in either vertical or horizontal configuration.

Pulp Wash Sumps. Stainless steel sump tanks, possibly with progressive cavity peel transfer pumps.

Dewatering Between Stages. We recommend the use of either static screens or rotary drum screens for dewatering between wash stages.  Water usage is reduced by pressing the solids from these screens with Vincent Series KP "soft squeeze" presses,

Vincent Screw Press. Traditionally the Series VP presses have been used to remove moisture from the peel prior to further dehydration in the dryer.  Oversize, low speed KP presses are proving to be a more economical alternative.  The Series TSP Twin Screw presses have also proven successful.

The press is a horizontal, all stainless machine featuring an interrupted flight design. The unit is equipped with an air cushioned cone, complete with pneumatic controls.  Rotating cones are used on the single screw machines.

The pectin peel is made from the cake, which usually comes out in the range of 84% to 86% moisture, depending if we are talking about lemon peel, or Persian, Limon Mexicano, Tahitian, and Key limes.

Furnace. The dryer comes with its burner and refractory lined furnace for burning natural gas, light weight fuel oil, or a combination of these fuels. A very low gas temperature, in the neighborhood of 1200º F or less, must enter the dryer. A low wet bulb temperature is important in the production of high quality pectin peel, whereas a feedmill dryer must produce high wet bulb temperature in order to drive the Waste Heat Evaporator.

Dryer Feeder. This is a stainless steel screw conveyor and feeder with a companion flange matched to the dryer throat. It has a variable speed drive.

Dryer Drum.  A triple pass dehydration unit with a stationary outer drum works best.  The unit is equipped with recycle extractor conveyors so that partially dried material is extracted at the end of the second pass and mixed with the incoming press cake.  Also important is a 180º elbow between the furnace and the inlet to the drum.  The selection of this dryer must be made using the appropriate de-rating associated with (low temperature) pectin peel production.

Exhaust System. This separation system features a low level entry cyclone separator that has been proven in producing pectin peel. The expansion chamber is complete with an air lock screw conveyor product discharge.

Exhaust Fan. A radial blade fan complete with inlet elbow and exhaust stack.

Standard Instruments. A solid state programmable controller modulates combustion through a sensor mounted at the inlet to the third pass of the dryer. This is required for precise control of product quality.

Cooling Reel. The cooling reel uses ambient air for final drying.  It is complete with a fan, dust collector, ductwork, supports, and electric motors. This type of cooler is not used in modern feedmills because of the need for a pellet cooler (which is not used in pectin peel production).

Product Elevating Screw and Surge Hopper. A carbon steel conveyor and hopper, leading to the bagging or baling equipment, are used.

Sewing Head and Bagging Scale.  Most pectin peel is baled, so that a maximum amount can be loaded into a cargo container.  If bagging is used, a Fischbein sewing head and conveyor with a bagging scale are typically included.

Despite the length of this letter, there are a great many details that have been left out.  We would be glad to work with your specific requirements.

Robert B. Johnston, P.E.


PS  The purchasing contacts are as follows:

CP Kelco
Paul van Wagernen
Skensved, Denmark
011-45-56-165 616

Renato Rodriguez
Tecoman, Mexico
011-52-332-40940 or 42155

Bernard Cerles
Wayzata MN 55391  USA
Tel 1 952 742 0291

Raymund Asmussen
Neuenbuerg, Germany
Tel +49 7082 7913 400

Citrus Pressing

September 25, 1996

We recently sent out a newsletter, Four Kinds of Water, that helps explain why it is not possible to take potato waste down to 50% moisture in a screw press. The problem is that potato has a lot of water that is chemically bound to other molecules. The water cannot be released without the addition of heat, as occurs in a rotating drum dryer.

If a screw press could reduce the moisture content to a low number, then there would be no need for a dryer. Yet the opposite is true: dryers are more common than screw presses.

Citrus peel presents a good illustration. The peel starts out at 82% moisture, and it is taken down to 10% in making by- products. If the plant is making cattle feed, they first add caustic lime (calcined calcium carbonate) to the peel to break down the pectin molecules. With this procedure it is possible to press citrus peel to as low as 62% moisture. The rest of the moisture reduction is achieved by adding heat in the form of fuel burned in a dryer.

If we try to press to less than 62% moisture, the peel just extrudes through the screen in the form of frit. Potato behaves very similarly; it comes through the screen looking like mashed potatoes. It is not possible to separate the water from the solids with the mechanical action of a screw press.

Another citrus peel by-product is pectin peel. This is dry peel in which the pectins have not been broken down. It is not permissible to add lime to peel that is used in this process, so instead water is used to wash the sugars out of the raw peel. This drives up the moisture content from 82% to over 90% (after screening). Next the peel is run through a screw press, and the best we can do is get down to 86% moisture. Thus the pectin peel goes into the dryer at 86% after pressing, which is wetter than it started.

Processors would love to run the moisture down to 50% in their screw presses because it would save them a fortune on their fuel bills. But it just can not be done.

Issue 50

Citrus Waste Disposal

September 30, 1998

In was in the 1930's that citrus canneries first addressed the problem of disposing of waste. This waste consists mostly of peel, along with other elements such as seed, rag, core, pulp, and others. As early as 1931 Dan Vincent was operating a peel dryer in order to produce a feed for dairy cows.

The investment required for a modern citrus feedmill is in the millions of dollars. And, at today's low grain prices, it is a poor investment. As a result the citrus processors in small countries cannot justify erecting a feedmill.

At the same time environmental laws are coming into play that limit the options for disposing of citrus waste. Basically, there are the following alternatives to consider:

    • In Sicily, Spain, Mexico and California the small plants give the peel to nearby farmers for livestock feed. The animals eat it fresh, within a couple days. No energy is required. The peel must be eaten before it starts to ferment.
    • There are medium sized processors in Belize, Sicily and Mexico that have too much peel to give away, even for free. Their options are to either landspread or landfill the waste. This practice is being challenged on the basis of groundwater contamination.
    • Many medium sized processors in Mexico have gone one step further. They react the peel with lime and then dry it in rotating drum dryers. The dry peel is then sold either as bulk dry feed or it is pelleted. About 1,500 BTU per pound of water evaporated are required to evaporate the moisture in the peel, so the fuel cost is apt to exceed the value of the livestock feed produced.
    • In California some medium sized plants react the peel with lime and press it into press liquor and press cake. They concentrate the press liquor into citrus molasses (in steam evaporators) which is sold, either to distilleries or as a liquid animal feed. The press cake is sold as livestock feed which has a shelf life of a couple weeks. Some farmers store the peel press cake in gigantic plastic bags (10' diameter, up to 300' long) for extended storage. The only energy required is the steam for the molasses evaporator. This system is quite economic, but it is practical only in California where immense dairies and feedlots are located near citrus processors.
    • In Florida and Brazil the citrus feedmills all have waste heat evaporators (WHE) in use. These greatly improve the thermal efficiency of the feedmill by driving the evaporator with the flue gasses from the dryer. The process is to react the peel with lime and press the peel into press liquor and press cake. The press liquor is made into molasses in the WHE, and this molasses is added back to the peel, usually in the reaction conveyor. The press cake is dried in a rotary drum dryer and subsequently pelleted. The process requires about 500 BTU per pound of water evaporated.
    • The new option is to burn the peel as fuel. The heat value of the solids in the peel is excellent. The heat released by combustion is used to dry the peel and to generate steam. The steam can be run through a generator in order to supply more than enough electrical energy to run the entire citrus processing plant. In addition, the steam can be extracted from the turbine at 35 psi so as to supply the steam required by the juice evaporators.

Vincent Corporation gave a presentation at the recent 1998 Citrus Processing Short Course. This paper details the process of burning citrus waste in order to make the processing plant energy self-sufficient. A summary will be released in a future issue of Pressing News.

Issue 84

Double Pressing Basics

February 23, 1999
Rev. 2008

Many people assume that a second press is used because the first press fails to remove all the free moisture. This is not the case; presses are designed to remove almost all of the moisture that can be removed in a single pressing. However there are two applications where double pressing is technically sound.

In the production of juices for human consumption, double or even triple pressing is common. This is because the moisture in the press cake from first pressing contains many of the dissolved solids which are the essence of the juice. To capture these solids, water is added to the press cake. The dissolved solids in the cake diffuse into the water. The water is separated in the second pressing. This water carries with it the dissolved solids from the previous press cake. These are valuable solids which would otherwise be lost. Production of apples juice and coconut cream are two applications where double pressing is recommended.

The second application where double pressing is sound is in the production of animal feed from citrus waste.

In 1970 Dan Vincent was awarded a patent covering this double pressing concept. The system described pressing citrus waste in two consecutive presses, positioned in series. The idea was to reduce the moisture content of the press cake going into the peel dryer, thus reducing the amount of fuel required to dry the peel.

The key to this double pressing is to diffuse dissolved solids into the peel. This is done in a diffusion conveyor located between the first and second presses. High Brix (solids) molasses is added to the press cake from the first pressing. After a couple minutes of stirring in the diffusion conveyor, some of the solids in the molasses diffuse into the moisture in the press cake. Equilibrium is reached at a medium dissolved solids content, a point which is between the low Brix press cake and the high Brix molasses. When this cake is run through a second pressing, the cake resulting will have a higher Brix and, consequently, lower moisture content.

With a lower moisture content it takes less fuel energy to dry the cake into cattle feed. The result is a lower fuel cost per ton of pellets produced.

A material balance shows us how this works. We start with peel at 80% moisture and 10º Bx. In a 100# pound sample this is 20# total solids and 80# water. The 80# of water, at 10º Bx, has 8.9# of dissolved solids (mostly sugars). The rest of the solids, 11.1#, are suspended (insoluble) solids.

If we press this peel, the cake will still have 10º Bx. By diffusing 50º Bx molasses into the cake, the Brix will equalize at around 20º Bx. When this mass is run through the second pressing, the resultant cake will still have 20º Bx. In effect water in the first press cake has been displaced with dissolved solids from the molasses.

Some people argue against double pressing because "the second pressing only squeezes out the molasses added in the diffusion conveyor." This is not an accurate evaluation. Solids from the molasses will have been diffused into the peel. This is seen in the fact that the press liquor from the second pressing will have a lower Brix than the molasses that was added in the diffusion conveyor.

Copies of the 1970 patent are available upon request.



Issue 91

Fiber Filter I

July 21, 1998

Vincent Corporation is introducing an exciting new product, the Fiber Filter. Featuring fine filtration of low consistency, high gpm throughputs, the Fiber Filter is a unique machine. There is nothing quite like it available in the market. It operates continuously with a fabric filter that is vibrated clean by the process flow, requiring only occasional back-flush cycles.

Liquid flows with fiber contents ranging from 100 ppm to 4.0% are thickened to a range of 2% to 14% solids with the Fiber Filter. The filtrate liquid is remarkably free of suspended solids. The Fiber Filter can replace equipment ranging from pre-thickening screens to centrifuges. Fiber Filters can be used both to thicken flow ahead of a screw press and to remove fiber from press liquor.

Mechanically the Fiber Filter consists of a rotating paddle impeller that whirls and pulses the incoming fluid against the inside of a cylindrical filter screen. The filter screen, held taught in a frame, is made of woven polymer fabric. The fabric is available in meshes ranging from 600 (25 microns or .001") to 70 (200 microns or .008"). The angle of inclination of the machine is adjusted to optimize flow rate and solids concentration.

External Fabric Tensioning is an important innovation. The springs that hold the fabric sleeves tight are tensioned at the discharge of the machine. This allows adjustment of the fabric tension with the machine in operation, an important operator convenience. Also, it eliminates springs, turnbuckles and threaded rod from the inside. This is important where the application involves products for human consumption because the machine becomes much more sanitary. There is a patent pending on this feature.

To date, only the engineering prototype and a short production run of FF-12's have been produced. These units are being placed in the rental fleet so that they can be used for field testing. Our key target applications for testing are: press liquor in food processing plants, breweries, and citrus feedmills; whey in the cheese industry; residual fiber in wet corn milling ethanol plants; screen rejects, black liquor and clarifier underflow in the pulp and paper industry; press water in manure dewatering operations; and juices.

Rental units are available on a first come, first served basis. The machines are all-stainless.

Issue 80

Fiber Filter II

February 5, 1999

After a year of testing, Vincent Corporation has gained a great deal of confidence in the Fiber Filter. It is a unique filtering machine that has broader market application than our traditional screw presses, dryers, and shredders. Once the newness is overcome, it is easy to understand.

The best place to test a Fiber Filter is where a centrifuge is being used. If the Fiber Filter works, it is a sure sale because its total cost is less than the routine maintenance of a centrifuge. There are applications in both fruits and meats where the performance of the Fiber Filter beats that of a centrifuge.

Another ready market for Fiber Filter is where the flow to be filtered tends to blind existing static or rotary drum screens. These traditional screens are very economical to acquire and operate. However they have been put into many applications where they are only marginal performers. The Fiber Filter not only features non-blinding characteristics but it also offers finer filtration.

Here is how a Fiber Filter works. A flow containing suspended solids is pumped into a fabric sleeve. The sleeves offered have hole sizes ranging from 0.001 to 0.006", which is finer than is available in metal screens. Normally a fabric with holes this small would rapidly become blinded by the solids being filtered from the liquid stream. This problem is overcome in the Fiber Filter by vibrating the fabric at high frequency. The vibration is induced by (a) tensioning the filter sleeves with a pair of springs and (b) a high speed rotor inside the sleeve induces pulse waves in the fluid being filtered. These pulses of liquid make the filter sleeve vibrate.

The whirling rotor also has ribbon flights to push the solids toward the sludge discharge end of the machine. At the same time the pulsing forces filtered liquid through the fabric.

Applications which promise success include:

    • Cleaning press liquor from a screw press.
    • Filtering waste water ahead of a treatment plant at vegetable, meat and fish processors.
    • Concentrating a dilute flow of suspended solids so that the solids can be further dewatered in a screw press.
    • Filtering a flow ahead of an evaporator so as to reduce evaporator fouling and to improve heat transfer efficiency.
    • Removing water from spent grain at breweries, distilleries, and ethanol plants.
    • Finishing fruit juices.
    • Thickening good fiber by filtering out the ink, ash (clay) and water in a paper recycling operation.
    • Removing fiber from black liquor ahead of the evaporators in a virgin fiber paper mill.

Because of the newness of this technology, we do not expect a firm to buy a Fiber Filter without first testing it. For that purpose a rental fleet is available. The small FF-6 rents for $200/week; the FF-12 for $350. The customer must also pay the freight to and from the test site.

Issue 90

Fiber Filter for Pectin Recovery

July 26, 2005

An interesting application for the Fiber Filter has evolved over the last few years.  The project started as a rental at a plant whose wastewater treatment plant (WWTP) was causing excessive odor. 

The customer's operation involves receiving fresh lemon peel as a raw material, washing the dissolved solids (sugars) from the peel, and then extracting pectin from the washed peel.  The precipitated pectin is dried and sold, in powder form, as a food ingredient.

The WWTP load came principally from the dirty water from the peel washing system.  This water contains both dissolved solids and suspended particles of lemon peel.  The initial project involved using a Model FF-12, with coarse 190 micron sleeves, to filter this wastewater.

The project was a success.  Odor from the WWTP noticeably decreased after filtering out the suspended solids.  This is true even though most of the solids are dissolved, so they pass through the Fiber Filter.

At first, the solids sludge from the Fiber Filter were trucked to a remote site.  Soon, however, it was determined that this sludge contained valuable pectin of good quality.

For the next season, a second Fiber Filter was added, and the sludge from the machines was pumped back to the peel wash system.  In this manner the pectin was recovered.

Today, a third Fiber Filter has been added.  The system has been further refined by pumping the sludge from the three machines directly to the acid/alcohol plant.  There it is mixed with the washed peel, and the pectin is extracted.  (They found that if this sludge was added back to the washing system, the screw presses did not seem to work correctly.)

Issue 163


IFT - Burning Citrus Waste

The two processing plant examples used in the September 17 presentation both are based on using existing rotating drum peel dryers. For the greenfield site, there exists a better investment. Instead of installing a dryer, the use of a screw press in combination with a steam driven evaporator is recommended. This will allow a significant improvement in efficiency over the use of a dryer. 

With a steam driven evaporator, the press liquor from the screw press can be made into 72º Brix or greater molasses. Diffusing the solids of this molasses into the citrus waste will allow the screw press to produce press cake with a moisture content below 60%. Such press cake can be burned directly in the fluid bed combustor. Blending the press cake with drier material is not required.

In order to minimize capital investment, a four effect steam evaporator has been selected for the calculations in Exhibit V. This evaporator will evaporate approximately three pounds of water for every pound of steam that it uses.

Exhibit V shows that the citrus processor can be entirely energy self-sufficient. A small turbine with 35 psi exhaust steam will be adequate to generate all of the process steam and electricity that is required. There is enough excess steam that the possibility of using an absorption refrigeration system should be considered.

From the standpoint of capital investment, the use of an induction generator is recommended. This is less efficient than alternative equipment; however, it does not require electrical switchgear to synchronize the electric current that is generated.

Addendum II, September 2010

Alex Andreassen of Danisco has pointed out that  burning citrus pellets will lead to slagging of the boiler tubes because of the alkali-metals (Na, K) content of the peel.  Thus applications would be limited to using pellets as dryer fuel.


1998 Citrus Processing Short Course
Energy Self-sufficiency: Using Citrus Peel as Fuel 

September 14, 1998


A citrus processing plant can be energy self-sufficient. The energy value of citrus waste, when used as a fuel, is sufficient to operate a citrus juicing and concentrating plant. That is, when burned in a steam generator, the BTU value of the peel is sufficient to prepare the peel for burning and to generate the steam required for process needs. With the added efficiency of a waste heat evaporator, there may be enough steam to drive an electric generator to supply the electrical needs of the plant.

Escalation of energy costs following the Oil Embargo in 1973 gave rise to theoretical analysis. Was the value of citrus peel greater as an animal feed or as a fuel? A paper by Kesterson, Crandall, and Braddock published in 1979 compared dried citrus pulp with Bunker "c" fuel as a source of energy. It was concluded that the peel was more valuable as a livestock feed.

My personal interest in using peel as a fuel came as a result of looking for alternative uses for citrus waste. The GATT agreements of about four years ago dictate that the tariffs on animal feedstuffs, such as wheat, corn and soy bean meal, will be reduced over the coming years. Since there is no tariff on citrus pellets, the concern was that this would reduce the relative attractiveness of citrus pellets as a dairy feed in Europe. As the great majority of the citrus peel in both Florida and Brasil is pelleted and exported to Europe, the future of the citrus feedmill was being questioned.

The situation came to a head as a result of a dioxin problem in Brazilian pellets. Minute traces of dioxin were found in German and Dutch milk products in April 1998. This was traced to improper fuel oil additives that were burned in some Brazilian orange peel dryers. An embargo went into effect as the citrus processing season was starting. Since the source of the dioxin was not known with certainty, there was urgent interest in disposing of citrus peel by burning. (A directive for individual European nations to control compliance remains in force.)

In Brasil processors such as Citrosuco, Cargill, Cutrale, Dreyfus and Bascitrus have fluid bed combustors that are used for burning sugar cane bagasse. Consequently the option of burning citrus peel in this existing equipment was given serious consideration.

Citrus peel has fuel value because carbon, hydrogen and nitrogen are present in the dry solids. Peel will burn if dried sufficiently. The spontaneous combustion that occurs in citrus pellets and dried pulp give evidence to this fuel value. A quick analysis showed that the energy released is more than enough to dry wet (fresh) peel so that it can be burned.

It was in 1997 that I was introduced to the concept of an energy self-sufficient citrus plant. Gioacchino Sardisco of FMC do Brasil explained that he had studied the matter, with encouraging results. The data that he has supplied for the preparation of this paper have proved invaluable.

Analysis has shown that it is technically feasible to burn the peel generated by a citrus processing plant. The heat released by this combustion is sufficient to drive the existing feedmill dryers and waste heat evaporators (WHE). Additional heat released in burning the peel is sufficient to satisfy the steam needs of the TASTE evaporators of the processing plant. In fact there is enough additional steam generated that a steam turbine can be used to drive an electric generator. With the proper equipment the electricity generated will be more than enough to fill all of the needs of the citrus processing plant. With such equipment surplus "co-gen" electricity will be available for sale by the citrus processor.

The economic feasibility depends, most of all, on the relative value of dried citrus peel that can be sold as livestock feed, as compared to the cost of energy (fuel and electricity) purchased by the citrus processor. This comparison depends heavily on the relationship between the value of livestock feed and fuel in the country where the processor is located. Clearly the situations in Brasil, the United States, and a Central American country will present three quite different situations.

The capital cost will depend heavily on the existing investment. The cost to convert a US plant with an existing dryer and WHE will be more than required by a Brazilian plant that has these plus the fluid bed combustor with an attached boiler. However, a processor who has been landfilling the citrus waste (but can no longer do so for environmental reasons) faces an entirely different investment analysis.

The first step was to find the heat value of citrus peel. This was measured in laboratory studies that were part of Bob Braddock's 1979 paper. The heat of combustion of dried citrus pulp was found to be 7,470 +/-212 BTU per pound. This figure was very consistent with a variety of measurements made more recently in both Brasil and Florida.

A quick calculation is as follows:
A short ton of pellets typically has 200 pounds of moisture plus 1,800 pounds of dry solids. When burned the solids provide 7,470 x 1,800 = 13,400,000 BTU.

This can be compared to the high thermal value of Bunker "c" fuel oil, 154,000 BTU per US gallon. Based on 10% moisture in the pellets, there are 200 pounds of water which must be evaporated in the combustion process. Using typical citrus peel dryers, this will require about 1,350 BTU per pound of water evaporated, for a total of 200 x 1,350 = 270,000 BTU. Thus, burning a ton of dried peel will release 13,400,000 - 270,000 = 13,130,000 BTU. This is equivalent to about 85 US gallons of heavy fuel oil.

In therms, this is about 131 therms since there are 100,000 BTU's in a therm. The therm is a unit of measurement used in the calculations for this paper.

In the recent depressed market the value of either 85 gallons of fuel oil or 131 therms of natural gas approached what Florida citrus processors were getting for a ton of pellets. Thus, if a processor had the required combustion equipment, he could have been better off burning his peel than selling it as animal feed!

There is another quick analysis that sheds light on the subject. As many of you know, the Florida Citrus Processors Association in Winter Haven has compiled records for many years for their members. These typically show that an average of 50 to 60 therms per short ton are required to produce dried citrus peel (47 was the figure selected for calculations). This would be peel at approximately 10% moisture.

The 50 to 60 therms/ton figure is typical because in Florida both (a) feedmills dispose of (evaporate) large amounts of wastewater along with the peel and (b) most feedmills do not operate with a full 2:1 WHE/dryer ratio. On the other hand, some plants require less than 40 therms per ton. Calculations in Exhibit I show that 38 therms/ton is a realistic optimum figure for drying peel.

In any case, it is apparent that the energy released by burning a ton of dry peel, 131 therms, is considerably more than is required to dry the wet peel. Therefore a citrus processor will have ample peel-fuel to dry all of his wet peel. In fact, the processor will not want to burn all of his peel unless he has a boiler which will make use of the excess energy.

The steam generated by such a boiler can be used to drive the juice evaporators. Typically a citrus concentrate plant uses from 12 to 25 pounds of steam to process a 90 pound box of fruit. (Eighteen pounds were used in preparing this paper, further assuming that a box of oranges yields 45 pounds of peel with 22% solids, with 8 pounds of wastewater being added per box of fruit.)

Two mathematical analyses have been prepared. The first, in Exhibit II, is for a small 1,000 box per hour plant. It presumes no peel presses or WHE are available. The reacted peel is fed through the dryer to produce partially dried peel at 50% moisture. This peel is burned in a fluid bed combustor ahead of the boiler.

The second analysis, in Exhibit III, has calculations based on a plant that processes 15 million boxes in a season. It assumes there are existing dryers and WHE's which are used. About three quarters of the press cake is dried to 10% moisture in the dryer. The peel dried in this operation is mixed with the remaining quarter of the press cake that is not placed in the dryer. This combination makes a mixture of peel at 35% moisture, which is what is burned in the fluid bed combustor.

To summarize the figures in Exhibit III: The peel from 15 million boxes provides 3,846 therms per hour of energy. Of this 1,011 therms/hour will be required to dry the peel. This will leave enough heat energy to generate 181,098 pounds per hour of high pressure steam. This steam will be used to generate 16,787 KWH of electricity, well over the 7,280 KWH required to run the plant. 93,600 pounds/hour of the steam will be extracted from the turbine at 35 psi for use in the evaporators, while the rest, 87,498 pounds/hour, will go to a vacuum condenser.

Note that these calculations are based on running only three quarters of the peel through a dryer. The dried peel can be mixed with press cake (or fresh peel) so as to form a mixture with moisture in the range of 25% to 55%. This mixture is then burned in the fluid bed combustor. A material balance is shown in Exhibit IV that supports Exhibit III.

In both examples the flue gasses from the boiler are directed through the dryer so as to assist in drying the peel. Since a WHE operates on high wet bulb temperature gas, and boiler exhaust is normally low wet bulb, close attention to the design is important.

In the small plant shown in Exhibit II with no WHE, all of the energy available in the peel is used to dry the peel and to generate process steam. Excess steam will not be available to generate electricity. If the plant needs to generate its own electricity, supplemental fuel will be required in the fluid bed combustor.

The efficiency arising from the WHE in the larger plant allows use of an electric generator driven by a steam turbine. The turbine is arranged so that both the high pressure injector steam and low pressure process steam are drawn off for use in the evaporators. The rest of the steam would go to a vacuum condenser.

The calculations in Exhibit II and III are very detailed. This was done so that they can be used to calculate alternative scenarios. Besides fitting data to suit a specific processor, the underlying assumptions must be carefully reviewed by fluid bed combustor and boiler experts.

Checking with processors, we have seen examples in which 25,000,000 to 40,000,000 KWH are required to run an equivalent 15 million box plant for a season. The product (FCOJ or NFC) will have a major impact on electricity consumption. Clearly the figures presented herein are only a starting point, not a blueprint.

Burning citrus waste will reduce operating costs. The processing plant will save the money spent on oil or gas. If a WHE is available, additional savings will come from the money spent on electricity. It is even possible to realize incremental revenue from selling electricity. The normal revenue from the sale of citrus pellets (but not all the d- limonene) would be lost, partially offsetting these gains.

What investment is required? It can be examined in steps. As we have seen, a peel reaction system and dryer will be required, while peel presses and a WHE are not necessarily required. The minimum requirement is a fluid bed combustion chamber in which to burn the peel. This alone will reduce the purchased fuel required to operate the dryer. The second step would be to acquire a boiler suitable for use with the fluid bed combustion chamber. This would save the fuel being purchased to run the existing boilers at the citrus plant.

The third step is to acquire the steam turbine, electric generator, and switchgear required to generate steam with the excess peel. This would greatly reduce the electric bill at the citrus plant, plus it can result in revenue from the sale of surplus electricity.

Here is the rough order of magnitude of the investment in an 18,000,000 box per year facility: Two existing 60,000 pound per hour dryers, matched with two existing 100,000 pound per hour WHE's, represent an equipment cost of about $ 6,000,000. The site work, construction, buildings, utilities and auxiliary equipment (presses, pellet mills, conveyors) probably double this figure to $12,000,000. The addition of a Fluid Bed Combustor, with a 200,000 pound per hour boiler and a 20 megawatt turbine/generator set could be in the range of $20,000,000 to $40,000,000.

The small 1,000 box per hour plant would probably be in the range of $2,000,000 to $5,000,000 depending on options on electricity generation.

Clearly the electricity generating business is more capital intensive than what citrus processors are used to. There is so much capital in an electricity generating plant that it must be run year round. This will require alternative fuels during the off-season. In all likelihood, the business would be financed and operated by a co-gen partnership rather than the citrus processing company.

Burning peel at 10% moisture is very easy. It can be burned clean, with a minimum requirement for excess air, in many kinds of combustion equipment. The soot (ash and unburned fuel in the exhaust gases) will be minimal. However, to burn peel at 50% moisture is more challenging. A fluid bed combustor will be required.

At this point I would like to describe the fluidized bed combustion system. I am deeply indebted to Energy Products of Idaho for this part of my presentation. This company specializes in designing and installing fluidized bed energy systems. They have sold systems in California that have operated with citrus peel in the fuel mixture.

The arrangement they use is called a bubbling fluidized sand bed combustor. The chamber in which the peel is burned can be either rectangular or circular. There is a two foot deep bed of sand on the floor through which the air of combustion enters. The sand and fuel remain suspended in mid-air (fluidized) during operation. The chamber is usually refractory lined, although with some fuels the walls consist of boiler tubes.

With most fuels the burning occurs at 1800º F or less. This is the key to minimizing emissions. A principal emission concern is NOx (nitrogen oxides) which form at higher temperatures. Since citrus peel has 2% nitrogen, this is definitely a design consideration. EPI uses the non- catalytic system for controlling NOx. In severe cases ammonia, at the proper temperature, is added as an abatement agent.

Citrus peel contains around 8% ash, which is greater than the 2% common to sugar cane bagasse. At the same time this is less than the 50% ash that is typical of certain paper mill sludges. In this perspective, the ash in citrus peel becomes manageable.

Ash, in the form of slag, becomes a problem if it comes in contact with hot surfaces. It sticks to hot surfaces, so screening tubes may be used ahead of the boiler superheater. These tubes cool the slag so that it falls into the ash hopper before it has a chance to foul the superheater. In some applications limestone is added because it raises the melting temperature of the ash, reducing the sticky nature of the material. (Limestone also captures sulphur, another contaminant.)

Dioxins and furans are another emission worthy of note. They are grouped with other products of incomplete combustion (PIC's) such as VOC's and carbon monoxide. Chlorines give rise to dioxin when incomplete combustion occurs. This occurs when the concentration of carbon monoxide is in excess of 100 ppm.

When burning organic waste on a grate it is not uncommon to find carbon monoxide concentrations in excess of 1,000 ppm. In contrast, the concentration of carbon monoxide in a fluid bed combustor will rarely exceed 50 ppm. Consequently, prevention of the formation of dioxins and furans is possible with fluid bed combustion technology.

The action in the fluid bed combustor is such that auxiliary fuel is not required. That is, peel conveyed or blown in at 50% moisture will dry out and burn without additional heat being supplied by oil or gas burners. However, if additional steam is required, auxiliary fuel can be burned.

The fluid bed combustors being referred to are about 50' high. Generally they are 20' wide. The length varies according to capacity. The 18,000,000 box per year plant will have a unit about 45' long. The footprint, including the boiler and generator, will be about 30' by 150'.

The fluid bed combustor usually is refractory lined because this helps assure uniform operation despite swings in inbound fuel characteristics. The refractory radiates heat to the peel so as to help evaporate the moisture in the peel. It is noteworthy that some of the sugar cane bagasse burners in Brasil do not use such refractory.

There is one consideration that has a significant effect on overall thermal efficiency. In the process of burning citrus peel all of the moisture must be evaporated. Evaporating this moisture in a fluid bed combustion chamber takes about 1250 BTU per pound of water. On the other hand, the combination of a screw press, dryer and WHE is considerably more efficient: they require only 500 BTU per pound of water evaporation. Thus plants that have existing WHE capacity should use this to its maximum capacity. The practical result is that the peel admitted to the fluid bed combustor will have a lower moisture content and, therefore, will be easier to burn.

The manner in which this works is that the dry peel from the dryer is combined with wet peel (presumably press cake from the peel presses). Some Brazilians have reported the practicality of blending press cake at 67% moisture with some dried peel at 10% to produce a 50% to 55% fuel. (Citrus peel will support combustion with moisture contents as high as 70%.)

The d-limonene in the press cake peel adds fuel value to the peel. It is interesting to note that it causes flashing in the furnace.

One important question arises: How does this relate to the Clean Air Act? Most citrus peel dryer operators in Florida are addressing serious VOC problems. It is thought that evaporation of d-limonene from the press cake in the dryer is a major contributor to the VOC's being measured. The following scenario should be considered: The oil in the peel going into the fluid bed combustor will be burned and thus cause no VOC problems. Conversely, the oil evaporated in the dryer is a source of VOC's. Therefore, to minimize VOC's, it could prove advantageous to dry a minimum fraction of the peel and burn as wet a mixture as practical in the fluid bed combustor.

This analysis assumes that the citrus molasses, which is part of the dried animal feed, is burned. That is, the molasses is either put on the peel going into the dryer or burned directly in the fluid bed combustor. Note that molasses at 50º Brix (50% moisture) has more fuel value than press cake which typically is 62% to 70% moisture.

An interesting alternative would be to sell the citrus molasses separately. This could be of interest to a citrus processor who needs to dispose of all of the peel but does not have a boiler to go with a fluid bed combustor.

This discussion confirms Sardisco's point: a citrus processing factory can be energy self-sufficient if the peel is burned.

Environmental problems are challenging, but manageable. Even the stringent regulations of the United States can be met.

The future depends on two major forces outside the control of the citrus industry: (1) Where will the market for citrus pellets stabilize in light of dioxin scares and the GATT elimination of the tariff umbrella enjoyed by citrus pellets? (2) Will the declining price of fossil fuels reverse course and go into an upward trend?

In closing let me reiterate that the figures presented here must not be taken as gospel. They are theoretical figures, and they must be modified according to the practicalities of actually burning peel as well as the characteristics of each processing plant.

References and Acknowledgments

  • The Heat of Combustion of Dried Citrus Pulp, Journal of Food Process Engineering 3 (1979) 1-5, by J. W. Kesterson, P. G. Crandall, and R. J. Braddock.
  • Sugar Cane Bagasse: An Alternate Fuel in the Brazilian Citrus Industry, Food Technology, May 1988, by Jose Luiz Guerra and Elizabeth Steiger.

Invaluable and important assistance in the preparation of this report was given by:

  • Ralph Cook of Cook Machinery, Dunedin, Florida (727-796-1367)
  • Kent Pope of Energy Products of Idaho, Coeur d'Alene, Idaho (208-765-1611)
  • Gioacchino Sardisco, FMC FoodTech, Araraquara, Brasil, (011- 55-16-232-1300)



Biomass Burning System

January 3, 2012

Vincent Corporation has extensive experience with dewatering spent coffee.  With spent coffee the press cake comes out at around 58% moisture content, depending on the extraction process used.

Most soluble coffee producers burn their spent coffee because of its high BTU content.  Historically, either grate furnaces or fluidized bed boilers have been used.

A much less costly, but equally efficient, method of burning spent coffee is common practice in Colombia.  They take the press cake from our screw presses and dry it down to 10% moisture content in a rotary drum dryer.  This material can be burned in a conventional boiler, without the cost and complexity of a fluidized bed unit.  In fact, the boiler is relatively inexpensive because it is deliberately undersized.  Being undersized, the chimney gasses come out quite hot.  Rather than put these flue gasses out the stack, they duct them to the drum dryer.  In this manner the flue gasses are used to dry the press cake down to a  required 10% moisture content.  At this low moisture, the cake burns in suspension, like pulverized coal or natural gas.  There is no auxiliary fuel required in the boiler (except for start-up).  There is no burner or furnace on the dryer, either. 

The boiler is an unusual design.  The furnace is a conventional water tube construction.  However, at the top exit of the boiler there is a fire tube section for pre-heating the feedwater coming into the boiler.  This seems an odd combination, but it must work since the Colmaquinas, Hurst and Cerrey boiler companies all offer it.

The chart showing this system is attached.

This same combustion system would work equally well in burning a variety of biomass by-products.

Burning Spent Coffee


Issue 241

IFT - Citrus Shredder Performance

August 3, 1996, Presented by Robert B. Johnston, P.E.

The aim of this study was to find some generalizations in regards to citrus oil in feedmill press cake. It was hoped that both useful guidelines could be developed and focus areas for further study could be identified. Peel samples were taken at sixteen different Florida citrus feedmills late in May 1996. These samples were quick snapshots, taken randomly at the time our engineers arrived at the processing plant. 

No definitive conclusions should be drawn because of the limited nature of the sample taking. While this study points out several interesting conditions, its purpose is to encourage further research.

An observation that gave initial impetus to this paper was made at the Cargill feedmill in Frostproof in January 1995. It happened when separate samples of press liquor were taken from the inlet hopper screen, main screen, and discharge cone screen of their horizontal screw press. It was noted that as the peel progressed through the press, both the pH and Brix of the liquor became progressively lower. This hinted that, as the peel was progressively squeezed, more cells were broken open and, possibly, more oil was being expelled with the press liquor. This is illustrated graphically in Exhibit I which compares mason jars of press liquor taken from the main screen and discharge cone of a press. In the end we concluded that a condition such as this is indicative of incomplete reaction between the peel and the lime.

It is uncertain which of the samples are representative of typical operation at each of the sixteen feedmills. There was room for error: upset conditions may have been occurring, especially because it was the end of the season and some plants were winding down; at least one plant was running sour peel; two plants were having press problems; molasses tank levels were not necessarily at equilibrium; some plants were running grapefruit along with their Valencias; etc. Rather than arbitrarily exclude data, we have attempted to present the full range of possible operating conditions.

The following are the tests that were conducted (Exhibit II):

  1. Oil content of the peel at the peel bin.
  2. Particle size distribution of the peel exiting the shredder.
  3. Particle size distribution of press cake leaving the screw press.
  4. Moisture content of press cake leaving the screw press (final pressing in plants with double pressing).
  5. Oil content of press cake leaving the screw press.
  6. Oil content of the press liquor.
  7. Brix of the press liquor and, where applicable, molasses.

The peel and press liquor samples were kept refrigerated from the time they were gathered until the tests were conducted.

Moisture tests were run with two different moisture balances as well as with a laboratory oven and scale. Several tests were run on each sample to verify the results; we feel that the readings presented herein are fair for analysis purposes. These readings are key because they were used to determine the proportion of press cake and press liquor, as a percentage of inbound peel.

Material Balances were found necessary to determine the proportion figures. These were run for each of the sixteen plants, taking into account single pressing, double pressing or pumped peel. It was during this step that something very interesting in regards to molasses diffusion was observed.

Almost half of the plants were running with press liquor Brix of 20º or higher. Despite many hours of computer time it was impossible to fit this high a Brix into a reasonable material balance for most of the plants. It possibly could be achieved by drawing down the molasses tank (using more molasses than was being produced), but this was not logically occurring at so many feedmills. Finally it was recognized that the most reasonable explanation for high press liquor Brix is incomplete diffusion of molasses into the peel.

This theory tied to the oft-repeated question, "Why add molasses in a delay conveyor between first and second pressing if it is just going to be pressed out again?" Our conclusion is that this is definitely what is taking place at many feedmills. Many years ago Dan Vincent did testing at Lykes Pasco that showed that it takes ten to twenty minutes for complete diffusion between peel and molasses. Yet most feedmills have only one to three minutes of delay between first and second pressing, thus explaining our data.

We feel that even a short diffusion period is better than none. Diffusing molasses into peel that is about to be pressed does improve the pressing action and ultimate thermal efficiency of a feedmill. We are anxious to see the results in the 1996-97 season at Southern Gardens: there a reaction conveyor has been relegated into service as a delay conveyor between first and second pressing. The size of the conveyor should allow around eight minutes for diffusion of the molasses. It will be interesting to see the extent to which pressing action is enhanced.

The press cake moisture readings of the samples taken for this presentation almost all read quite a bit higher than was expected for late season Valencias. We feel that this can be related to the fact that the Brix readings of peel coming from extraction were unusually low: our readings were almost all in the range of 7º to 9º, whereas normal readings are 10º to 11º Brix.

Oil analyses were made using the Scott method.

Peel samples were taken from four different models of shredders. The two most common were the Rietz RD-18 Disintegrator manufactured by Hosokawa Bepex and the 18" horizontal shredder manufactured by the former Gulf Machinery Company. Both models are 75 hp machines.

The other two brands are relatively new to Florida citrus: the Jacobson and Gumaco (Brazil) hammermills. These are larger machines, ranging from 150 to 300 hp. Exhibit III has photos of these various machines.

All four shredders can be operated with a variety of screen sizes. In fact, some were being operated with no discharge screens, and, being the end of the season, some were being operated with damaged screens and worn hammers.

An interesting technique was used to measure the particle size distribution of the shredded peel. The required equipment was loaned to us by CSC Scientific of Fairfax, Virginia. Their laboratory air lift dryer was used to gently dry the peel before vibrating it through a stack of sieves.

Samples from the shredder frequently were quite wet with molasses, and they took 25 minutes to dry. In contrast, samples of press cake dried out in 15 minutes. Appendix I shows and describes the apparatus that was used.

The photos in Exhibit IV show some typical peel samples before and after they were air dried and sieved. In the tests, sieve screen sizes ranging from 9.5 mm down to 0.212 mm were used. The photos illustrate the separations that were achieved.

The bar charts in Exhibit V illustrate the particle size distribution by weight. In general, one of two distributions was found: ether a bell shaped curve or a curve skewered to the larger sized particles. It is interesting to note that the same shredder will produce different particle profiles depending on the type of juice extractor that is used.

The results in the bar charts are in remarkably close agreement with measurements published by Dr. Bob Braddock in 1978 (slide).

Our preconception was that the best shredding resulted in (a) a minimum of fines and (b) a minimum of large pieces. The fines are undesirable because they are likely to either burn in the dryer or to be carried into the waste heat evaporator (WHE) where they result in problematic black water. At the same time the large pieces were thought to be undesirable because they seemed apt to contain oil that is not expressed from the peel in the pressing operation. (This proved to be not necessarily true.)

The reason that fines are likely to burn in the dryer is explained by the concept of latent heat of evaporation. As long as a particle of peel in the dryer contains moisture, it is cooled by evaporation and will not go much above 212º F. A small particle has much more surface area in proportion to its volume; evaporation is proportional to the surface area, so small particles become bone dry before the larger particles. Once bone dry, the particle increases in temperature until a point is reached where combustion occurs.

Fines leaving the dryer are very low in moisture, and some of these escape past the cyclone dust separators. Such particles either go to the WHE or they are recirculated back to the burner area. Being dry to start with, they are likely to burn upon being re-admitted to the hottest portion of the dryer.

In the study it was found that the percentage by weight of fine particles in the peel (the two smaller sieve sizes) varied significantly. The range was 1/2% to 6% fines in samples of peel coming from the shredder. If these are lost in the dryer, they can have a measurable effect in peel recovery (as measured by pounds of citrus pellets produced per box of fruit).

The percentage of fines could not be tied to any particular style of shredder or hammermill. As one would expect, the peel from FMC extractors did average somewhat more fines than that of Brown extractors, but this was not enough to explain the range of values that was measured. Possibly the disposition of extraction pulp would explain the differences we observed. I wish I could say more, but more study will be required to explain the wide range in the percentage of fines.

The percentage of fines did increase during the reaction and pressing operations. This increase of about 2-1/2 percentage points is shown in Exhibit VI.

The increase in the amount of fines was compared between the vertical and horizontal presses. They averaged virtually the same increase, right at 2-1/2 percentage points. Furthermore, the fines could not be tied to the moisture content (tightness of pressing) of the press cake from these presses.

It is noteworthy that in 1949 Dan Vincent was awarded US Patent 2,490,564 covering a "Vegetable Pulp Shredder Screen Having Cutter Blades". This patent dealt with using thin 1/16" blades to both reduce fines and improve the peel reaction. These machines were used in citrus for many years, and they gave good results compared to units with 1/2" and wider hammers. However, the design ultimately proved impractical due to its vulnerability to tramp metal.

We did not measure oil recovery in this study. Clearly the oil recovery systems used in both the juice extraction operation and in the WHE will govern oil recovery. Instead, we looked at the oil (mostly d-limonene) carried into the drier with the press cake. This oil is almost entirely evaporated in the dryer and released to the atmosphere. It exhausts as an unburned hydrocarbon.

Seeking a correlation between large pieces of peel and the oil going into the dryer with the press cake proved interesting. To begin with there are two key measurements: (1) the pounds of oil going into the dryer per ton of peel entering the feedmill, and (2) the percentage of oil going into the dryer relative to the quantity of oil in the peel entering the feedmill.

Note that the raw measurement of percent oil in the press cake is only part of the equation. A tricky part of the analysis is to recognize that the percentage of oil in the press cake must be adjusted for the pounds of press cake per one hundred pounds of peel. Because of this, a feedmill that presses very tight will have a little less oil going into the dryer. This is true even though the percentage of oil in the press cake may be higher than what is found in more moist press cake.

In general, as expected, the plants running Brown extractors had a higher proportion of large pieces of peel after the shredding operation than did those plants with FMC extractors. We were interested to see if the presence of large pieces of peel led either to increased oil in the press cake or to higher press cake moisture. Therefore a comparison was made separating samples from the extractor manufacturers. Each of these two groups were further split so that comparison could be made between shredders that were producing predominantly large pieces of peel and those that had a lesser proportion of large pieces.

The results were surprising, as shown in Exhibit VII. The pressing operation was definitely able to achieve dryer press cake when there were fewer large pieces of peel. The average was about 2-1/2 percentage points lower moisture content.

On the other hand, the pounds of oil in the press cake per ton of inbound peel went down only slightly. In the spreadsheet it is seen that generally the presses that pressed tighter had only a little less oil in the press cake than the pressing operations characterized by high press cake moisture.

In other words, shredding to reduce the fraction of large pieces of peel will reduce press cake moisture (and therefore improve thermal efficiency). However, the quantity of oil going into the dryer does not change appreciably.

Looking at it from another perspective, contrary to our expectations, we cannot say that press cake oil was significantly higher in samples that had a higher percentage of large pieces. Thus the data supports the postulate that fine shredding allows oil to be absorbed into the albedo, and that this oil does not press out of the peel.

The oil analysis brought attention to another condition. On the average, there was a noticeably higher oil content in peel from plants using Brown extractors as compared to FMC extractors. On an approximate basis, raw Brown peel had 1.0% oil, while FMC had 0.5%. The surprising thing is that about one third of the oil in the Brown peel was measured going into the dryer, as compared to two thirds of the oil in the FMC peel. The end result is that almost equal pounds of oil per one hundred pounds of peel were found in the press cake, regardless of which juice extraction system is employed!

Unfortunately our study of shredding and press cake had to ignore some very important considerations. Brown plants that made more use of the BOE (Brown Oil Extractor) did better than those that did not. Similarly, the FMC oil recovery system employed undoubtedly governed the results of the FMC plants. Other important factors which could have distorted our analysis are (1) the sufficiency of the peel reaction system and (2) the oil stripping characteristics of the WHE.

Before concluding this presentation I want to make mention of the new feedmill at SunPure. This processor takes pride in the high level of citrus oil recovery that they achieve. The day that we took the first samples there was an upset that led to a second set of samples being gathered.

Both sets showed a high level of oil recovery. In fact, the inclusion of the SunPure results are enough to distort the averages shown in Exhibit VII.

The minimal amount of oil going to the dryer at SunPure is helped by the fact that they are able to press the peel to the same low level of moisture content as the best feedmills in the State. However, we suspect that the outstanding low levels of press cake oil can be tied to the Cook Machinery Company technology used in the feedmill. This technology involves a combination of (1) improvements on the Brazilian pumped peel flow schematics, (2) using available heat to accelerate the peel reaction, and (3) WHE technology.

Recently a number of modifications have been made at the SunPure feedmill, so we are anxious to measure performance once again in the 1996-1997 season.


To summarize this presentation, let's look at citrus oil recovery in a broader sense. Clearly the two most important considerations are the oil recovery systems used (1) at extraction and (2) in the WHE. This paper has not examined either of these. Rather, we have focused narrowly on the shredding and pressing operations. It should be obvious that differences in extraction and WHE systems may have distorted our analysis.

At the same time some interesting points can be made:

  • A decline of press liquor pH between the inlet and outlet of the screw press is indicative of under-reacted peel.
  • High Brix press liquor is frequently an indication of incomplete diffusion of molasses into the peel.
  • Plants with Brown juice extraction systems will tend to have a higher proportion of larger pieces in their shredded peel. They should be sure their shredding equipment is doing a good job in order to achieve the best thermal efficiency.
  • There can be a significant fraction of peel fines going into the dryer, more so at plants using the FMC juice extraction system. Therefore dryer dust separation equipment is of importance.
  • Shredding the large pieces of peel into smaller pieces does not significantly improve oil recovery in the feedmill. However, it does improve pressing action and, consequently, thermal efficiency.

Let me conclude by warning against blindly accepting the results of this study. Our intent has not been to give the final word, but rather to point the way and to encourage additional and more thorough investigation.

This paper could not have been prepared without the assistance of a great many individuals and their firms. We want to extend our appreciation to the following:

    • CSC Scientific Company, 8315 Lee Highway, Fairfax, Virginia. Telephone 1-800-458-2558. The loan of their Test Sieves, High Performance Compact Shaker, and Fluid Bed Dryer proved invaluable.
    • Automatic Machinery and Electronics, Inc., 333 Avenue M, N.W., Winter Haven, Florida. Telephone 941-299-2111. Their laboratory took on the task of running oil content analysis on almost eighty samples of peel and liquor.
  • Lala Produce Inc., 1402 25th Street, Tampa, Florida, 33605. The generous use of their cold storage facilities was most helpful in controlling close to one thousand pounds of peel samples. 

    Participating Citrus Processors
    • Alcoma Packing Company
    • Cargill Citro America Inc.
    • Citrus World, Inc.
    • Coca-Cola Foods, Auburndale
    • Coca-Cola Foods, Leesburg
    • Florida Juice Partners, Ltd.
    • Golden Gem Growers Inc.
    • Holly Hill Fruit Products
    • Indian River Foods Inc.
    • Orange-co of Florida Inc.
    • Peace River Citrus Products
    • Silver Springs Citrus Co-op.
    • Southern Gardens
    • SunPure, Ltd.
    • Tropicana Products, Inc., Bradenton
    • Tropicana Products, Inc., Ft. Pierce

    Technical Review

    • Dr. Robert J. Braddock, University of Florida, Lake Alfred
    • Messrs. John and Ralph Cook, Cook Machinery Company, Dunedin
    • Mr. Don Kimball, retired, Coca-Cola Foods, Winter Haven
    • Dr. Ashley Vincent, Savant-Vincent, Tampa



Material Balance

January 14, 2006                                                                                                                                                                                                  ISSUE #169

A material balance is a set of equations that express the flows of materials. The mathematics is all based on the simple premise that what comes in must equal what comes out. Variables are easily changed in order to gauge the impact on a system. Material balance is key to analyzing, and understanding, the flow of material in a processing plant. 

The concept of Brix is vital in a material balance done for fruit and vegetable processing facilities. Brix is much like a percentage, denoting the amount of sugar dissolved in water. It is measured in degrees, using an instrument called a refractometer. The equation for Brix is as follows: Bx = (Ds x 100)/(Ds + w), where Ds is the weight of dissolved solids and w is weight of water.

Note that suspended (or, insoluble) solids, which are almost always present, do not enter into the equation.

The beauty of Brix is that it holds constant as a flow of material is divided. That is, if a flow at 7° Bx is pumped into a screw press, the press liquor will have 7° Bx. Furthermore, if a drop of water is squeezed from the press cake, then it, too, will measure 7° Bx.

For example, if orange peel with 11° Bx and 9% suspended solids is fed into a screw press, both the press liquor and press cake will measure 11° Bx. (Naturally, the amount of suspended solids will be higher in the press cake than in the press liquor.)

Another important characteristic of dissolved sugar is that if flows of different Brix are mixed, diffusion occurs until a balance is achieved. Thus, if a pound of 50° Bx citrus molasses is added to two pounds of orange peel with 80 percent moisture and 11° Bx, the result will be three pounds of material with a moisture content of 70% and 25° Bx. When this material is pressed, the cake moisture content will be significantly lower than if the straight orange peel were pressed. This is simply because of the greater dissolved solids content in the water contained in the press cake.

Vincent has available a large number of material balances. These reflect single and double pressing, counter-flow diffusion, recirculation of press liquor, addition of oil house water, and many other options. These are transmitted by e-mail, in Excel.

The Excel spreadsheets contain a large number of simultaneous equations. Thus, Excel must be set on "reiterate" in order to find the common mathematical solution. Excel will freeze up if an illogical number is entered in error, so work must be saved frequently. In the event that a spreadsheet freezes, it must be closed without saving it.



Moisture Content

August 1, 2000

Everyone knows that screw presses can be used to reduce the moisture content of a material. Less appreciated are the limits that exist. Each material has a natural limit below which the moisture content cannot be reduced in a screw press.

These limits vary widely. For example, lumber sawdust can be pressed down to almost 50% moisture; fresh green alfalfa will go to 72%, while tomatos can be reduced to only 86%. These limits arise from the chemistry of the water in the material.

A screw press will remove the free and interstitial water in an organic material. However there are two forms of water that cannot be separated by mechanical force: (1) the water that is electrically attached by hydrogen bonding and (2) the hydrated water that is chemically bound to the molecules of the solids.

To remove these two forms of water the chemistry must be changed. In the case of citrus peel, this is achieved by adding lime, which reacts with the peel.

Most commonly the chemistry is changed with heat. Heating press cake through a dryer will reduce the moisture content right down to zero. In some cases, the heat is added in the form of steam: a steam dryer will do the same thing.

As recently as 1970 steam was added in Vincent screw presses used for pressing both citrus peel and fish. This was done by injecting the steam through holes drilled in the resistor teeth. About once a year we sell a press with provision for steam or water injection through the resistor teeth.

Some competitors direct steam through a hollow screw shaft. FKC and Dupps offer the heated shaft feature for paper mill sludges. It is not an energy efficient way to dewater sludge; but, the few points of moisture content reduction achieved can be sufficient to meet regulatory demands.

Some screw presses are designed to apply a great deal of friction to a material. The heat generated is sufficient to cook the moisture out of the cake. Low cake moisture is obtained; however, the electrical energy requirement is great. Stord uses this technique in pressing citrus waste.

Issue 108

New Citrus Feedmills

March 21, 2011

Two greenfield citrus feedmills have recently been commissioned in the Valencia area of eastern Spain.  Both turnkey projects were designed and constructed by FOMESA AGROINDUSTRIAL, a firm long based in Valencia.

ZUVAMESA with a 50 WHE was €8M, while CITROTECNO was €12M, each plus 18% VAT. The CITROTECNO feedmill with a 40 WHE was €7-7-1/2M; the rest was for the ethanol plant."

The CITROTECNO project is rated for 25-30 MTPH of citrus waste.  The waste comes from several citrus processors in the area as well as packing houses.  An ethanol plant at the site, using de-oiled and pasteurized press liquor, is entering the start-up stage.

Both local and national government entities have given financial support to the operation. 

The ZUVAMESA project is rated for 50 MTPH.  The waste comes from a juice extraction plant at the same site.  The company is owned by several hundred citrus growers in the area.  The local government has provided financial support.

The two feedmills are quite similar.  Both feature the use of a Waste Heat Evaporator (WHE) to achieve high thermal efficiency.  These WHE's are a three effect, vertical tube, falling fill design.  In the construction 304 stainless is used for vapor and water components while product contact is in 316L.  Durco pumps, imported from the States, were selected for their known reliability.

Single pass rotary drum dryers, standard of the citrus industry, are employed.  The CITROTECNO unit, rated at 30,000 pph of water evaporation, is paired with a 40,000 pph WHE.  At ZUVAMESA at 40,000 pph dryer is paired with a 50,000 pph WHE.

The dryers and WHE's were designed and constructed by FOMESA.

Both feedmills feature double pressing with Vincent screw presses with 24" diameter screws.  First pressing is done with a low torque Series KP press, while second pressing is done with a high torque Series VP press.  All presses use 50 hp motors.

The flexibility offered by double pressing has been advantageous where spoiled fruit is being processed.  This is quite common at CITROTECNO.

During start up a great deal of difficulty was encountered with the high viscosity and insoluble fiber content of the press liquor.  There is something different, possibly in the firmness, about this Mediterranean fruit as compared to fruit in Brazil and Florida.  As at FMC's Parmalat job in Sicily, it was necessary to add centrifuges to remove fiber from the press liquor.  Only after this was done was satisfactory WHE performance achieved. 

Both WHE's produce 45 Brix molasses on a consistent basis.  A 24 hour cleaning cycle is used.  An Alfa Laval centrifuge is used at ZUVAMESA while the unit at CITROTECNO is a GEA WESTFALIA.

The shredders feature hammers made of Duplex stainless steel, which is proving exceptionally durable.  The inlet housings are square, an innovation first introduced by Tegreene in Florida.  The blades are 180 degrees apart, and innovation introduced by CORENCO.  The discharge screens are exceptionally thick, 5/8", with square round holes.

The reaction conveyors are sized for 15 minutes reaction time, with 0.5% hydrated lime addition.  Inclined units are used to elevate the peel from the peel bin up to above the screw presses.  These use slow turning 24" diameter screw conveyors with half pitch flighting.

Pellet mills supplied by Van Aarsen are used at both feedmills.  These produce excellent pellets with a minimum of difficulty.

ADDENDUM: The CITROTECNO ethanol plant made 14,000 l of 90% ethanol the first season. They run on press liquor which is pasteurized at 90 C. They pump it to a flash tank to remove the d-limonene. When they had no press liquor, they kept the alcohol plant running by diluting molasses to 15-20 Bx."

Vincent Corporation is proud to have played an important role in the success of these feedmills.

PelletmillsPellet Mills


The photos and layout drawing show how Zuvamesa does first pressing with two Model KP-24 presses, and then second pressing with two VP-24's. After that the press cake goes to the dryer. In the photos the two KP-24's are on the right hand side, and the dryer is off to the left. You can see that they used screw conveyors to lift the cake up into a horizontal screw conveyor which runs from right to left. The peel comes into this conveyor on the right hand side. The peel can then fall into the two KP-24's, or it can by-pass to the two VP-24's, or it can by-pass all four presses and go to the dryer.

The cake from the two KP-24's is elevated in a screw conveyor which has a circular (cylindrical) trough; it is mounted at about 60 degrees. Similarly, the cake from the two VP-24's is elevated in a screw conveyor which has a circular (cylindrical) trough; it is mounted at about 60 degrees. The cake coming up in these two elevating conveyors drops into the long horizontal conveyor which runs from the far right to the dryer at the far left.

This is a very effective system of double pressing.



Issue 231



Orange Peel as Fuel

January 25, 1999
Rev. 2008

In September 1998 Vincent Corporation gave a presentation to a group of over five hundred citrus processors. The subject was using citrus waste as a boiler fuel.

It was years after this presentation that a fundamental observation was made. In order to burn biomass such as orange peel, the moisture content must first be reduced to zero. That is, as long as moisture is present, the temperature cannot rise above 212 F (at atmospheric pressure). Since combustion cannot occur until the mass reaches a much higher temperature, any burning system has an absolute requirement of first reducing the moisture content to 10%. If the system is frozen (on paper) at that point, it is easy to calculate if the mass now has more value as animal feed or as the fuel. Invariably, the feed value is greater than the fuel value.

There was interest in the paper for special reasons. The price of orange peel pellets, which are used as cattle feed, had been a very depressed $40/ton the previous season. Furthermore, dioxin had been found in Brazilian pellets, resulting in a European embargo. In the end the interest was academic because of the large capital requirements.

The price of pellets has currently (2008) gone to $170 per short ton, further reducing the financial justification of such a project.

On a dry solids basis, orange peel has a BTU content of 7,500 BTU/pound. This compares quite favorably with material like wood. It is enough energy value to satisfy several needs:

  1. Dry the wet peel sufficiently so that it will burn.
  2. Release energy to generate steam in a boiler.
  3. Generate enough steam to run the juice evaporators in an orange juice concentrate plant.
  4. Generate enough steam to produce electricity to run the citrus plant.

Several equipment alternatives were evaluated. A practical configuration recommended was to first use a screw press to remove moisture from the peel. Solids from high Brix citrus molasses could be diffused into the press cake until the moisture content was reduced to 60%. Press cake (peel) at this level of dryness will burn in either a fluid bed or stoke grate boiler. The high-pressure steam generated in the boiler would be used in a turbine to generate electricity. The low-pressure steam extracted from the steam turbine would be used both to (a) produce high Brix molasses from the press liquor and to (b) drive the TASTE evaporators that are used to produce orange juice concentrate.

The adoption of this system is attractive where fuel costs are high and the value of citrus pellet animal feed is low. Unfortunately, as is the case with all steam based electricity generators, the capital costs are extremely high. This high investment requires a long amortization period.

Copies of the paper that was presented are available from Vincent Corporation.

September 2010:  Alex Andreassen of Danisco has pointed out that  burning citrus pellets will lead to slagging of the boiler tubes because of the alkali-metals (Na, K) content of the peel.  Thus applications would be limited to using pellets as dryer fuel.

Issue 89

Pumped Citrus Peel

April 14, 1998

Last month Vincent presented a paper at the Citrus Engineering Conference of the ASME. This paper, Pumped Peel - Five Years Later, discusses advances in citrus peel processing technology.

In 1940 Dan Vincent was awarded a patent covering the mixing of hydrated lime with citrus peel. The lime attacks the peel and makes it possible to dewater it with a screw press. From that day forward the lime/peel chemical reaction was done in reaction conveyors.

It was Brazilian citrus companies that introduced a process whereby the orange peel is pumped and the reaction is completed in tanks. This has the advantages of using pipes and tanks instead of screw conveyors. This technology was the subject of a 1993 paper at the annual ASME conference.

Since then the Florida processors have leapfrogged the Brazilian technology. The greatest advances are attributable to Ralph Cook, best known as the inventor of the TASTE juice evaporator. Cook Machinery did two feedmills (both using Vincent presses!) improving on the pumped peel concept. The major changes were: (a) Better tramp metal separation; (b) Drastic improvement in the reaction tank; (c) The use of pre- presses ahead of the normal "hard" presses; (d) The use of spent caustic (a waste) as part of the liming system; and (e) Using molasses, with no press liquor, as a pumping medium.

In 1997 Vincent contracted to convert a Tropicana feedmill to our own pumped peel technology. The most notable feature is the elimination of the reaction tank: the reaction takes place in the mixing tank and in the pipeline. Another feature is direct (hard) piping the peel from the mixing tank directly to the presses.

It was found that progressive cavity pumps were suitable even when using a low ratio of molasses to peel. This eliminated the need for pre-presses at Tropicana.

The new systems represent a significant simplification of peel processing technology. Initial capital investment and operating maintenance costs have been reduced accordingly.

Issue 75

Pumped Peel

June 16, 1997

Traditionally screw conveyors have been used to convey citrus waste from the juice extraction building through the feedmill. The waste is mostly orange peel, and it is dehydrated and pelleted into animal feed in the feedmill.

About ten years ago Brazilian citrus juice concentrate producers developed a technology to replace the screw conveyors by pumping the peel from extraction to the feedmill. They used a ratio of one part peel to two parts press liquor to liquify the peel prior to pumping. Moyno progressive cavity pumps were used. (The press liquor is the liquid separated from the peel with screw presses.)

This technology was improved two years ago by the Cook Machinery Company. They designed and built a citrus feedmill (using Vincent VP-22 presses) that pumps the peel in the ratio of only one part peel with one part molasses. (The molasses are made from press liquor in a Cook evaporator.)

During the last month a Vincent designed and installed pumped peel system has undergone trials at a Tropicana feedmill. Here the peel is pumped in a ratio of two parts peel to one part molasses. A new design Geremia moyno pump was imported from Brazil to do the pumping.

The Tropicana project has proven remarkably successful. The mixing tank, pump, and pre-presses have performed with minor hitches under a wide range of adverse conditions. The 10" piping burst on occasions; however, the addition of a pressure relief by-pass has solved the problem.

Before peel can be pressed, it must be reacted with lime in order to break down the cell walls. At Tropicana this lime reaction is done in a Keller mixing tank and in the pipeline. The existing 4' diameter by 96' long reaction conveyor is bypassed.

Probably the most innovative feature of the Tropicana system is that the peel is hard piped (under pressure, without a vent) directly to the presses. Two pressing options are being tested. In one, the peel is pumped to a Model KP- 16 for pre-pressing the loose liquid from the peel. The cake from the KP-16 is then pressed again in a heavy duty Model VP-22.

The second option allows for the peel to be pumped directly into a Model VP-22. High capacity runs have been made with pressures up to 50 psi in the inlet hopper, producing press cake with 67% moisture content. The moisture content would have been even lower, but only 30º Brix molasses were available.

Both options work. The use of the KP pre-press appears to relieve problems when it is necessary to process bad (old, underreacted, or underlimed) peel. Further testing and evaluation will continue through June.

We hope to present a paper on this technology at next year's Citrus ASME meeting.

Issue 62

Small Scale Citrus Feedmill

Citrus plants around the world are facing the same problem. The problem faced by these juicing plants is the disposal of orange peel. They are finding increased costs associated with landfill or with finding farmers willing to take the wet peel for animal feed. This is occurring at the same time as increased environmental regulations are being applied.


These plants are very small compared to the large scale operations in Florida and Brasil. That is, they generate a few tons per hour of peel, generally running only eight hours per day, as compared to 1,000 tons per day at the larger plants.

Because of the vast difference in scale the smaller plants cannot justify the investment associated with a highly efficient, full blown feedmill.

There is one solution that was popular among Florida's smaller processors in the 1960's. It is a "beginners" feedmill plant. It minimizes the capital expenditure at the expense of requiring more energy.

To understand this "beginners" plant, it is important to first understand how a large plant operates. In the large scale plants, peel moisture is removed in three independent operations:

  1. Firstly the peel is pressed to separate it into press cake and press liquor. This is a very energy efficient operation as the press horsepower is relatively low.
  2. The press liquor is evaporated in a waste heat evaporator. This heat exchanger evaporates water out of the liquor and leaves behind dissolved solids in a solution commonly called molasses. This water removal process is very economical: it requires no fuel because its energy source is the waste heat in the exhaust gasses leaving the dryer. The molasseses produced are then added back to the press cake.
  3. The press cake, with the added-back molasses, is dried in a rotating drum dryer. This is the least efficient of the three water removal devices. It requires about 1,600 BTU in the form of fuel oil or natural gas per pound of water removed from the peel.

In the process just described citrus peel, which starts at about 82% moisture, is dried down to 10 to 12% moisture. (This means that for every 100 pounds peel entering the peel bin, about 20 pounds of finished animal feed will result). As a final step the dried peel is pelletized in order to reduce its bulk. This is done in order to minimize transportation and storage costs.

The previously mentioned "beginners" process that may be economical for smaller processors calls for using only a dryer to remove all the moisture. This eliminates the need for investment in a dewatering press and a waste heat evaporator. In such a "beginners" plant we also recommend not investing in a pelleting mill and its associated pellet cooler.

To dry peel in this manner will require approximately 85 U.S. gallons of heavy fuel oil per short ton of feed produced. This compares to a range of 30 to 45 in Florida citrus plants. Thus we can see that the "beginners" plant has its lower capital investment being offset by higher operating costs.

The dried peel produced in this process is an excellent, palatable animal feed for dairy or cattle. Because of its low moisture content, it can be stored for prolonged periods with minimal spoilage.

The enclosed diagram shows the equipment required for drying the peel in this manner. One notable item is the reaction conveyor. It is necessary to add lime to the peel prior to drying; this is done in the reaction conveyor. The lime attacks the cells and releases the moisture so that it can rapidly and efficiently be evaporated in the dryer.

A frequent query has to do with incorporating a press into the cycle. The difficulty that arises involves what to do with the press liquor. The authorities will not accept it in the sewer system, and it can be used for irrigation purposes only if it is mixed with a great deal of water. (In heavy applications it kills the soil where land spreading is performed.)

Sometimes alcohol producers will buy press liquor at 8 to 12 Brix. It ferments readily and makes an excellent citrus alcohol. But how many small citrus processors have a nearby distillery?

Generally the only practical thing to do with press liquor is to run it through a steam or waste heat evaporator. A waste heat evaporator system generally costs almost as much as all of the rest of the feedmill put together. This investment becomes difficult to justify until all alternative methods of disposing of citrus peel have been exhausted.



Vincent Drawing C-91310 shows a citrus peel drying plant based on a Model 150 Dryer. The plant will dry approximately 19,000 pounds per hour of 82% moisture citrus peel, without the benefit of pressing or the use of a waste heat evaporator. The plant will produce approximately 3,800 pounds per hour of citrus peel dried to 10 to 12% moisture content.

The principal items, in their sequence in the production cycle, are as follows:

  1. Peel Bin. This vertical front peel bin, with hydraulically operated doors, is of carbon steel construction. A caged ladder to the top and a catwalk across the top are included. The unit is prefabricated and knocked down for shipment, to be welded together at the job site.
  2. Peel Bin Discharge Conveyor. Vincent will supply an ultra heavy duty conveyor, including three-bolt drilling, Gatke hanger bearings and a variable speed electric drive. This conveyor is of stainless steel construction, with a metering orifice plate. The peel bin is constructed with sufficient elevation such that the Discharge Conveyor can feed directly into the Peel Shredder.
  3. Liming System. A Vincent VL-450 Hydrated Lime Proportioning System, mounted on a fabricated steel base, is included. The lime hopper, sized to hold one and a half bags of lime, is installed adjacent to the shredder. An auger from this hopper adds approximately 1/2% by weight of hydrated lime to the peel as it leaves the peel bin.
  4. Peel Shredder. A Vincent VS-180 Shredder is included. This horizontal rotor machine reduces the peel mostly to a range of 1/4" to 3/4", with a minimum of fine material. It is of the thin, rigid blade design, as contrasted to the hammer mill concept. All contact parts are of stainless steel. The blades, which are fixed, cut the material before it is discharged through the perforated screen. The shredder housing is hinged so as to allow ease of washing, inspection, and changing the screens. In operation the housing fits folded onto the chute that feeds the shredder, assuring a tight fit. The rotor turns in only one direction; however, the blades can be reversed to give double life.
  5. Reaction Conveyor. Shredded peel drops directly into a slightly inclined Reaction Conveyor. This conveyor is sized to allow approximately 10 to 12 minutes dwell time. It is of carbon steel construction and features a notched blade screw. The chemical reaction between the lime and the peel that occurs in this conveyor is required in order to break down the cell structure of the peel so that moisture can be better removed in the drying operation.
  6. Elevating Conveyor. Limed peel from the Reaction Conveyor is elevated to the Dryer Feeder by this stainless steel conveyor. Also, recycled material from the second pass of the dryer is mixed with the limed peel in this conveyor. The design is such that, if required, material can be dropped back into the inlet of the reaction conveyor.
  7. Dryer Feeder. This screw conveyor receives peel from the Elevating Conveyor and feeds it into the Dryer. This is a stainless steel screw feeder fitted with a companion flange matched to the dryer throat. It has a variable speed drive to control the process feed rate.
  8. Burner. The burner will require up to 150 U.S. gallons per hour of fuel oil. The burner package is suppled with dampers and valves and a steam heater for the oil. The burner is capable of burning optional lighter fuel oils, or natural gas. It comes with the required combustion air blower.
  9. Furnace. Vincent will supply a Model VF-150 refractory lined furnace consisting of a carbon steel shell mounted on a fabricated steel base. It is designed to receive and mix recirculated exhaust gasses from the Dryer discharge in order to control the gas temperature entering the Dryer. The firebrick lining is supplied and installed by the customer.
  10. Return Elbow. There is a 180º Elbow between the Furnace and the Dryer so as to minimize the possibility of overheating peel in the Dryer.
  11. Controls. Vincent supplies a solid state programmable controller that modulates combustion and monitors the flame. Control of the combustion rate is through a sensor mounted at the inlet to the third pass of the dryer. This is required for precise control of product quality.
  12. Model 150 Dryer. This is a Vincent triple pass dehydration unit with an insulated, stationary outer drum. The unit includes recycle conveyors so that partially dried material can be extracted at the end of the second pass and mixed with the incoming material. This is especially important for the proper drying of unpressed citrus peel. The drum is carried on machined steel tires, mounted on an expansion type steel base with cast steel machined trunnions. The rotor is driven by a chain and sprocket system with a speed reducer. The base frame can be bolted to a 6" concrete slab without any special foundations; this saves installation costs.
  13. Separation System. The Vincent low level entry cyclone separator, ductwork, dampers, and stack are supplied. This system assures gentle handling of the dried peel. A motorized air lock and carbon steel screw conveyor are used to move the peel from the separation chamber to the cooling reel and bagger. A radial blade exhaust fan with its drive are also included.
  14. Cooling Reel. The Vincent Model 525 Cooling Reel gently cools the dried peel with an action similar to that of a large diameter clothes drier. Ambient air is drawn counter- current through the unit to achieve an evaporative cooling effect. Cooling is required in order to prevent the phenomena of re-heating of the stored peel. In the cooling process, evaporation results in a further reduction of moisture content of about 1%. The unit comes complete with a fan, dust collector, duct work, supports, and electric motors.
  15. Bagging System. This system includes an surge hopper and a semi-automatic weighing and bagging unit. This unit consists of a hold/weighing bin with an adjustable discharge, a weight indicator, a bag holder, and a compact Fischbein sewing head. The take-away belt, belt trays and motor and drive are included.



Spent Pectin Peel

February 17, 2016

Over a period of fifteen years Vincent participated in tests with spent pectin peel at four citrus pectin production facilities. The goal was to reduce the moisture content of the residue (spent pectin peel) which remains after pectin is extracted using the normal acid and alcohol precipitation process. Until 2013 none of these tests showed much promise.

Trials have shown that successful dewatering of spent pectin peel with a screw press requires two elements: (1) press aid (cellulose fiber) must be blended into the material, and (2) hydrated lime [calcium hydroxide, Ca(OH)2] must be mixed into the spent peel for a chemical reaction. Meeting these requirements involves quite a bit of equipment besides a screw press.

Alternatively, a belt press can be used to dewater spent pectin peel. Starting with 10% to 12% solids, this press removes free water, and a cake with about 16% solids can be produced.

In contrast, with the proper mix of lime and press aid, a screw press can increase the solids into the range of 30% to even 40%.

The advantage of dewatering the spent peel is that it becomes a saleable animal feed. Since large amounts of water no longer need to be transported, the geographic range in which the material can be sold is greatly expanded. One pectin producer has done very well by assigning a trade name to their spent pectin peel, giving it market identification.

An important consideration is that a large amount of wastewater is produced when the spent peel is dewatered. Since the flow of press liquor can be four times greater than that of the press cake, most of the dissolved solids go out with the press liquor. Although it can vary quite a bit, typically the press liquor has 5% solids, which translates into high BOD effluent. To overcome this, some pectin producers are considering the use of multiple effect evaporators to concentrate their wastewater into a molasses.

It is notable that, because of the dissolved solids, the solids capture rate in the press cake is only about 70% of the total solids entering the screw press. The rest go out with the press liquor.

Typically from 1% to 2.5% hydrated lime is added to the spent pectin peel. The lime is mixed with about ten parts water prior to blending with the spent peel.

We have tested a variety of press aids. By far the most successful is ground wood, sold commercially in both Europe and America. Suppliers include SCM in Sweden, International Fiber Corp. in North Tonawanda, NY, and Mat, Inc. in Floodwood, MN. The primary market for these press aids are factories engaged in the production of fruit juices such as apple juice. Typically 2.0% to 2.5% press aid works with spent pectin peel.

The main piece of equipment needed to blend press aid with spent pectin peel is a mixing tank commonly known as a hydrapulper. Bales of press aid are mixed with liquid in the hydrapulper. This fiber is pumped to be blended with the spent peel and the hydrated lime. This mixing can be done in a blender such as a Lodige or Khal. More economically, the mixing can be performed in a mixing paddle conveyor (known as a reaction conveyor in the citrus industry). The mixed and chemically reacted material is what is fed into the screw press.


Recently we tested dewatering the spent material after the pectin has been removed from apple pomace. We found that there was an excellent reaction with hydrated lime. The addition of press aid was not required. Once reacted with the lime, the material shows great promise in being dewatered with a screw press.

Steam Injection

July 5, 2002                                                                                                                                                                                                         ISSUE #129

Up until the Oil Embargo of the early 1970's it was common practice to inject steam into screw presses. The steam was injected directly, through hollow resistor teeth, into the material being pressed. This was done to reduce the moisture content of orange peel that was being made into cattle feed. The practice seems to have been abandoned for two reasons: the high cost of steam energy, and the fact that most citrus feedmills lacked the Waste Heat Evaporator capacity to dispose of all the press liquor being produced.


Driven by the need to reduce VOC (Volatile Organic Compound) emissions, interest has resumed in pressing as much liquid as possible from citrus waste. One solution has been to use high pressure, high horsepower screw presses. To evaluate an alternative, Vincent Corporation acquired a boiler and conducted tests with live steam injection.

Initially we were cool to the idea of using steam. We reasoned that it would be more efficient to evaporate moisture with a direct fired rotary drum dryer. However a California research firm, Altex Technologies, brought to our attention that steam addition in a press will drive out liquid water, whereas a drum dryer removes the moisture in the form of water vapor.

The difference is very important: by pressing out liquid water, there is a savings of about 1,000 BTU's per pound of water. This is because the drum dryer requires this energy to convert the water from the liquid to vapor state.

To prove the concept, a basic test was conducted. Drums of peel were brought to the Tampa works from two local feedmills. This peel had been reacted with lime and single pressed. The peel was collected at the inlets to rotary drum dryers. The samples from both feedmills had a respectable 18o Brix. However the moisture contents of both samples were high, 71% to 73%, because of special conditions existing when the peel was collected.

This cake was second pressed in a laboratory screw press in Tampa. Probably because of a delay of a few hours that occurred after the samples were collected, the resulting press cake was reduced (consistently) to about 59% moisture. Part of this moisture reduction was due to using the press electrical drive to heat the peel: cake temperature increased by 10° F to 15° F while passing though the press.

Addition of steam, at various flow rates and at pressures up to 45 psi, significantly improved the press cake moisture that could be achieved. Final moisture contents of 55% to 57% resulted. In the process the temperature of the discharge cake and liquor was increased to about 160° F.

Most importantly, the extra moisture separated by the screw press came out as a liquid, not as vapor. Therefore the old steam injection technology appears worthy of further investigation. We hope to participate in full scale testing during the next citrus season.



Twin Screw Press

October 24, 2000                                                                                                                                                                                                 ISSUE #110

Following field tests during the last six months, Vincent is introducing the Twin Screws Press. Designated the Series TSP, five models are being offered.

These presses have very positive feeding characteristics, making them well suited for slippery materials. The strong pressing action of overlapping screws, plus the use of seven stages of compression, result in the best dewatering action we have ever seen in a Vincent screw press.

The Twin Screw Press is well suited to many traditional markets: citrus peel, fruit and vegetable juicing, fish waste, spent brewers' grain, shrimp shells, and alfalfa. We do not anticipate application in the pulp and paper industry, but we think that sugar beet pulp should work well.

There are three principal advantages to the Vincent design:
Automatic Control. The use of an air cylinder operated discharge cone allows the press to work well with changing feed material conditions and throughput capacities. The press has above average turn-down characteristics.

Low Horsepower. To improve dewatering, material is sliced in the press. This is a characteristic of the interrupted screw with fixed resistor teeth that can be seen in the brochure photo. The press requires less horsepower than a continuous screw press where the action is more like mashing than slicing. Also, the result of this particle size reduction is that, if the press cake goes to a dryer, better dryer performance is achieved.

OEM Gearbox. We have carefully selected major OEM gearboxes for use with our press. A choice of Sumitomo and Foote- Jones/Illinois Gear drives are available.

Overall, Vincent is delighted with the Twin Screw Press. It marks a significant advance in screw press design because the pressing performance is equal to or better than anything achieved in the past. In financial terms, it is possible to guarantee a machine with double the capacity of a single screw press, but at less cost than two single screw presses of the same diameter.



Pulp & Paper

 Click on the following links to know more about Pulp & Paper applications:

Bagasse Paper Mill

February 21, 2008

Productora de Papeles (PROPAL), based in Cali, Colombia, is a group of two paper mills. Originally International Paper operations, they are now owned by the Carvajal family group. Both mills produce paper using sugar cane bagasse as furnish. There are many sugar cane mills in the area, so a year-round supply of raw material is assured.

Commissioned in 1990, today their #2 Mill produces 330 metric tons of paper per day. This paper is used for copier paper, although books and notebooks are also produced with it. Propal has recently purchased a Model VP-24 screw press which will dewater the primary clarifier underflow at this mill.

The project was driven by two factors: environmental and economic. From the environmental standpoint, using the press will eliminate a landfill operation. This landfill can cause run-off and groundwater contamination, besides presenting an ever-growing environmental situation.

Economically the press has a quick payback because the press cake will be dry enough to be combined with their boiler fuel. The press cake has a BTU value of approximately 8,500 BTU per pound of dry matter (compared to 10,000 for coal). Propal's B&W boilers burn coal. By blending the press cake with this coal, a reduction in coal consumption will result. The use of such biomass fuel has been receiving much attention at paper mills because of increasing energy costs.

The load to be dewatered is 40 metric tons per day (MTPD) of dry solids. It was felt that a Model VP-16 could likely have handled the load. The VP-24 was selected on a conservative basis, anticipating future operating conditions. It is also possible that it may be used to remediate the material in their landfill.

It is noteworthy that the mill already burns 70 MTPD dry solids of chaff and pith that is separated ahead of the digester. This material is pumped to an Andritz belt press where it is dewatered to 40% solids prior to burning.

Propal made use of the Vincent rental fleet. A Model CP-4 press was air freighted to Cali and used for a variety of testing. With this testing it was determined that no pre-thickening or polymer will be required, and press cake with a solids content of 50% can be produced without undue strain or problems. Rent was waived for the test period, and a Vincent engineer assisted at no charge.

The clarifier is an Eimco, 150' in diameter, handling 9000 gpm. Sand is separated ahead of the clarifier in order to reduce torque loading, and the flow is neutralized. The reject material, mostly medulla or pith, settles to a thick 5% underflow. It is because of this relatively high underflow consistency that no pre-thickening is required.

The original equipment at the WWTP (wastewater treatment plant) consisted of a small Eimco rotary drum screen, followed by a pair of Andritz belt presses. The rotary drum screen is only, approximately, 3' diameter by 5' long. This increases the underflow consistency from 5% to 8%. The belt presses, now worn and in need of overhaul, are about 3 meters wide. The cake produced by the belt presses normally has only 15% solids.

The new installation will place the screw press in parallel with the belt presses. That way it will be possible to retain the belt presses, at least for the time being, as back-up. It will also permit the rebuilding of these belt presses. In the future the belt presses may be used to for pond remediation, dewatering sludge from the mill's treatment lagoons.

The Vincent press was selected over competition because we were able to clearly demonstrate the performance being guaranteed. Because it was an export contract, strong financial assurances were offered in the form of two Letters of Credit. The first L/C, issued by Bank of America to Propal, assures Propal that their down payment money will be refunded should Vincent fail to ship them the press as promised. The second L/C will assure Propal that Bank of America will refund the full purchase price of the press should Propal elect to return the machine. Customer satisfaction is guaranteed.

Issue 197

Boiler Ash

October 16, 1997                                                                                                                                                                                                       ISSUE #68

Recently our sales rep in North Western Ontario, Process Flow Systems, took us to visit the one of the largest paper mills in North America. There are kraft, newsprint, and recycle mills all on the same property.

We were asked to demonstrate our small CP-4 with the sludge that comes from a scrubber on their hog fuel boiler. The water and particulate coming from the spray chamber were a filthy jet of boiler ash.

We did not expect the test to work. As expected, the material just oozed through the press with no dewatering. However it looked like there was potential because some polymer had been added. With the polymer, clear water could be seen forming in the nearby puddles and streams.

By chance nearby there was a pile of paper mill waste fiber. This was added to the ash and water solution, and, bingo! It was like magic. With the fiber as a press aid, the press started producing cake that measured 60% solids.

The application was found to work well with 10% by volume reject fiber. By weight the percentage would have been much lower, as is normal with the use of a press aid.

On-site testing is planned with a larger scale rental press.

Boiler Fuel

January 11, 1995
Rev. Oct 1997

We frequently are asked about the fuel value of waste materials from pulp and paper mills. This question arises because, when screen rejects and knots & shives are pressed, the dry press cake that is formed can be burned instead of landfilled. The combustion can be either in a coal fired boiler or in a bark burner. Tipping fees are an important part of the analysis. A high rate, like $30/ton, would make press cake disposal more important.

The heat value of the press cake is a function of the percent moisture as well as the ash and clay content. In general, the solids will have 2,900 BTU/# "as fired". Even when you take into account that there can be up to 60% water in the press cake, there is still some economic advantage to burning the sludge, in terms of energy contribution. That is, if you start with two pounds of press cake at 50% moisture, there will be one pound of solids burned, contributing 2,900 BTU, but there will also be one pound of water to evaporate, requiring 1,200 BTU. Thus there would be a net contribution of 850 BTU per pound of press cake.

Comparable figures are 10,000 BTU/# for coal and 5,000 BTU/# for wood. The fuel value of primary sludge, 4,000 BTU/#, is good. Coal is an ideal fuel for burning along with pressed screen rejects because it burns hot and has low moisture.

Most commonly the coal fired boiler will use one of two types of grates for burning press cake (rejects, sludge): Rotograte and Vibratory. With the Rotograte there is a limit of 400º F inlet air temperature, so the amount of sludge that can be dried is limited. Blending 10% press cake with coal would be recommended.

With the Vibratory grate the inlet air temperature can go up to 600º to 650º F because the grate is water cooled. This permits mixing the press cake with the fuel up to a higher percentage. General guidelines for the mixture are 30% press cake with 70% bark or 40% press cake with 60% coal.

It should be noted that, with the low inlet air condition, the system counts on radiant heat to evaporate the water in the press cake. This cools down the furnace, causing combustion problems. Also, running up the ratio of press cake to coal leads to poor air distribution across the grate, which also leads to uneven drying and burning.

It should be remembered that if a ton of press cake is burned, there will still be 400 pounds to haul to landfill: that is 1,000 pounds of water evaporated, 600 pounds burned up, and 400 pounds of ash.

Issue 20

Clarifier Sludge

August 28, 1998                                                                                                                                                                                                    ISSUE #82

In 1997 Putney Paper in Putney, Vermont purchased a Vincent VP-16 screw press. Its function was to further dewater sludge from the primary clarifier in their wastewater treatment plant. The sludge was pre-thickened with a belt press ahead of the screw press.

The mill both recycled OCC (Old Corrugated Container) and did deinking of other waste paper. The OCC operation put fiber in the clarifier, which improved the subsequent dewatering. Deinking, on the other hand, results in a higher proportion of clay and other materials that are hard to dewater in a screw press.

Testing with a rental machine and initial operation with the VP-16 gave excellent results. Press cake solids of 55% were obtained. This addressed problems associated with landfill hauling and fees.

A year later the press would not work. Capacity had fallen off and dewatering was minimal. Examination revealed that the sludge no longer had the fiber content that had existed previously. This had occured as a result of improved fiber recovery. Nothing could be done with the mud-consistency material coming from the belt press. The mill stopped using the screw press.

Trials elsewhere prompted Vincent to make this proposal to mill management: if they would substitute the existing 1800 rpm drive motor with a 900 rpm model, Vincent would supply the belts and sheaves to cut the screw speed in half. This combination cut the speed of the press from the normal 13 rpm down to about 3 rpm.

The results were a dramatic improvement in dewatering capability. The 35% solids cake from the belt press was further dewatered to a respectable 45% solids in the Vincent press.

Unfortunately capacity of the screw press fell off with the speed reduction. At times this was a problem for the mill, so the 1800 rpm motor was re-installed. With this change, press cake solids fell to 40%, but capacity was up. Later, a frequency inverter was installed so that the press could be run at speeds from 3 to 7 rpm. The speed was set according to the nature of the sludge being pressed at any given time.

Clarifier Underflow - A

October 11, 1999

An excellent installation was made in 1999 at a Weyerhaeuser paper mill. The mill installed a Model VP-16 screw press, along with a pair of sidehill screens. This equipment is used to dewater the underflow from their clarifier. Photos of the installation are available.

The clarifier is located at the waste water treatment plant. The flow into the clarifier is the combined flow of all of the waste streams in the mill. It includes the knots, shives, and screen rejects from all sources. Since the mill is a virgin fiber Kraft mill, there are negligible contaminants such as the ash (clay), dirt and ink that typify a recycle paper mill. We did note the presence lime, which comes from the lime kiln and cooking liquor preparation areas.

This waste stream dewatered and pressed in very good fashion. The cake, with over 40% solids, is added to the bark pile and sold as fuel to a local co-gen (electricity generating) plant.

The two Vincent sidehill screens, each 3' wide, were installed over the inlet to the press. These face each other so that any splash flow falls into the press. We have nearly identical installations at Bowater and Kimberly-Clark.

At Weyerhaeuser the clarifier underflow pumped to the sidehills was anticipated to be 300 gpm at 1.5% solids. The flow is thickened to an estimated 5% to 8% by the time it falls into the screw press. The press capacity was measured in excess of 40 TPD,DS (tons per day of air dry solids), which is somewhat greater than the expected load.

The original inquiry came from a direct mailing of the Tappi Journal article co-authored by Vincent. Two problems came together that made possible the justification required for the project. There was an existing belt press that was severely deteriorated and in need of major maintenance. Furthermore, the cake from the belt press was too wet to sell along with bark. This cake had to be landfilled, and the mill's landfill was nearing its maximum capacity.

Issue 98

Contract Wastewater Treatment

December 4, 2001                                                                                                                                                                                                   ISSUE #123

It was at a Tappi Environmental show that Vincent met representatives of Integrated Technical Services of Baton Rouge, Louisiana. This firm specializes in handling waste disposal on a contract basis. Pulp and paper is but one of many industries served by ITS.

Working with Vincent, ITS secured a three year contract to handle wastewater disposal at a Georgia-Pacific mill. The mill, in Crossett, Arkansas, was once the largest mill in the United States. It is rated at 1,600 tons per day, producing softwood Kraft pulp.

The combined wastewater flows of the mill are pumped a few miles off-site to an in-the-ground clarifier. The flow to the clarifier averages fourteen million gallons per day. It includes the undercooked chips, shives, screen rejects, and wash water from all sources.

Underflow from this clarifier is pumped to sidehill screens mounted above Vincent Model VP-16 screw presses. The arrangement has a pair of 3' sidehills over the inlet of each of two presses. These face each other so that any splash flow falls into the press.

The flow to the sidehill screens averages 1% to 2% solids. Even under adverse conditions this is concentrated sufficiently by the screens for the screw presses to operate reliably. Only under very difficult conditions is any polymer used in the treatment.

Press capacity is extremely high. This is due to the effectiveness of the sidehill screens and the high freeness of the Kraft fiber coming from the mill. Throughputs in excess of 70 TPD of air-dry solids per press have been measured. This is an outdoors installation. The only building is a trailer used by an operator. Currently the cake from the presses is landfilled, although there are plans to use the cake as boiler fuel. 


July 13, 1999                                                                                                                                                                                                         ISSUE #96

Deinking Mills are a major specialty among paper recycling mills. The principal raw material categories for these mills are newsprint, magazines, telephone directories, and mixed office waste. There are many sub-specialties. For example, some mills will recycle only newsprint, while others will mix magazines with newsprint. This adds fiber strength and brightness, but it requires the addition of equipment to screen ash from the furnish. (Ash is mostly the kaolin clay coating used in glossy magazine paper.) MOW (Mixed Office Waste) mills use the least expensive material; however, it requires special equipment for removing a broad range of contaminants such as Styrofoam and stickies (contact cement).

The common feature of deinking mills is that they must separate printers' ink from the fiber. This is made difficult because the objective of ink formulators is to produce a product that stays bound to the paper fibers. Obviously there are many types of ink: water based, latex, those that work on ground wood paper, those that work for glossy coated paper, etc. One of the worst is laser printer ink, because it is heat bound to the fibers.

Once the ink and ash have been separated from the fibers, these contaminants must be screened from the flow. Traditional technology is to use a machine similar to a belt press for that purpose. The performance of these deinking machines is principally measured by (a) the brightness of the good fiber that is accepted, and (b) the amount of good fiber going in the reject steam.

Last year a Fiber Filter machine was tested for deinking capability. This was done in the laboratory of Thermo Black Clawson, the premier manufacturer of recycle paper mill machinery. The results were extremely encouraging. Compared to the conventional equipment, the Fiber Filter scored higher in brightness and, simultaneously, higher in fiber recovery. This means that more ink went through the fabric sleeve while at the same time that less good fiber was getting through the same sleeve. Ash separation was also excellent.

Feed consistencies ranging from 0.25% to 2.0% were tested. Accept consistencies were in the range of 7.5% to 14% solids, with flow rates of 150 to 250 gpm in the Model FF-12.

Kneader Prethickener

September 19, 1997

In 1997 Vincent was awarded a contract for a Model VP-16 screw press that was used in an important pulp & paper application. The order was received from Thermo Black Clawson, the leading American supplier of paper mill machinery. The press is for Papelera Aragua, their client in Cagua, Venezuela.

The application was at a deinking mill that recycled ONP (old news print). Once hydrapulped, the newspaper must be scrubbed to remove ink from the cellulose fibers. This is achieved in a Thermo Black Clawson machine known as a Kneader. In the Kneader the fibers are rubbed against one another in order to separate the ink.


The Kneader requires a furnish with 25% to 30% solids. This is pre-thickened from a flow with 2% concentration by the Vincent screw press. The installation processes 30 MTPD (metric tons of air dry solids per day). The freeness varies considerably, from 150 to 500 csf (Canadian standard freeness).

The Vincent interrupted screw negates the need for a variable frequency drive. This press design uses interruptions in the screw flights with stationary resistor teeth inserted in the gaps. The resulting agitation allows the press to operate consistetly, without co-rotation, over wide ranges of both throughput and feed consistency. The use of an air cylinder actuated discharge cone allows production of press cake of steady solids content.

This job is important to Vincent because it is a step into yet another pulp & paper application: thickening pulp for both wet storage and baling purposes. Frequently there is a need for storage between pulping operations and the paper making machine. Water must be removed, without damaging the fibers, to reduce the storage bulk to a manageable volume. We have one small press operating in this capacity at a Georgia-Pacific mill, so we have confidence our larger presses can do the job.

Issue 67

Knots & Shives - B

October 4, 2001

Vincent has supplied screw presses to several Kraft mills for use on knots and shives. These rejects are material that is not made into paper pulp. The knots come from knotters following the digester, while shives are bundles of fiber, high in lignin, that are separated by pressure screens.

This waste is screened. Shaker screens are used to separate fiber and chemical-rich liquor from the knots, and commonly dewatering screens separate wash water from the shives. Depending on the quality of paper being produced, these rejects may be redirected to the digesters. More commonly, after screening the waste is landfilled. At other mills the shives are left in the water going to the wastewater treatment plant.

The advantage of adding a screw press to this process is that the knots and shives can be made into a press cake. The cake moisture can be held in a range of 35% to 50% by adjusting the air pressure on the discharge cone. Mills use the dry cake as supplemental fuel for their boilers. Other mills have found that run-off problems are avoided at the knot pile, the knots do not drip while being hauled to the landfill, and the press cake adds stability to a landfill.

Advantageous chemical and fiber recovery results where hot stock screening is used. With hot screening the rejects from the unwashed stock, at 190° F, are the material furnished to the Vincent screw press. The press liquor, containing 15% chemicals and some usable fiber, is returned to the chemical and fiber recovery flow. Chemical recovery (mostly caustic) can be increased by 10%.

Typically the primary knotters account for about one quarter of the load. The shives usually arrive in a flow of 1% to 2% consistency. Sidehill screens have been used successfully in installations that required pre-thickening. Mills where shives were sluiced with wastewater have benefited from reduced loading in the wastewater treatment plant.

The most commanding performance feature of the Vincent screw press is the ability, without operator attention, to handle a wide variety of conditions. Flow rates can be varied from "off", to surge, and back to normal. Tests were run with only mill water going into the press, followed by thin and thick flows. The press rarely wants to purge. There is a tendency to overload and jam at very low flows, so reinforced profile bar screens and heavy duty drives and frames are used for knots and shives.

One characteristic that catches everyone's eye is that knots are disintegrated into small bundles of fiber in the Vincent press. This results in an excellent boiler fuel and opens the possibility of additional fiber recovery. This will depend on the paper quality produced at the mill.

Issue 55 - B

Knots & Shives

November 30, 1994
Rev.Aug 1997

In 1994 Vincent presses were used for on-site testing at two paper mills, a James River plant and Buckeye Florida in Perry, FL. The tests at James River were arranged by the Atlanta office of Sandwell Inc., a consulting firm, while the tests at Buckeye were initiated by Agri-Products, a landscaping materials firm. Since then both mills have bought VP-16 presses.

Both plants produce paper pulp, which starts with wood chips that are digested. The mass discharged from the digesters contains pulp fiber, spent chemicals, and waste materials. The liquid is very black in color, hence its name, black liquor. This liquid gives pulp mills their characteristic odor. Conventional practice is to screen out the usable pulp fiber. The screen rejects are waste materials which, along with some black liquor, are sent to landfill.

These screen rejects consist of knots, shives, as well as some good pulp fiber. The shives are little bundles of cellulose fiber that are still bound by lignin that failed to get dissolved in the cooking process. At James River the knots were fairly evident, about the size of quarters, while at Buckeye they rarely appeared. This was a function of the species, as well as age and condition, of the trees being harvested.

The amount of good fiber present in the waste stream varied considerably; at Buckeye it was low, around 25%, while at James River, on the softwood side, it was running unusually high, probably around 80%.

Moisture content of the material coming into the presses from the vibratory screens varied widely. Readings ranged from 76% to 91% moisture. Successful operation is also achieved with some flows in the 96% to 99% moisture range.

Excellent results are evident pressing the knots and shives at both plants. Black liquor, with its chemicals, is a financially important recovery at James River. At this hardwood mill, the rejects are unwashed, coming directly from a continuous digester. At Buckeye the chemicals are less concentrated because the rejects come from the brown stock wash system.

Solids content of the press cake at both mills averages 40% to 50%. Some material can be taken up to 55%. The James River material can be pressed so that it is suitable for a boiler fuel.

Buckeye is entertaining a proposal involving mixing the pressed material with cypress mulch for landscaping application. Another potential use at James River is as a filler in the production of tar paper. In any case landfill problems of contamination and availability are avoided.

The most commanding performance feature of the press is the ability, without operator attention, to handle a wide variety of conditions. Flow rates can be varied from "off" to surge to normal. Tests were run with only plant water going into the press, followed by thin and thick flows. The press rarely wants to purge. There is a tendency to overload and jam on dry material, so reinforced profile bar screens and the heaviest available drives are used for knots and shives.

One characteristic that catches everyone's eye is that knots are disintegrated into small pieces in the Vincent press. This opens the possibility of additional fiber recovery.

In anticipation of future pollution regulations, presses for black liquor applications are offered with vapor barrier construction.

Issue 18

Non-Pressable Sludge

October 4, 1994
Rev. Jul 1997

Very frequently we are asked if some material can be dewatered in a Vincent press.  There is a very simple fist test that indicates if a screw press will work: First, put a small mount of material in the palm of your hand.  Next, close your fingers gently around the mass of material.  Work the material with your palm and fingers so that something is squeezed out between your fingers.  If a liquid comes out between your fingers and if, in the end, there is some solid material left in your palm, then a screw press might succeed.

For example, if you ran this test with mashed potatoes in your fist, you would see that it cannot be pressed.  On the other hand, if you shredded some paper, mixed it with water, and worked that material in the palm of your hand, you would see that paper pulp can be pressed successfully.

Digested organic material is the most important non-pressable sludge.  This includes sludge from sewage treatment, slaughterhouse, and cooked food plants. At these treatment facilities, the fine cloud in the wastewater is agglomerated with polymer flocculent.  In a DAF (Dissolved Air Flotation) system this sludge floats to the surface and is skimmed over the edge of a tank.  In other systems it is allowed to decant to the bottom of a clarifier tank, from which it is pumped out as underflow.

When sludge is skimmed off it will have 80% to 95% moisture; clarifier underflow is even wetter.  It is very expensive to dispose of because it can represent a huge tonnage going to landfill.  Generally, belt presses can be used to filter out some more of the water. But the end result cake is still likely to have more than 80% moisture.

Other sludges that will not press are finely ground inorganic materials.  These include settled materials such as pond dregs, tank bottoms, and clarifier silt.  Use the fist test if you are in doubt.

Because of the big potential payoff, we have run sludge tests using variety of press aids.  We also tried heating sludge to 200°F before pressing it.  Another effort involved adding bleach to break down the polymer.  Not one of these efforts has come close to working.

We have seen conflicting results with the use of polymer. We had a case where water was readily squeezed from a belt press cake with a bare hand; yet, the Vincent screw press could remove nothing.  In fact, after passing the sludge through our screw press, the fist test was no longer successful. At the same time there are several paper mill installations where the Vincent screw press works only when polymer is used on the waste stream.  The fist test is not a fail-proof determinant.

Issue 16


Paper Mill Prethickening Options

December 12, 2000

In some pulp & paper screw press applications there is no need to prethicken the flow to the press. This is the case both with rejects from pressure screens and knots from shaker tables. Similarly, most clarifier underflow has 2% to 3% solids consistency, which, especially in virgin fiber mills, is adequate for dewatering in a screw press.

Even in these easy applications it is recommended that a simple sidehill screen be installed over the inlet to the screw press. This assures proper press operation even under upset or shut-down conditions where the flow can become very dilute. (In dilute flow conditions the high flow of water through the press screen washes the solids through the screen so that the capture rate becomes unacceptable.)

Where a paper mill wastewater flow is being coagulated and/or flocculated, there is an aversion to using a sidehill screen. This is because the surface of the screen will become coated with the polymerized sludge, blinding the screen.

In these installations there are a number of prethickening machines that can be used. The simplest is a rotary drum screen. The use of continuous sprays on the outside of the drum keep the screening surface clear. FKC is a competitor who makes frequent use of these devices. Where the mill specifies a rotary drum screen ahead of the press, Vincent has included equipment designed and manufactured by IPEC Industries in British Columbia.

Many times the mill will specify that a gravity table (or table thickener) be supplied with the press. These are a specialty of Andritz, a very strong competitor that offers the Dupps screw press. A gravity table is in principle the upper deck of a belt press.

Probably the most effective prethickening machine is a belt press. Cake solids from a belt press will range from a low of 20% where there is a high content of secondary sludge, to a high of 35% or 40% solids where there is no biological content. For the last five years Vincent presses have been offered in conjunction with Phoenix belt presses.

In one mill Vincent screw presses were supplied along with gravity tables whose cake was fed to belt presses before being fed to the Vincent presses. The final cake is burned.

Issue 113

Paper Recycle Mills

April 23, 1996

Paper recycling is not new: Vincent presses have been installed at two mills that are over fifty years old. At the same time there has been a large construction boom of paper recycling mills in the 1990's. The mills are scattered across the country, generally being located close to population centers. There are seventeen in Los Angeles alone.

Each of these mills specializes in recycling a specific kind of waste paper. The most common is OCC (old corrugated container). Most OCC mills avoid waxed corrugated or corrugated from the far east (because of its weaker fiber make-up). Other mills handle these sub-grades.

The other recycle mills are called deinking plants. They specialize in categories such as ONP (old newspaper), telephone directories, MOW (mixed office waste), magazines and MWP (mixed waste paper).

Each of these categories of waste paper presents special challenges and requires specific technology. Much of the chemistry has to do with ink. Ink manufacturers continuously improve their ink for better adherence to paper fibers, while the recyclers are focused on separating the ink from the fiber. Equally important to the paper recycler is the technology to separate the ink not only from the pulp fibers but also from the stream of usable fiber. The waste rejects frequently end up in a Vincent screw press.

Recycling high quality, glossy magazines presents special challenges. These magazines are generally made of one third kraft fiber for strength, one third ground wood fiber for economy, and one third clay coating for printing quality. The high proportion of clay in the waste stream can make it all but impossible for a Vincent press to operate correctly.

MOW is one of the least desirable forms of waste paper to recycle. The wide variety of contaminants, especially plastics, cause problems for the paper maker. Laser printer inks affect quality because they are thermally (opposed to chemically) bound to the paper fibers.

The common characteristic of recycle paper mills is that they generate a considerable load that most frequently goes to landfill. For example a 300 TPD OCC recycle mill will generate 10%, or 30 TPD (solids) of reject material. This waste is rejected by screens that sort out the cellulose fibers that can be used to produce acceptable pulp. Reject streams containing 1% to 2% solids can be fed directly into a Vincent press to reduce the solids to press cake.

Reducing the solids to press cake reduces the tonnage that must be hauled to landfill. Many landfills require at least 30% solids before they will accept loads of waste. An additional bonus is that pressing eliminates liquid drainage on the highway when the material is being hauled.

Some paper mills press the reject material in order to dewater it to the point where it becomes a suitable boiler fuel.

Issue 42

Paper Cup Trim Recycling

Pressing News
August 3, 2015

An interesting niche exists in the secondary fiber market. It involves firms which recycle cut-out scrap from producers of water resistant paper containers.

There are many firms which produce pails for KFC® chicken, paper cups for Coca Cola®, gable top containers for Tropicana® orange juice, boxes for Ben & Jerry's® ice cream, and similar containers. These items are made of high quality bleached paper which is coated on both sides with printable polyethylene. The products are made from shapes which are die cut from large rolls of paper. This paper is produced by well known firms such as International Paper and Georgia-Pacific.

The trim resulting from the production of the required cut-outs can be recycled to recover the long fiber pulp found between the layers of polyethylene. The pulp is sold as market pulp. Because of the high quality of the fiber, the pulp is blended with other fibers to improve the overall strength of specialty papers.

The recycling begins with loading the trim into a hydrapulper. Water is blended with the trim and a thick slurry is produced. The pulper can have a screened bottom which holds back the plastic film, but which allows the fiber slurry to pass through.

As the trim is pulped, the fiber is rubbed free of the plastic film. A dilute flow of this fiber is drained from the pulper. At one mill is it prethickened with a sidehill screen and then dewatered with a Vincent screw press. The press cake is filled into bulk bags for shipment to the end users.

Typically the pulp is run through a dryer to produce thick sheets of market pulp.

Another application for a Vincent screw press, at these same facilities, is to dewater the rejected polyethylene film. This plastic is sold to plastic recyclers who process it into plastic pellets or proprietary plastic products.





Issue #275

Pressing Cake from a Belt Press

May 30, 2002

Energy costs have caused several mills to look at adding a screw press to their wastewater treatment plant. This is done so that the sludge from the facility can be used as boiler fuel. Typically the screw press is fed the cake produced by an existing belt press.

Belt presses and screw presses have fundamental similarities. Both operate on a continuous basis (not batch) to separate liquid from solids. However, each machine design has different strengths and weaknesses.

Because a belt press works with a filter made of fabric, it achieves much finer filtration than is possible with a screw press. The metal screen (perforated metal, profile bar, or drilled plate) in a screw press results in far more suspended particles in the press liquor than is characteristic of a belt press. The screening area of a belt press is much greater than a screw press, so it has greater hydraulic capacity.

The other side of the coin is that a screw press can squeeze a lot tighter than a belt press. The all-metal construction of a screw press allows higher, more concentrated, pressure and higher torque. The result is that a screw press can make press cake of a lower moisture content than is possible with a belt press.

Several paper mills have taken advantage of these characteristics by adding a screw press in series with a belt press. The belt press filters out the suspended solids, and the screw press squeezes out additional water.

Other mills have been motivated to add a screw press because of trouble maintaining acceptable consistency in the cake from their belt press. With surges in secondary (biological) sludge flow, the cake can become too moist. Instances of landslides at the landfill are not unheard of. Placing a screw press after the belt press will increase the final press cake solids from a range of 20% to 35% up to 25% to 50%, depending on the amount of secondary treatment sludge that is present.

A benefit to adding a screw press is that the belt press can now be operated with minimum belt pressure and no nip. A belt press will run almost maintenance free under such conditions.

The Vincent interrupted flight design has a particular advantage in this application. It can handle a wide range of input consistencies and flow rates without adjustment, all while continuing to produce a consistently dry cake.

Issue 58 - D

Pulp & Paper Installations


JULY, 2010


1994 Smurfit-Stone Container, Wabash, Indiana (now Paprworks Industries)
Two VP-16's doing screen rejects at a recycle boxboard mill. Tom Manley,
513-746-6493, was the plant engineer; we co-authored a TAPPI paper. We
arrived at this, our first paper mill, in June 1994.

1995 Domtar (formerly Georgia-Pacific), Port Edwards, Wisconsin
They bought a CP-6 to thicken screen rejects which are stored and later added to
special runs of bond paper. [Mill closed.]

1995 Coastal Paper, Mississippi
This is a paper maker that buys market pulp and converts it into specialty papers.
The tiny CP-4 works perfectly for their screen rejects.

1995 Bowater (formerly Halla Paper), Mokpo, Korea
This is a deinking mill. The furnish is 95% old newspapers and 5% groundwood a
fiber. They have four CP-12's, which are beautiful machines. The presses dewater 3
screen rejects and some primary clarifier sludge, all coming from belt presses.
The cake, at 55% solids, goes to a fluidized sand bed boiler.

1996 Georgia-Pacific (formerly Fort James), Pennington, Alabama
The VP-16 for dewatering knots and shives at this large virgin fiber mill is
working well. Pat Braud, 205-459-1737, is the cognizant engineer.

1996 CANFOR (Formerly FIBRECO), Taylor, British Columbia
This CTMP mill has purchased a VP-16 for pressing primary sludge with some
fraction of secondary sludge blended in. The sludge comes from a belt press.
They produce and sell market pulp made primarily from wood chips

1996 Evergreen Pulp (Formerly Samoa Pacific Cellulose) , Samoa, California
The last virgin fiber mill in California. They have a pair of VP-10's plus a rental
CP-10. One is used to dewater bleached rejects from just ahead of a paper
machine. Another is for shives. It enables them to haul the rejects to landfill
without environmental problems. [Mill closed.]
1996 Celotex, Quincy, Illinois
They had a CP-10 rented medium term and have since commissioned a VP-
16. They are a recycle mill that makes the outer paper layer for plasterboard.
The press is used to dewater screen rejects after the hydrapulper. They solve
a landfilling cost and problem by dewatering the rejects. [Mill shut in 2002.]

1996 Liberty Paper, Becker, Minnesota
This is an OCC recycle mill pressing tertiary screen rejects plus DAF sludge.
Following successful tests, they purchased a pair of VP-16's. Steve McPherson,
Production Manager, 763-261-6120.

1996 Durango Paper (formerly Gilman), St. Marys, Georgia
This firm has a pair of VP-12 presses, all-stainless construction (including the
frames), along with sidehill pre-thickening screens. Quaternary rejects are pressed
prior to burning. [Mill shut in 2002.]

1996 Georgia-Pacific (formerly Fort James), Clatskanie, Oregon
Two VP-30 presses were intended to take rain water out of sawdust. With 400 hp
drives, these are 35' long and weigh 80,000 pounds each. The units are now idle.

1996 APC Paper Company, Claremont, New Hampshire
This firm has a VP-10 to dewater OCC waste sludge prior to landfill.
Environmental problems associated with an unstable landfill led to the testing that
led to the purchase. They pre-thicken the flow to the press with a sidehill screen.

1996 Millar Western, Meadow Lake, Saskatchewan
A Model VP-16 dewatering screw press is used to increase solids in cake from a
belt press. This zero effluent mill burns the cake in a hog fuel boiler. The primary
sludge solids are increased from 30% or less to 40% or more with the screw press.

1996 Simpson Paper, Gilman, Vermont (Dirigo Paper)
This mill uses market pulp to make high-grade specialty paper. Reject material
from a large clarifier is fed to Somat presses. The sludge from the Somat's, at 10%
to 15% consistency, is fed to a Vincent Model CP-6 press. The Vincent takes it up
to 35% or 40% solids. [Mill closed in 2007.]

1997 Ponderay Newsprint (AbitibiBowater) Usk, Washington
This newsprint mill is 80% virgin fiber, 20% recycle. They are pressing a wide
range of screen rejects from both operations. Following a long rental period, they
bought a VP-16 in T-316 stainless. Their order included sidehill screens for use
ahead of the press.

1997 Buckeye (formerly Merfin), Delta, British Columbia
This mill makes sanitary napkins. A rental CP-6 worked well in competition
with a FAN press. They purchased a CP-10 for more capacity. They are pressing
reject pulp, which is collected in a Krofta clarifier.

1997 Louisiana-Pacific, Chetland, British Colombia
This mill acquired a CP-10 for sludge dewatering shortly before the mill was
1997 Buckeye (formerly Merfin Europe Ltd.), County Cork, Ireland
This sister plant has purchased a VP-10 for dewatering reject pulp from a system
that converts market pulp into paper product on a dry basis (Air Laid).

1997 Kadant Black Clawson, Mason, Ohio
A VP-16 press for use in a secondary fiber mill in Venezuela. The press,
positioned head of a deinking kneader, is used to thicken 35 TPD of stock to the
range of 30 to 35% solids. The user is Papelera Aragua.

1997 Putney Paper, Putney, Vermont
This firm purchased a VP-16 for dewatering clarifier underflow. An improved
fiber recovery system seriously reduced the capacity of the press. [Mill closed.]

1997 Buckeye Florida, Perry, Florida
After on-site testing, this 1,200 TPD softwood Kraft mill purchased a VP-16
for dewatering knots and shives. This relieves landfill load and groundwater
contamination, while creating a saleable by-product. A sidehill screen thickens
the flow ahead of the press.

1998 St. Anne-Nackawic, Nackawic, New Brunswick
This mill rented a VP-16 for two summers before purchasing the machine. It is
used to dewater reject fiber that was otherwise being taken to landfill in a dripping
wet condition. After pressing the cake burns extremely well in their hog fuel

1998 Kerwin Paper, Appleton, Wisconsin
This recycle paper mill produces colored construction paper. The VP-10 press
dewaters rejects that arise when a color change is made. The press cake is re-used
in black construction paper.

1998 Terrace Bay Pulp, Terrace Bay, Ontario
(Formerly Neenah Paper, Kimberly-Clark)
This large virgin fiber mill ran tests using a rental CP-10, dewatering primary
sludge that was pumped directly from the clarifier. They ordered a pair of VP-
16's and sidehill screens, and they are very pleased with these. The press cake
is burned in their boiler. In 2001 a third VP-16 was ordered to handle a mill
expansion, and all the presses were relocated from the WWTP to the boiler house.

1999 ALBERTA RESEARCH COUNCIL, Edmonton, Alberta
A Model CP-10 press is used for laboratory and pilot testing at the Alberta
Research Council.

1999 International Paper, Oswego, New York
This mill had a CP-6 rented for half a year. While we were switching up to a
CP-10, they tried a press by Press Technology, a Springfield, Ohio firm. That
press failed due to wear which was related to high screw rpm. [The mill is shut.]

1999 Crown Vantage, Milford, New Jersey
This mill produces food grade wrapping paper from market pulp. Rated at 200
tons per day, the mill was sending 4 to 8 tons of clarifier underflow sludge to
landfill daily. The purchase of a CP-10 screw press was justified by reduced
landfill charges. The screw press increases the solids of cake from a Komline-
Sanderson belt press from 20-27% to in excess of 50%.

1999 Corrugated Services, Forney, Texas
This recycle mill uses a small KP-6 for light dewatering of solids screened from
the wastewater flow. "The best capital investment this company ever made."

1999 Weyerhaeuser Paper, New Bern, North Carolina
This Kraft mill replaced a worn belt press with a Model VP-16 screw press and a
pair of Vincent sidehills. Final press cake solids were improved from the 30's to
45%; the cake is now sold as a fuel to a cogen power plant. No polymer is used in
the clarifier.

1999 Nevamar (formerly International Paper), Hampton, South Carolina
This mill is using a Model CP-12 screw press to dewater fiber and phenolic dust.
The dust comes from the spray chamber dust collector. The mill specializes in the
manufacture of hard board used in decorative door facings, counter tops and screw
conveyor hanger bearings.

1999 Celulosa Arauco (Alto Parana), Misiones, Argentina
This Chilean paper company procured a Vincent Model CP-12 screw press for
dewatering rejects from a brown stock tertiary screening stage. The installation is
at a softwood Kraft mill in Argentina. The objective is to recover the chemicals in
the black liquor filtrate.

1999 FiberMark, Brattleboro, Vermont
This specialty mill produces coated or embossed pressboard, using a furnish of
30% virgin and 70% recycled market pulp. They have a Vincent Model CP-12
screw press that is used to further dewater primary clarifier sludge that is first
prethickened to 22% solids with a vacuum coil filter. The Vincent press increases
the consistency to the 45% range, significantly reducing hauling and landfill

1999 Minas Basin Pulp, Hantsport, Nova Scotia
This mill has a CP-12 to dewater OCC waste sludge and tertiary/quaternary rejects
prior to hauling them to landfill. Press cake is in the range of 50% solids, and
alternatives such as burning are being considered. Pre-thickening is done with a
sidehill screen.

2000 Georgia-Pacific, Crossett, Arkansas
Integrated Technical Services of Baton Rouge, LA bought a pair of VP-16's, each
with a pair of sidehills for prethickening, for dewatering the clarifier flow at this
1,600 TPD hardwood and softwood mill. Later, LARCO purchased another VP-
16 for use under a similar contract at the mill.

2001 Gulf States Paper, Demopolis, Alabama
This mill used a VP-16 from our rental fleet while a new machine was built to
their specifications. The load is estimated at 41 TPD, dry solids.

2001 Rock-Tenn, Sheldon Springs, Vermont
A small CP-6 is used to dewater 7 TPD of rejects. They feed from the Kadant
Black Clawson Ultra Sorter at 25% solids. The press cake, at 45% solids, is sent
to landfill.

2001 Caraustar Mill Group (formerly Smurfit-Stone), Lafayette, Indiana
A rental CP-10 was used dewatering rejects from screens at this recycle paper
mill. Mark Lindstrom, 765-423-5631, is the cognizant engineer.

2001 Durango-McKinley Paper, Prewitt, New Mexico.
Furnish for this 550 TPD linerboard mill arrives by train and trailer. Four waste
streams, with varying flow rates, including one that is biological, are fed to an
Andritz belt press. The 35% solids cake from the belt press is further dewatered
to 37% to 45% solids (depending on the biological component) with a Model VP-
16 turning 5 rpm. This rental press was used until another press at the mill could
be rebuilt. Ed Tom, 505-876-2171, supervises operations. Rented another unit in

2002 Georgia-Pacific, Cedar Springs, Georgia
All wastewater solids from this 2,300 tons per day mill are dewatered in a pair
of VP-16 presses. Pairs of sidehill screens are mounted over the inlet of each
of screw press. The WWTP is operated and managed by Integrated Technical
Services of Baton Rouge, Louisiana.

2002 Rock-Tenn, Aurora, Illinois
A rental CP-10 was purchased for dewatering screen rejects in this book binders
board mill. John Goll, Assistant General Manager, 630-898-4231.

2002 Noss AB, Sweden
This paper industry equipment supplier has purchased a Model CP-4 laboratory
press for use in pulp thickening trials.

2002 Ohio Pulp Mills, Cincinnati, Ohio
This mill recovers secondary fiber from gable-top cartons, ice cream cartons, and
meat pads. A great deal of plastic film is present in the rejects. A custom Model
KP-10 press, cut short for low headroom, dewaters their waste flows ahead of the

2002 Buckeye, Mt. Holly, North Carolina
This conversion mill has air laid paper machines making diaper products. Excess
pulp from the paper machines and floor drains feeds to a DAF or sidehill, then is
pumped to a CP-10. The Vincent press replaced a plate and frame press. Contact
is Tim Kistemaker, 704-822-6400.

2002 Linpac Paper, Cowpens, South Carolina
Rejects at this 450 TPD OCC mill include unusually high quantities of plastic.
A flow of 200 gpm is fed directly to a Model CP-12 screw press, without
prethickening. Bill Johnson, 864-463-9090, is the Mill Engineer.

2003 P. H. Glatfelter Co., Spring Grove, Pennsylvania
A simple, robust Model CP-10 screw press was purchased in 2003. An enlarged
headbox was included to handle surges. Trials were run with a rental CP-6 prior
to the purchase. Since the feed flow can reach 100 gpm, a 3/32" perforated screen
was selected. Reclaimed liquor is returned to process.

2003 Flakeboard Company, St. Stephen, New Brunswick
A small CP-4 press was purchased to recover valuable oil from waste in this board
manufacturing facility.

2003 AV Cell, Atholville, New Brunswick
This mill has a Model VP-16 press on extended rental. (A new 316 stainless press
was purchased in 2006.)

2003 Inland Paper, Orange, Texas
A VP-16 was purchased by Bruce Brothers Dredging under a contract to dewater
WWTP sludge at this virgin fiber mill. Clarifier underflow is prethickened with
sidehill screens.

2003 US Gypsum, Gypsum, Ohio
This mill makes liner for gypsum wallboard. They use a Model VP-16 press for
sludge dewatering. An IPEC rotary drum screen is used to prethicken the flow to
the press.

2004 Blue Ridge Paper, Canton, North Carolina
This virgin fiber mill purchased CP-10 presses for dewatering screen rejects in
both their softwood and hardwood mills. The reclaimed liquor is returned to the
system. The press cake is burned.

2004 Sindihan Paper (UEM), Egypt
A Model CP-10 press was sold for dewatering clarifier sludge at this Egyptian
paper mill. In 2006 they inquired about purchasing another identical press for a
new project.

2004 Georgia-Pacific, Green Bay, Wisconsin
The KP-16 press at this 1000 TPD recycle mill is in an unusual application.
Floating wastes, mostly Styrofoam and woodchips, are skimmed at about 200 gpm
from the WWTP clarifiers. The press dewaters this waste stream. This is our first
installation of a Model KP-16 press in the pulp and paper industry.

2005 International Paper, Pensacola, Florida
Two screw presses, a VP-16 and a KP-16 were used in series and parallel to
thicken stock for a specialty paper.

2005 Eurocan, Kitimat, British Columbia
A Model VP-22 is used by Jose's Excavating, under contract with the mill,
to dewater primary clarifier sludge. The sludge is loaded to the press after
draining in a pond. The press cake is landfilled. [Mill closed in 2009.]

2005 Rayonier, Fernandina Beach, Florida
A Model VP-22 was purchased for dewatering knots. The press was built in
all-316 stainless, including the base frame, because of adverse environmental
conditions. The press cake is burned in a mill boiler.

2005 Evergreen Packaging (formerly International Paper), Pine Bluff, Arkansas
This mill is renting two Model VP-16 presses for dewatering a combination of
clarifier sludge and knots/rejects. Vincent Sidehill screens are used to prethicken
the flow to the presses. The cake is burned.

2006 Elite Kraft, Thailand
A Model CP-12 press is used to dewater sludge that is prethickened with a tray
belt prethickener.

2006 AV Cell, Atholville, New Brunswick
This mill purchased a Model VP-16 press built in 316 stainless construction. This
followed extended use of a similar model in 304 stainless.

2006 Inland Paper, Orange, Texas
A KP-16 was rented by Bruce Brothers Dredging under a contract to dewater
WWTP sludge at this virgin fiber mill. Clarifier underflow, at very low
consistency is pumped directly into the press. The cake produced is quite suitable
for landfill stacking.

2006 Evergreen Packaging (formerly International Paper) Pine Bluff, Arkansas
This mill rented (since purchased) a Model KP-16 press for dewatering small
reject fibers after bleaching. A feed of 200+ gpm at 0.5 - 1.3% consistency
results in press cake at 38% solids. The load is about 7 TPD dry solids. This is
a very successful application for a Series KP press. The cake is sold to a roofing

2007 Elite Kraft, Thailand
A Model KP-16S press has been ordered to dewater small pieces of plastic film,
Styrofoam and similar Combisorter or Serraplast rejects.

2007 First Quality Tissue, Lock Haven, Pennsylvania
A pair of CP-12 presses, each with paired sidehill screens for pre-thickening, is
used to dewater clarifier underflow.

2007 Pactiv Corporation, Plattsburgh, NY
A Model CP-6 press was purchased for de-watering tertiary rejects.

2007 PROPAL (Productora de Papeles), Cali, Colombia
This bagasse paper mill purchased a Model VP-24 for dewatering clarifier
underflow. No polymer was required. The cake was to be blended with coal
for use as boiler fuel. This job was a failure; however, it presents an interesting

2007 Sappi Fine Papers, Cloquet, MN
A Model VP-24 has been purchased for dewatering knots. The load is
approximately 50 TPD of dry solids. The liquor will be recycled and the crushed
knots returned to the digester.

2007 Flambeau River Papers, Park Falls, Wisconsin
A Model CP-10 has been used on a rental basis for an extended period. With a
3600 rpm motor, this press achieves outstanding capacity.

2007 Inland Paper, Orange, Texas
A KP-16 was rented long term by Bruce Brothers Dredging under a contract
to dewater WWTP sludge at this virgin fiber mill. Clarifier underflow is
prethickened with sidehill screens.

2008 Rayonier, Jesup, GA
A model KP-16, owned by Absorption Corp, is in service at the mill. The
dewatered fiber is used in the production of litter for domestic pets.

2008 UPPC (United Pulp & Paper Company), Philippines
A Model CP-12 is giving excellent results dewatering cake from belt presses at the
wastewater treatment plant.

2008 Blue Heron Paper, Oregon City, OR
This recycle mill has rented a Model KP-10 press for an extended period. The
waste includes a considerable amount of Styrofoam and plastic.

2008 Hartford City Paper, Hartford, Indiana
Based on a project carried out by AMEC consulting engineers, this mill has
purchased a Model KP-10 press for dewatering WWTP sludge. The flow comes
from a Poseidon clarifier and an Andritz sidehill screen. The sidehill, with 0.005"
slots, is PLC controlled.

2008 SAICA, Venizel, France
This large recycle mill uses a Model KP-16 to dewater sludge ahead of landfill.
The press was selected after trials with German equipment.

2008 Georgia-Pacific, Crossett, Arkansas
Larco, a contractor operating the WWTP, bought a Model KP-16 for assisting in
dewatering the clarifier flow at this 1,600 TPD combined hardwood and softwood

2008 Fiber Solutions, Pine Bluff, AR
This contractor has rented a Model KP-16 for over a year. It is being used to
recover fiber from whitewater. The press cake is sold for the manufacture of
shingles and other by-products.

2008 Georgia-Pacific, Palatka, FL
This mill rented a Model KP-16 press was used on knots and shives. The
installation was temporary while other mill machinery was being rebuilt.

2008 Sonoco, Menasha, WI
This secondary fiber mill installed a Model KP-16 to de-water sludge and screen
rejects. It replaces a screw press associated with excessive maintenance expense.

2008 NGC (National Gypsum Company), Pryor, OK
This plant uses a Model KP-16 press to dewater screen rejects and clarifier sludge.

2008 SAICA, Zaragoza, Spain

2008 Alabama Rivera Pulp, Perdue Hill, AL
A ModelVP-16 screw press is used to dewater knots at this pine mill. The press
cake is conveyed to the chip yard.

2009 Norampac, Niagara Falls, NY
This mill has rented a Model KP-16 de-watering sludge.

2009 University of British Colombia, British Colombia, Canada
The University has purchased a Model CP-4 press for laboratory and pilot
operations at the Pulp & Paper Centre.

2009 PCA (Packaging Corporation of America), Filer City, MI
This mill has installed a pair of Model VP-16 presses. An initial objective was to
reduce landfill expense. Permitting was sought to allow the cake to be sold for a
biofuel project. Additional savings were realized by the elimination of polymer
usage. A biological waste stream is to be blended into the feed to the press.

2009 Hutamaki, Sacramento, CA
This secondary fiber mill is using a Vincent Fiber Filter to pre-thicken a dilute
flow of extractor pressate ahead of a Model KP-6 screw press. This has resolved
problems with a minor waste stream and provides a saleable by-product which is
shipped to a plastics recycler.

2009 Tama Paperboard (Caraustar Industries), Tama, IA
This mill is using a rental Model KP-10 to de-water sludge and Poseidon rejects.

2009 Kimberly-Clark, New Milford, CT
This mill purchased a Fiber Filter FF-6 to separate plastic flakes and beards and
crumbs from a clarifier overflow.

2009 Kimberly-Clark, Beech Island, SC
This mill is using a rental Fiber Filter FF-6 to clean up short fibers and stickies
from a stream. The sludge from the Fiber Filter is then de-watered in a Model CP-
4 screw press.

2009 Lydall Filtration/Separation, Rochester, NH
This mill is using a rental KP-10 for dewatering sludge. This unit is replacing a
PT&M press.

2009 Glatfelter, Spring Grove, PA
This mill has a specially modified CP-4 which is used to de-water grit produced
when they slake their lime.

2009 PCA (Packaging Corporation of America), Counce, TN
A rental KP-16 has seen extended service dewatering screen rejects at a recycle

2009 Weidmann Electrical Technology, St. Johnsbury, VT
This mill purchased a CP-12 press for dewatering sludge. The mill produces paper
insulation for electrical transformers.

2010 Bataan 2020, Philippines
A Model CP-12 is giving excellent results dewatering cake from belt presses at the
wastewater treatment plant. The flow is pre-thickened with a sidehill screen.


Pressing Dilute Flows

November 30, 2005                                                                                                                                                                                              ISSUE #167

Occasionally questions arise about feeding a screw press with extremely dilute flows. We have one good set of data that involves this condition. They come from an OCC (old corrugated container) recycle mill, Liberty Paper, in Becker, MN.

They fed a flow of 260 gpm into a Vincent Model VP-16 press. This flow was mill effluent with a solids consistency of only 0.7% (7,000 ppm). This represents a feed of 11 tons per day of dry solids going into the screw press. The result was that 4 TPD,DS were captured and came out as press cake with 45% to 50% solids. The press liquor (effluent) from the press had about 4,500 ppm of solids. Thus the capture rate of the press was about 35%.

This operating condition occurred only during mill shut-downs because normally the feed to the press was in the range of 2% to 3%. (The city objected to the 4,500 ppm discharge periods, so at the time Liberty had to add sidehill screens ahead of the screw press, just to cover down periods.)

Thus it is seen that the press does not become inoperable due to extremely low consistency feed. Even with straight water going into the press, water will not purge from the solids discharge end of the press. On the other hand, the capture rate does go down significantly.

The Smurfit mill in Wabash, Indiana tested this to the limit in 1994. They ran the press normally for a while and then replaced feed flow to the press with a firewater hose. The press was run this way in order to confirm that a plug of fiber at the solids discharge would hold, preventing any water from coming out the solids discharge end of the press. All of the fire water came out through the screen. Normal press operation resumed automatically when the normal flow was re-admitted to the press.

(The other extreme of this same test was to have the press in normal operation and then switch the flow into press to cake from the press. That is, the press was fed only cake with 50% solids. This material passed through the press without the press tripping out on overload or damaging itself. Negligible press liquor came through the screens when operating in this manner.) 

Prethickening with a Sidehill Screen

July 22, 2004                                                                                                                                                                                                      ISSUE #151

Many flows require prethickening before they can be dewatered in a screw press.  If the feed to a screw press is too dilute, two problems are likely.  The obvious problem is that the press may not have sufficient open screen area to pass all the water.  The press can become limited by its hydraulic capacity rather than the solids discharge capacity.  This can be avoided with either a larger screw press or some form of prethickening.  The prethickening option almost always costs less.

A more subtle problem associated with dilute flow in a screw press is that the solids capture rate will drop.  The reduced capture of solids occurs because the velocity of water passing through the screen increases to where the solids particles are swept through the screen.  This is apparent in manure dewatering applications:  the solids capture rate with scraped manure barns is 50%, while it drops to only 25% at flush barn installations.

In general, the least expensive prethickening device is a sidehill screen.  (These are also known as parabolic, gravity, sloped, and static screens.)  Sidehills are inexpensive, and they have the advantage of having no moving parts.  However, sidehills get a bad rap.

Engineers and operators will frequently voice objections to sidehills because they are not consistent.  It is common for them to flood when the flow goes up or when the screen surface becomes dirty and blinded.  This changes the consistency of the discharge sludge, which may cause problems in downstream equipment.

If the downstream equipment is a screw press of the continuous flighting design, yes, there are apt to be problems.  A reduction in feed consistency to a screw press of this design can cause the press to produce wet cake, or even purge, if its speed is not reduced.

In contrast, the Vincent screw press, because of its interrupted flighting design, works very well with sidehill prethickeners.  The gaps in flighting between each of the compression stages of the screw must fill with solids of some consistency before material will move toward the discharge of the press.  Consequently, even if the feed consistency decreases due to flooding of the sidehill, the Vincent screw press will continue to produce discharge cake with a steady solids content.  No adjustment or change in speed is required.            

This advantage of the interrupted screw design has been demonstrated most vividly in the pulp and paper industry.  A significant number of installations, in both virgin fiber and recycle mills, have now been operating for enough years to offer convincing evidence.

Pulp & Paper I

August 30, 1994

It was in 1994 that Sales Representative Gary Gann came to us with a chance to test in a paper mill. His customer, a major recycle paper mill, had a severe problem because their primary and secondary sewage treatment plants were no longer able to carry the load. Would we be able to filter the waste stream?

Despite four decades of pressing, Vincent had never had equipment in a pulp mill. Sensing a unique opportunity, we responded by dispatching two small presses for trials. By the time these presses made it back to Tampa they had been modified many times. It took that to meet the challenge.

Engineering Management at the plant hoped that a screw press would be able to remove solids from their waste stream. They wanted to avoid adding another belt press because of the high maintenance expense and need for an operator. It turned out that three other screw press manufacturers had tried their equipment at the plant, without success.

We learned from their experience. Blinding on ash and clay was avoided by going to a profile bar (heavy wedgewire) screen. A purging problem was solved by improving the arrangement of the auto- adjusting discharge cone. Press plugging was avoided with a combination of the interrupted screw flight design along with a unique by-pass and dilution system. It took several modifications to our standard citrus screw press to make it work.

Today the plant is avoiding pollution problems. They used one of our larger rental press until a pair of all-stainless VP-16's could be delivered. In fact, they were able to shut down one of their two waste digesters.

The application was challenging because of the very wide range of conditions that exist. The plant produces boxboard by recycling pre-consumer waste paper, so screen rejects from a variety of stages reach the press. When metal is detected, thick stock is diverted to the press. Periodically their clarifier backwashes fine sludge to the press. Other times the inflow becomes extremely dilute because flushing is going on in the plant. Our one press is handling this full range of materials!

5/97 Update: Today Pulp & Paper is more than half our business!

Issue 13

Pulp & Paper II

March 21, 1996
Rev. March 1998

It was in June of 1994 that Vincent was invited to their first on-site testing in a paper mill. This has led to a major change in the Company: today more than half the presses being built are going to the pulp and paper industry.

Paper mills fall into three main categories:

    • The virgin fiber mills where digesters cook wood chips to make paper pulp
    • Recycle mills where waste paper is pulped by agitating it in a water bath
    • Mills that buy market pulp from other mills and convert it into their own specialty papers.

Vincent has screw presses operating in all three of these industry segments. In most cases our press is being used to dewater waste streams.

The waste streams generally have consistencies in the range of 1% to 12% solids. They are dewatered so that the solids become a bulky material that can be readily handled. At the same time the pressate liquid frequently becomes clear enough that it is acceptable for re-use in the mill.

The waste streams that can be dewatered in a Vincent press consist of various forms of screen rejects. In a virgin fiber mill rejects come both before and after bleaching. Ahead of bleaching we deal with brown stock rejects: knots from the knotters, and shives (along with a fair percentage of good fiber) from the tertiary or quatenary pressure screens.

In a recycle mill a variety of screenings are used to separate unusable fiber along with dirt, ink, plastic, etc. All of the waste streams will contain some measure of good fiber.

The press cake will typically be in the range of 40% to 50% solids. The lower solids content is adequate for easy handling and transport, while the higher solids material might be used for boiler fuel. (In the boiler fuel application the press cake is combined with 80% to 90% coal.) Frequently the press cake is landfilled. However occasionally the press cake is sold to mills capable of using the material in the production of lower grade pulp products. Other uses include filler for tar paper and shingles as well as landscaping mulch.

This is where we find the market.

The most common inquiry from the pulp and paper industry involves pressing clarifier sludge at the wastewater treatment plant. We have found that our press will usually work well on this material. This is especially true if there is little or no biological (secondary treatment) sludge present. Our competitors in this market are the immense continuous screw presses offered by Andritz and FKC.

With our press design we have found that the best performance is achieved if the clarifier sludge is prethickened with a gravity table or a belt press. To address this opportunity we have established a relationship with Phoenix Process Equipment Company, a major supplier of belt presses to the pulp and paper industry.

Future issues of Pressing News will detail our applications in both virgin fiber and recycle mills.

Issue 40


January 23, 1996
[Rev. September 2002]

Largely because of action by environmental groups, the cost and availability of timber in the northwest has become a problem for paper mills. Paper makers now make paper that contains fiber extracted from lumber mill sawdust. Because lumber mills normally burn their sawdust, it represents an economic source of raw material for a pulp mill.

In 1996 this situation led to pressing trials using sawdust. The tests were conducted in Tampa with engineers from Fort James trying out three different Vincent screw presses.

The thin, high speed saw blades used at the lumber mills are cooled with water. This process increases the moisture content of the sawdust slightly from the normal 52% found in green lumber. Rainfall adds even greater moisture content. The samples tested in Tampa had 65% moisture (35% solids).

The normal press configuration was found to produce press cake with 42% solids. The horsepower required was in the high range for Vincent presses. Since the Fort James specification called for 45% to 48% solids, a special screw design was used in subsequent testing.

It is noteworthy that the pressing action is only removing free water. We are not breaking open the cells of the wood. A competitive press requiring 3,500 hp could achieve solids closer to 60%. However this broke down the cellulose fibers, reducing the quality of the paper being produced.

Therefore, the final contract called for two VP-30 presses, each with 300 horsepower drives. These subsequently were modified to 400 horsepower. The bulk density of the sawdust usually is low, about 22 pounds per cubic foot. This is compressed dramatically, to the point where water is expelled, by changing the screw shaft diameter just ahead of the first resistor tooth. The pair of presses can handle approximately 100,000 pounds per hour of sawdust.

The presses were supplied with an unusual feature: The resistor teeth were drilled for the possible addition of steam directly into the sawdust as it is being pressed. This technique was used many years ago in both fish meal and citrus peel to achieve lower cake moisture. To date it has not been used at the paper mill.

Unfortunately, the need at the Fort James Clatskanie mill is unique. They have an overloaded sawdust digester. The arrangement does not allow for the addition of sufficient steam when the sawdust is wet. Thus the capacity of the digester drops from 300 TPD in the summer to 240 TPD in the winter rainy season.

Another problem is that James River in Clatskanie has a limited amount of white liquor generating capacity. The excess water in the sawdust requires extra white liquor to overcome a dilution effect.

On the other hand, improvements in the material handling system appear to have resulted in increased digester capacity. Simply being able to feed more tonnage of the damp sawdust into the digester may have been all that was required.

The installation of the VP-30 screw presses never quite succeeded, primarily due to stick-slip vibration that occurs. This vibration occurs when tight pressing is attempted. A variety of mechanical failures have resulted from the vibration, in spite of numerous modifications.

Issue 38

Shower Water Filtration

October 25, 2001                                                                                                                                                                                                 ISSUE #122

Tests were recently conducted using a Vincent Fiber Filter on shower water at Atlantic Packaging in Scarboro, Ontario. The Fiber Filter was selected because of its small footprint and attractive capital cost compared to conventional filters.

This recycle paper mill has a combination OCC (Old Corrugated Container) and tissue operations. The most important use of shower water is on the felt of paper machines. Other applications are on trommel and rotary drum screens.

The primary source of shower water comes from disc strainers used at the end of the stock prep process. The disc strainers raise the paper pulp from 1.2% to 12% consistency. There are three effluents: cloudy, clear, and super clear. The cloudy effluent is pumped back to the start of the process at the hydrapulpers. The clear effluent is re-used half way back in the stock prep process, with the excess going to sewer.

The disc filter itself uses some of the super clear; the rest is filtered prior to use as shower water. The existing super clear water filters are Sweco machines that feature a vertical axis with a spinning drum screen. The drums have fabric panels backed up with coarse mesh steel screen. The drums are about 4' in diameter.

These Sweco's are very old and have served their purpose; maintenance expense has become excessive. Thus our Fiber Filter is being evaluated as a potential replacement.

The very low solids consistency of the super clear water resulted in high capacity in the Fiber Filter even with very fine fabric sleeves. With a feed consistency of 70 ppm, using a 31 micron sleeve, we were able to produce filtrate with 20 to 25 ppm. This was done with the Model FF-12 being fed about 200 gpm and producing about 1 gpm of fiber-sludge discharge.

A goal of the project is to eliminate the need for addition of city water make-up to the shower water tank.

There is a rule-of-thumb used in selecting filters used on flows ahead of spray nozzles: The filter basket should have openings one tenth the size of the openings of the shower nozzles. This is achieved with the 20 and 31 microns sleeves available for use with the Fiber Filter machines.

Spray Chamber Dust

February 27, 2001

Everyone is familiar with Formica counter tops.  This material is made from ground wood dust that is combined with phenolic resin.  The material is heated and pressed to produce a rigid, homogeneous, void-free material.  In addition to counter tops, the material is used for wall paneling (Masonite board) and furniture.  Vincent Corporation buys rods and tubes of this material, called Ryertex, to manufacture certain bushings and screw conveyor hanger bearings.

The International Paper plant in Hampton, South Carolina produces Micarta sheets and rods of this material.  It is known for its electrical insulating properties.  One of their engineers happened upon the Vincent web site,, and thought of using a screw press to dewater their waste stream.  A phone call was made and, within a very few months, a Model CP-12 screw press was built and installed.

Sawing and sanding operations are part of the manufacturing process, which creates a lot of dust.  Dust-laden exhaust air is drawn through the chamber, and water is sprayed into the air.  The dust and water fall to the bottom of the chamber, forming a sludge.  There was a need to separate the free water because the waste is sent to landfill.

To dewater the sludge from the spray chamber it is elevated by a drag flight conveyor to the CP-12.  This flow is about 1,000 pph at 16% consistency.  The press cake produced by the press is a dry material with only 32% moisture, and the press liquor is clear enough for reuse within the plant.

Initially the CP-12 did not perform very well.  Then the screw was slowed by switching to a 1200 rpm motor.  With this change the cake became much drier.

An unexpected problem was encountered at the installation.  The powdery press cake entered between the screw shaft and the cone bushing.  The heat was sufficient to melt resin that is present, and the cone started seizing to the screw shaft.  The condition was caught before serious damage occurred.

To address the situation an automatic lube system was designed and supplied.  It uses compressed air to pump lubricating grease to the cone bushing.  A timer sets the frequency and duration of the pump cycle.  This system is now being offered as standard in a variety of Vincent applications.

Issue 115


Stock Thickening

April 20, 2004

The best Pulp & Paper application for Vincent presses has been to squeeze as much water as possible from reject fiber. Typically we are working with screen rejects, knots & shives, and clarifier underflow. If the waste solids are to be landfilled, they are squeezed to only 35% to 40% solids, minimizing abrasive wear within the press. If the waste is to be used as boiler fuel, then the discharge pressure of the same press is increased and cake with 50% solids is achieved.

A different application involves thickening a flow of fiber and water to a solids consistency of only 30% to 35%. This need exists where good fiber must be thickened (a) for temporary storage, (b) ahead a deinking kneader, or (c) between stages of a counterflow wash or bleaching operation. In these applications it is important not to squeeze too hard as fiber damage can result, and the cake produced will no longer be sufficiently fluid.

On three occasions we have sold Series VP presses for stock thickening, with good results.

Earlier this year excellent results were achieved using a Series KP press. This series of machines was introduced in 1996 for "soft squeeze" applications. The initial market, dewatering cannery and fresh-cut produce waste, required a light, low-torque machine. This changed almost immediately as we entered the farm market for producing cow bedding from manure. This application required the same economical press, but with three times the horsepower.

Until last year the market for Series KP presses was limited to 16" screws. However sales were made to corn canneries that needed machines that could handle up to 100 tons per hour of corn husk and cob. That led to the introduction of 24" and 30" Series KP machines. Converting this waste into silage by-product was once again a high torque application.

It was recognized that the Series KP press technology had evolved to where it could be suitable for stock thickening in paper mills. Tests were run, demonstrating that the press was easy to set to hold 33% to 36% output solids. Typical of operation with the interrupted flight screw design used by Vincent, this output consistency held over a wide range of feed consistencies. Capacity of the 20-hp KP-16 was 30 tons per day, air dry solids, so a Model KP-30 press was recommended for the 100 TPD load at the mill.

This testing was performed at the Linpac mill in Cowpens, South Carolina, where deinking capacity is limited by insufficient prethickening capacity ahead of the kneader. The testing demonstrated that a Series KP screw press could be placed in parallel with the existing prethickening press in order to relieve the bottleneck.

Issue 152

TAPPI - Pressing Knots & Shives

Tappi Journal, Vol. 82, No. 2, February 1999

The project described in this article all started with an ad in The Tappi Journal. The ad was brought to the attention of Joe Lukasik, an engineer at the Atlanta office of Sandwell Inc. At the time Sandwell was working on a fiber recovery project at the James River Naheola Mill in Pennington, Alabama. Through Sandwell, arrangements were made for on- site testing. The success of the trials ultimately led to the four installations described in this article.

An unusual project with many advantages has recently come on stream at the Gilman Paper Mill in St. Marys, Georgia. The installation features a pair of screw presses that are used to dewater quaternary screen rejects. This technology parallels a similar project at Fort James Naheola Mill, with interesting differences.

The Gilman mill, rated at 1,200 tons, has been in service since 1941. It has both hardwood and softwood kraft operations employing thirteen batch digesters. About half of the tonnage goes to bleached and unbleached kraft multiwall specialty products, with the other half going to bleached board, coated and uncoated.

Similarly, the Naheola Mill, rated at 1,100 tons, has both hardwood and softwood kraft operations. About half of the pulp produced in converted on-site to tissue and towels, while the rest is used for packaging board.

At both mills the screw press project was part of a new fiber preparation system that features Thermo Black Clawson pressure screens. At Gilman, the principal benefit of the new system is improved stock quality to the #1 paper machine, while at the same time converting waste materials into useful boiler fuel. In contrast, at Fort James the principal benefit is increased chemical and fiber recovery, while at the same time reducing loading at the wastewater treatment plant.

At Gilman prior to the installation of the new pressure screens and screw presses, rejects from secondary screens were refined and pumped to the blow tank. This was undesirable because it resulted in poor stock quality to one of the paper machines.

In contrast at Fort James, prior to the installation, insufficient quaternary screening was available. Rejects from vibratory (secondary) knotters were accumulated at ground level prior to hauling to landfill, and rejects (mostly shives) from the quaternary pressure screen were diverted to the wastewater treatment plant. This system had poor yield and excessive loss of digester chemicals.

With the new systems, both mills use Vincent screw presses to dewater combined flows of knots, shives, and other rejects.

At Gilman the new system uses a Vincent sidehill screen to thicken the 160 gpm 2.3% consistency flow ahead of each of the screw presses. The screen tailings are funnelled directly into the 12" presses. At Fort James, in contrast, the flow of quaternary rejects and knots from the knotters flow directly to a 16" press without benefit of a sidehill screen. Surge flows of up to 400 gpm go to the press.

Both mills use a hot stock screening system. The rejects from the unwashed stock, at 190º F, are what go to the screw press. The press liquor, containing chemicals and some usable fiber, is returned either to the rejects tank supplying the pine side secondary screen or to the chemical and fiber recovery flow.

The horizontal screw press has two screening sections: at the inlet hopper and over the compression stage. An initial knot dewatering application supplied by Vincent Corporation to Fort James Naheola mill had profile bar screens (baskets) with nominal 0.020" (one half millimeter) slots. To optimize chemical and fiber recovery these were subsequently changed to 3/32" perforated screens. Based on this experience, the Gilman presses had press screens with 3/32" perforations from the start.

It was found at Fort James that in normal operation the inlet hopper screen of the press allows free liquor to drop out, which consists of up to 40% of the total pressate flow. In addition an unexpected source of liquor recovery was found to arise from pressing the knots. Testing showed that 20% by weight of knotter rejects is converted into press liquor in a Vincent screw press. It is estimated that this liquid flow amounts to 10% of the total chemical recovery, as well as some of the fiber recovery.

The screw presses were designed specifically for the pulp and paper industry. All contact parts are made of stainless steel (316 at Gilman; 304 at Fort James), and weld applied hardfacing is used on the wear areas of the screw and discharge cone. Heavy duty drive and screw flighting allow the press to operate under conditions of a "hard cook" when material similar to ground wood enters the press. Vibration was minimized in the Gilman presses by specifying that the drive motor be mounted in line with the gearbox. Since this eliminates V-belts from the drive train, a variable frequency drive (VFD) is available. Gasketing compatible with H2S was employed, and all bronze materials (nuts and bushings) were eliminated.

Gasketed covers were supplied with provision for modification for vacuum recovery of vapors. This is in anticipation of future requirements for collection of Total Reduced Sulphur (TRS) emissions.

In passing through the press, the knots are broken into small bundles of fiber. This occurs because the press design is based on an interrupted screw flight with stationary resistor teeth. The agitation and shear caused by these members break down the knots. Some fiber recovery improvement is achieved as a result of this action. It is difficult to spot the difference between the knots and the shives in the press cake.

The press cake moisture can be controlled by adjusting the air pressure actuating the discharge cone (also called a stopper or plug). With this devise press cake moisture in the range of 45% to 55% solids is maintained. In mills where the cake is landfilled, lower cone pressures and higher cake moistures are typical.

At Gilman the press cake is made of elements that previously were refined and recirculated, while at James River they were sent either to landfill or wastewater treatment. With the new installations the rejects are used as boiler fuel at both mills.

Similar installations exist at two other paper mills. At these the press cake is being sold as landscaping mulch and as raw material for an asphalt shingle manufacturing operation. Vincent has supplied screw presses for use on shives to Louisiana-Pacific, Samoa, California and for knots and shives to Buckeye Cellulose, Perry, Florida. The motivating factors at these mills were to facilitate off-site hauling, to avoid landfill problems, and to extend landfill life.

The success of these installations has generated interest in pressing knots and shives. The projects are relatively small and simple. Incremental improvements in pulp making and abatement of environmental pressures are the benefits.

Ross is Chief Engineer, Gilman Paper, 1000 Osborne St., St. Marys, Georgia 31558; and Johnston is Professional Engineer, Vincent Corp., 2810 East 5th Avenue, Tampa, FL 33605.


The flow of hot black liquor being squeezed from the quaternary rejects is seen dramatically when the screw press covers are removed.


One of a pair of Vincent Model VP-12 presses. Tailings from sidehill screens on the floor above drop through the vertical chute into the press.


Press cake drops to a concrete bunker at ground level prior to being transported to the hog fuel boilers.


This press cake typically has 50% solids and has excellent combustion characteristics.

TAPPI - Pulp & Paper Waste Dewatering

Tappi Journal, Vol.78, No. 12, December 1995.

Prepared by Thomas H. Manley, Plant Engineer, Boxboard Mill Division, Jefferson Smurfit Corporation, Wabash, Indiana; and Robert B. Johnston, P.E., Vincent Corporation, Tampa, Florida.

Screw presses installed at the Jefferson Smurfit boxboard mill in Wabash, IN have significantly decreased the load on the wastewater treatment facility and facilitated the capture and disposal of fines in the primary clarifier sludge.

These benefits were achieved by reversing the position in which screw presses are normally used. In the typical installation, the screw press goes at the end of the cycle, receiving the sludge from clarifiers and/or DAF systems. At Jefferson Smurfit the presses were instead placed to receive reject material flows ahead of the clarifiers.

Higher than anticipated reject rates from the mill's cleaning systems had increased the load on the existing wastewater treatment facilities. Conditions reached a level where, during upsets, unacceptable discharges could occur. Resolution of this problem was necessary to ensure continued compliance with the mill's NPDES permit.

Screw presses offered key advantages. They operate continuously through wide swings in flow rate and solids concentration; they operate unattended; and they require minimal maintenance.


Established as a recycle mill in 1892, today this plant specializes in producing high quality boxboard. Typical end uses include breakfast cereal boxes.

The nominal mill capacity is 365 TPD. Basic machinery includes six Hydrapulpers and two paper machines: a 96" ten cylinder (400 fpm) Multiply and a 120" eight unit (500 fpm) Ultraformer. Both machine coated and uncoated combination boxboard is produced.

Wastewater Sources

There are a great many point sources of wastewater in the plant. Important ones include pulper detrashing screens, pressure screen rejects, unclaimed cooling water, and tank overflows. Rejects from the pulp cleaning system are the focus of this paper. These rejects are pumped directly to a screw press. They include forward cleaner rejects as well as fine and coarse screen rejects.

Large trash from the Hydrapulpers is removed continuously by a continuous scavenger system. This bulky material is moved by conveyor to a dump hopper.

Wastewater Treatment

Primary wastewater treatment is performed in an Infilco clarifier.

The secondary treatment plant is an activated sludge system. It is physically located on an adjoining property. Originally it was operated by the City of Wabash, treating both mill and municipal wastewater. It consists of three rectangular aeration basins, two rectangular digesters and three final settling tanks. The water is discharged into the Wabash River in accordance with an NPDES permit.

Polymer is added to sludge that is pumped from the Digesters. This sludge is then dewatered on a belt press. The belt press requires an operator on each shift, and it is generally regarded as a high maintenance machine.

To minimize the tonnage or cubic feet going to landfill, 40% or higher solids is desirable in the press cake. The belt press used at the secondary treatment plant can achieve only 30% (approximately). Although screw press material, due to its characteristics, can be spread with solids up to 50%, the belt press cake material cannot be spread at consistencies above 30% solids. This is due to the operation of the feeders on the trucks that are used to landspread the press cake.

There are various practical and theoretical means of disposing of sludge from the belt press. One of the most economic is land application: farmers accept the material without charge because of its benefits to the soil, and the farm acreage in the immediate area of the plant currently supports these operations.

Placing the press cake in a landfill was very economic in the past. However with the decline in landfill sites in the immediate area, plus regulations applied to landfill operations, this disposal option has lost favor.

Additional potential future disposal means are under review. The sale to other business operations is especially attractive. Potential buyers include paper recyclers capable of using the fiber that is rejected at Wabash because of stringent product specifications. Also, it is recognized that material that is dewatered to approximately 50% moisture might be used as a boiler fuel by blending with coal. A final option under review involves coal mine reclamation activities.

Press Application

Most waste water streams from the mill are combined ahead of wastewater treatment. The combined flow is pumped across a bank of inclined screens to remove long fiber prior to entering the primary treatment. The long fiber is returned to the mill for re-processing.

Reject streams from forward cleaners and pressure screens do not pass over the sidehills. Instead they are fed directly into a pair of screw presses. Filtrate water from the screw presses flows to the primary clarifier. Excess clarified water then overflows to the secondary treatment plant.

The screw presses generate 7 to 21 dry tons per day of press cake at up to 50% moisture.

It is important to note that the wastewater treatment facility does not have to handle this tonnage of solids. By capturing the solids with a screw press, a significant reduction of load on the wastewater treatment plant is achieved.

Capture of clarifier sludge in a screw press is difficult. There is a tendency for the fines (clay or ash) to blind the screens of the press, which results in drastically reduced press throughput capacity.

The operation results in screw press filtrate water with 500 to 1000 ppm solids. This range of solids is within an acceptable range for treatment and capture in the secondary treatment plant.

Selection of a Screw Press

Six presses by four different manufacturers were tested on-site with varying results. In the end a design manufactured by Vincent Corporation was selected. The design is a modified version of their standard citrus press, a machine used in converting orange peel into cattle feed. The modifications were required because, while wet fiber dewaters much more readily than citrus peel, it is much less compressible once the free water is removed.

During the trial operation, efforts were made to develop a set of specifications for the screw presses. This effort began with a focus on normal technical details such as gpm capacity, horsepower requirements, press cake moisture and screw diameter. This proved unsatisfactory because of the very wide range of flow rates and solids concentrations that were encountered. The varying nature of the inbound flow (easy to press fiber as compared to difficult to press sludge) made the specifications difficult to write.

In the end, the unique purchase specifications were as follows: The primary performance criteria for satisfactory operation of each press are (1) it must not plug or jam and (2) it must not pass large quantities of unpressed liquid into the flow of press cake. The press must operate like a pump: reliably, unattended, and with very infrequent maintenance.

The presses that were purchased have many unique features. For example, it was found that the use of wedgewire screens, as opposed to perforated metal, not only increased physical strength but also reduced the concentration of suspended particles in the press filtrate. Wedgewire appeared to be more self-cleaning than perforated metal.

Accommodating the absolute peak flow under conditions of maximum blinding would have required an excessively large screw press. Rather than purchasing such a large machine, provisions were made to allow the incoming flow to overflow the inlet hopper during the unusual peaks. This overflow is directed back into the treatment system. It is estimated that this overflow provision is used less than 5% of the time.

A pneumatically adjustable cone at the press discharge allows the press to operate satisfactorily over a wide range of flow rates and solids concentrations. If the inbound solids are low, the cone pinches off the discharge to prevent liquid from purging into the press cake discharge. The design of this cone mechanism negated the need for a variable speed drive on the screw press, which represented a significant capital savings.

The presses also feature an interrupted screw flight design, as opposed to a continuous screw. Because the screw is discontinuous, fixed resistor teeth can be mounted to the press frame, protruding into the flow of material inside the screen. This design reduces co-rotation, the condition where material rotates with the screw and nothing either enters or leaves the press. The stirring action by the teeth allows for a shorter machine that requires less horsepower to operate.

To assist in un-blinding the filter screen, presses were acquired that have a wiper-brush mounted on the screw auger. This clears blinding material from the screen surface. The feature assists operation during periods of high sludge content.

Maintenance requirements also guided the press selection process. Presses were purchased with all contact parts made of T-304 stainless steel, which specification will minimize maintenance requirements over many years. Similarly, presses in a horizontal configuration were selected because of the ease of disassembly in the event of screw, screen, drive, or cone maintenance. Finally, the presses selected make use of standard OEM gear boxes, bearings, seals, etc., which further reduces maintenance expense over the long run.


The principal result of the installation of the screw presses has been to relieve solids loading on the wastewater treatment facilities. A recent expansion of the mill cleaning system had resulted in serious overloading of reject material going to the wastewater plant. With the addition of the screw presses this condition has been resolved.

One side benefit of removing such large quantities of solids ahead of the treatment plant has been a reduction in the amount of sludge to be belt pressed. The sludge from this source has been reduced from 1,000 to 600 dry tons per month.

Results from when the wastewater treatment plant was at times overloaded to conditions following the installation of the first screw press have been compared. The analysis shows that suspended solids were reduced from an average of 75 mg/l (or ppm) to 25 mg/l.



During an extended period of trials at Jefferson Smurfit, numerous problems were encountered. These included:

  1. Overload and Trip-Out. This was apt to occur when pressing too tight. Typically it was a consequence of feeding thick stock to the press during upset conditions. Solutions included providing for dilution water at times of high amperage draw and oversizing the press.
  2. Purge of Liquid in the Press Cake. Some presses had difficulty when insufficient fiber was present to form a press cake. Pre-thickening can relieve this problem. The design of the press discharge cone is very important.
  3. Screen Blinding. The screens of most presses tend to blind on clarifier sludge. It appears that platelets of clay in the sludge bridge the openings in the screen and prevent the flow of liquid through the openings. This problem is even more pronounced if biological (secondary treatment) sludge is present. At times the addition of fiber waste will act as a press aid and wipe the screen clear. Also, pre- thickening with a belt press can help. Alternatively, the use of a low rpm continuous screw press will address this problem.
  4. Excessive Solids in Press Filtrate. With certain screen configurations, the parts per million of suspended solids in the press filtrate were found to be ten times greater than the acceptable range. The use of wedgewire screens resulted in the best performance.
  5. Interrupted Operations. Some presses required operator attention before satisfactory operation was achieved on a re-start. This occurred under conditions such as a period of no incoming flow followed by resumption of mill operations. Dilute flows during flushing and wash-down can also require operation attention to the screw press. The machines at the Wabash boxboard mill were selected to be able to handle these swings without adjustment.
  6. Screw Wear. Excessive abrasive wear was noted on press components such as the screw flights and discharge cone. This is addressed with the addition of hardfacing in the wear areas.

Venezuelan Paper Mills

January 21, 2001

In December Vincent conducted a screw press workshop and presented a paper at a Pulp and Paper conference in Maracay, Venezuela. The trip offered a chance to study the pulp and paper industry typical of many small countries.

There are nine paper mills in Venezuela, one of which is shut down and another operating in bankruptcy. All of the nine have secondary fiber (recycle) operations. Four mills have virgin fiber operations: one Kraft long fiber (pine) mill; one CTMP (Chemical Thermo Mechanical Pulp) mill; one ground wood, and one that uses sugar cane bagasse as a furnish. Almost all of the mills have US parent firms. There is only one small mill that is still locally owned. Because of parent firm involvement, the paper making technology is relatively advanced. The engineers we met, all Venezuelan, were at a par with the personnel found in North American mills.

At a typical mill we saw coarse hydrapulper rejects going, quite wet, from a trommel (rotary drum) screen to landfill. No baler or screw press was used for further dewatering. The same mill had a pair of belt presses dewatering flocculated (polymer added) sludge and clarifier underflow. The cake from these was quite dry, 35% solids, due to a high ash content. This cake also was sent to landfill.

In North America we would have been enthused with the possibility of using a screw press for further dewatering in order to prevent drainage on the highway or to produce boiler fuel. However, in Venezuela the environmental regulations are fairly lax, and fuel is very cheap, so there is little opportunity of selling a press.

One mill did use a screw press on their sludge. This was acquired with an aim to producing fuel for a boiler. However the project was abandoned because of the high capital cost of a fluid bed combustor along with the low price of fuel oil.

The country is in poor financial condition and relatively unstable.

Issue 114

Virgin Fiber Mills

June 4, 1996

Paper mills that process chipped logs and sawmill waste into paper are located in the woodlands of the northern and southeastern United States.

We have found several applications where Vincent screw presses can be used advantageously. These involve dewatering waste material such as screen rejects, shives and knots.

Screen rejects are bits of material that are not suitable for making paper. They can come from pressure (filter) screens both ahead of and following a bleaching operation. At times they are in thin flows containing 1% solids, while at other times they may have been thickened to approximately 10% solids. Because the solids are large enough to be caught in the screen of our press and the water is loose (that is, not bound) excellent pressing results are achieved.

Shives dewater beautifully in our press. Shives are tiny bundles of cellulose fibers and lignin that are not suitable for producing paper. The shives are screened from the acceptable pulp and become a waste stream. Dewatering in a press removes them from the waste stream going to the wastewater treatment plant. The press liquor from the press can contain both fiber and chemicals that are worth recycling. At the same time, the press cake will be useful as boiler fuel; landscaping mulch; and filler for asphalt shingles and tar paper.

Another waste product at a virgin fiber mill is knots. These are the remnants of branches that are seen in lumber products. Knots absorb a great deal of digester chemicals, but they do not become useful pulp fiber. They are screened from the flow of cooked wood chips with vibrating shaker screens called knotters. Knots are either burned or sent to landfill. Pressing knots in a Vincent press results in 20% by weight being separated as a thick black liquor. This enables valuable chemical recovery and also makes the knots into a better fuel. Pressing knots also addresses an environmental run-off situation which can occur if high pH (12 or more) drainage occurs from the knot pile.

Issue 44

Wax Coated Box Recycling

July 30, 1998

Recently Thermo Black Clawson of Middletown, Ohio has started promoting a new, patented recycling process. The system, trade named Xtrax, is used to recycle wax-coated corrugated containers. Inland Paperboard and Packaging Inc. is a partner with Thermo Black Clawson in the development.

Wax-coated corrugated containers have largely replaced wooden crates for transporting produce and fruit. The tonnage of these cartons produced per year is quite large: an estimated 1,500,000 tons. We were surprised to learn that, by weight, these cartons are 30% wax.

Paper machines at normal OCC (Old Corrugated Container) recycling mills can tolerate up to about 3% wax. Because of the problems caused to the paper machine clothing by excess wax, the wax-coated boxes are segregated. Up until now the great majority of them have been incinerated or landfilled.

The new Thermo Black Clawson process features the addition of steam to the hydrapulper. The heat melts the wax. Then a conterflow series of TBC Reverse Screens are used to wash the wax from the flow. In the end the furnish has less than 1% wax.

In April of 1998 Vincent Corporation was honored to be invited to a Trial Demonstration held at the Middletown laboratory of TBC. Representatives from ten paper companies attended along with engineers from Poseidon (clarifiers), BetzDearborn (flocculents), Brown & Root (consultants), and CITGO (waxes).

Vincent screw presses were used in two phases of the process. One CP-4 was used for primary, first wash dewatering. Testing was done at 165º, 185º and 150º. The wax content in all press cake samples was on the high side, 4-1/2%; we feel that this can be improved by using higher cone pressures.

A second CP-4 was used on the DAF sludge coming from a unique Poseidon clarifier. Most clarifiers are very large in diameter and of relatively short height. The Poseidon machine was shaped more like a grain silo, with up-side-down umbrellas on the inside. Flocculated wastewater is pumped into the side, at the bottom. The clarified water makes a U-turn into the umbrellas and drains from the bottom. The sludge floats to the top and over a weir. Excellent results were achieved pressing this sludge by greatly reducing the rpm of our press.

Issue 81

Fiber Filter

Click on the following links to know more about Fiber Filter applications:

Chilli Peppers

February 22, 2000

Some plants and factories pay a municipal sewer surcharge based on the quantity of suspended solids in the wastewater from the plant. We have worked with food processors, plastic recyclers and even a paper recycle mill that operate on this basis.

Usually these plants filter their wastewater with conventional devises such as either static (sidehill) screens or rotary drum screens (internal and external feed). Adding a Fiber Filter to remove further solids from the filtrate from these screens can have a quick payback.

One successful operation is at Gilroy Foods in Las Cruces, New Mexico. This ConAgra plant processes and dries chili peppers in order to produce powder and flakes used as food flavoring ingredients. Both red and green chili peppers are processed during a harvesting season that runs from July into November.

The typical wastewater flow is 200 gpm, well within the range of a Model FF-12 Fiber Filter. The inbound suspended solids will range from negligible to 1% or 2%. During the most recent season use of a Fiber Filter cut in half the total suspended solids measured by the city. This success as resulted in a commitment to rent another Fiber Filter during the next harvest.

The sludge from the Fiber Filter is trucked, along with static screen tailings and other solid waste, to landfill. (If a screw press were being used on solid waste, the Fiber Filter sludge would be fed to such a press.)

It is notable that this plant also rents a Model KP-10 press each year. It is used to dewater skins from blanched green peppers. This raw material is obtained from nearby green pepper canners. The press cake is dried to produce powder that is used to blend color and taste into the red chili peppers.

Issue 102


July 13, 1999

Deinking Mills are a major specialty among paper recycling mills. The principal raw material categories for these mills are newsprint, magazines, telephone directories, and mixed office waste. There are many sub-specialties. For example, some mills will recycle only newsprint, while others will mix magazines with newsprint. This adds fiber strength and brightness, but it requires the addition of equipment to screen ash from the furnish. (Ash is mostly the kaolin clay coating used in glossy magazine paper.) MOW (Mixed Office Waste) mills use the least expensive material; however, it requires special equipment for removing a broad range of contaminants such as Styrofoam and stickies (contact cement).

The common feature of deinking mills is that they must separate printers' ink from the fiber. This is made difficult because the objective of ink formulators is to produce a product that stays bound to the paper fibers. Obviously there are many types of ink: water based, latex, those that work on ground wood paper, those that work for glossy coated paper, etc. One of the worst is laser printer ink, because it is heat bound to the fibers.

Once the ink and ash have been separated from the fibers, these contaminants must be screened from the flow. Traditional technology is to use a machine similar to a belt press for that purpose. The performance of these deinking machines is principally measured by (a) the brightness of the good fiber that is accepted, and (b) the amount of good fiber going in the reject steam.

Last year a Fiber Filter machine was tested for deinking capability. This was done in the laboratory of Thermo Black Clawson, the premier manufacturer of recycle paper mill machinery. The results were extremely encouraging. Compared to the conventional equipment, the Fiber Filter scored higher in brightness and, simultaneously, higher in fiber recovery. This means that more ink went through the fabric sleeve while at the same time that less good fiber was getting through the same sleeve. Ash separation was also excellent.

Feed consistencies ranging from 0.25% to 2.0% were tested. Accept consistencies were in the range of 7.5% to 14% solids, with flow rates of 150 to 250 gpm in the Model FF-12.

Issue 96

Dilute Flow Filtration

June 25, 1999

Recently we tested the Fiber Filter at Liberty Paper in Becker, Minnesota. This is a modern OCC (Old Corrugated Container) recycle mill. Rated at 300 tons per day, the mill specializes in producing linerboard. The test machine was a FF-6, the smaller version of the FF-12 machine that would be required to satisfy the mill loading.

We were working with dilute feed flows, .02% to 0.20% solids consistency, and remarkable success was experienced. The results broaden the market for Fiber Filters from deinking to include most recycle paper mills.

The applications tested were (a) filtering press liquor from Vincent screw presses that are used on the mill wastewater stream; (b) filtering the flow of wastewater ahead of the clarifier; and (c) filtering the final wastewater flow that goes into the city sewer system.

Feed:  Press Liquor from Vincent VP-16's screw presses.  These are used on the mill wastewater stream after it has been across sidehill screens.
          Feed:          .06% consistency      620 ppm TSS *
          Filtrate:      .02% consistency      330 ppm TSS *
          Cake/Sludge:  3.0% consistency

Clarifier Feed Chest
          This includes sidehill screen filtrate, press liquor, and other waste streams.
          Feed:          .15% consistency   1,970 ppm TSS *
          Filtrate:      .04% consistency     460 ppm TSS *
          Cake/Sludge:  4.1% consistency

These two tests were run with an 86 micron sleeve in the FF-6, very high elevation adjustment, 30 to 60 gpm, no VFD.

* The differences between percent solids consistency and parts per million of total suspended solids arise from using two different laboratory procedures for measuring the same thing.

We also ran tests on the city sewer flow. The results were surprising:

City Sewer Water:

    • Feed: 204 ppm
    • Filtrate: 148 ppm

This test was run with a 43 micron sleeve, very high elevation adjustment, 90 to 120 gpm. Their normal flow is 400 gpm, so a FF-12 may carry it all with a 31 micron screen. The cake/sludge we collected had sand and grit, with some fiber.

The cake/sludge from the Fiber Filter would be fed back into the screw presses.

Two alternate projects are being reviewed for potential financial justification:

    • Filtration of clarifier feed so as to reduce polymer consumption in the clarifier.
    • Filtration of final flow to the city sewer so as to reduce sewer surcharges.

Issue 95

Fiber Filter Operating Hints


The Fiber Filter may tend to vibrate, so for a permanent installation you will want to anchor all the feet of the machine to supporting structure.

Note that, since the angle of inclination to be adjusted, flexible hoses must be used for the inlet flow and, possibly, the filtrate flow.  Be sure to allow enough hose length for full travel of the tilting mechanism without interferences.

Changing the filter sleeve assembly is required periodically.  To accomplish this, convenient floor space must be left at the sludge discharge end of the machine.

Operating the optional sleeve flushing mechanism requires space at the drive end of the Fiber Filter so that the flush liquid supply hose and tube can move in and out.

The filtrate flow can be allowed to empty into a tank or collection pan mounted under the machine.  (Such a pan is useful to the operator for detecting a torn filter sleeve.)

It is important that provision be made to immediately shut off the flow of liquid going into the Fiber Filter in the event that the drive motor is stopped or trips out.  The inbound flow going into the Fiber Filter will purge through the sludge discharge chute if the rotor stops turning.  Provision should be made for this eventuality.

It is best to make provision to by-pass both part and all of the inbound flow to the Fiber Filter.

Spill containment is a consideration.



The Fiber Filter may have a lifting eye that is positioned at the top of the machine, near the center of gravity; a chain can be slung through this hole for lifting.  Alternatively the machine can be lifted from below with a forklift.



Before putting power to the Fiber Filter, the rotor should be turned by hand to make sure that it turns freely.  This can be done by taking the cover off the end of the motor and turning the cooling fan by hand.  Also, it can be done by reaching through the sludge discharge chute to grip and turn the rotor.  Be sure the motor starter is locked out when performing this procedure.

The rotor of the Fiber Filter turns in a counter-clockwise direction, when viewed from the drive end of the machine.

Be sure that the spring tension is set correctly tight prior to start up. 



In almost all cases satisfactory operating conditions can be achieved by adjusting the elevation of the Fiber Filter.  However in some cases, driving the Fiber Filter with a Variable Frequency Drive can be useful in optimizing performance.  The use of a VFD can be valuable during initial start-up for establishing the best pulley ratio for future fixed speed operation (if a belt drive is used).

A useful instrument for testing a Fiber Filter is an ammeter.  This is particularly true if there are high concentrations of solids in the flow to the Fiber Filter.



The Vincent Fiber Filter features an External Fabric Tensioner.  These springs can be adjusted with the machine in operation.  Usually spring tension is adjusted only once after initial stretch has occurred in a new sleeve.

The effect of spring adjustment on capacity and filtration is minimal.  However, tight spring adjustment is vital for achieving long sleeve life.  The fabric must be kept taught; otherwise it will flutter and fail in a few days.

On the Models FF-12 and FF-30, the springs have a free length of 6".  These should be compressed 1", to 5" length, for proper tension on the fabric sleeves.  In the case of the FF-6, the springs are 4" long and they should be compressed to 2-1/2" length.  (Some FF-6 machines have 6" orange springs; these should be compressed to 5-1/2".)



The springs will normally stretch out by 3/8" to 3/4" during initial operation of the Fiber Filter.  The spring compression should be re-set after this occurs.



The Fiber Filter separates a flow containing dilute solids into a stream of filtrate and sludge.  This sludge will be quite wet; however, it will contain the majority of the insoluble (fiber) solids.  The Fiber Filter is not a press, so it does not separate the solids into a cake.  When starting with a clean, empty Fiber Filter, it can take several minutes for the first sludge to appear at the discharge.  This is because the fabric sleeves can hold up to five minutes worth of sludge.

With a very dilute feed, one would expect around 95% of the flow fed to the Fiber Filter to come out as filtrate and 5% as sludge.  This can vary significantly in applications where there is high solids consistency in the feed to the Fiber Filter.

If excessive vibration or high motor amps are evident, it is likely that the solids are not discharging from the sleeve.  This can be remedied by either (a) lowering the elevation angle of the machine or (b) increasing the flow of liquid into the machine.  (It can also be an indication that sludge has bridged and is accumulating in the sludge discharge spout.)

In some applications the operation of the Fiber Filter is cyclical.  The operating cycle can range from a few seconds up to two minutes.  The cycle starts with a longer period of minor vibration and minimum solids (sludge) discharge.  This is followed by a shorter period of stronger vibration and a heavy discharge of sludge.  This occurs with a constant, uniform inbound flow and a steady discharge of filtered liquid.

It must be anticipated that the Fiber Filter may purge.  Under this condition the inbound flow will discharge, unfiltered, through the sludge discharge chute.  This condition will occur if the electrical power to the Fiber Filter is interrupted without the inbound flow being shut off.  It can also occur if the sleeve becomes blinded (coated over); if the elevation angle is too low; or if inbound flow conditions change.

The Fiber Filter will overload and trip out if excessive solids accumulate within the sleeves.  This occurs if there is insufficient liquid flow through the machine.  The condition can be avoided by reducing the angle of inclination of the Fiber Filter.  The overload condition will occur either if the machine is set to operate with a thick inbound flow and this flow is significantly reduced, or if the solids content of the inbound flow is significantly increased, without lowering the angle of inclination.  Alternate rotor configurations are available that avoid this problem.

fiber filter fiber filter

Excessive splashing of liquid from the sludge discharge chute is corrected by backflushing the sleeves, by increasing the angle of elevation, or by reducing the inbound flow (gpm).

The rotor of the Fiber Filter turns in a counter-clockwise direction, when viewed from the drive end of the machine. 

However, it has been found that operation in the reverse direction, with certain rotor designs, may produce improved results.  Reverse operation may be appropriate if excessive splashing of liquid from the sludge discharge chute occurs.  Try this before you give up.



The five variables, in order of importance, that affect Fiber Filter operation are:

  • FEEDING:  Volume of inbound flow;
  • INCLINATION:  Angle of inclination of the rotor;
  • SLEEVES:  Mesh of the fabric sleeves; and
  • BACKFLUSH:  Cleanliness of the fabric sleeves;
  • RPM:  Rotational speed of the rotor.

This assumes that solids consistency in the inbound flow is not a controllable variable.



Fiber Filters require that the feed to the machine be at a constant flow rate.  The feed must be at low pressure.  Good performance of the Fiber Filter can be achieved by gravity feeding from above.  An overflow line can be used to maintain constant head and flow.

The Fiber Filter can also be fed by pumping a flow directly into the machine.  A variable speed pump, especially a diaphragm pump, works best.  A regulating type valve, such as a globe valve, may be required to adjust the inbound flow.



The principal adjustment of the Fiber Filter is made by changing the angle of inclination.  In general, with a steeper angle, greater dewatering is achieved.  Usually greater throughput capacities can be achieved with a more gentle angle.  The fluttering cycle and vibration intensity are also affected.

If the angle of inclination is too great, or if the inbound flow is too little, it is possible that no sludge will be produced.  In this situation the suspended solids in the flow are being disintegrated and beaten through the sleeves by the action of the rotor.  This condition is normally accompanied by mild to severe fluttering of the sleeves.

Not uncommonly, with certain rotor designs it will be necessary to aim the Fiber Filter downward, with the discharge below the horizontal.  This occurs with either very thick flows or very low gpm flows.  It occurs when there is not enough liquid present to flush the slurry/sludge from the Fiber Filter.  (It may be necessary to place a block under the elevation pivots or the feet of the machine in order to achieve a downward angle.)

If the angle of inclination is too high for a given flow, or if the inbound flow is too low, the fabric sleeve will fill with solids.  This can lead to severe fluttering of the fabric, and the Fiber Filter may trip out on electrical overload or the sleeves may fail.



The fabric sleeves of the Fiber Filter are made of tweed woven monofilament fabric.  The synthetic polymer fabric is selected according to a rating of micron size.  In addition, the fabric is selected for its rating in terms of tensile strength (circumferential as well as axial) and chemical and temperature resistance.

Standard polyester sleeves are good to 220o F and are resistant to both caustic and acid cleaning solutions.  PEEK sleeves are good for 350o F. 

Micron ratings of 20 to 190 are typical.  These relate to the size of the particle that will pass through the sleeve, not to the passage size through the filaments of the fabric.

The following chart lists common sleeves:

Micron Rating Air Perm Mesh Nominal Opening Material
RLX 572 80 0.007" 0.190 mm Polyester
155 260 100 0.006" 0.150 mm PEEK
132 299 110 0.005" 0.118 mm Polyester
118 501 120 0.005" 0.118 mm Polyester
86 234 170 0.0035" 0.086 mm Polyester
50 72 270 0.002" 0.050 mm Polyester
43 208 325 0.002" 0.045 mm PEEK
31 39 500 0.001" 0.030 mm Polyester
20 24   0.0008" 0.020 mm Polyester
12 19   0.0005" 0.012 mm PEEK

PEEK sleeves are seven times stronger that polyester, but cost twice as much.  This fabric is more chemical resistant, also.

The sleeves quiver while the Fiber Filter is in operation.  This action keeps the sleeve from blinding.  A quivering action is normal and will result in very long sleeve life.  Fluttering, on the other hand, reduces sleeve life.  It ultimately results in the failure of the fabric.  Replacement is simple.



In certain applications the fabric sleeve of the Fiber Filter may become blinded with usage.  This may be corrected by using the backflush system.  The frequency at which this is necessary varies considerably: it can be as often as twenty times an hour.  Or, operation once a shift or once a day may be all that is required.

Some sanitary applications require that the machine be flushed for CIP purposes.  This is done with the backflush system. 

This backflush system consists of an internal spray rings with nozzles directed to spray the outside of the fabric sleeves.  The spray ring is moved back and forth inside the Fiber Filter either by hand or by an air cylinder mounted on the outside.  A booster pump is included to increase the pressure of the spray fluid.  A canister filter is included to prevent plugging the spray nozzles.  A control panel is included that allows setting the frequency and duration of the spray cycle.

The backflush system is designed to operate with 200 to 250 psi at the nozzles.  It can be operated with or without the rotor in operation, and with or without flow through the machine.  The preferable mode is with the machine in normal operation (full flow through the machine at normal rotor rpm).

Backflush fluid can be water or CIP solution.  In some cases it is necessary to use chemical cleaners such as caustic or acid in addition to a water flush cycle.



Optimal operation of the Fiber Filter is almost alwaus achieved by adjusting the elevation.  With consistent material being fed to the machine, especially with an elevated tank for gravity feed, constant speed should be perfectly adequate.  In a few cases superior performance may be achieved by driving the unit with a Variable Frequency Drive (VFD).  In such case the Fiber Filter speed (rpm) can be set later by changing drive sheaves (if a belt drive is used).

In general, higher speed results in higher throughput capacity.  It can also result in splashing of wet material from the discharge and reduced solids concentration in the sludge/slurry discharge.  High speed operation increases the power draw of the motor.

In applications involving filtration of a variety of solutions, or inconsistent inbound flow, the Fiber Filter is best equipped with a VFD.



The most common sleeve failure is a tearing at the hem.  The second most common is a failure of the seam.  These failures generally occur because the machine is allowed to operate with the fabric in a fluttering condition.  When this occurs the machine will be seen to vibrate, and rattling noise will be heard from the spray rings inside the machine.

To prevent fluttering: 

  1. Be sure the springs are quite tight (not loose).
  2. Lower the inclination so that wetter sludge is produced. 
  3. Increase the flow into the machine so that solids do not accumulate inside.
  4. Switch to a heavier, preferably PEEK, fabric sleeve.



The best way to measure capacity of a Fiber Filter is to collect timed samples of filtered liquid and discharge sludge.  Allowing the filtered liquid to accumulate in a tank, and measuring the change in depth over time, works well.  Similarly, a 5-gallon pail is suitable for collecting discharge sludge.



For a quick performance measurement of the Fiber Filter it is convenient to collect samples of inbound and filtered liquid.  These should be equal size samples (one fluid ounce is typical).  These samples are poured into the center of a piece of cotton cloth; making a ball and twisting the cloth will force the liquid through the cloth.  The fiber will remain on the cloth, allowing a visual comparison between inbound and outbound.

Similarly, samples of inbound and outbound liquid can be collected in Imhoff cones or jars and allowed to settle.  The differences noted give an idea as to the effectiveness of the machine.

Use of a laboratory centrifuge on inbound and outbound samples permits a more quantitative measurement of performance.  Similarly, oven drying of filter samples permits a quantitative analysis of suspended (insoluble) solids.  If the fluid being filtered contains dissolved solids (sugars), the samples should be washed to zero Brix as part of the testing procedure.



In some sanitary applications it is necessary to remove the filter sleeve assembly from the Fiber Filter and soak it in a cleaning solution such as caustic.  This may have the benefit of shrinking the fiber back to a taught condition, depending on the fabric material being used.  Purchase of a spare sleeve assembly is recommended for this type of operation.



When shutting down the Fiber Filter, the sleeve assembly should be cleaned.  If practical, this should be done by admitting fresh water to the inlet of the machine. 

Also, the backflush system should be used.  This is done by leaving the machine in operation (rotor spinning) but with no flow being admitted.  It will help to lower the angle of inclination of the Fiber Filter.  Operate the back flush system to clean the fabric sleeves.  This will prevent solids either from overloading the machine on start-up or from crusting on the fabric.



A metal screen can be installed over the filtrate drain in the barrel of the Fiber Filter.  Should a sleeve fail, fiber will blank over this screen and cause liquid to drain from the discharge head, alerting an operator.  This type of screen is illustrated below.

screen failure detection fiber filter alert fiber filter screen



There are up to four grease lubrication fittings on the Fiber Filter.  These are on the shaft seal housing and flanged bearing at the inlet as well as the shaft seal housing and flanged bearing in the discharge head.  Normal bearing grease is suitable for the shaft seals. 



The most important item in changing a fabric sleeve is to note that the seam is either a lap or double hook joint.  Arrows are printed on the sleeves to denote the direction in which the rotor should go past (sweep over) the joint (seam).

The arrows assure that the seam is installed so that the waves of liquid sweep over the blunt edge of the seam, not against it.  That is, sleeves should be installed so that the blunt edge of the lap joint is not facing into the waves of liquid that are pulsed by the rotor.  While it is harder to visualize, the same effect is true with the double hook seams. 

If the sleeve is installed the other way around, the wave of liquid created by the moving rotor paddle will hit an edge of fabric.  This leads to early seam failure.  This is true although there may be a film adhesive, which laps over the joint of fabric in a smooth manner.

It is important to take a few extra minutes when changing a sleeve.  The seam should be straight with the main axis of the machine; the two hems should be uniform, without any pinches; there should be no dips or ripples in the fabric surface.

To properly install a new sleeve, first position it reasonably uniformly and clamp it tight.  Next, slightly tension the sleeve temporarily with the tensioning springs.  This will make evident any non-uniformly tensioned areas.  Loosen the sleeve clamp at one end and tap it so as to pull the fabric tight; then re-tighten the sleeve clamp.

The location of the seam of each sleeve should be noted.  Most commonly the seam is placed where it can be seen through the inspection door.

Safety tip:  when inspecting sleeves with the machine in operation care must be taken.  There is a natural tendency to poke a finger through a suspected hole.  If this is done with the machine in operation, the rotor will surely sever the finger.



To remove the assembly that holds the fabric sleeves, first shut off the flow into the Fiber Filter and then lock out the machine.  It will help to operate the backflush system before disassembly.  Set the level of the rotor at an attitude, most generally the horizontal position, which will be convenient for removing the discharge head and sleeve assembly. 

An Allen head wrench is used to loosen the setscrews (usually four) that hold the inner race of the bearing that is mounted to the discharge head. 

At this point, there are two options:  (1) The springs can be left in place and the entire discharge head and sleeve assembly can be removed as one piece, or (2) the springs can be removed, followed by the discharge head.  Once this is done, the sleeve assembly can be slipped out of the barrel of the Fiber Filter. 

Note that the discharge bearing comes off with the head; there is no need to loosen the four bolts which hold the bearing.

Axial rails support the sleeve assembly.  The inlet end slides over a spout ring in the inlet head of the machine.

Look through the open end of the sleeve assembly to make sure the fabric is not dragged or pushed into the rotor.  Do this during both disassembly and re-assembly operations.

Following re-assembly and tightening the springs of the Fiber Filter, check the fabric sleeves through the inspection panels.  This should be done before putting power to the machine, as a loose sleeve will become entangled in the rotor.



Several rotor designs are available for Vincent Fiber Filters.  Most designs have straight paddles with ribbon flighting added to direct fiber toward the discharge.  Contrary to normal screw conveyor logic, a tight pitch ribbon flight is used to move large quantities of solids, while a long pitch ribbon flight is used when the solids flow is minimal.  Switching to a long pitch rotor can reduce excessive water being present in the discharge sludge.



The rotor is supported by two spherical self-aligning roller bearings.  These are mounted at the drive end and on the discharge head. 

Special care must be taken when re-installing a rotor.  The drive end of the rotor must be slipped through the shaft seal housing.  To do this properly, remove the seal housing and insert the end of the rotor through the hole in the inlet head.  The rotor should be pushed in just far enough that the seal housing can be slipped onto the end of the shaft.  Then the rotor shaft can be pushed through the drive-end bearing until the thrust shoulder on the rotor shaft seats against the bearing.  The seals can be damaged if the seal housing is not loosened during rotor installation.

Care must be taken that the rotor spins freely after assembly.  Rarely, this may require relocating one or both of the two main bearings.  Both of these bearings are self-aligning.  The rotor shaft should not ride heavily on the seal housing when assembly and alignment are complete.



Fiber Filters use Johns Manville JM Clipper lip seals.  These are the c-cup style.  There will be a pair in the housing at the drive (inlet) end of the machine, mounted on the inlet head.  These seals have internal springs to hold the lip against the shaft. 



Most Fiber Filters are supplied with a backflush system.  This consists of a pressure boosting pump, a solenoid valve to open the water line when the pump is in operation, a filter for filtering the flush water, and a control panel.  The control panel has a timer with two clocks:  the top clock sets the time interval between flushings, and the lower clock sets the time duration that the pump will run during the flush cycle.  There is also a solenoid valve which supplies air to the air cylinder which is used to move the spray ring assembly along the length of the sleeves.

fiber filter



The most common wear parts in the Fiber Filter are the sleeves, the sleeve clamps, the seals, and the bearings.  These are stocked by Vincent.  Be sure to specify the Serial Number of your machine when ordering replacement parts.  The seals and bearings, like the sheaves and belts, are standard OEM components that can be purchased from the original equipment manufacturer (OEM).  The specification of these items is included in the O&M Manual.



These Operating Hints have left unstated the obvious safety hazard:  a Fiber Filter, like any rotating machine, is unforgiving.  If clothing or limb gets caught in the rotor it will not stop until damage has been done.

The easiest way to get hurt with a Fiber Filter is to reach inside the sludge discharge while the machine is operating.  There has already been one minor injury as a result of this, so do no let yourself become the second.

A second way to get hurt is to press your hand or finger against the fabric sleeve while the rotor is in operation.  If you push your finger through a hole, the rotor will cut off the finger.

The use of common sense is all that is required.


Robert Johnston, P.E.

fiber filter parts list

HINTS-FF.pdf462.67 KB

Fiber Filter Patent

November 20, 2000

Here at Vincent we are proud of the award on September 12, 2000 of United States Patent number 6,117,321. It describes an EXTERNAL TENSION ADJUSTMENT DEVICE FOR A FILTERING SLEEVE IN A FILTERING MACHINE. This came as a result of our work over the last three years with the Fiber Filter.

This is a machine design feature used in all Vincent Fiber Filter machines. The Fiber Filter works on the principle of inducing high frequency vibration in a fabric sleeve that is stretched with springs. The patent covers mounting the sleeve tensioning springs on the outside of the machine.

Prior technology used tensioning springs that are mounted on the inside of the machine. The primary disadvantage of this arrangement is in filtering food products where it fundamentally less sanitary to have springs in the flow of filtrate.

An additional advantage is that the tension of external springs can be adjusted with the machine in operation.

Only twenty months elapsed between the application and issue dates. This speedy action can be attributed in part to the fact that a law firm was not used in the process. The initial disallowance of the patent claim was resolved by telephone, without the requirement of any correspondence.

A copy of the patent is available upon request.

Issue 111

Fiber Filter for Pectin Recovery

July 26, 2005

An interesting application for the Fiber Filter has evolved over the last few years. The project started as a rental at a plant whose wastewater treatment plant (WWTP) was causing excessive odor.

The customer's operation involves receiving fresh lemon peel as a raw material, washing the dissolved solids (sugars) from the peel, and then extracting pectin from the washed peel. The precipitated pectin is dried and sold, in powder form, as a food ingredient.

The WWTP load came principally from the dirty water from the peel washing system. This water contains both dissolved solids and suspended particles of lemon peel. The initial project involved using a Model FF-12, with coarse 190 micron sleeves, to filter this wastewater.

The project was a success. Odor from the WWTP noticeably decreased after filtering out the suspended solids. This is true even though most of the solids are dissolved, so they pass through the Fiber Filter.

At first, the solids sludge from the Fiber Filter were trucked to a remote site. Soon, however, it was determined that this sludge contained valuable pectin of good quality.

For the next season, a second Fiber Filter was added, and the sludge from the machines was pumped back to the peel wash system. In this manner the pectin was recovered.

Today, a third Fiber Filter has been added. The system has been further refined by pumping the sludge from the three machines directly to the acid/alcohol plant. There it is mixed with the washed peel, and the pectin is extracted. (They found that if this sludge was added back to the washing system, the screw presses did not seem to work correctly.)

Issue 163



Maximizing Capture Rate

September 18, 2002

The unique fine filtration and capture rate characteristics of the Vincent Fiber Filter have resulted in successful operation in pineapple juice and paper mill shower water applications. The same principle is used in both these two very different installations.

The Fiber Filter separates a sludge of fiber from the flow admitted into the filter machine. Usually the goal is to produce a firm, bulky sludge in order to (a) maximize yield of filtrate and (b) facilitate handling of the sludge.

In other applications the goal is to maximize the capture rate. That is, the need is to have as high as possible a percentage of suspended solids captured in the sludge discharge. Usually this is achieved by simply installing filter sleeves with smaller micron openings. However, because tighter weave fabric results in lower gpm capacity, this is not always practical - nor necessary.

Another way of achieving high solids capture in a Fiber Filter is to reduce the consistency of the solids in the sludge discharge. Reducing the elevation angle of Fiber Filter, other things remaining constant, will result in a watery sludge discharge, along with a higher capture rate.

In the case of pineapple mill juice, excessive wear and poor capacity was being experienced with a centrifuge that is used to filter the juice. A Fiber Filter was added in series, ahead of the centrifuge. This Model FF-12 sees a feed of 100 to 120 gpm, and 118 and 190 micron sleeves are used. Filtrate from this Fiber Filter now goes to the centrifuge. Increased centrifuge capacity and decreased maintenance have been achieved.

The elevation of the Fiber Filter is kept low, resulting in a low consistency sludge discharge of about 5 to 10 gpm. This flow, which contains the majority of the suspended solids, is sent to a decanter. This decanter works well in separating good juice from the sludge.

The second similar application is in filtering shower water used on a paper machine. This shower water keeps the paper machine clean so that the sheet of paper forms and separates, at high speed, without blemishes or tearing. Trash material cannot be conveyed to the paper machine in the shower water, nor should particles large enough to plug the nozzles be present.

In practice it was found that a milkshake-thick 0.5 gpm flow of sludge could be produced by the Fiber Filter. This was with 31 micron sleeves and flow of 200 gpm, with 70 ppm suspended solids in the feed flow. By reducing the elevation, the sludge discharge jumped to 5 gpm. The important part was that the capture rate improved, with the solids in the filtrate dropping from 30 to 18 ppm. The change in waste discharge, from 0.5 to 5 gpm, is insignificant in the overall operation of a paper mill.

Issue 131

Meat Flavor Extracts

July 11, 2001

Ariaki U.S.A., a Virginia firm, has been running a new oil recovery system. The elements of the installation include a Model KP-16 screw press, the press liquor from which flows directly into a Model FF-6 Fiber Filter. Waste materials from the plant are run through the system in order to recover oils.

Ariaki produces meat flavored extracts from by-products that are acquired from hog, broiler, beef and turkey slaughter houses. These materials are processed in extractors to recover food grade meat flavorings. The waste material from the extractors resembles hot stew.

In the past this waste has been turned over to a rendering company for disposal. It has had little value because of the high moisture content.

The new system recovers oil from the extractor waste flow. This is done by pumping the waste to the Vincent screw press where a thick liquid is expelled through the screen. The liquid is high in both oil content and suspended solids.

This flow of press liquor, about 5 gpm, drains from the screw press to a Fiber Filter that is mounted directly below. The Fiber Filter, using a coarse fabric sleeve, removes suspended solids from the flow. These solids, along with the cake from the screw press, fall to a waste hauling trailer that is parked below the Vincent machines. (The system may be modified so that the sludge from the Fiber Filter can be pumped back to the inlet of the screw press.)

The filtered press liquor is pumped to heating tanks where the oil is recovered. Water separated from the oil is treated in the Ariaki wastewater treatment plant.

It is notable that the material pumped to the screw press has chunks of bone. These range in size from a dime to pieces that cannot be covered by a fifty cents piece. They are pumped with a V-Ram piston pump to the screw press. These bone fragments pass through the press without difficulty.

Issue 118

Peach Cannery

September 20, 2000

A lead from the 1999 IEFP (International Exposition of Food Equipment) show led to the placement of a Model FF-12 Fiber Filter at the Del Monte peach cannery in Kingsburg, California.  This eighty-year-old cannery operates during a three month season each year.

Wastewater from the plant is used to irrigate a sorghum field a few miles away.  An environmental problem existed because suspended solids from the wastewater formed deposits in the field.

The suspended solids come from the peach peeling operation.  Caustic peelers are used, with a continuous cycle to reuse the peel water.  Make-up water is adjusted so that approximately 300 gpm flows to the waste water stream.

This wastewater is filtered in rotary drum screens.  In order to maximize solids capture, screens with very fine slots are used.  However, even with wedgewire with 0.012" slot widths excessive suspended solids were present in the filtrate water.

The Fiber Filter was installed in series with the rotary drum screens, in the final filtering position.  Dramatic improvement in solids removal was evident even with coarse 190 micron sleeves in the Fiber Filter.  Since there was excess capacity in the Fiber Filter, a switch was made to finer 86 micron sleeves.

The Fiber Filter was supplied with an automatic spray ring feature.  This is used to back-flush the filter sleeves.  A booster pump was provided to increase the spray water to 200 psi.  A timer control panel assures fully automatic, continuous operation.  The timer was set to backflush every six to ten minutes.

The sludge (peel and some pits) from the Fiber Filter is landfilled.

It is notable that the wastewater contains a significant amount of dissolved solids.  These measured 2o Brix.  Naturally these dissolved solids cannot be captured in a filter, so they go to the spray field.  Fortunately they are an acceptable environmental condition.

2013 Note:   Use of the Fiber Filter was discontinued when the plant's wastewater treatment facility was expanded.

See photos below.





Issue 112



Shower Water Filtration

October 25, 2001

Tests were recently conducted using a Vincent Fiber Filter on shower water at Atlantic Packaging in Scarboro, Ontario. The Fiber Filter was selected because of its small footprint and attractive capital cost compared to conventional filters.

This recycle paper mill has a combination OCC (Old Corrugated Container) and tissue operations. The most important use of shower water is on the felt of paper machines. Other applications are on trommel and rotary drum screens.

The primary source of shower water comes from disc strainers used at the end of the stock prep process. The disc strainers raise the paper pulp from 1.2% to 12% consistency. There are three effluents: cloudy, clear, and super clear. The cloudy effluent is pumped back to the start of the process at the hydrapulpers. The clear effluent is re-used half way back in the stock prep process, with the excess going to sewer.

The disc filter itself uses some of the super clear; the rest is filtered prior to use as shower water. The existing super clear water filters are Sweco machines that feature a vertical axis with a spinning drum screen. The drums have fabric panels backed up with coarse mesh steel screen. The drums are about 4' in diameter.

These Sweco's are very old and have served their purpose; maintenance expense has become excessive. Thus our Fiber Filter is being evaluated as a potential replacement.

The very low solids consistency of the super clear water resulted in high capacity in the Fiber Filter even with very fine fabric sleeves. With a feed consistency of 70 ppm, using a 31 micron sleeve, we were able to produce filtrate with 20 to 25 ppm. This was done with the Model FF-12 being fed about 200 gpm and producing about 1 gpm of fiber-sludge discharge.

A goal of the project is to eliminate the need for addition of city water make-up to the shower water tank.

There is a rule-of-thumb used in selecting filters used on flows ahead of spray nozzles: The filter basket should have openings one tenth the size of the openings of the shower nozzles. This is achieved with the 20 and 31 microns sleeves available for use with the Fiber Filter machines.

Issue 122

Food Waste

 Click on the following links to know more about Food Waste applications:

Bagged Feed Storage

November 30, 1995

One of the largest citrus processors in California uses an interesting technology to dispose of their orange peel. Like their Florida counterparts, they run the citrus peel through screw presses, getting the peel from 82% down to 70% press cake moisture. However, they have no dryer or WHE (waste heat evaporator) for processing their peel.

Instead they use a steam evaporator for processing the press liquor from the presses. The evaporator removes 60,000 #/hr of moisture at a feedmill that processes the peel from 2250 boxes (use 44 pounds of peel per box) of oranges an hour.

They process the press liquor (plus spent caustic, oil house water and other waste streams) in the steam evaporator. It makes molasses at 50º to 55º Brix. Originally they put some of the molasses on the press cake, and they sold the rest as a liquid cattle feed.

Later they found they could make higher profits by selling the molasses to a distillery. The distillery makes citrus alcohol at 195 proof. This alcohol is used at a winery that produces fortified wine.

The processor's practice has been to sell the press cake under an annual contract with commodities brokers, either Foster or Coast Grain. These brokers take it in bulk, 30 to 40 loads a day (nominal 40,000 pounds per truck). At peak season this was too much press cake for the farmers to accept: the material would spoil before the cattle would consume it. As a result, at one time the press cake was piled on a concrete airport runway. This was not satisfactory because soon liquid started to drain from the press cake (contaminating the area), and solids (nutrients) were lost. Also, the cake started to ferment: the cows liked it that way, but it released CO2 in the digestive process which was harmful to the cows.

Given this situation, one of the brokers developed the technology to bag the press cake. The bag keeps the oxygen out, and the material will keep for several months. Ensilage (anaerobic acid fermentation) takes place.

The bag is made in the pasture at a dairy or feedlot. The press cake truck coming from the citrus processing plant dumps its load into a hopper or funnel. This field hopper has wheels and a frame that forms the plastic bag. At times the brokers put in other feedstuffs (by-products from local agricultural processing plants) besides the citrus press cake. The bags are about 10' in diameter. They look like giant sausages, about 8' tall, 100, 200, and even 300 feet long.

The farmer slits the plastic bag as needed to expose feed to his livestock. Sometimes the feed is removed from the bags with a front end loader.

The possibility of using this technology has been raised for storing forage grasses and other feeds. There have been inquiries regarding alfalfa, sugar cane, and produce waste, but so far we are not aware of any projects that have been funded.

Supplier: Ag-Bag International, Ltd., Warrenton, OR 1-800- 334-7432

Issue 36

Bush Brothers

APRIL 5, 1993 Rev. Sept. '96

Bush Brothers, a leading canning company in Tennessee, is making excellent use of a Vincent VP-16 dewatering press.  They have integrated the press into several facets of their business so as to achieve outstanding synergy.

The three principal products being processed are cabbage, green beans, and potatoes. In the processing a considerable load of waste products such as culls, stems, trims, leaves, and peels are generated.  The press was acquired to reduce the bulk of the waste materials and to improve the quality of these materials as a cattle feed.

In operation it has been found that high concentrations of low fiber materials, such as whole potatoes and dried beans, press poorly.  That is, they become mush: the cake is not firm and solids pass into the expelled liquid.  To avoid this condition the plant operators make a point of mixing in fibrous material, such as cabbage leaves, as needed.

The cake produced by the press is fed into a trench silo where it is conveyed to the company’s cattle feeding area.  The cake is referred to as silage, and it is fed directly to the cattle.

The press liquor produced in the press is drained to the company’s waste water pit.  This pit is of considerable capacity as the canning factory generates up to one million gallons per day of waste water.  The water from the pit is used to irrigate the company’s pasture grounds.  Thus the nutrients in the press liquor are ultimately used to fertilize the fields.

In summary, the synergy of the Bush Brothers operation is self evident.  A wide range of waste materials are processed through a single press that converts them into useful by-products for a minimal cost.

September 1996 update: Few canners can afford a VP model press for waste disposal service.  For that reason the new Series KP presses have been developed.  These models are currently undergoing field trials.

Issue 2




December 13, 2015

Issue #279

Corn wet milling is an extremely large but relatively little known industry. It is where corn is processed into vital products, of which the four principal ones are corn oil, starch, fructose, and animal feed. Facilities are located in dozens of corn-growing nations around the world. The best known producers are multinationals like ADM, Bunge, Cargill, Ingredion, and Tate & Lyle. In addition there are a great number of lesser known local companies in this industry.

The process used is to first steep the harvested corn kernels in a caustic solution. This allows the corn to be cracked so that the germ can be separated. The germ is the part of the kernel which contains corn oil. Most facilities ship their germ to yet other facilities which specialize in recovering the oil.

After separating the germ, the next step is to separate the starch. Corn starch is converted, in yet another process, into fructose. Fructose is a substitute for sucrose (which is produced from sugar cane and sugar beets). There is intense competition between the fructose and sucrose markets.

Screw presses have two important applications in the corn wet milling industry. One of these is in dewatering the residual fiber after the starch has been removed. This fiber is dried to low moisture content and then pelleted for sale as animal feed. To minimize the fuel required by the dryer, screw presses are used, ahead of the dryer, to remove as much water as possible. Our customers' specification usually is that the moisture content of the press cake should be in the range of 55% to 58%. Our high torque Series VP screw presses are well suited for this application.

The second screw press application in corn wet milling is removing water from the corn germ. In order to liquefy the fat in the germ, it is run through an oil Expeller® type screw press. Typically these are supplied by Anderson International. However, before the germ can be pressed in an Expeller®, it must be dewatered. That is where Vincent screw presses prove their value. Although the press cake moisture content comes out lower, 50% to 55%, the pressing action must be gentle in order not to squeeze out the oil. We use Series KP screw presses in corn germ applications.

Historically, the industry was dominated worldwide by Vetter screw presses. However, today most of these presses are very old machines, subject to frequent maintenance requirements and costly repair parts. This has opened the market to other press manufacturers.

An interesting fiber application for Vincent screw presses is as a pre-press, for a first pressing ahead of existing Vetter's. Low-torque, high capacity Series KP presses have proven effective in separating the "easy" water ahead of Vetter presses. This has resulted in a small, but valuable, increase in starch yield. More importantly, it has taken load off the Vetters so that a mill can continue operating at a high throughput rate even when presses are down for repairs.

There is yet another application for Vincent presses in corn wet milling. It is found in facilities which produce corn oil. The oil flowing from an Expeller® contains some fiber and moisture. These foots sink to the bottom of a settling tank. Their name, foots, comes from the fact that they are found at the foot of the tank. They are scooped, or dragged, from the bottom of the tank and then run through a Vincent screw press.

The Vincent press has proven effective in separating the oily water (as press liquor) from the fiber (press cake). This cake contains residual oil, so it is re-admitted to the Expeller® presses. Pressing News #70, from 1997, describes this application.

An alternative system being testing involves pumping oil from Expanders® and Expellers® to a simple prethickening screen to separate the foots. These fall into the screw press. It is hoped that reduced floor space and construction costs will result.


Chitosan (Shrimp)

May 18, 1999
2001 Update

Chitosan has been receiving considerable attention as a natural diet additive. It absorbs fat and oil, so it is deemed to be good at reducing cholesterol levels and helping a person to control weight. It is also used commercially in such products as swimming pool cleaners.

Chitosan is found in the exoskeleton of insects and crustaceans. The commercial product is made from shrimp and crab shells. Vincent has worked in plants in Washington and Iceland, and the material is now being produced in India.

Chitosan is produced from shrimp waste by a multistage process. First the salt is washed out and the material is shredded. Then the protein, which makes up 30% of the waste, is removed in a hot bath. The calcium, 50%, is removed with acid. After caustic neutralizing the remaining material, chitin, is first pressed and then dried in a rotary drum dryer. Another process is used to convert the chitin into chitosan. This process, too, involves pressing water from the material and then drying it.

Vincent screw presses are used in three steps of the extraction process. First, the raw shrimp waste is dewatered in a Series KP "soft squeeze" press. The other two applications are ahead of the chitin and chitosan dryers. Here the tighter squeezing Series CP or VP presses are needed for maximum dewatering.

Pressing ahead of the dryers is difficult. The material is very slippery and it has a high propensity to bridge, even inside a screw press. At the same time it can be over-pressed so that it jams the press. (In trials with a Stord twin screw press, the material jammed so tight that both screws broke in half!)

Recently we assisted pre-start-up trials at a plant in Iceland where our presses are used ahead of the dryers. Many modifications were made in order to improve the press operation. Changes included:

    • Cutting the resistor teeth in half.
    • Removing the resistor teeth on one side of the press.
    • Switching between perforated screen and profile bar screens.
    • Both standard and Sterile Butterfly screws were tested.
    • Sharpening the leading edge of the flights.
    • Beveling the resistor teeth.
    • Adding a stripper in the inlet hopper.

We tried hard piping the flow and forcing material into the press with a progressive cavity pump. The material jammed so tight the pressure went to 80 psi and all the joints started to squirt.

Both thickening and thinning the material entering the press were tried. A static screen was used for the thickening, and a water jet wash used in the inlet hopper for thinning.

A VFD drive allowed testing over a wide range of press speeds.

The feeder flighting was notched at the point where it leaves the inlet hopper, and the stripper was extended downward, like an additional resistor tooth.

A Series KP press was flown in so as to test rounded teeth and only three stages of compression. At this writing Teflon sheet material is being bonded in the inlet hopper.

In some instances it has been found that the effectiveness of the press is tied to the pH of the shrimp material.

One thing has never failed: if the press stops processing material, it is always possible to resume operation by reversing the direction of rotation for a few seconds before proceeding.

Despite the difficulties implied by this number of modifications, we now have three satisfied customers.

2001 Addendum: The Twin Screw Series TSP presses have overcome the above described co-rotation problems.

Issue 94


February 18, 1997
Nov 01 Update

Over the years Vincent has had many inquiries in regards to using a screw press with a coffee waste product.

The Vincent press is well suited for dewatering waste streams in the coffee processing industry. This is most commonly done with chaff and with spent grounds in soluble coffee (instant and decaf) operations. The objective is to remove the excess water so as to produce a press cake suitable either for incineration or landfill.

One local coffee bean processor has a Jones vertical press in daily use on chaff off the bean. The press cake goes to a fertilizer company that uses it as a filler.

A large coffee bean processor in Texas is getting 50% to 55% moisture content in the press cake with either a Davenport or a Rietz V-press. These robust machines come in two sizes: 3' and 5'. They consist of two rotating cones with perforated screen on the faces of the cones. The shafts are mounted at an angle to each other so that there is a large gap on one side and a small gap on the other. Material is fed into the large gap and as the cones rotate the material is compressed by brute force until it is allowed to fall out at the small gap: The pressing is very gentle as there is absolutely no agitation. These machines are expensive because of their heavy construction, and they are of low capacity as compared to screw presses. Their maintenance cost is regarded as excessive by most users we have talked to.

These Davenport presses will handle from 4,000 to 10,000 pounds per hour of inbound material. Their press cake will consistently be in the range of 50% to 55% moisture, which makes the press cake suitable for incineration. Some Folgers and Maxwell plants were originally set up for incineration, but most seem to have abandoned the practice or been shut down over the years.

In 1986 Vincent ran tests for Westreco (Nestles) with inbound material that contained 70% to 74% moisture. This was for a waste disposal project involving canned iced tea and a coffee drink. Moisture contents in the press cake of 58% to 63% were achieved with our press. This was regarded as good as was being achieved elsewhere with vertical presses with the same material, but no better. Thus they could not justify buying our press even though they liked its performance.

Recently we received an order for a CP-10 that will be used to dewater coffee grounds for a venture with Starbucks coffee. The press will reduce the moisture content of the grounds to the point where they can be conveyed in a pneumatic vacuum system.

There is another interesting application of Vincent equipment in the coffee industry. It has to do with one of the first steps in the production of coffee, near the site where it is grown. Coffee growers must dispose of the red pulp that they remove form the coffee bean. This pulp can be converted into a material to be blended with animal feedstuffs. This is achieved by first pressing and then further drying the material.

November 2001 Addendum: Vincent has been selling about one Series CP press per year for dewatering spent coffee.

Issue 56

Coffee Pulp

May 21, 2004

A layer of soft pulp surrounds coffee beans when they are harvested. This pulp is removed with abrasive rollers and a flow of water. The bean that remains is dried and, later, roasted.

For at least twenty years, Vincent has had inquiries about processing the wet pulp into a by-product. Generally, the goal was to convert the pulp into animal feed by dewatering and drying it. For economic reasons, none of their projects have gone ahead.

During the last few years, a new system has been developed in conjunction with Swisscontact. Swisscontact is a foundation based in Switzerland, dedicated to environmental projects in developing nations. Their office in Costa Rica has focused on coffee pulp.

At present, coffee pulp is landfilled. As rainwater seeps through the rotting mass, groundwater contamination becomes a problem. At the same time, rainforests are being harvested and used as firewood for drying the coffee beans. The Swisscontact idea was to dewater the pulp sufficiently for it to be used in place of firewood for drying the beans.

Efforts to dewater the pulp with a screw press were futile. After the free water was expelled, the press cake still had 80% moisture. In general, organic matters need to be reduced to 50% moisture before they will burn.

The bitter, acid nature of the coffee pulp reminded us of orange peel. Only because of this similarity did we suggest trying to react the pulp with hydrated lime. To our delight, it worked the same as it does with orange peel: the chemical reaction with the lime broke down the pulp. This done, the screw press was able to produce press cake with 65% moisture.

This press cake is tumbled in a duct that carries the flue gasses from the bean dryer. These gasses dry the pulp to 50% moisture, after which it is burned as fuel.

A problem remaining with the system is disposal of the press liquor. The liquid is loaded with solids, which kill vegetation and load up wastewater treatment plants.

Issue 149

Dole KP Test

August 13, 1997
Rev.May 1998

The commercial production of salads has grown exponentially for several years. The original large market was fast food restaurants such as McDonalds and Taco Bell. This has now spread to bagged assortments in the public supermarket.

The factories producing these salads produce huge tonnages of waste material. As much as 30% of the as-received lettuce is scrapped. Most factories sluice the waste with water in floor drains. It goes into pits from which it is pumped with chopper pumps. The flow is run across screens, and the tailings are usually hauled to landfill.

Since these tailings are sopping wet, their disposal presents nasty problems of draining in the parking lot, freezing in the dumpster, and acceptance at landfill. The obvious solution is to run them through a Model KP screw press. However, it has been difficult to close a sale because the press liquor from the press is so loaded with vegetable material that the BOD (Biological Oxygen Demand) is unacceptable to most sewer systems.

In recent months a series of tests have been run at the Soledad, California factory of Dole Fresh Vegetables. Unlike most salad factories, Dole conveys their waste material in a pneumatic system. This greatly reduces the amount of water present.

Testing was done with and without shredder ahead of the presses. Two presses were used: a KP-16 with .095" diameter perforated screen, and a VP-6 with 0.030" perforated screen and a rotating cone option.

The results of BOD measurement are important to note. Despite the wide differences in hole size, only 5% more BOD was measured with the KP. In fact, changes in discharge cone pressure had noticeably more effect on BOD than the hole size.

Physical volume reduction is a goal with Dole. The following results were achieved on cabbage leaves, lettuce and carrot peel:

Using The Shredder Not Using The Shredder
70% by volume reduction 40% by volume reduction
60% by weight reduction 50% by weight reduction

BOD levels were 20,000 to 22,000 mg/l on the press liquor from shredded material, as compared to 16,000 to 17,000 mg/l without the shredder. These are very high levels, but it must be kept in mind that there was very little wastewater present.

Initially the Dennis Jones Group of Salt Lake City, consulting for Dole, was pleased with these results. It was felt that the BOD would be reduced to an acceptable level by dilution into the plant wastewater stream. However, calculations revealed that this would not be the case. The alternative of hauling the press liquor in tanker trucks for land application also proved uneconomical.

If we are to satisfy the market demand for produce and food disposal equipment, a practical means must be found for disposing of press liquor.

Revision May 1998. Dole Fresh Vegetables is very pleased with the results of the KP-16 at their Springfield, Ohio facility. It is operated with a minimum air pressure on the discharge plate so as to minimize solids in the wastewater. It is felt that the loads of waste material are reduced to one quarter of what they would be without the use of the press.

Later Visit: The plant had raised the air pressure so that fully one half of the waste load was going to the WWTP. This cut the hauls per week in half from what it would be otherwise.

Issue 65

Dryer For Mango Waste

January 12, 1999
Rev. February 2009

Vincent is currently manufacturing a small rotary drum dryer that is destined for the interior of Venezuela. It will be used to convert mango waste into a dry animal feedstuff. This will be done at a small plant that produces aseptic drums of mango puree from a plantation of 15,000 trees.

The waste, 40% of the delivered fruit, consists of peel and seeds. The material is quite nutritious; however, it spoils rapidly unless the moisture content is reduced to about 10%.

Prior to drying the waste, which has about 80% moisture, it will be shredded into small particles. This will improve the heat transfer within the dryer, allowing quick and uniform drying.

The dryer is a triple pass unit with a full rotating outer drum. The burner is specified for natural gas, with complete safety and operating controls. The furnace is a carbon steel shell lined with refractory fire brick. The mango is conveyed through the dryer drum by the hot gases from the furnace. The dried material is separated from these gases in a separation chamber located at the drum discharge. An induced draft fan draws gases and mango through the dryer and separation chamber.

The mango waste can be sticky, and there is a danger that it will stick to hot metal as it enters the first pass of the dryer. When this happens to a material it can dry out completely and begin to char. To prevent this situation from occurring provision has been made to blend some dried mango waste into the wet material being delivered from the puree extraction building. It is expected that the mixture of wet and dry material will lose its sticky nature and pass through the dryer in a proper manner.

The capacity of the dryer is small, only 2,500 pounds per hour of water evaporation. This will allow converting approximately 3,000 pph of mango waste into 650 pph of dried animal feed.

Selection of the equipment for this plant started with an inquiry for a screw press. It was hoped that a press would remove the moisture from the mango waste. An experiment was run in which lime was added to the waste, following the steps in Dan Vincent's 1940 patent. We found that, while lime breaks down citrus peel so that it can be pressed, it has no such effect on mango peel.

[February 2009 The use of this dryer was rapidly abandoned. Even in a country with fuel oil as cheap as it is in Venezuela, the cost of fuel exceeded the value of the animal feed which was produced. The experience helped Vincent decide to get out of the dryer business in 2007.]

Issue 88


Egg Shells

May 19, 1998

Egg crackers make up an industry that not many people are aware of.  Their business is to process truckloads of eggs from layer farms into basic food ingredients:  egg whites and yolks.  These two bulk commodities are sold to food processors who use them as food ingredients.  They ship their products in refrigerated tanker trucks containing approximately 5,000 gallons each.

One member of the industry is Daybreak Foods of Minnesota.  We visited one of their plants where they have six egg cracking machines.  These are contained within the "sanitary" half of their small factory.  They crack about 3,000,000 eggs per day.

Banks of suction cups lift the eggs from the shipping cartons.  Some cracked and broken eggs are culled by inspectors.  Next the eggs are candled:  a bright light is shined through the egg to detect internal impurities.  This is done to eliminate any fertile eggs containing
blood spots (embryos).  Following an automatic wash cycle the eggs are conveyed into the room with the egg cracking machines.  These are Lazy Susan type machines that automatically crack the eggs and separate the egg whites (albumen) and yolks into two separate flows.

This factory generates about 18 tons of waste material per day.  This waste is mostly eggs shells, but it also includes the cull eggs, the no-cracks from the egg crackers, and other "bad" eggs.  This material is sent to a landfill.

As an experiment we tried pressing this waste material.  One objective was to crush the shells so as to increase the bulk density; this was aimed at reducing the number of truckloads being hauled to landfill.

Another objective, with a much better payoff potential, was to separate the yolk and egg white from the shells.  The yolk and egg white "juice" is classified as non-edible since it is unfit for human consumption.  However pet food companies will pay $0.045 per pound for the material.

Our press definitely ground up the eggshell.  The testing was done with a KP-6 press, and the press was easily overloaded.  Consequently we would recommend a Series CP press for the application because it has the screw shaft supported at both ends of the press.  [In 2004 this is no longer so.]

In one test we ran 56 pounds shells and got 43 pounds of fine ground shell (press cake) along with 12 pounds of "juice" (press liquor).  Unfortunately the juice was (1) very foamy and (2) full of eggshell chips.  But it did represent 20% yield by weight (including chips) salvaged for sale to the pet food companies.

In another test we pressed whole cull eggs.  The press liquor yield was 85% of the inbound flow.

The foam was not a real problem, but it was felt that the shell bits would have to somehow be screened out.

In the end the use of a press could not be justified by Daybreak.  They have installed a drain pan system at the back of the waste truck.  It allows the juice to drain into a tank while the truck is being filled.  The juice is rather clear, and they screen it through a 3/8"
perf sheet followed by 3/32" perf on its way into the tank.  The tank holds about 25 gallons.

We did get measurements of flow rate and bulk density improvement.  Ten gallons of eggshell from the truck came down to seven gallons of press cake.  Flow of this material was 2,000 pph in the KP-6 at 30 rpm.  On another flow test results were even a little better.

2011 UPDATE: Be sure to see the EGG SHELL UPDATE newsletter. This market has really taken off!

Issue 77


Egg Shells Update

April 22, 2011

A lot has happened since we wrote a rather negative Pressing News in 1998 about egg shells.  For one, the plant where we did our testing, Daybreak Eggs, finally bought a screw press from us in 2010.

Literally dozens of KP-6, KP-10 and KP-16 presses have been sold for this application.  In fact, a new model, the KP-12, is being developed as a specialty for egg shells.

The egg shells come from at least four basic sources:  egg inoculators, poultry hatcheries, egg graders, and egg breakers.  The inoculator market rejects infertile eggs, while the graders and breakers reject fertile eggs:  our presses do the same job either way.

The market has been given a boost by new regulations involving inedible egg material.  For example, infertile eggs destined for a hatchery can no longer be sold for human consumption.  A bigger impetus to the market has been regulations limiting the transport of inedible egg material.

The albumen recovered from the egg shells is a high value protein which is used for animal feeds.  Because of its value, it is used in specialty applications such as mink feed, pet foods, and piglet starter feed.  A significant amount is exported from the United States.

As a rule, the crushed egg shells are land applied to farm land where they improve soil properties.  Also, they can be used in specialty applications like litter in horse barns and riding arenas.

The alternative to using a screw press to separate albumen from egg waste is a centrifuge.  These are unpopular due to heavy maintenance requirements.  In addition, they do not crush the egg shells to the extent that occurs in a screw press.

For the last two years Vincent has had a booth at the International Poultry Expo held in January in Atlanta.

Model KP-6 For Egg Shell Perforated Screen Note Press Cake





Issue 232

Feather Meal

November 9, 1995                                                                                                                                                                                                  ISSUE #35

Modern broiler plants will process 200,000 to 1,000,000 birds per day. With average live bird weights running from four to six pounds, the tonnage of waste material is enormous. All of this waste material (feathers, offal, trims, blood, and DOA's) goes to the By-Products operation. The by-products are mostly animal feed, which is produced by rendering (cooking) the waste materials.

A most important by-product at a rendering plant is feather meal. Feathers constitute 9% by weight of the live bird, and they are rich in protein content. This protein is in a form, like hair, that is not digestible. To make it digestible it must first be converted through a hydrolysis process. Hydrolyzation is accomplished by cooking the feathers with steam. This was previously done in batch cookers; the current technology is to use continuous hydrolyzers.

Hydrolyzed feathers are produced with moisture contents in the range of 45% to 65%. This moisture must be reduced to 8% for the product to have adequate shelf life as an animal feed. Vincent rotating drum dehydrators are used to remove this excess moisture.

In the Spring of 1995 we worked with a rendering plant that had reached the capacity limit of their feather meal dryer. Immediate relief was required because of the economic opportunity being lost.

Trials were run and it was found that their continuous hydrolyzers were producing feather meal at 55% to 56% moisture. This contrasts to another renderer with whom we have worked where the meal leaves their homemade continuous hydrolyzer at 47% to 48% moisture. There is a third western firm with whom we are in contact where the meal has 60% moisture prior to drying.

A series of tests were run using a rental VP-16 screw press. Running the press at 60 Hz corresponds to the standard 13 rpm screw speed. At this speed the press did very little dewatering. It reduced the moisture content of the feather meal by only one or two percentage points.

However when the press speed was reduced to half speed performance improved. Running at 30 Hz, readings of 49% to 50% press cake moisture were obtained. This does not sound like much, but the impact on dryer capacity is surprisingly large.

Here is how we calculate the impact: If we put 2,000 pounds of feather meal at 56% moisture into the dryer, and dry it down to 10% moisture, we end up with 978 pounds of finished meal. This is calculated by taking 44% of 2,000 (which is the pounds of dry solids in the 2,000 pounds), and dividing those solids by 0.9 (which is 1.0 minus the final 10% moisture). To check that answer we can multiply the 978 figure by 90% to see if that is indeed all of the solids in the 2,000 pounds we started with.

We can see that to produce 978 pounds of meal, it was necessary for the dryer to evaporate (2000 - 978) or 1,022 pounds of water.

For the alternative case, let us assume the screw press takes the moisture down to 50%. If we put 2,000 pounds of that material into the dryer, we will be putting in 1000 pounds of dry solids. If this is dried down to the same 10% moisture, we end up with 1,111 pounds of finished feather meal. To produce this meal the dryer had to remove (2000 - 1111) or 889 pounds of water.

We can compare these two results to determine the factor by which dryer capacity is affected. In the first case the dryer must remove 1,022 pounds of water to produce 978 pounds of meal. This calculates to removing 2,090 pounds of water per ton of 10% feather meal.

In contrast, in the second case the dryer needs to remove only 889 pounds of water to produce 1,111 pounds of meal. This works out to evaporating 1,600 pounds of water to produce one ton of 10% feather meal.

Since the dryer is running flat out, it will evaporate the same number of pounds of water per hour in both cases. Thus we can calculate that with the press in operation the production of feather meal increases by 30%!

This is figured by dividing the capacity of the dryer (in pounds of water evaporation per hour) by 2,090. Since the dryer in question has been evaporating 14,100 pounds of water per hour, the production calculates at 6.7 tons of 10% meal per hour. Under the second operating condition, 14,100 divided by 1,600 gives 8.8 tons per hour. This is a production increase of 30% with the same dryer.


September 10, 1996

There are two types of fish processing plants where Vincent finds applications. (1) Fish Meal plants which convert trash fish and fish wastes into fish meal, a valuable animal feedstuff, and (2) Plants which process fish such as menhaden and anchovy to recover fish oil as well as produce fish meal.

Once a mainstay of Vincent Corporation, the industry has almost entirely moved offshore in recent decades. The industry decline has been due to a combination of both fish migration to other areas and environmental problems associated with odor and wastewater.

A popular combination in the fish plants consisted of a Vincent screw press, flash (or steam) evaporator and rotating drum dryer. The presses were of carbon steel construction because the fish oil prevented rusting. The flash evaporator was inexpensive, but relatively inefficient and odorous; few of these remain in operation today, none in the United States.

Oil Recovery plants process anchovies and menhaden, among other fish. These are caught in purse seines that are a quarter mile long. The usual catch is 5 to 30 tons per set of nets. A full boat will have 500 to 1,500 tons in its refrigerated hold.

At the docks the fish are pumped into a storage "raw box" and then metered to a live steam cooker. The cooked fish are pressed in screw presses (double pressing has been used successfully).

The press liquor, which has about 10% solids, goes to a centrifuge to separate oil. After the oil is removed the press liquor, which is called "stick water", goes to a steam evaporator. The concentrated stick water is called "solubles" and is sold (at 50% moisture) as an animal feed ingredient.

The press cake is made into fish meal in a dryer without recycle capability. Extensive (triple) cooling is required for the meal coming out of this dryer. Either an antioxidant must be added or it must be shifted from pile to pile because the high protein is prone to spontaneous combustion. It is sold as fish meal, a very valuable ingredient for animal feedstuffs, especially chicken feed.

Oil recovery from menhaden can be 7 to 15% oil. Menhaden is known as the fish the pilgrims planted with their corn seeds; they did this with it because the fish was too oily to eat.

Fish meal is produced as a by-product in the second type of fish processing plant. The facility works with waste materials such as scrap fish from shrimp boats, crab shells, or trim materials and viscera from a larger fish processing plant. The raw fish (whole or pieces) are coarse ground at the start of the process. Small plants run the ground material directly to a rotating drum dryer, while the larger plants will first run the fish through a screw press, followed by a dryer. The fish meal comes out of the dryer at around 10% moisture.

Dryers used to produce this fish meal require the capability to recycle the fish meal; commonly they are small 10,000 #/hr systems. The rotating drum dryer is ideally suited for preparing fish meal because it very efficiently removes the moisture. The key design feature for making whole fish meal is that partially dried material is extracted from the triple pass dryer and mixed with the incoming material. This recirculation assures both that the product will not be overheated and burned, and that the dryer will not plug with sticky substances.

Fish meal has 60% protein or more, with only 5% fat, so it is a valuable ingredient for animal feedstuffs. The final product is fine ground (not pelleted) before being loaded out to a feedmill. At the feedmill, typically 5% is blended into broiler feed.

Issue 49


August 20, 2003, Revised November, 2010                                                                                                                                                              ISSUE #141


At least once a year we are approached by entrepreneurs who conceive a system for converting garbage into animal feed. The garbage in question is frequently restaurant waste, although it may also be institutional or even residential waste.

Invariably these projects collapse under harsh realities.

The request is frequently made for a screw press that will dewater the waste to some unrealistically low percent moisture, like 50% or less. In reality, garbage is 85% to 95%
moisture, and, after pressing, the press cake will still have over 80% moisture content. At that point there is no more free liquid to squeeze out of it.

Specifying a machine to remove more moisture means nothing if a machine cannot do it. Pressure in a screw press will remove only so much moisture. After that, the solids will extrude through the screen like thick milkshake. To remove additional water, a change,caused by chemical reaction or adding heat, will be required.

In order to prevent spoilage, the moisture content of an organic material must be reduced to a range of 10% to 15%. This dehydration must be done in a rotary drum dryer, and the fuel costs will exceed the value of the dry garbage. That is, to produce a ton of 12% moisture material from press cake with 80% moisture, the dryer will require over one hundred therms of energy. That is more than $50 worth of fuel alone to produce one ton of animal feed.

Besides this, pressing garbage to remove the moisture creates an impossible sewage disposal problem. The press liquor from pressing garbage is a thick goo of suspended
solids. The BOD loading of this liquid will overwhelm most wastewater treatment systems.

In addition, the labor costs to remove contaminants are significant. Restaurant waste typically has plastics (shrink wrap and Styrofoam), metal (silverware and coins), string
and cord, not to mention broken chinaware, glass and pop cans. Farmers are reluctant to buy feed that might contain these items, even at discounted prices.

None of this seems to faze our would-be garbage millionaires. What should bring them down to earth are two facts: (1) the opportunity they see has been obvious in America for at least a century, and no one has made a go of it, and (2) nobody has made a go of this business potential in third world countries where labor is cheaper, farmers are less picky, feed is more expensive, and businesses are less encumbered by environmental regulations.

November, 2010. More recently garbage inquiries have focused on biofuel applications. A key bit of logic is as follows: before something can be burned, all the water must first
be removed. In this water evaporation process, a point is reached at which there is only 10% moisture left. If we freeze the system at that point, an analysis of value will show that the material at 10% moisture has greater market value as animal feed than it does as boiler fuel. The only exception we have found to this is in Europe where use of biofuel is being mandated by government regulations. Pity their taxpayers.

Hake Fish

November 13, 1997

Not many people have heard of a fish called "hake", even under its proper name of Pacific Whiting. Part of the reason is that hake have not been harvested commercially until recently. This was because the fish has a built-in enzyme that takes action soon after the fish dies. Only recently has an inhibitor been developed to prevent this spoilage.

Recently we ran tests at Bioproducts, Inc. with a rental CP-10. This firm produces meal that is fed to salmon (farm fish) that is made from waste generated in hake filleting operations. Unfortunately the tests proved a total failure.

Seventy percent of the hake is scrap. This waste, cooked, is what we were attempting to press. The problem encountered was that the material was spoiled. It was in the form of a "pudding" at 86% moisture. This waste is trucked from a nearby fish processor, which results in a delivery delay. Worse yet, the processor uses a chopper pump to transport the waste within his plant, and this process opens up the digestive enzymes to the entire mass.

We suggested adding more inhibitors to stop the enzyme action. Unfortunately this could not be done because the final product is a fish hydrolysate. The hydrolysate is digested material produced by enzymes that are added at the end of the process. It was felt that, if we added inhibitors, they would interfere with the final enzyme action. (In addition, inhibitor residuals can have a negative impact on the environment at the fish pen operations.)

Bioproducts had hoped this process would work because of the potential to save energy. Their process involves taking the fish scrap down to 55% moisture content in Dupps cookers. This is followed with open kettle cooking and mixing with previously dried fishmeal. Going from 86% to 55% in the steam cookers involves a significant fuel expense that Bioproducts would like to avoid.

We were told of one hake plant with a decanter (centrifuge) that reportedly takes hake waste down to 60% moisture. This is used in place of steam cookers. Decanters have the disadvantage of being very expensive both to acquire and maintain.

We have continued to pursue hake pressing. Larry Hess, our sales rep, arranged for us to tour the Arctic Five, a Tyson Seafood factory ship. Aboard this vessel cooked hake scrap is in the screw press within hours of swimming. They currently have Atlas-Stord twin screw presses which achieve 70% to 55% press cake moisture. The performance depends on variables such as the species, the length of cook, the amount of oil, the speed of the press.

These presses have corroded severely in the saltwater environment. Consequently Tyson personnel were much impressed with the all stainless construction of Vincent presses. We hope to have our units in their 1998 budget.

Issue 69

Hydroponic Tomatos

December 24, 1996

Recently a Model KP-6 screw press was tested on cull tomatos at Vine Ripe in Owatonna, MN. This firm serves the Twin Cities with premium quality tomatos. They have four acres of greenhouses, to which they are in the process of adding three more. Dutch firms dominate in the growing technology, so the greenhouses are imported, knocked down in cargo containers, from Holland. Dutch crews erect the houses, with only the glass windows being supplied locally.

The greenhouses use glass as it is far more durable than plastic film and it does a better job of transmitting light.

The vines are rooted at ground level in rock wool batting, roughly three inches thick by twelve inches wide. There is no dirt used in the production process. Food for the plant is supplied by a drip irrigation system that feeds nutrients and water directly onto the rock wool.

A tomato plant will yield fruit several years. However, because yield tends to fall off, the plants are replaced once a year in Holland. In Minnesota, because of the adverse and varying weather conditions, the plants are replaced twice a year.

The tomatos are harvested continuously, except during the months of January and February. These months are skipped, even though November and December are the coldest months, because window frost in January and February reduces the sunlight that reaches the plants.

The greenhouses are equipped with rails between each row of plants. These guide electric carts that are used for weekly maintenance and harvesting of the plants.

Weekly maintenance consists of attaching plastic clips to hold the vines to strings that are suspended from the ceiling beams of the greenhouse. The vines grow to be thirty-five feet long. The clips are about a foot apart, roughly the length grown each week. Also, arched plastic supports, called trusses, are attached to the vine where there is a branch with tomatos. This allows the tomatos to grow without dragging down the stem to which they are attached.

Bumble bees are kept in the greenhouses to provide pollination. Without pollination, the tomato does not have seeds and it grows to a dwarf size. The bumblebees eat some pollen as a source of protein. Sugar water is kept in their hives so as to provide other nutrients. The bumblebees do not make honey as the tomato flower does not have sufficient nectar.

Pest control is critical. One factor that add difficulty is that special insecticides must be selected to prevent killing the bumblebees.

Large hydroponic operations are found in states such as Arizona and Texas where up to 300 days of sunlight are available per year. A typical large operation would have 40 acres of greenhouses.

The flow rate through the Vincent KP press was excellent. In pressing the cull tomatos we found it easy to achieve a separation of 50/50 between press liquor and press cake. The cake is suitable for composting, and it was hoped that the liquor could be sewered. Most of the seeds ended up with the press cake.

The reason for pressing the cull tomatos is to reduce the charges for hauling the tomatos to a disposal site.

Issue 53

Meat Plant Waste

December 4, 1998

Ed Miniat Inc. is a large specialty meat processor in the Chicago area. They produce meats commonly found in delicatessens. Boneless Cooked Seasoned Beef Ribs would be a typical product.

Early in 1997 our sales rep arranged for Ed Miniat to rent a KP-6 press, with a two week free trial period. A few weeks later they purchased that machine. It was not until recently that someone from Vincent visited the firm. We found a unique application.

The meat packing plant generates 4,000 to 5,000 pounds per day of "inedible". This is trim fat, gristle and other unusable meat. Some is collected in garbage pails, while other is flushed in floor drains. The drain water is run through a rotating drum screen, and the solids from this filter are collected in pails.

All of this inedible material is sold to a rendering plant. The problem that existed was that the waste contained so much free water that the renderer was refusing loads.

The problem was solved by processing all of the inedible through the KP-6. This is done on the second shift, with the press being fed from buckets that are lifted by hand. The water that drains from the press goes to the wastewater treatment facility.

For added convenience the press is mounted on a stand with casters. This stand was supplied by Vincent at the time of the original rental.

Issue 87


September 20, 2011
Every couple years Vincent receives an inquiry about pressing mushroom compost.  We have had limited technical success and absolutely no commercial success.

Our most recent serious testing was with samples of mushroom bedding, before and after composting.  These were supplied by Monterey Mushroom in Zellwood, Florida.

Monterey grows the mushrooms in 4' x 8' trays, 8" deep.  The trays are filled with wheat straw, chicken manure, and cotton seed meal, along with 2" of peat moss (rich soil).  (Sussex Mushroom in England said they use 80% straw.)  Monterey incubates the mushroom spores in rye or millet grain. 

Each week Monterey produces three compost batches of 28,000 cubic feet.  This is neutralized to a pH of 6 to 7-1/2 by adding sugar beet lime (possibly gypsum or alum?). 

Monterey wanted to know about the nitrogen in the press liquor, because of fertilizer applications.  Pressing this compost was just like pressing peat:  only single cell biological mud, no free liquid at all, came through the screen.  That happened with materials from both before and after composting.  Worse, both materials just sat in the press and co-rotated. 

We could not get cake to come out of the presses.  We tried two CP-4's and one KP-6, and achieved the same bad results with all of them.  Consideration was given to trying a 1/2 pitch screw, or a perforated screen, but it was clear that would not make enough improvement to justify the effort. 

The "as received" non-composted material was 67% moisture; the composted, 64%.  The press cake of the composted material came out 61%.  There was no free water in this material; not a drop could be squeezed from a fist full.

Most mushrooms come from Pennsylvania; mushrooms are Pennsylvania's biggest export.

Issue 112


November 1, 2013

Last month we had an opportunity to runs tests with mushrooms.  Button mushrooms were purchased at the produce market, and we tried squeezing liquid out of them using a variety of tactics.

The most interesting thing that happened occurred when we used steam injection in a screw press.  This, as hoped, did increase the dewatering.  But what was strange was that the press liquor, as it cooled down in our sample collection bags, turned into jelly.

We started running the fresh mushrooms in a laboratory CP-4 press.  A video of this is posted on YouTube; enter VincentCorp1931 on their web site and you should be able to find it.  Extremely low air pressure had to be used on the discharge cone, and low screw rpm.  Even then the material channeled (squirted) out from one side of the cone.  50% juice yield was obtained.

Because of the channeling, our next test was run with a KP-6 press with the rotating cone option in play.  This eliminated the channeling, and much better results were obtained.  The mushrooms as we received them had 93% moisture content; this went down to 91%, with a 25% juice yield.

In order to improve the moisture reduction, we switched screws in that press.  Re-running the test with a screw with a tapered shaft made a notable improvement.  50% juice yield was obtained, and the moisture content of the press cake dropped to 90%.  The tapered shaft adds a third squeezing mechanism to the normal tightened pitch of the screw flights and pressure exerted by the discharge cone.

Since it was still possible to squeeze quite a bit of liquid from the press cake, we tried double pressing.  It appeared that the mushrooms were torn apart in the first pressing.  Consequently, with the second pressing, a significant amount of additional juice was obtained.  The moisture content of the press cake dropped a couple percentage points, to 88%.

Along the line we chopped some mushrooms, and we put them in a Baggie with some hydrated lime.  With a bit of massaging, it was evident that a chemical reaction was occurring that released moisture.  So, we took some of our press cake from previous runs, added 3% hydrated lime, and tried pressing that.  The results were impressive.  An extremely dry press cake was produced, with only 74% moisture content.

While the press liquor generally seemed rather clear, the dry matter solids in it measured fairly high.  Checking the Brix, we found that mushroom juice measures 3° to 4° Bx.  That helps explain the high dry matter content of the press liquor.  In all of our trials the total dry matter content of the press liquor measured 5% to 6%.

Our final test of the day involved pressing fresh mushrooms in a screw press that was set up for steam injection.  Steam was injected through the resistor teeth, achieving temperatures around 160 F.  As with fresh organic materials like orange peel and fish, a great deal of moisture was released from the mushrooms.  This took the mushrooms, with 93% as-received moisture content, down to 89% moisture in the press cake.

This was the test with steam injection which lead to the observation that the press liquor, which flowed freely from the screw press, turned in jelly once it cooled down.

There is one thing we did not try which would work very well.  If a shredder were mounted over the inlet to the screw press, surely high juice yield would be obtained.

Test results are pasted below:




Issue 258



May 25, 2009                                                                                                                                                                                                       ISSUE #211

In one month we had four different inquiries dealing with pressing okara. One, with White Wave, reached the point of bringing two 55-gallons drums of okara to Tampa for testing.

Okara is a waste product resulting from the production of tofu. The process for making tofu starts with soaking soybeans overnight, and then grinding them. The beans are about the size of baked beans. After soaking they are fairly soft and crumbly. Following grinding, the material is heated by being pumped through a heat exchanger.

A leading producer of tofu in the States is White Wave. Years ago we tested a Fiber Filter at their factory in Boulder, Colorado. At that time, the heated flow was pumped to 3 hp "centrifuges"; these were more like clothes dryers. The hot okara dropped to a narrow belt conveyor and was sent to farmers, for animal feed. When squeezed, not much water came through your fingers, and the moisture which squeezed out soaked right back in.

The hot soy milk was pumped into pails, along with some coagulant, and agitated a little. After a short dwell time the pails were dumped onto a 1 meter belt press, with fabric on the bottom and with metal slats forming the top belt. The filtrate liquid went to the drain, and the tofu cake that come out was about 1-1/2" thick. It was sliced into bricks that were dumped in a tub of cold water. After cooling the bricks were put in packages, water was added, and then the packages were sealed. Next they were pasteurized.

The plant waste water is what we were running through the Fiber Filter. The particles were too fine for the machine to work. We wrote it off as an another unsuccessful trial.

Today there are likely both specialty screw presses and proper centrifuges which replace some of the equipment such as the belt conveyor.

The purpose of our recent testing was to remove additional moisture from the okara. It had 86% moisture, which is way too high for economical production of animal feed in a dryer.

The okara we tested in Tampa, measuring 86% moisture, had come from a centrifuge, so there was no water left which a screw press could remove. Therefore we tried various press aids which are acceptable in animal feed, such as lime, gypsum and alum, along with cellulose fiber. None of these worked at all. The screw press removed negligible water. We have written it off as yet another unsuccessful trial.

Onion Waste

June 20, 2003

Vincent screw presses are used to dewater the waste from a wide range of fruits and vegetables. We have had outstanding success in applications such as (1) lettuce and cabbage from prepared salad factories, (2) carrot waste from facilities that produced baby carrots, (3) peel from plants that use steam and brush peelers on potatoes and carrots, (4) corn cob, husk, and silk at sweet corn canneries.

One very challenging application has been onion waste. Onion processors will easily generate 10,000 to 100,000 pounds per day of waste. This waste comes from two flows: cull onions (spoiled, bruised, crushed), and the skins (parchment with outer layers of onion, with top and bottom trims).

When cull onions were run in a screw press, a paltry 20% was converted to drain liquor. With this poor a volume reduction, there was no justification for pressing the waste. The results pressing skins were even worse. Some improvement was achieved by pressing the waste in a twin screw press; however, the cost of these presses is excessive for the application.

In order to achieve significant volume reduction, it is necessary to shred the material before it is placed in the screw press. This is done with a shredder, or pre-breaker, that is mounted over the inlet to the screw press. This means, essentially, that two machines instead of one must be purchased. There is a good payback on this investment: waste can be reduced by 50% to 70%.

Issue 142

Pea Waste

April 23, 2009                                                                                                                                                                                                         ISSUE #210

                                                                                                           PEA WASTE

Pea cannery operations generate a lot of waste which is screened from their wastewater. Generally the flow is pumped over static (sidehill) screens, which separate a sopping wet mass, mostly peas. These screen tailings must be trucked from the site.

Because the tailings hold so much water, the tonnage is significant. More importantly, free water jostles free in transport, leaving a trail of water behind the waste hauler.

Dewatering this waste is a good application for an inexpensive Series KP screw press. When the screen tailings are fed to the press, depending on the effectiveness of the static screen, from 60% to over 80% of the weight is separated as wastewater.

This press liquor does not contain an excessive amount of suspended solids. Regardless, it should be directed to the wastewater flow which goes to the static screens.

In one installation the cannery also has a flow of waste which is exhausted from the factory with a fan system. The discharge of the fan is blown to a chicken wire cage built over the inlet to the screw press. This waste, along with screen tailings, falls into the press.

The peas are so soft and squishy that low discharge cone pressure is used. The rotating cone feature is very important to successful operation. Also, the new two-thirds pitch screw has proven especially effective. With these options, high press screw press capacity is achieved without pushing excessive solids into the press liquor stream.

In one application a 10" press worked fine on peas. However a larger 16" press was required, due to increased load, when the plant switched to canning corn.

Pickle Waste

July 8, 1993
Rev. Nov.'96

We recently had a chance to visit the Claussen pickle factory. The plant runs year around by bringing in cucumbers from all across the United States, especially Florida, plus Costa Rica, Honduras, Mexico and other countries.

The variety was impressive. They pack jars of spears, chips, relish and whole pickles. They have a whole pickle pack where the pickles are all standing on end, called a soldier pack. The biggest pickles they receive are about 6" long, and the biggest diameter is 3". They also pack five gallon institutional tubs.

Plant personnel always refer to the vegetable as pickles. Technically, however, the cucumbers do not become pickles until they sit in a sealed jar along with spices, salt water, and vinegar. This was significant in that it means that all the waste material going to the Vincent dewatering press is really cucumbers.

The plant runs two shifts, processing about 400,000 pounds per day. They have several each of both automatic bottling lines and manual filling lines. Typically they will run all chips for a day or two and then switch to all spears for a while.

Waste material is generated at every step of the way. Pickles are culled for discoloration, deformity, and size. Slices will be culled for something as simple as the way the cut goes through the cells. Stems are trimmed, as are the parts that protrude above the necks of the jars. Because of this, waste material seems to run about 5% of the throughput.

Some of the culls can be made into pickle relish. However, the market demand apparently is not near enough to use them all. Consequently large amounts of material were being sent to landfill.

To relieve landfilling expense, Vincent supplied a VP-6 press with a VS-12 shredder mounted at the inlet. This combination of equipment receives about 2,500 pounds per hour. The pressing operation divides the flow roughly half into press liquor and half into press cake. The liquor is discharged to the plant sewer stream, and the press cake is added to dumpster material. In this manner the amount of material going to landfill has been reduced by half.

Issue 5

Pineapple Waste

September 22, 2009                                                                                                                                                                                             ISSUE #215
                                                                                                    PINEAPPLE WASTE

In 1975 Vincent Corporation sold equipment for a feedmill that would process pineapple waste. The project, sold by FMC Corporation, was for Dole Pineapple in Mindanao, in the Philippine islands. Now long abandoned, the project involved dewatering waste from pineapple juicing so that it could be sold as animal feed. Because of the current high value of animal feed, several inquiries have been received recently about the process.

Dave Kalashian's trip report from Mindanao mentions that the cake was coming out of the press at no more than 78% moisture content, that being acceptable. We also found a material balance prepared by FMC in which they worked with 76% press cake moisture.

This leaves too much water to be evaporated in a dryer. The cost of the fuel required would exceed the value of the animal feed produced. Therefore recently tests were undertaken in Tampa.

Pineapples were shredded and pressed to remove the juice. The waste from this process was tested with three different press aids. We tried varying percentages of hydrated lime, gypsum, and alum. The gypsum and alum had no effect. However, an excellent reaction with lime was achieved.

The waste with lime pressed to much lower values, in the range of 60% to 70% moisture content. A relatively high amount of lime was required, 1% to 3% by weight. This is similar to what we have found with other wastes such as potato peel, onion peel, and tomato waste. It compares to 0.5% which is typically used on orange peel.

Pressing material with this much lime is a high torque operation. The cake becomes very hard and dry. Lime mixed with water makes cement, as used for concrete. It is likely that to some extent this reaction is occurring in the press. Nevertheless, the pressing operation is within the range of normal screw presses.

We were not able to test with steam injection, due to the small scale of our trials. However, we know that direct injection of steam into the pineapple waste will reduce the moisture content of the final press cake. In the case of orange peel, moisture content is reduced by up to four percentage points with steam injection (Pressing News #129 of July, 2002).

In the pineapple waste feedmill, the press cake would be dried to 10% moisture in a rotary drum dryer. This would be pelleted and sold. Reportedly the value is higher than that of dried citrus waste because the nutritional value is greater.

Pineapple waste has a little more Brix than citrus waste. This means that it is practical to use a conventional Waste Heat Evaporator (WHE) to make pineapple molasses out of the press liquor. Unfortunately, most likely candidates for a pineapple feedmill are too small to afford the investment required for a WHE. (The use of a WHE would reduce fuel consumption per ton of finished product by as much as two thirds.)

This means that the press liquor will be sent to the wastewater treatment plant (WWTP). This will present a severe load on the WWTP as about two thirds of the solids in the pineapple waste, in the form of dissolved sugars, will be lost with the press liquor. If a lagoon system is used, odor problems are likely.

One alternative under consideration is to use the press liquor as a feed to an anaerobic digester. The biogas produced therein would be an excellent boiler fuel. And the odor problem would be addressed.

Pistachio Nuts

February 1, 2005

Pistachio processors in California operate during a short harvest season, from September into October. The green berries, as harvested, are about the size of an olive. At the processing plant, an exterior layer of pulp is removed. This is done in abrasive peelers, with water. Once the rejects (immature and hollow seeds) are removed, the pistachios are dried, usually in GSI dryers. The product that comes out is the snack we are familiar with: a white shell, cracked opened by the heat, containing a delicious nut.

Setton Pistachio in Terra Bella is a very large processor. They use three Vincent KP-16 screw presses to separate the waste pulp from peeler water. The dewatered pulp is given to farmers for blending as a cattle feed.

Setton processes 120 tons per hour of green berries. About one third of this weight, 40 tph, is pulp that surrounded the shell. Most of the time two KP-16's can handle the load, giving the KP-16 a maximum rating of 20 tph of pulp.

Static screens are used ahead of the KP presses. These separate large quantities of water. This is effective in pre-thickening the flow to the presses. The solids from the screw press come out as a thick, fibrous mass. The rotating cone feature of the KP presses is not necessary at all.

Smaller scale pistachio operations might drain the pulp in static screens and then haul the soggy pulp for landspreading with a manure spreader. Others pump the wastewater flow with the pulp into a settling pond; between harvests, the dried ponds are emptied with excavators.

Issue 157

Potato Peel

November 18, 1994
Rev. November 2007

We have a few inquiries each year about dewatering potato peel.  This peel is a waste product that comes from peeling machines used by potato processors.  Well known manufacturers of potato peelers include Kusel, Magnuson, and Odenberg.  These machines usually feature a large diameter drum that is lined lengthwise with brush rollers, generally 8" in diameter.  The bristles on the brushes remove the peel.  Often the peel is loosened from the potato, ahead of the peeler, with caustic or steam.

The peel is very wet, which limits its value as an animal feed.  Also the wet weight results in significant haulage costs.  By running it through a screw press its value is enhanced and trucking costs are reduced.

Normally the peel comes to the screw press with 86% to 93% moisture.  The lower figure may result from an existing screening device that drops out free water.  This device is best left in place as a pre-thickener for the screw press.

Dewatering potato peel is a tough application.  The best way to make it pressable is to react it with hydrated lime [calcium hydroxide, Ca(OH)2].  Doing this allows the press to separate up to 70% of the flow as press liquor, and the rest is firm cake at 75% moisture content.  A short reaction time, with 2% lime by weight, is required.

When a press works without lime being used, typically the incoming flow of wet peel can be divided into a 50:50 split of press cake and press liquor.  Separation performance depends on the air pressure setting of the discharge cone.  Press cake moisture of 82% can be expected.

With a low cone pressure setting, the press liquor is relatively clear.  With high cone pressure a noticeable amount of "mashed potatoes", or starch, will be forced through the screen and into the press liquor.  This may or may not be acceptable to the processor, depending on his wastewater treatment facility. 

The starch can be separated from the press liquor by directing it through a gravity decanter tank.  Alternatively, hydraclones and the Vincent Fiber Filter may be suitable.  When solids are screened from the press liquor, they are often added back to the flow of material going into the press. 

The less expensive Series KP presses, operating at very low speed, have found acceptance in this application.  These feature wedgewire screens with slot widths of 0.015".  Auto-reversing VFD’s are provided where screen blinding problems occur. In addition to presses, Vincent maintains lime metering dosers and gravity screens in our rental fleet.  These are available for demonstrating peel dewatering techniques.


Issue 17


Potato Peel, Improved

August 1, 2008

A Model KP-10 screw press was recently put into service dewatering wastewater at a plant processing sweet potatoes and Russet (white) potatoes. All of the waste peel, starch, and water collects in a pit and then is pumped to the wastewater treatment area.

The waste first flows through a rotary drum screen, 24" in diameter by 48" long, with 0.020" diameter perforated screen. The helicoid flights attached to the inside of the screen are 2" high with 11" continuous pitch. The drum is angled upward at 15 degrees. Hot water flows through the backflush which runs continuously while the drum turns. The screen is also scrubbed with bristles, and it is washed once daily with a degreaser.

The sludge drops out of the rotary drum screen into the Vincent reaction conveyor. The reaction conveyor is essentially a trough with a special design ribbon-flighted auger that mixes hydrated lime [calcium hydroxide, Ca(OH)2] from the Vincent Doser with the sludge. The sludge and lime have a one minute reaction time at default speed.

During the reaction stage the sloppy, starchy sludge releases free water and turns into a wet, very press-able cake. Without proper reaction the waste peel is a sloppy, slimy mess that simply CANNOT be mechanically dewatered. When squeezed in one's fist, it oozes between one's fingers like raw egg yolk or mashed potatoes. The change in body is truly remarkable to observe. Note: Only the Russet potato waste required treatment with lime. The sweet potato waste dewatered fine by itself.

After reaction, the wet cake drops into the screw press where it is easily dewatered. Press cake from a recent start-up was measured as low as 65% moisture. This cake crumbled into a powdery pile as it dropped out of the press. Discharge cone pressure was left at 15 psi because at higher pressures the material would jam inside the press. At higher pressures the material continued reacting with the lime inside the press and would harden like cement. The spider bushing at the C-plate in this particular press created a bridging point where the over-reacted potato peel would jam.

Vincent sent three VFD's to individually control the lime doser, reaction conveyor, and screw press. One of Vincent's engineers was on-site to experiment with different lime dosages, mixing cycles, and press cycles. Lime dosage was critical for success. Without sufficient lime the material simply would not gain enough body to be pressed, even with a long (two minute) mixing time. Screen blinding was never an issue, and the reacted potato waste pressed very well at 60 Hz (18 rpm). Lime content seemed to have the biggest effect on how well the press dewatered. 3% lime by weight ended up being the magic number.

During trials the press was fed 1,500 pph reacted potato waste. It generated 500 pph press cake and 1000 pph press liquor. It was judged that the KP-10 press was running at no more than 20% capacity. (Two thirds of the spider bushing was plugged with cemented solids, and the press was definitely running under capacity.)

It is important to note that the press liquor was very high in starch, too high to be dumped straight to sewer. A hydrocyclone was used to pull the starches from the press liquor. This waste could be added back to the reaction conveyor.

The press cake will be offered to local farmers as feed.

Issue 201

Potatoes & Carrots

November 5, 2007

For several decades, Vincent has attempted to use a screw press to dewater potato peel. Our 1994 Pressing News described the best results that could be obtained. These results were relatively marginal, limiting the market for screw presses. After all, it is hard to justify a screw press if all you are going to do is put half the waste into the sewer and reduce the moisture content of the remaining solids to 82%.

Good results on carrot peel have been even more difficult to come by. Dewatering the pulpy waste from the Grimmway baby carrot factory was successful. However, waste from conventional brush peelers was virtually impossible to dewater in a screw press.

The problem has been that these vegetables contain a high amount of bound water. Some of this water is held within cells, by the pectin. Other water is found in long-chain organic molecules. The mechanical pressure of a screw press is not going the break loose this water. It takes heat, or chemistry, to break down the pectin and organic molecules.

For over sixty years the citrus industry has known that the addition of hydrated lime [calcium hydroxide, Ca(OH)2] causes a chemical reaction in orange peel that allows the waste to be dewatered by pressing. It is thought that the presence of hydrated lime and water breaks down the pectin in the cell walls. The end result is that the cake produced by a screw press will have a solids content half again higher if the orange peel is first reacted with hydrated lime.

It is worth noting that the presence of calcium hydroxide in the waste does not adversely affect its value as an animal feed.

In 2006, a number of tests were run that demonstrated that this same chemistry, that of adding hydrated lime, works for both potato and carrot peel. At one French fry plant, potato peel (with 9% solids content) was mixed with a small percentage of hydrated lime. With the addition of lime, the screw press increased the solids content of the waste to 25%, compared to 13% solids without lime. Similar results have been obtained on carrot waste.

To facilitate on-site demonstrations, Vincent has added lime dosing machines and reaction conveyors to our rental fleet. The lime dosers take 50 pound bags of lime, and generally one bag is used per shift. Bulk bag lime dispensers have been offered for larger scale operations. The reaction conveyor is a 12' long section of 12" diameter screw conveyor, with a mixing section at the inlet. Cut flights and VFD's are used in order to delay the flow of material through the reaction conveyor.

Issue 193

Rice Wine

November 12, 1996

Two Vincent CP-10 presses are being commissioned in Taichung, the third largest city in Taiwan. These units are at the new rice winery of the Taiwan Tobacco & Wine Monopoly Bureau.

The Bureau had previously purchased two VP-12's in 1988. They were selected to dewater rice dregs prior to delivery to local farmers for animal feed. One of the machines is in the old downtown Taichung winery that is being phased out. The second unit is lost somewhere in the group's eight wineries.

The rice dregs are a waste product resulting from the fermentation of rice. The liquor produced is called rice wine, and it is sold at 37 proof. It is used for cooking purposes, especially with chicken. The taste is bitter, and only the island's aborigine people are known to drink it.

Another product to be made at the new brewery is yellow wine. It too is made from rice, but by a process that makes it more drinkable.

Popepack Contrashear rotating drum style screens from New Zealand will be used on the rice mash ahead of the Vincent presses. These are expected to concentrate the mash inbound at 5% - 10% solids into the 10% to 20% range. A 2.8 meter headbox will be mounted at the inlet of the press. This will improve throughput and dewatering.

The 1988 presses were sold with a guarantee of 60% press cake moisture. A supervisor at the brewery told us that his has tested at 55%. For reasons that are not clear, 68% moisture was specified for the new presses.

A Ponndorf steam dryer will be used to dry the press cake from the Vincent presses. It has a rotating drum about 30' long, of stainless steel construction. The end product will have approximately 12% moisture content.

The new plant has an anaerobic digester installed in which the press liquor will be processed to produce methane. In the United States Anheuser-Busch has six breweries with this system. They report that the methane is capable of supplying 10% to 15% of the brewery's fuel needs. In Taiwan the intent is to flare the methane.

Anaerobic digestion is ideal for the press liquor because of the nature of the organic material it contains. BOD (Biological Oxygen Demand) concentrations of 1,000 milligrams per liter (mg/l) to 5,000 are common, compared with 150 to 200 in normal municipal wastewater.

The press liquor digestion system came into usage in the 1970's. Currently more than two hundred plants around the world, thirty-five of which are breweries, use the process. The six at Anheuser-Busch cost $150,000,000 and save about $30,000,000 per year in fuel and wastewater treatment costs.

A filter press will be used to dewater the sludge from the press liquor digester.

Issue 52

Series KP Presses

October 17, 1996
Rev. October 2002

Vincent Corporation has introduced a new series of screw presses. These have been designed to serve two applications where light dewatering is required. In both applications free water is removed more thoroughly than can be achieved with conventional screening devices.

The broadest market for the KP presses is waste from canneries and food processing plants. In these facilities waste is normally sluiced to a collection pit from which it is pumped with a chopper pump. Static and vibratory screens are generally used to strain the waste water from the solids. The solids are then transported to landfills, or given to farmers for animal feed or landspreading.

The problem with this system is that water continues to drain from the solids after the screening. This results in dripping in the parking lot, citations for leaking wastewater on the highway, and loads that are rejected at the landfill because of excessive moisture content.

A conventional screw press is not suitable for dewatering this waste both because the cost of the press is excessive and because the press loses capacity and forces excessive solids into the wastewater stream.

The KP press, with three stages of compression instead of five, addresses these problems. It dewaters far better than a screen, yet it drives less suspended solids into the press liquor than a conventional press. Waste streams that have been successfully tested to date include: cull tomatoes, potato peel from peelers, egg shells at an egg breaker, spent brewers grain, trim material at a facility producing TV dinners, and out-of-date produce at a vegetable and fruit warehouse. One unusual application in this category involves pressing dairy manure to reduce load on the waste treatment lagoon.

The second market for the KP presses is in place of a screen ahead of a conventional screw press. This screening allows conventional presses to press tighter, with higher throughput capacities. It is expected that the KP press will be a significant improvement in this process.

Two applications where the KP press is used ahead of conventional presses are being tested: (1) thickening pumped corn waste materials at wet corn milling plants, and (2) thickening shredded citrus peel in plants that pump the peel to the feedmill. In describing the application we are referring to the KP as a pre-press, suitable for pre-thickening. In essence we are offering double pressing at a bargain capital cost.

The cost of manufacturing a KP press is approximately half of that of a comparable Model VP or CP press. Costs were reduced through a combination of several unique features:

The inlet hopper was simplified, eliminating the inlet screen.

The thrust bearing was eliminated by selecting gearboxes with suitable thrust carrying capacity.

The discharge cone was replaced with a simple discharge plate actuated by a 4-bar mechanism.

The screen covers, spreader bar, and collection pan were replaced with either a single piece of pipe or a pan and cover.

The press does not have a base frame; prior to operating the press the customer must anchor it to steelwork or other suitable foundation.

The value of the KP presses must not be underestimated. The construction is entirely of stainless steel; drive motors have half again the anticipated horsepower requirement, and the gearboxes have been selected for a twenty-year life expectancy.

Issue 51

Shrimp Waste

June 30, 1998

For almost a year [in 1998] we have been averaging one inquiry per month in regards to dewatering shrimp and crab waste.  The material to be pressed includes shrimp heads; the shells from the shrimp tail; and both hard-shell and soft-shell crab waste.

Samples of these materials have been run in a variety of screw press configurations.  The amount of dewatering that can be achieved is limited: the press will knock out the loose water, but most of the water does not separate mechanically because it is bound chemically in the organic material.  Only heat will break it loose.  Both the Series CP/VP and KP presses have proven successful, depending on the client’s objectives.

It is difficult to get representative samples of either inbound or pressed material.  In the case of inbound material, the presence of flush water and/or ice varies greatly.  With press cake, the amount of shell in the sample distorts the results.  Typically we read 88% moisture in the press liquor and 78% to 80% in the press cake.

These results are measured even though we know that shrimp shells are 50% to 70% moisture to start with.  On a dry basis they are 51% calcium, 30% protein, and 17% chiten.

More important is the separation: typically we can achieve a yield of up to 30% to 40% press liquor.  We call the press liquor “strawberry milkshake".  The color and consistency are very similar to the fountain drink.

To further research the subject, we have visited a local plant, Tampa Bay Fisheries, which uses Vincent equipment to process shrimp tail shells.  They pump their waste to a static screen and then use a 6" screw press.  The press dewaters the screen tailings ahead of a Vincent triple pass rotary drum dryer.  This is an older installation, dating back to the late 1960’s.

The screw press is run without a discharge cone.  Its function is to remove only the water that can be readily separated.  This is because the “strawberry milkshake" is a pollutant stream that is so rich in organics that its disposal is expensive.  The function of the press is to take some load off the dryer.

The press cake is dried to about 10% moisture in the dryer.  Probably the most unique feature of the dryer is the way in which odor is controlled.  (Fish drying plants are notorious for their foul odor).  At Tampa Bay Fisheries our dryer does this with an afterburner furnace.  The second furnace is mounted above the first furnace, ducted so that some of the hot gasses help dry the shrimp shells.  Odor control is quite acceptable.

Tampa Bay Fisheries sells the dry shrimp waste as animal feed.  It was used as cattle or poultry feed additive.  It has little value because the shrimp heads, containing the protein, are no longer removed at this plant.  In fact, there are immediate plans to shut down the drying plant as the local landfill will now accept the shells.

Other uses have come to our attention.  There is a small market as feed for pet fish.  A significant market is feed for pen salmon in order to add red color to the meat.  The more profitable market involves extracting chitin from the dried shells.  This is used to produce chitosan, the miracle weight-loss remedy.

One potential customer is exploring the possibility of processing the strawberry milkshake into a bisque base for human consumption.  Protein assays of the liquid show excellent nutritional value. 

Update August, 2013

In the intervening years since 1998 this market has gone nowhere.  There was a period of strong interest in producing chitosan, but most of our customers went out of the business almost as fast as they got into it.  The industry is dominated by suppliers in Asia.  

The use of chitosan to prevent the body from digesting fats proved to be a total fantasy.

Technically we learned that shrimp waste has an extremely strong tendency to co-rotate with the screw of a press.  That stops the press from working.  The solution to this is to use an automatic-reversing feature in a single screw press, or to use a twin screw press.  Both have proven successful with shrimp waste.

Issue 79


Shrimp Waste, Cooked

June 25, 2008

Historically, Vincent has had trouble pressing shrimp shells. A "strawberry milkshake" would ooze through the screen of the screw press, and, since the shells would co-rotate with the screw, capacity was dreadfully low. To combat these difficulties, a VFD would be programmed to auto-reverse periodically; this proved to be an acceptable solution.

However, a recent start-up at a shrimp processing plant proved to be an astounding success. Before one of Vincent's engineers was on-site, the customer started the press and ran it without a VFD. It worked perfectly with no attention until it was shut-down for the night, seven hours later. What was the big difference? These shrimp shells were cooked, not raw.

The shrimp were steam blanched in equipment from Laitram Machinery of New Orleans, Louisiana, Following shelling, the shells were flushed to a collection pit with the rest of the wastewater. The waste was first pumped through a horizontal rotary drum screen 100" long by 36" in diameter. The woven metal screen had .020" (0.5 mm) openings.

The wet solids dropped from the screen into the Vincent press, which was angled upward at 30 degrees. The Model CP-10 easily handled 4,500 pph feed. It produced 1,200 pph of press cake and 3,300 pph of press liquor. The press liquor was truly a liquor: it was pink with a viscosity near that of water.

The feed averaged 85% moisture and, at 40 psi discharge cone pressure, cake was produced with 55% moisture. Higher cone pressures had no measurable effect on the dryness of the cake. At the medium pressures (30-40 psi) the cake was dry to the touch and flaky.

The shell is sent to a rotary drum dryer after mechanical dewatering, so moisture content is very important. The shell is eventually made into commercial fish feed.

Issue 200

Spent Brewers' Grain

December 4, 2011

One very old application for a screw press is dewatering spent brewer's grain. In his April 1900 US Patent, Valerius Anderson mentions that his invention of the interrupted flight screw was "one capable of handling brewers' slops, slaughter-house refuse, and like material which oftentimes is so soft and mushy as to be handled only with difficulty".

Beer, of course, can be made from a wide range of grains. Most commonly wheat, barley, corn and rice are used. After the fermentation process, wet fiber, called spent brewer's grain, is a waste residue. It is used as animal feed.

As spent grain comes from the brewery it is high in moisture content, generally 78% to 86%. Sometimes the spent grain is pumped to a filter screen, like a sidehill, to drain off some of the free water.

At that point the grain can be hauled to a farm, for use as animal feed. Small breweries frequently make arrangements for a farmer to pick up their spent grain. There is little value in the product, and it may be given away for free.

Larger breweries used to dry their spent grain down to 10% moisture and sell it, usually in pellet form. This commodity is known as DDG, Dried Distillers' Grain. Production of DDG involves first pressing the waste and then drying the press cake in a rotary drum dryer. Both steam tube dryers and direct fire dryers (the old Vincent design) were used. However with the advent of high fuel costs following the oil embargo of October 1973, the use of dryers was largely discontinued, especially in the United States.

Typically today the spent grain is run through a screw press, and the press cake is sold in wet (moist) form. Usually a moisture content in the range of 68% to 70% is specified.

The moisture content achieved by the screw press depends greatly by the type, and mix, of grain that is used in the beer production process. In one famous case in 1994, Vincent ran tests with an entire trailer load of spent grain from the Busch Gardens Brewery in Tampa. On the basis of this testing, screw presses were sold with a guarantee of 68% moisture because values of 66% easily were achieved in the tests. When these presses were put in service at the Anheuser-Busch brewery in St. Louis, it proved very difficult to get below 70%. The difference was traced to the differences in grains used in the two breweries.

We have seen other spent brewer's grains which can be pressed to as low at 55% moisture. It is all up to the brew master.

Competitors known in the brewery industry include Ponndorf and Vetter. Features of the Vincent press which result in superior performance include tight pitch flighting in the inlet hopper, a tapered shaft screw design, flight notches, and the use of wing feeders.

Note: Distilleries where spirits like whisky are produced rarely use screw presses. At distilleries the grain is first milled into a flour-like consistency. These fine particles, the spent grain, are very difficult to dewater in a screw press.

Issue 240

Spent Coffee

October 10, 2004

Producers of soluble coffee generate waste that is an excellent boiler fuel.  As described in the February 20, 1997 Pressing News #56, "Coffee", traditional technology has been to press this waste, spent coffee grounds, as tight as possible and then burn it. This material, at 55% moisture, was burned in stoker grate furnaces.

Industrias Aliadas in Ibague, Colombia has added a twist to this technology. They dry the waste in a rotary drum dryer, to about 10% moisture. The resulting powder is then blown through 4" tubes into a refractory lined combustion chamber, where it burns in suspension. Excellent combustion occurs. Flue gasses from this chamber will provide the heat required by a new 18,000 pph boiler.

Until recently, Industrias Aliadas has processed 15 MTPD of "green" beans. These beans are first roasted, in twelve minute cycles, at temperatures of about 200o C. Next they are rapidly air-cooled and then flaked. The flakes are fed to GEA Niro extractors. The extractors, which run 400 kilo batches on a 40 minute cycle, are steam heated pressure vessels.

The coffee solubles are separated in the extractors. These solubles are then concentrated, either in an APV steam evaporator or in an ammonia cooled scraped surface heat exchanger. At this stage, the coffee concentrate is either bagged, in 50 kilo drums, for sale in liquid form, or it is directed to a spray dryer. The spray dryer is eight stories tall. The powdered instant coffee that we are all familiar with is the product of the spray dryer.

The 15 MTPD of beans at Industrias Aliadas results in 9 MTPD (60%) of waste coffee solids. These spent coffee grounds are diluted to about 85% moisture in the extractors. Currently this waste stream is drained a little and then directed into their rotary drum dryer.

An expansion to 45 MTPD is underway. As part of this project, a new Vincent VP-16 press is being built. This press will reduce the moisture content of the spent coffee from 85% to 60% moisture or less. The existing dryer will have ample capacity to further dry the waste to the 10% range required for burning in suspension.

The VP-16 provided is a successor to the traditional VP-16 screw press. The design retains the recognized high performance, with significant reductions in manufacturing cost. Coffee being a high torque application, the robust press will have a 30 hp motor driving the screw at only 9 rpm.

Issue 153

Spent Grain

July 17, 1996
Rev. June 2006

Firms that produce alcoholic beverages from grain are an important market for dewatering screw presses. The industry firms consist mostly of beer brewers and distilleries. Their raw materials are barley, corn, wheat, rice, and other grains. They all produce a common by-product: spent grain.

Spent grain is the name given to material left after the grain is fermented and the alcoholic solution is drawn off. It is used as a cattle feed because of its protein content. The value to the farmer is not great, so smaller breweries are pleased to give the material away for free if the farmer will truck it.

Spent grain is normally wet, with 80% to 85% moisture content. In this state it is heavy to haul, and it is likely to drip while being transported. Furthermore, it will go sour in a few days. Therefore there is a need to dewater the spent grain if the brewer is of any significant size.

The practice is to run spent grain through a press. Typically a screw press will reduce the moisture content into the range of 64% to 70%. At this point the weight will have been reduced by a third to a half, and the "shelf life" will have been extended.

For many years it was common practice to use a rotating drum dryer to reduce the moisture content on down to 10%. In this condition the spent grain could be stored and marketed as a commodity. With the increase in energy costs, the value of the product has, by and large, not justified the final drying step.

In the past Vincent has supplied screw presses to Coors in Colorado, a brewer in Costa Rica, and a sake winery in Taiwan. Also, a distiller in Kentucky has used Vincent presses that he swears by.

This hit-or-miss picture ended in 1995 when Anheuser-Busch placed a major order with us to replace the spent grain presses in their St. Louis facility. This contract was awarded after extensive testing here in Tampa. We have an engineering video available that shows some of the trials.

Our main competitor for the contract was Stord, who has a number of their double screw machines in use in breweries. These are extremely heavy duty and press very tight. However they represented overkill and were not competitive.

At Anheuser-Busch our presses were selected to replace a group of very old Davenport V presses. These come in two sizes, 3' and 5'. They consist of two immense cast iron cone faced wheels. The cones are mounted so that they turn with a big gap at one side and a small gap at the other. Liquid drains through screening mounted on the faces of the cones, and it comes out at the bottom. Once the operator gets a plug established, the V press operates with intense pressure. The design is rarely sold today because (a) it is of limited throughput capacity, (b) it is expensive, and (c) it is even more expensive to maintain.

Initially it was thought that the use of a tall headbox above the inlet to the Vincent screw press would be valuable. This feature creates a hydraulic head at the inlet of the press. In practice, it appears that this pressure can plaster solids against the screen, causing blinding that reduces dewatering capacity.

One problem encountered was that, during idle periods, starch dries on the outside of the screens. This was solved with the use of spray washers.

The rotating cone option was not used, and the horsepower drawn by the presses is relatively modest. Nevertheless the pressing results have been excellent, especially at low screw rpm.

We now (1996) have in production a pair of CP-10 presses that have been sold to yet another rice winery in Taiwan. The rice is used to produce sake, and the presses will be used to dewater the rice mash.

More recently, the trend has been to offer Series KP presses for spent grain. These do not remove quite as much moisture as the Series CP and VP presses. However, if the grain is not being dried in a dryer, this does not matter. The KP presses are the most economical presses available.

Issue 46

Sweet Corn Advances

May 18, 2012

As detailed in the 2002 Pressing News #135, Vincent Corporation did their first work on waste from sweet cone canneries in 2001.  The large Series KP presses were introduced as replacements for the traditional baling machines.  The use of the screw presses has since proven to result in better dewatering of cob and husk, while providing more reliable performance and lower maintenance costs.

It is important to note that the moisture reduction objective in all of these installations is limited and realistic.  The silage going into the press has a moisture content which can range a lot, typically 80% to 84%.  The cake produced generally has 75% to 80% moisture.  The objective is only to remove free water.  This prevents dripping on the highway when the material is transported, and it eliminates a stream of water previously seen running from the pile when it is unloaded at a farm.  We field many inquiries from parties seeking a miracle press which will reduce the moisture content to 65% or some such other impractical number.

During the 2008 harvest advances were made by using the twin screw press.  The objective of the tests was to replace not only the baler, but also the shredder.  Besides being extremely noisy, the shredders are so maintenance prone that most canneries mount them on wheeled carts.  This allows them to be removed from service and by-passed when necessary.

It was hoped that a horsepower reduction would result.  Most shredders use 100 hp motors, and presses normally use much smaller drives.  However it was found that when the shredding task is added to the pressing task, the motor of the screw press ended up being as large as that of the shredder being replaced.

Distinct advantages did result from the use of the twin screw presses.  Compared to a single screw press, the degree of shredding showed noticeable improvement, as did the amount of dewatering.  This means that the waste is made into a more desirable animal feed.  From the farmers’ standpoint, corn silage goes from being a cheap waste to a favorably viewed product.

An Allens cannery in Bergen, New York uses a twin screw press.  This TSP-16 unit handles 50 tons per hour of waste.  It is fitted with a 150 hp drive.

Another twin screw press, a Model TSP-12, is in service at Barfoot Energy in England.  This press is used with a biogas digester which produces methane from corn waste.  The system was engineered by MT Energie of Germany.

Another interesting installation was at Birds Eye in Waseca, Minnesota.  They used a pair of single screw VP-22 presses, without benefit of a shredder.  This was an unusual installation because the presses, which ran at an extremely high 70 rpm, were driven by hydraulic motors instead of the conventional electric drives. 

The Waseca plant out-grew the VP-22's and is installing a pair of KP-30's for the 2012 season.  The choice was made because, at this point, Minnesota KP-30 installations at Lakeside Food plants in Plainview and Owatonna, and Del Monte in Sleepy Eye, have been running successfully for seven to ten years.  These each handle 75 to 85 tons per hour of silage.

The KP-24 has done equally well, in Idaho at Bybee Foods and National Frozen Foods, as well as the Lakeside Foods plant in Brooten, Minnesota and Allens in Fairview, Wisconsin.  These handle 40 to 50 tons per hour of silage.



Issue 245

Tetra Brik

October 14, 2011

Everyone is familiar with Tetra Brik juice containers.  These are the rectangular juice boxes with a straw on the side and a tinfoil spot on the top through which you punch the straw.  This packaging is supplied world-wide by Tetra Pak, a well-known packaging machinery company.

The major producer of Tetra Brik beverages in Saudi Arabia is Binzagr Co-Ro Ltd., headquartered in Jeddah.  Not long ago we did some very interesting testing for them.

Binzagr fills millions of these per day, and 1% may be rejected during start-up, transitions between flavors, CIP, etc.

Initially the goal was to separate the liquid from reject containers, using a single machine.  This meant that we needed to achieve shredding action as well as squeezing forces.  A twin screw press would have been good for this, but it was ruled out because of its cost.

A relatively inexpensive Model KP-10 press was modified for the task.  Shearing action was achieved with a combination of strippers, cord cutters, and resistor teeth.  In addition the screw was machined to an undersize diameter so that packaging material would not pinch and co-rotate with the screw.

A load of 4,000 Tetra Briks was used in the testing, and the results were outstanding.  However fiber contaminants in the juice precluded salvage of the juice. Tetra Brik boxes have six layers of paper, poly, and tinfoil.  That must be poly on both sides of the paper and tinfoil.  It turned out that we could find no way of keeping torn paper, cellophane, and tinfoil particles from getting into the juice.  In the end the client reverted to our original recommendation, a screw compactor built by our European distributor, RUNI.    

in and out results

In & Out Results

Issue 238

Plastics Recycling

 Click on the following links to know more about Plastics Recycling applications:

Carpet Fiber

November 22, 1993
Rev. March, 1997

Vincent Corporation recently shipped a VP-6 press for an unusual application. This press will be used to wring wash water from carpet fibers in a recycling operation.

Vincent's customer is operating a pilot plant program under a contract with a joint venture formed between two major U.S. and European companies. The key to the process being tested involves removing the fibers from the backing of used carpets. Since carpet is made up of roughly a 50/50 split between fibers and backing, the process will allow recycling half of the incoming material.

Once the fibers are shaved from the backing, they will be washed. Next they will be separated and dewatered in devices such as a hydroclone and a vibratory screen. At that point the washed fibers will flow to the Vincent press, arriving with a moisture content ranging from 70% all the way to 85%.

The Vincent press was selected for the pilot operation after testing in our Tampa laboratory. Excellent results were achieved, with moisture contents of under 55% and under 50% being reached with single and double pressing, respectively.

Once the fibers leave the press they will be transported to an air lift or fluid bed dryer, followed by a cyclone separator and bag house. The resulting end product will be used as raw material in applications ranging from cement reinforcement all the way to carpet manufacture.

Should the process prove out, plans call for processing modules based on 6,000 pounds per hour of incoming carpet. A model VP-12 press will probably be used for this purpose.

March, 1997 update. The funding ran out. Today we would use a Sterile Screw configuration in the this application in order to keep the horsepower down.

Issue 8

Plastic Recyclers

May 3, 1995
Rev. January 1998

Because of the increasing prices of virgin pellets [in 1995], plastic recyclers are at long last enjoying a measure of prosperity. This cyclical upswing has coincided with the refinement of Vincent products for the recycling industry.

Dewatering wash tank sludge is an application in which Vincent presses have been used since 1990. The screw press is used to dewater the sludge that settles when the paper label, dirt and residues are washed from post consumer plastics. A 1993 survey of the industry showed that few firms could afford a VP-6 press to dewater this waste material. Based on the survey, the CP-4 press was developed. At a third of the price of a VP-6, it is proving highly successful.

A related application involves the removal of water from the washed plastic. Prior to extruding the recycled plastic into a final pellet form, normally a series of machines are used to remove water from the clean plastic: screens, presses, spin dryers and fluidized bed dryers. Vincent presses with special low compression screws have found some limited use in this dewatering application on film, fiber, ground bottles and polystyrene.

January 1998
Lower prices for virgin plastic have driven many recyclers out of business. The industry is largely made up of small companies that have little, if any, cash available for equipment. Despite these conditions, a number of the very economical KP-6 presses have been sold for dewatering wash tank sludge.

Issue 25

Plastics Recycler Users


Mr. Doug Brooks
A.E.R.T., Inc.
P. O. Box 1237
Springdale, AR 72765

Mr. Joe Warren
Dart Container Corp.
500 Hogsback Road
Mason, MI 48854

Mr. Ed Farley

Wellman, Inc.
P. O. Drawer 188
Johnsonville, SC 29555-0188

Mr. Steve Adams
1909 NE 25TH Avenue
Ocala, FL 34470

Mr. Ed Nummer
Cadillac Products, Inc.
P. O. Box 1345
Sterling Heights, MI 48311

Mr. Francisco Morales

Eagle Brook Plastics
2600 West Roosevelt Road
Chicago, IL 60608

Mr. Franco Previd
Enviro Plastics
P.O. Box 363
Auburn, MA 01501

Mr. Doug Meredith
Image Industries Inc.
106 John Bankson Drive
Summerville, GA 30747

Mr. Tom Hart
Waste Alternatives
(Out of business)
Ocala, FL

Mr. Bill Anderson
Merlin Plastics
Unit 109 - 917 Cliveden Avenue
Delta, BC CANADA V3M 5R6

Mr. Greg Davis
Orion Pacific
P. O. Box 4148
Odessa, TX 79760-4148

Mr. Ernie Maroschak
Plastic Tubing
P.O. Box 878
Roseboro, NC 28282

Mr. Adam Marciciszyn

Plastics Forming Ent.
850 E. Industrial Park, Unit 1
Manchester, NH 03109

Mr. Gary Fish
Premier Midwest Plastics
201 W. Plymouth
Jefferson, WI 53549

Mr. Ajit Perera
Talco Plastics, Inc.
3270 East 70th Street
North Long Beach, CA 90805

Mr. Jerry White
Envision Plastics
(FCR Plastics; Resource Recycling)
606 Walters Street
Reidsville, NC 27320

Mr. Walter Aristondo
Envision Plastic
14312 Central Avenue
Chino, CA 91710


Plastics Recycling

June 3, 1993                                                                                                                                                                                                           ISSUE #4

The industry that recycles post consumer plastics is divided into three main segments. These are the recycling of bottles, film, and polystyrene. The bottle segment is the largest, and it has several specialists: PET (two liter Coke bottles); clear high density polyethylene (HDPE) (one gallon milk containers); and colored HDPE (laundry detergent, cooking oil, hair shampoo). The film comes mostly from industrial wrapping and supermarket bags. And we are all familiar with the sources of polystyrene foam.

The Vincent dewatering screw press has found a common application in the factories of all of these segments. That application is the dewatering of wash tank sludge.

The recyclers of post consumer plastics all grind (shred) their incoming waste material after it has been sorted. Next it must be washed in order to assure purity of their end products. This washing is done in tanks, and sludge with a high fiber content accumulates in the process.

The need is to dewater the sludge arises because all the recyclers send the sludge to landfill. Without dewatering the sludge drips water, and highway officials will not permit hauling material that drips on the roads. Further, landfill tipping fees are less for dewatered material.

A question that invariably comes up is how to feed the sludge into the Vincent press. We find that in practice plastic recyclers do this in a variety of ways. Some pump the dilute sludge directly from the wash tank to the press. Other recyclers pump the wash water over a screen and feed the tailings into the press. The recyclers frequently have more than one source of sludge, so they might end up using a combination of these methods with one or more presses.

The screens being used ahead of our presses are both the static sloped screen with wedge wire and the round Sweco vibrating variety. In at least one case the tailings drop directly into the press, but most commonly the tailings are fed to the press with a screw conveyor.

In all cases the objective is simply to turn the sludge into a cake that will not run or drip. The volume typically is such that the smallest capacity presses are used.


 Click on the following links to know more about Manure applications:

Capture Rate

June 28, 2001                                                                                                                                                                                                     ISSUE #M17

Engineers designing manure handling systems frequently ask about capture rate. They need to know the percent of the solids in the manure that will be captured in a manure separator. 

The captured solids are those that come out in the press cake. The solids not captured are those that flow in the liquid stream draining from the screen of the separator. The capture rate is calculated by dividing the solids in the press cake by the total solids pumped to the screw press.

Late last year capture rate tests were run at the University of Tennessee Dairy Experiment Station in Lewisburg, Tennessee. These tests confirmed a very significant difference in capture rate between flush and scrape barn systems.

The data show that when manure with 7% solids, typical of a scrape barn, are pumped to a screw press, the capture rate runs about 50%. In contrast manure with 2% solids, typical of a flush barn, had a capture rate of only 25%. (These figures are from a graph prepared by Dr. Robert Burns.)

The problem with a very dilute inbound flow can be explained as follows: The freeness tends to be high and a very large amount of water rushes through the screen. It goes through the screen so fast that what fiber is present tends to wash through the perforations or slots of the screen. Thus the capture rate is low with very dilute flows.

With thicker flows the longer particles tangle together, acting as a press aid. This forms a mat that entraps the finer particles. Thus the capture rate is higher with pre-thickened feed to a screw press.

It is noteworthy that solids in manure can be classified as either suspended solids or dissolved solids. The dissolved solids are like sugar in water: they cannot be captured with a mechanical filter. Since most of the manure flow to a screw press leaves as liquid, most of the dissolved solids pass through the press with this liquid. This places a definite limit on capture rate.



Cushman Farm Digester

October 1, 2001                                                                                                                                                                                                      ISSUE #M19

The Cushman Dairy in Franklin, Connecticut is a show case farm. The electrical energy used at this farm comes from a manure digester system developed by CST Industries (better known as Harvestore - Slurrystore). The original installation was made in 1998. 

The farm has 700 head, utilizing coarse sawdust as bedding. A scraped barn system is used to collect the manure, which is pumped to the digester.

The digester is an insulated tank made of the traditional Harvestore glass porcelainized steel panels. Manure is pumped in at the two-thirds level. Agitation is achieved with a centrifugal pump that takes its suction off the bottom of the tank. Digested manure sludge floats over a weir at the top and goes to a Vincent screw press for dewatering.

The biogas collected from the top of the digester flows to a positive displacement blower and then to a Cummins internal combustion engine. The engine is coupled to an induction generator that fills the farm's electrical needs. Radiator cooling water goes through a tubular heat exchanger that heats water used to maintain the digester temperature.

Digested manure flows to a Vincent Model KP-10 manure separator that was installed in 1998. Typically this produces 20 gpm of press liquor which flows to the manure pond. Press cake production normally runs 600 pph, with the press operating about ten hours per day.



Dairy Manure

April 15, 1997
Rev. 2008

The then-new KP screw press was first shown at the 1996 World Dairy Exhibition in Madison, Wisconsin. Rather than a sales effort, the objective of our booth was to determine the marketability of the product and to find suitable channels of distribution.

We knew that dairy farmers, especially large-scale operations, had been processing their manure through screw presses. With 68,000 attendees, the show gave us ample opportunity to find out why.

Keeping bedding and manure out of the treatment pond extends lagoon life. This reduces the frequency necessary to dredge the lagoon. This cost deferral is a financial benefit.

Environmental regulators are also a driving force. By keeping the fibrous solids out of the lagoon, odor generation is significantly reduced. Also, by pressing the manure ahead of the waste lagoon, a farmer can extend the capacity of existing lagoons. This avoids a number of permitting difficulties.

Farmers in northern climates must store their manure until the spring thaw. Pressing it to remove the solids can greatly facilitate this operation.

Pressing the manure separates it into two flows: dirty liquid and damp fibrous solids. Weather permitting, the liquid can be drained to the waste lagoon, or it can be pumped for irrigation purposes. (Full strength manure is too thick to pump very far, and it plugs irrigation spray nozzles and cakes the soil).

The manure solids from the screw press are composted for approximately ten days. This produces a rich fertilizer that is excellent for landspreading or tilling into a field. Some dairy farmers are selling this compost in bulk to nurseries and municipalities, while others are bagging the material for retail sale to home gardeners.

One increasingly common use of the compost is as bedding for dairy barns. The farmers we interviewed were using materials such as sand, sawdust, and rice hulls, which go either on the concrete floor or over a foam pad. (In fact, there were at least four exhibitors showing rubber or plastic "cow mattresses".)

University studies have shown that pressed manure has just the right moisture content (70%) for composting. This raises the manure temperature sufficiently to kill bacteria, thus making the compost safe for use as bedding. However, most of the farmers we talked to were reluctant to use the material for fear of infection (principally mastitis) spreading to the herd. (Since this original writing, it has become common to bed with manure solids straight from the screw press, without composting.)

Three different "manure separating" devices were exhibited at the 1996 show: sidehill screens; drag flight conveyors with slotted bottom troughs; squeeze rolls; and a screw press. Besides being large and mechanically complicated, the drag flight conveyors had limited, if any, squeezing action, so the dewatering that they achieved was marginal. The squeeze rolls dewatered a little better, but they were maintenance prone and costly.

The screw press being displayed was made by FAN of Germany. The principal complaint we heard were that it is expensive to maintain. Maintenance concerns centered on the availability and cost of spare parts such as the gearbox, screen and screw.

These areas have been addressed in our KP series of presses. The screw of the press is supported at both ends, rather than using a cantilevered support. This prevents the screw from hitting the screen once the machine loosens up. Also, the gearbox is separated from the inlet hopper by a drop-out gap; this saves the gearbox upon failure of the shaft seal in the inlet hopper. Our use of standard NEMA (American) motors also reduces maintenance costs.

A marketing problem was evident in that Vincent's industrial sales representatives do not call on dairy farms. To address this Vincent signed an agreement with A.O. Smith Harvestore. This firm, a leader in farm feed storage systems, will work with Vincent to develop models suitable for not only dairy, but also swine and cattle. This development contract is expected to lead to a distribution agreement. (This relationship failed to develop, and Vincent now sells through dairy equipment dealers.)


The KP-10 press on test at the University of Wisconsin will handle 50 gpm of manure and bedding, with only milking parlor water being added. The press achieves a separation of 43 gpm of liquid. The inbound solids split evenly, with 50% in the press liquid and 50% in the press cake. (This split is low because of the dissolved solids in the manure; a screw press cannot capture dissolved solids.) Press cake moisture content measures 72%. They process all the manure and bedding from 500-confined head in three and a quarter hours each day.

Issue 59

Fairgrove Farms Digester

December 6, 1999
Rev Jan 2001

Almost twenty years ago John Pueschel, Dave Pueschel, and Larry Kelly, owners of Fairgrove Farms in Sturgis, Michigan, installed a system to generate electricity from cow manure.

Manure from the dairy barns and milking parlor is pumped to a digester. This "plug flow" digester was designed by Perennial Energy of West Plains, Missouri. The digester is in the form of a horizontal concrete tank, like a long swimming pool. It is covered so that the bio-gas from the digestion process is collected. This gas flows, without the aid of a booster blower, to a Caterpillar internal combustion engine. The engine drives an induction generator. The generator in turn produces about $3,200 worth of electricity per month.

An induction generator was selected although it is a little less efficient that other types of generators. Its advantage is it produces electricity that is automatically in phase with the power grid that supplies the farm. The result is that surplus electricity can be pumped into the grid (sold to the public utility) without the need for expensive switchgear.

Selecting a Caterpillar engine that would run on the low 600 BTU (mostly methane) biogas, without a need for filtration or pressure boosting, was a key element in minimizing the capital investment.

In 1999 Fairgrove Farms purchased a Vincent Model KP-10 Manure Separator. This machine is used to dewater the sludge from the digester. It is manufactured in Tampa, Florida.

This separator is an all-stainless screw press with only one moving part, the auger. This screw features three stages of compression with weld applied hardsurfacing in the high abrasion surfaces. A screw recently completed over 4,000 hours of service before refurbishment was required.

The screen of the press is made of perforated metal screen with 3/32" openings.

The sludge is pumped to the screw press at the rate of about 40 gpm. The press liquor goes to the wastewater pond, while the press cake (at 70% moisture) is sold as bedding to nearby dairy farms. This generates an additional $3,000 in monthly revenue.

Issue 100

Fighting Cocks

June 29, 2005

We have a customer who, with an extended farm south of Guadalajara, Mexico, purchased a KP-6 screw press. They refer to it as "the recovery machine". It is used to separate undigested food solids from manure at the pig farm. Originally, this press failed to adequately dewater these solids. Both 0.030" perforated and 0.020" wedgewire screens were tried. It was only with the addition of a small 18" static screen, to pre-thicken the flow, that successful operation was achieved. The press cake is used as a feed supplement in the cattle grow-out operation.

One Sunday, after I ran out of things to tell him about screw presses, the owner told me of his own avocation. He spent twenty years playing and breeding fighting cocks. In his career he regularly worked in Argentina, Brazil, Chile, Peru, the United States (mostly in Arizona and Louisiana), and other countries.

For breeding, he imported birds from the Far East and Spain. The birds were characterized by their strength, how high they jump, and the skill with which they aim their spur. The trick is to breed the best of these qualities.

The fighting spurs are different in each country. Made of forged steel, some are longer or shorter, serrated or smooth, flat or pointed. In all cases the points are needle sharp, and, in the case of a flat blade, it is sharp enough to shave with. The spurs are made from spring steel, and some Swiss alloys are popular.

Mounting the blades is a science. Generally, the first step is to wrap two 3/8" wide bands, on the leg, above and below the bird's spur. Dr. Scholl's elastic bandage, cut into narrow strips, is preferred.

The bird's spur is a bony protrusion on the back side of the foot. It has a nail, but this is trimmed off. The saddle, made of leather or plastic, is wrapped around the foot, at the spur. There is a hole in the saddle that fits around the spur. Some saddles have aluminum inserts in these holes. The saddle is tied in place with a yard of surgical suture.

The saddle has a flat platform on which the metal spur is mounted. This is tied in place with the thread. The final assembly must be extremely rigid on the bird's leg.

In Mexico, only the left foot is armed. Just as most humans are right handed, most birds are left-footed. Right-footed birds do poorly in contest.

In the States, both feet are armed. The long, pointed spurs are bent inward at a slight angle. Because of this, spurs manufactured in the States are carefully etched with LH and RH markings. The SPCA has put great pressure on the sport in the States. The customer gave up the business three years ago. The participants were bringing in more weapons than before. Also, narcotraficantes have gravitated to the sport, and the police tend to arrest everyone when they conduct a raid, not just the drug people. Also, the hobby was too much of a distraction from his core businesses. Today the customer has reduced his flock to 1,500 birds. He belongs only to a local club that meets for a match every two weeks.

Issue 162

Gearbox Protection

June 26, 2000                                                                                                                                                                                                           ISSUE #M8

Vincent has never had a gearbox failure in a Series KP screw press. This record is attributable to two design features of these machines.

A critical observer will note that the construction used to mount the gearbox on the press is relatively expensive. The gearbox is mounted on a plate with four legs that are welded to the inlet hopper (A-plate) of the press. It would cost a lot less to simply bolt the box to the A-plate.

The reason for the separation is to provide for leakage at the shaft seal. There are a pair of Johns Manville seals located in a seal housing that is bolted to the A-plate. The four legs are used to make a large physical separation between this seal and the gearbox. That way, when the seals eventually fail, leakage will be to the structure below the press.

Without this provision the leakage would be against the gearbox shaft seal. Gearbox seals are designed to keep oil in, not to keep manure out. It is common for competitors to have bearing and gearbox failures due to manure contamination since provision is not made to drain away leakage. It is all but impossible for this to happen with a Vincent press.


Inclined Discharge


Screw presses used to dewater manure are notorious for "purging" or "blowing the plug". The condition is one where all the manure being pumped to the press simply flows out through the cake discharge, with no liquid being separated through the screen. Whether it is 20 gpm or 600 gpm does not matter: if it starts at midnight and no one notices until dawn, the mess is terrible.

Improving the screw press design to address this problem has been difficult because a press will operate for weeks or months without an occurrence. Gradually a number of different factors have been observed that contribute to blowing the plug.

  1. In the winter the cake being discharged can freeze and jam the discharge door open.
  2. When the screw becomes worn, manure can flow between the screw and the screen, wetting the plug and allowing it to wash away.
  3. When the manure pit is near empty, the flow from a centrifugal pump can go down by 75% compared to when the pit is full. The plug will tend to blow when the pit is low.
  4. A change in feed or bedding (like going from sawdust to manure) results in reduced dewatering and wetter cake.

The latest improvements in press design that address the problem are (a) Extending the screw shaft through the discharge so that the cake door is breaking up a donut, rather than a solid plug, of manure, and (b) Double flighting the screw over the first half of the screen where the manure is wettest. This produces drier cake, earlier in the dewatering process, which is less likely to purge.

Another useful remedy is to elevate the discharge end of the press. This has been found to be particularly effective when the pit is low and the flow of solids to the press is reduced. At this time the cake discharge becomes so slow that water wicks (soaks) into the cake on the lower side of the screw, allowing part of the plug to become soft and to blow out. Without sufficient solids being fed into the press, the plug does not re-form. A 5º incline to the press can make a world of difference, and it can cause no harm.

The photo at the top right hand corner of our brochure shows an installation with an elevated discharge. This was retrofit, during start-up, in a successful effort to eliminate blowing the plug.


Installation Quick Tips

May 9, 2001, Revised April 2003                                                                                                                                                                             ISSUE #M16

There are a number of details relating to the installation of screw presses as manure separators that should be noted:

Unless a piston pump is used, it is necessary to have a line that allows manure to recirculate from the press inlet back to the manure pit. This will prevent pressurizing the inlet of the press, which can be a cause for purging.

It is best to have a vent line at the inlet to the press. A 1" line, 5' tall, is adequate for breaking a suction in the recirculation line. Such a suction can lead to reduced press capacity.

The drain line from the press should go below the surface of the pit or pond into which it drains. If this line is relatively small in diameter and has a steady downward slope, a vacuum will be induced around the screen of the screw press. This will increase press capacity.

The amount of vacuum is a function of the elevation between the press and the drain pond. Where convenient presses should be mounted on 20' or higher stands.

The control panel for the manure pump and the press should have a timer. This timer should be set to have the press run for two minutes after the pump shuts off. This will partially clear the press so that it will not trip out on overload when it is re-started.

Minimize the time that the press is run with no material being fed into it. Running dry will allow abrasive rubbing. The last manure admitted to the press will dry to an abrasive powder.

When bolting the frame of a manure separator to its platform, look into the cake discharge end. Note if the screw is being pulled into the screen. This is an indication that the frame is racking. If this occurs, shims should be used so that the mounting bolts tighten evenly. The screw must be kept centered in the screen.

Elevate the discharge end of the press a few inches to minimize any tendency for the press to purge. This has been found to be particularly effective when the pit is low and the flow of solids to the press is reduced. At this time the cake discharge becomes so slow that water wicks (soaks) into the cake on the lower side of the screw, allowing part of the plug to become soft and to blow out. Without sufficient solids being fed into the press, the plug does not re-form. A 5º incline to the press can make a world of difference, and it can cause no harm.

Where the manure is very thin, it may be necessary to pre-thicken the flow to the screw press. This is best done with a sidehill (inclined) screen. Without pre-thickening, some dilute flows will flush the solids through the screen. This makes it difficult to form a plug, and the capture rate is reduced excessively.


Iowa State Digester

DECEMBER 5, 2001, Revised September 2010                                                                                                                                                          ISSUE #M21

The Dairy Foundation in cooperation with the Iowa State University has started up a new dairy manure digester system.  The installation is at the model farm located at Northeast Iowa Community College in Calmer, Iowa.

The school has opened a new campus with a herd of 170 cows.  The manure and bedding from one hundred of these cows are disposed of in a digester.  The biogas generated is used to produce hot water used on the farm.

The manure digester is the plug flow type.  This uses a concrete tank 10' deep by 13' wide by 68' long, holding a nominal 50,000 gallons.  Foam insulation helps keep the liquid at 95o F, which is well suited for producing methane.

Biogas from the digester is burned in a boiler system designed and manufactured by Perennial Energy of West Plains, Missouri (417-256-2002).  Rated at 150,000 BTU/hour, this heats water that is used to maintain the digester at temperature and to supply floor heat and hot wash water for the milk pipeline.

The manure sludge from the digester is pumped to a Vincent Model KP-6 screw press.  The cake from this press is composted and used for bedding, while the press liquor flows to a treatment pond.  Normal cake production is in the range of 150 to 250 pounds per hour, and press liquor flow of 34 gpm was measured recently.

Daniel Meyer of Fayette IA (319-425-3331) has been actively involved the $200,000 project since its inception.  He favors the plug-flow type digester for dairy manure.  He has also noted that scrape barn manure works better than flush barn for digesters because of the greater concentration of solids.

Mr. Meyer describes biogas production as a two stage process.  In the first stage the solids are broken down with acid forming bacteria.  In the second stage methane forming bacteria cause gasification.  The pH must be kept about neutral during the process.  The average electric production is one kilowatt of generator capacity per 10 cows.

Ray Crammond of Ankeny IA (515-965-8301) was a consultant on the design of the system.

September 2010
Like most manure digester projects, this one has been shut down. 
When the digested plugged with solids (sand?) which settled out, a group of students were drafted into digging it out.  The system was altered so that the manure was pressed ahead of the digester.  Only the press liquor was put into the digester.  This should have worked.

Layer Manure

December 10, 2014
ISSUE #269

Layers (egg-laying chickens) are kept in wire cages which allow the manure to fall through. The manure can either fall into a pool of water or onto a belt conveyor.

In late 2013 we were approached by inventor Woody Cronin in regards to a system he developed for layer manure. Years before, we had tried dewatering the manure from water-bottom barns, with poor results. Because of this we were cool to the idea of running a screw press on the material from a conveyor-bottom barn.

To our surprise, with Woody's technology, it works well. Press cake with only 65% moisture content can be produced. This material is undigested food. It has very high nutritional value, and it makes an excellent feed additive for farm animals. Conceivably it could qualify as biomass fuel for a boiler.

We were told that layers digest only 40% of their feed. The operation of the screw press system results in a recovery of half of the feed found in the manure. Mathematically that calculates to a 30% recovery of the poultry feed.

Overall the operating system is as follows. The manure is first mixed with press liquor in order to fluidize and dilute it. (The system is started up with water since there is no press liquor.)

Next the flow goes through equipment which separates out the calcium (it looks and feels like sand) and the feathers. That is a gravity separation process.

From there the flow is dosed with organic polymer. Most polymers are made from natural gas, and they are not good as feed additives. However natural polymers, like those made from shrimp waste, are acceptable in feed rations.

Next the flow goes to the screw press. The flow is dilute, so pre-thickening ahead of the press may be required. This pre-thickening can be achieved with either a rotary drum or a sidehill (parabolic) screen. Prethickening can greatly increase the throughput capacity of the screw press.

The as-received manure typically had 75% to 80% moisture content. The press cake produced typically had a moisture content of 64% to 68%.

The press liquor from the press goes to the mixing pit where it is added to incoming chicken manure. High in urea, the excess press liquor is drained off for use as a liquid fertilizer.

Alternatively, with heavier dosage of polymer, the press liquor can be made very clear, with as low as 0.5% total solids.

Manure Brix

April 24, 2010                                                                                                                                                                                                    ISSUE # 221
                                                                                                             MANURE BRIX

There is a tremendous focus on animal waste. This is true around the world, especially in Europe and the United States. Dairy manure gets the most attention, closely followed by swine. University studies and EPA pronouncements come out on a monthly basis. Much of this work is labeled "nutrient management". This has to do with the how, when, and where of disposition of the various nutrients in manure.

If I were going for a PhD in Ag Engineering, I would do my dissertation on "The Role of Dissolved Solids in Manure". A basic characteristic of manure is that the moisture
fraction in it contains dissolved solids. This characteristic deserves special attention because the dissolved solids in a mass cannot be separated by mechanical filtration. That
is, if there are 3% dissolved solids in the water in manure, there will be 3% dissolved solids in the moisture in the both the fiber and liquid which are separated by separation
equipment. This is basic to all conventional equipment such as sidehill screens, rotary drum screens, screw presses, belt presses, centrifuges, etc.

This means that a dissolved nutrient in manure cannot be concentrated (let alone separated) by running the manure through any of the aforementioned equipment.

Vincent engineers have gathered some interesting data in regards to dissolved solids:
Scrape barn manure measured 6º to 7º Brix.
Pond water measured 3º Brix.
Manure from a flush barn measured 4º Brix
Effluent from a dairy manure digester read about 3º Brix.
Human urine reads a real sharp 2º Bx.

This has an important effect on the moisture content of the press cake produced when manure is run through a screw press. We have seen manure press cake from a scrape
barn that contains 68% moisture and 7 Bx. In round numbers, if before pressing this  same manure were diluted (by flushing) with pond water to where it had 4º Brix, then the press cake would measure 70% moisture.

In other words, the cake from flush barn manure will typically be two percentage points higher in moisture content than that from a scrape barn. This is because the moisture
does not carry with it as many dissolved solids.

Separately, we queried Dr. Robert Burns of Iowa State University about the dissolved solids in manure. His reply has good insight on digester operation:

"You are on the right track in thinking about the bugs eating sugars. In reality, they are consuming carbon as a food source. Some carbon sources (like sugar) are very easy for bugs to utilize, while other, more complex carbon sources are harder to digest, and some may even be recalcitrant to the point that they can not be digested within the HRT that a given digester operates at. Unlike fruit juice (where most of the dissolved solids are sucrose), manure contains lots of complex compounds (like proteins, carbohydrates and lipids), so I believe that your hypothesis that the dissolved solids you are seeing with your refractometer are a mix of digestible and undigestible dissolved solids is the correct one.

"The question of should you press manure before or after digestion is one that can be answered pretty easily. My lab regularly runs Biochemical Methane Potentials (BMPs)
which are an effective method to determine the anaerobic degradability of a given substrate. We run these on a fee basis for companies all of the time to determine what
mix of substrates will yield the most biogas. You can take a look under the AD portion of our webpage ( for more info. It would be pretty simple to run some BMPs on raw manure and then run some on the press liquor to see which yields more biogas."

Robert T. Burns, Ph.D., P.E.
Agricultural & Biosystems Engineering
Iowa State University
3224 NSRIC, Ames, Iowa 50011
Email -

Note from Pressing News #190:
Brix is a unit of measurement named after Adolph Brix. It is used commonly by food technologists to measure the amount of sugar dissolved in water. It can be calculated
by dividing the dissolved solids by the sum of the dissolved solids plus the water, all multiplied by 100. That is, Bx = (Ds x 100)/(Ds + w), where Ds is the weight of
dissolved solids and w is weight of water. ((Note that suspended (or insoluble) solids do not enter into the equation for calculating Brix.))

Manure Digester Bio-Gas

SEPTEMBER 6, 2001                                                                                                                                                                                              ISSUE #M18

Due to renewed energy awareness there has been a surge in interest in manure digesters.  In these digesters the manure decomposes anaerobically (without Oxygen), releasing bio-gas. This bio-gas is collected and burned to release its energy.

These dairy systems have environmentally attractive features.  Energy is produced from a waste source.  Also, the digester action treats the manure, which addresses other problems:  run-off is controlled and odor from the dairy is reduced.

The bio-gas (methane with CO2, SO2 and other gasses) can be burned in a boiler to produce either steam or hot water for the farm.  Alternatively, this low BTU gas can be burned in a Waukesha or Caterpillar internal combustion engine.  These engines are coupled to induction generators that more than fill the farm's electricity requirements.

Besides internal combustion engines, mini gas turbines are being offered for use on biogas.  The metallurgy of the engine and other components is critical because of corrosive gases.

Two types of digesters predominate.  In both the gas is collected off the top.  The most common, a plug flow digester, is a long pit where the manure enters at one end and progresses slowly to the discharge.  Our presses are used with this type of digester at Fairgrove Farms in Michigan, High Plains Dairy in Kansas, and Iowa State University.

Mixed flow digesters using tanks are a second type of digester where extensive development has been done.  A.O. Smith Harvestore leads in this technology, and Cushman Farms in Franklin, Connecticut is a good installation to visit.  Manure solids flow off the top of the digester into our Model KP-10. 

Another type of mixed flow digester uses a pit instead of a tank.  A good example is under construction at Matlink Dairy in Clymer, New York.  This 660,000 gallon pit digester has propeller agitators on two sides.  Digested manure will flow over a weir to be pumped to a Vincent press.

The manure can be pressed in a screw press ahead of the digester, with the press liquor being directed into the digester.  However the more common arrangement has the press dewatering the sludge that comes from the digester.  The press cake, from either raw or digested manure, has about 70% moisture.  This is ideal for composting and producing a rich soil amendment, or for immediate use as barn bedding.

It is surprising how accurate this report is.  The trend has been toward mixed flow instead of plug flow, and gas generation and recovery technology has improved.  However politically incorrect unstated facts from ten years ago remain true:  No digester project goes ahead without a government grant because the investments do not pencil out.  And, most digester projects get abandoned.  For example, all five showcase digesters mentioned in this Pressing News have been shut down.

Manure Incineration

July 28, 2006


Van Der Geest Dairy, located near Wausau, Wisconsin, has developed a unique technology for manure disposal. The farm has 3,800 cows and uses a flush-barn manure collection system.

Bedding, in the form of dried manure, is produced by burning about half of the manure generated by the herd. To do this, the manure from the dairy is first dried to a low moisture content so that it can either be incinerated or used as bedding. The heat released in the incineration process is what is used to dry the manure to low moisture content.

Initial dewatering of the manure is achieved by pumping the manure across two sidehill screens, one curved surface Houle and one flat panel Agpro. Both have 0.080" slot widths. The narrower, but taller, Agpro is preferred.

Prior to selecting the sidehills, the farm operated both Integrity roller drum machines and the Accent internally fed rotary drum screen. Sidehills won out because of their high capacity and simplicity.

Solids from the sidehills fall into a pair of KP-16 screw presses. The Vincent press was selected, after a nine-month testing program, over FAN, Manure Monster, and Boldt screw presses. Both Vincent and FAN modified their presses numerous times. Efforts by both companies failed to adequately press the manure without prethickening.

Key features that led to the selection of the Vincent press are as follows:

    • The KP-16, with its larger screw diameter, has greater capacity.
    • There is ample separation between the gearbox and the inlet hopper seal, assuring long gearbox life.
    • Vincent presses are available with standard NEMA motors which are readily available throughout North America.
    • The Vincent press has removable covers over the screen, making it convenient to pressure and acid wash the screen.
    • The screw of the Vincent press is supported at both ends, at the gearbox and at the cake discharge, which assures the screw-screen alignment that is necessary for long screen life.

The cake from the screw presses is conveyed to a system developed by Energy Unlimited. The key component is a Heil triple pass rotary drum dryer. Here the manure press cake, at 70% moisture content, is dried down to 10%.

Next, the dried manure is separated from the gas stream in a cyclone separator. The solids are blown into a storage bin, from which they a blown into a vertical combustion chamber. The solids are burned in the combustion chamber without the need for auxiliary fuel. The products of combustion (hot gasses) are directed into the dryer drum, where they dry the manure press cake.

An induced draft fan draws the gasses through the dryer and combustion chamber. From the dryer, the gasses go to a covered trench. Filtrate from the sidehill screens and press liquor from the two screw presses flows through this 450' long trench. Particulate and gas pollutants are captured and oxidized, and aeration is achieved. Another induced draft fan draws the gasses through the trench and pushes them to a smoke stack. A white plume of water vapor is generally visible from the stack.

Water from the trench is directed into a treatment pond. The treated water is used for barn flushing.

About half of the dried manure is used as bedding for the cows, with the other half being used as fuel for the combustion chamber.

This unique system for manure disposal is receiving a great deal of attention from environmental specialists.

Issue 176

Manure Installations


Ohio State University in Wooster, Ohio is running at 40 gpm press liquor from their KP-10. This is the machine in the video that Harvestore made; we have a copy if you want it. The new barn manager is Kevin Miller, 330-263-3924, Dairy Research Center Manager, Krauss Dairy Center. They have 120 cows, scrape barn, feeding our press. They run only 16 hours a week, making bedding. They put the press cake fresh into the stalls, without composting.

The original KP-10 at the University of Wisconsin goes great. We are not sure who the farm manager is, so the best contact would be Dr. Dick Koegel ("Cagle") at 608-264-5149 or 608- 264-5355. He is at the U.S. Dairy Forage Research Center. The KP-10 processes 50 gpm of dairy manure, with a separation of 43 gpm of liquid. The inbound solids were split evenly, with 50% in the press liquid and 50% in the press cake. Press cake moisture content measured 72%. Scraped barn.

One we have not heard from for a year is Warren Hatcher, mobile 423-309-8108, farm 423-338-2780 at Riverside Dairy Farm in Benton, Tennessee. They have a KP-16 on 800 head, flush barn. I saw a good 800 gpm going through the machine.

A good for sure KP-16 is at McArthur Farms in Okeechobee, Florida. They run 1,500 cows in a flush barn. Their pump was limited to 600 gpm, and the press took it all easily. The contact would be Maintenance Manager Rick Amadon 941-763- 8986. This farm has at least 5,000 head. Bob Rydzewski is the VP-GM, 941-763-4719 or 941-763-4373.

The KP-10 machine at Fairgrove Farms is a winner. Our Pressing News #1 describes this biogas system for electricity generation. At the farm, Warren Kelly's numbers are 616-651-6646, 616-651-8903, and cell 616-268-3747; John Pueschel's cell phone is 616-341-3053. The farm is two miles west of Sturgis, Michigan.

As at Fairgrove Farms, a KP-10 is used on digester sludge on an A.O. Smith Harvestore dairy manure biogas system at Cushman Farm. The biogas is used as boiler fuel. Our contact is Dave Smith at 860-234-0285 and Nathen Cushman, 860-642-4711, 120 Kahn Road, North Franklin, CT 06254.

Our little KP-6 is well loved at the University of Tennessee. Contacts would be Dr. Robert Burns, 423-974-7266, 865-974- 7237 and farm manager Henry Dowlen, 931-270-2240. They have 150 to 200 cows, scrape barn.

We have sold three KP-6's to pig farmers in Costa Rica. Since the sales came one year apart, we know the machines are working well. These farmers are bagging the cake and selling it as cattle and goat feed. The only person to call would be our distributor, Wilfred Korte at Industrias Bendig, 011-506- 259-7379. Wilfred's English is good.

Gary Hodgson, cell 403-340-9727, of United Livestock in Alberta, Canada sold a KP-10 to the Pibroch Colony, part of the Hutterite or Hutterian Brethren. The farm is north of Edmonton. George Walter is the Minister; Ely takes care of the manure system. They installed a tiny static screen over the inlet to the press. The press liquor runs a good 60 gpm. They have 4,000 pigs in the finishing barns. They produce 22 tons per week of press cake.

A KP-6 has been sold for the Futura Dairy in Central City, Iowa. This unit will dewater sludge from a biogas digester. Start-up is scheduled for later this year.


Manure Separator Inquiry

April 18, 2001, Revised October 2002                                                                                                                                                                      ISSUE #M15

Recently an inquiry was received that highlighted the need for information in quoting a manure separator. The e-mailed inquiry read: "Please quote the price for a manure separator to handle 100,000 liters of manure." 

Here are questions that we asked in order to select the proper size machine, with the right screen and drive motor:

What animals does the manure come from? Cows or pigs? 
We avoid poultry layer manure, although broiler grow-out house litter can be pressed.

By chance, is the manure actually sludge from a bio-gas digester?
Capacity goes down significantly on such sludge.

Assuming it is dairy cow manure, how many cows are on the farm? Are they confined (100% of the manure is captured), or is the manure only from a milking parlor or feeding barn?
Is a flush barn or scraped barn system used to collect the manure? This will tell us the dilution to expect.

What is the gpm capacity of the manure pump? 
How many hours a day is the manure separator expected to run? Some farms want to run only four hours a day, while others run up to twenty four hours a day.

What kind of bedding is used? 
Sawdust will require more horsepower than straw. Sand must be separated before the manure is pumped to the separator.

What is the power supply at the farm, single phase or three phase? What voltage? 
Most small farms are single phase 220 volt, while some large farms have 440 volt three phase power.

Is compressed air available for use with the manure separator? 
The large Model KP-16 has a discharge door that is actuated by an air cylinder. This feature is an option with the smaller 6" and 10" machines.

Is the manure currently being separated? If so, how? What is the cake used for? 
Reviewing these questions will result in a much more satisfactory machine selection.



Manure Separator Screens

May 24, 2000                                                                                                                                                                                                        ISSUE #M7

All categories of manure separators use metal screens made of stainless steel. These screens all fall into one of two categories: either perforated metal or wedgewire.

The perforated metal screens are made of medium gauge stainless sheet. The smaller the hole, the thinner the sheet. The most popular size is 3/32" perf (0.093" or 2-1/4 millimeter holes). This is generally made of 14 gauge metal, which is 0.075" thick. Another popular size, used in the small KP-6 separators, is 0.050" perf (1-1/4 mm); it is made from 24 gauge sheet which is 0.024" thick.

Wedgewire is the name given to a screen that is made from wires that are roll formed into a truncated pyramid cross section (a triangle with the top cut off). These wires are welded into flat panels with a fixed distance between each wire. By putting the broad base of the triangle against the liquid, a self-relieving passage is formed that has a minimal tendency to plug. Any solids getting through the narrow entrance between two wires will be swept away with the filtrate.

The flat panels thus produced can be used at the bottom of drag flight separators. Or, the panels may be curved to a gentle radius to make a sidehill (gravity) screen. The panels can be rolled to a cylindrical shape for use in a screw press, but they are expensive and tend to lack durability and burst strength.

The opening between adjacent wires is referred to as a slot. Typical slot widths used on manure range from 0.020" (1/2 mm) to 0.040" (1 mm).

The relative amounts of free area are of interest. For comparison purposes, 3/32" perf has 23% open area, while .030" wedgewire has only 15% open area.

Extensive testing has shown that changing the size of the opening has little impact on the solids capture rate. Oversimplifying a little, manure seems to be split between big particles and little particles. That is, almost all the little particles are small enough to get through any opening 0.010" or larger, while most big particles will be caught by an opening as long as it is under 3/32" inch (2-1/4 mm). (We tested 5/32" perf, and abandoned the effort.)


Manure Variations

September 22, 2000                                                                                                                                                                                               ISSUE M11

It is the goal of Vincent Corporation to have one basic press design that will work in all manure applications. We feel that it is reasonable to expect to separate all manure types with a single screw configuration, one screen selection, and one discharge plate mechanism. It is because of this goal that each production run of Series KP presses shows some improvement over its predecessors.

A wide variety of manure is being run through KP presses. The machines have proven themselves in four broad areas: cow, pig, biogas digester sludge, and slaughterhouse pauch manure. The varieties within these categories are surprising.

Cow manure general is split into scrape and flush barn systems. Obviously one has thicker solids than the other, and consistent agitation is required for consistent feed. However an equally important variable is the type of bedding that is in use. After all, the bedding can be a major component going into the pit. Straw and shredded paper make a great press aid and facilitate operation of the separator. Sawdust will press well, but it will draw more horsepower. (Of course, sawdust can range from sawdust to wood shavings or sanding dust; they behave differently in the press.) When manure is the only bedding used, we must count on the screen to pass the tiny digested solids into the press liquor flow; otherwise they tend to blind a screen.

Pig manure and sludge from a biogas manure digester have an important characteristic in common. Both have a high percentage of micron size particles that pass through the screen of the press. Thus, the solids capture rate is lower than when there is a preponderance of large particles of undigested food.

Definite variations exist in pig manure. For example, in Alberta, barley is fed to pigs. This is a coarse grain that puts fiber in the manure that facilitates press operation. On the other hand, in the States the feed is milled to 750 micron average particle size. This makes a manure whose tiny solids are hard to capture.

The absence of bedding in pig manure is normal, as is a lack of agitation. Flow starts with thick solids, material that has floated to the top. Then there is a prolonged flow of highly clarified water, followed by bottom sludge. To handle this range of conditions requires careful press design.


Manure as Bedding

October 20, 2001                                                                                                                                                                                                 ISSUE #M20

For many years leading agricultural universities have recommended dewatered manure as a dairy bedding material. Until relatively recently the recommendation has been that the manure be composted prior to use in the stalls.

The dewatering requirement gave rise to a number of pieces of equipment that are commonly called manure separators. They separate free water from the manure.

The reason for the composting requirement was twofold. Firstly, some manure separators leave a visible amount of moisture with the manure solids. This material is too soupy or slushy for use as bedding. Composting allows removal of the excess moisture.

The second reason for composting had to do with sanitation and disease control. It seemed obvious that fresh manure was full of bacteria that could cause mastitis in the herd. And it was shown that the heat generated in composting killed off the great majority of these bacteria.

Composting is no longer being regarded as an absolute requirement. Two observations have led to this. One observation was that cows in southern states, like Florida, wallow in ponds in order to keep cool. These ponds contain a great deal of manure, and yet mastitis is a manageable problem.

Another observation was that the few bacteria left after composting multiply exponentially. Composted manure ends up in the barn with the same bacteria count as the original material. Despite this, mastitis was shown to have low incidence in dairies using composted manure as bedding.

This has led to the use as bedding of material straight from the manure separator. This practice has been used at the Ohio State farm in Wooster, Ohio. Press cake from a Vincent Model KP-10 press has been used immediately as bedding for over a year.

The excellent dewatering characteristic of screw presses is recognized. This is resulting in increasing popularity of these machines on the farm.


Matlink Digester (Continued)

MAY 28, 2002, Revised September 2010                                                                                                                                                                 ISSUE #M23

Three months ago we wrote about an extremely smooth start-up that had taken place at the Matlink Farm in Clymer, New York.  This involved a manure digester system designed by RCM of Berkeley, California, 510-658-4466. 

The Vincent screw press worked very well dewatering the digester sludge.  However this only lasted for a few months during which sawdust was used as bedding.  When the farm switched over to using composted press cake, troubles were encountered.  The gpm capacity of the press went down by about 50%. 

A worse problem was that the press would occasionally go into a purge condition.  This condition is commonly referred to as having the press "blow the plug" at the cake discharge.  At this time unpressed manure flows through the press without any dewatering, flooding the area where press cake normally forms a pile.

It was observed that the purge condition occurred when firm, solid press cake held open one side of the discharge door.  This reduced the pressure against the cake on the other side of the door.  The cake would become more and more moist, eventually reaching a condition where it flowed, without being pressed, past the door.

After two visits and testing a number of experimental doors, a very satisfactory solution was developed.  The shaft of the screw was extended an additional 14".  This makes the screw extend well past the cake discharge of the press.  A door with a hole in the center, to allow for the extended screw length, was required.  The result was absolute:  there is no longer sufficient door area for cake to hold the door open.  The purging characteristic has been totally eliminated.

Retrofit kits are being produced to modify manure presses that have had problems with purging.  The kit consists of an extension that is welded to the end of the screw shaft along with a new door and yoke style actuator arms.  The kits can be installed without the need to disassemble the machine. 

At the same time a screw design has been developed that drastically increases the capacity of the press on digester sludge.  This design, operating at Matlink, includes double flighting in the inlet portion of the press where the manure is thin.  This design has also been found to significantly improve screw press capacity on flush barn systems where press cake is used for bedding.

September 2010
The farm entered bankruptcy and the digester is no longer being operated.  The Vincent press was purchased by Noblehurst Farms.  Today we would eliminate the purging problem by using half pitch (not double pitch) flighting and the rotating cone feature.

Matlink Digester

February 13, 2002                                                                                                                                                                                                    ISSUE #M22

An extremely smooth start-up has taken place at the Matlink Farm in Clymer, New York. Owned and operated by Ted Mathews, the farm has installed a manure digester and electricity generating system designed by RCM (Resource Conservation Management, Berkeley, California, 510-658-4466). The system employs a 660,000 gallon stirred pit digester. Manure from the 1,200 head dairy is scraped and pumped to the concrete pit.

Digested manure floats over a weir and into a secondary pit. The manure in this secondary pit is pumped to a Vincent Model KP-10 screw press. In normal operation the press dewaters the manure at the rate of 120 cows per hour.

Methane from the digester is burned in a Waukesha internal combustion engine. This engine is coupled to an induction type electric generator. The rating of this generator is 130 kilowatts (175 hp), at which rate the system is currently operating.

Waste heat from the motor that drives the generator is used to heat the digester. Cooling water from the radiators is circulated through the pit so as to maintain a temperature of approximately 100° F.

Circulation is maintained in the digester with a pair of sidethruster propeller pumps. These are positioned diagonally opposite in the sides of the pit. 

Pig Manure

October 30, 1998; Update August, 2013

Trials running pig manure through our KP presses have been run in the States and Canada, and KP-6 presses have been sold to pig farmers in Costa Rica and Sri Lanka.  In all cases the press has done its job of separating solids and liquids, but machine sales did not result in the States.

Pig Manure is highly digested and contains a large portion of the solids in the form of very small particles.  The larger particles are basically undigested food. Typically pig manure is pumped to a KP press with a dilute inbound solids consistency in the range of 1% to 6%.  At the lower solids content, the gpm capacity of the press goes up, reaching 100 gpm in the KP-10.

However there are two problems that can occur when very low consistency flows are pumped to a press.  Either the solids capture rate goes down, or the screen of the screw press tends to blind.  For that reason, Vincent insists that flows of pig manure be pre-thickened with a sidehill screen before being admitted to the press.

Regardless of inbound solids content, the cake produced by the press will have a moisture content of about 70%.  This cake material is quite dry to the touch, and it composts very readily.  Remarkably, it has almost no odor.

Since the cake is essentially undigested animal feed, it provides a good feed additive.  Our Costa Rican customer sells his press cake, in 50-pound bags, to nearby cattle ranchers. The investment in the press has significantly reduced a pond odor problem while paying for itself in by-product sales.

Testing sponsored by A.O. Smith ESPC (Harvestore) was conducted by the Dairy Forage Research Department at the University of Wisconsin.  They found that the capture rate for the KP press was in the range of 20% to 25%.  This means that at least three quarters of the inbound solids go through the screen and are carried away with the filtered liquid.

Advanced animal husbandry practices in North America result in a higher proportion of the feed being digested.  Overseas it is typical for coarser ground material to be feed, and for less complete digestion to take place.  Thus the solids capture rate is higher outside of North America.

The low capture rate is the reason that sales were not achieved in the States and Canada.  In these countries the reason for pressing manure was the hope that most of the solids would be separated from the liquid and that the odor and wastewater treatment problems associated with hog farms would be addressed.  A belt press would be better suited for this task than a screw press.

Issue 85


Sand Bedding

October 24, 2000, Revised April 2003                                                                                                                                                                      ISSUE #M12

Questions about sand bedding as it relates to manure separators came up many times at this year's World Dairy Show. It is clear that sand bedding is very popular, and dairy farmers are well aware of the abrasion it causes.

Earlier this year a Vincent KP-10 was tested at the Everett Williams 400 head dairy in Pennington, Georgia. Good results were expected because of minimal wear experienced at McArthur Farms in Okeechobee, Florida. McArthur's has a great deal of coral sand in their manure, their press has held up very well over a period of years. (Although McArthur's is currently adding settling basins.)

The opposite occurred at Williams' farm. In only a few weeks the Georgia sand wore out a screw. The screw was replaced with one using improved technology: the screw flights were made of abrasion resistant plate, with two layers of MIG applied hardsurfacing followed by TIG applied Stellite or Colmonoy. This was a notable improvement and minimal wear ensued.

However in no time at all the screen was worn through. (The latest Vincent manure presses use sleeve insert screens that are inexpensive to replace.)

It was concluded that sand bedding and screw presses do not mix.

This same knowledge applies to other manure separators exhibited at the World Dairy Show. A drag flight conveyor separator is vulnerable because of chain and sprockets that must operate in the sand/manure environment. The same goes for the wringer/roller type machines.

Our advise to farmers who use sand bedding was to either have good separation of the sand and manure ahead of the separator, or to avoid manure separation. Sand can be separated by flowing the manure through a trench with velocity such that the sand settles out and the manure stays in the flow stream.

If this separation is not possible, then the farmer is better off draining the manureand sand into a pond, which will have to dredged periodically. If they buy a mechanical separator based on savings of avoided dredging costs, they are likely to face repair and parts expenses before the payback period is complete.


Screen Patching

It is not uncommon for the screen of a screw press to wear out. Abrasion from dry manure is a cause. Also, operating with a worn screw puts increased loading on the machine. This can cause the screw to shift sideways, leading to rubbing between the screw and the screen. 

When a screw is tight against a screen, the screen material bows outward, minimizing wear. Consequently wear tends to occur where there are reenforcing rings on the screen that prevent it from bowing away from the screw.

Screen Patch Kits are available for all the Series KP presses. The patches supplied by Vincent are made of 11 gauge steel (1/8" thick) with 3/8" hole perforations. This assures plenty of draining surface even when extensive patching is required.

The patches can be welded in place without having to remove a screen from a press.

The kits can be used only if the screen is still relatively intact. If it has been torn into two or more pieces or if it has been beer-canned, it is likely beyond repair.

The kits consist of a series of pairs of half-cylinder sleeves that fit around the outside of the screen. Each sleeve is about 180º so that the two pieces of a pair can be wrapped around a worn or torn part of a screen.

Once the sleeves are in position they should be TIG welded in place. (Stick welding can be made to work.) The width of the patch sleeves is such that they fit between two adjacent reinforcing rings of the original screen. The patches are welded to these rings and to each other.

The patches, like the original screens, are made of stainless steel.

In a bind, patches can be made of any sheet metal. Because of the excess of open area in the original screens, patches need not be made of perforated material.



Screw Removal and Replacement

Removing and replacing the screw of a Series KP press is a matter of pushing or pulling against an internal snap ring. This snap ring is located in the hollow shaft of the gearbox. A large washer, almost as large in diameter as the hollow shaft of the gearbox, is seated on one side or the other of the snap ring. All-thread rod and a nut are used to push or pull against this washer in order to move the screw in the desired direction.

Complete tool kits and drawings of these kits are available upon request. The Operating Hints section of the O&M manual has a number of helpful suggestions:

The snap ring, washer, and all-thread rod combination must be used to remove the screw from the press. Using a wheel puller can destroy the gearbox.

It is common that heavy force may be required in either removing or reinstalling a screw.

Be sure to lubricate the screen when reinstalling a screw, and be sure to apply Never Seize to the portion of the screw shaft that goes into the gearbox.

Heavy industrial snap ring pliers will be required for use with the internal snap ring.

A special nut with a lug that catches in the keyway is required when pushing the screw out of the press.

When pushing a screw out of the press a steel disc should be placed over the end of the all-thread rod in order to prevent it from screwing into the threaded hole in the end of the screw.

When reinstalling a screw, the screw must be pulled in until the step in the shaft seats against the thrust bearing of the gearbox. Be careful when guiding this step in the shaft through the shaft seals. It is best to remove the four bolts holding the seal housing during the screw installation.

When pulling a screw into the press the all-thread rod must be screwed into the end of the screw. This can be done before starting to put the screw into the press.


Types of Manure Separation

March 8, 2000                                                                                                                                                                                                        ISSUE #M4

There are four different types of machines commonly seen separating dairy manure: sidehill screens, drum screens, drag flight conveyors, and screw presses.

Sidehill screens are the least expensive and require the least maintenance. These are simple sloped screens (alternatively called static and gravity screens) with a weir box at the top. The manure is pumped to flow over the dam of the weir box and down the screen. The filtered liquid goes through the screen, while the solids (tailings) fall off at the bottom.

The disadvantage of a sidehill screen is that even under the best of operating conditions the solids come off as a wet sludge. This sludge is almost too wet to compost, and it is difficult to handle for spreading on the field. Additionally, sidehills tend to blind over, requiring a farm hand to wash down the screen. A sidehill will keep a lot of solids out of the pond, but it is definitely not a strong manure separator.

Drum screens use a drum made of perforated metal to separate the solids from the liquid. Alfa Laval previously offered one, and Houle currently has a unit in their line. These will produce drier cake than a sidehill. However they are rarely popular. Maintenance is frequent because of all the moving parts and adjustment; screens can be damaged by large solid tramp materials; and they are exceptionally dirty.

Drag flight conveyor separators come in two varieties. The Blossom and Agpro machines are single pass: the lower end is submerged in the manure pit, and the solids are dragged up perforated or wedgewire screens to where they fall into a small screw squeezer. The Albers unit is a double pass design. The manure starts by being dragged down a sidehill. It makes a U-turn in a sump and is dragged back up to where it falls into a roller squeezer.

Drag flight separators have the disadvantage of many moving parts: chain, sprockets, drag flights, bushings, besides an optional squeezer at the discharge. Leakage and large size are negatives. The manure cake is dryer than achieved with a sidehill screen, but not up to that produced by a screw press.

The screw press, which produces the driest cake, is the fourth category of manure separator. These are designed to operate intermittently, unattended, with a minimum of maintenance. They will be further described in later Pressing News issues.


Vacuum Testing

March 1, 2001, Revised August 2001                                                                                                                                                                           ISSUE #M14

In February tests were run to test vacuum on the outside of the screens of a screw press. The testing was done with a Model KP-6 press operating at the Lewisburg dairy of the University of Tennessee. Manure is pumped to the press from the pit into which it is scraped. There is a recirculation line from the inlet of the press back the pit, which assures that the inlet hopper will not become pressurized. The press liquor drains though a hose, going down 12' to a point where the drain line could be either open-ended or sealed under liquid in a 5-gallon pail.

The tests were facilitated by the fact that the screen of the KP-6 is surrounded by an integral, airtight, combination cover and press liquor collection pan. A hole was drilled through this cover, and a manometer was inserted to measure the vacuum surrounding the screen.

We were in for a number of surprises. While there are several unanswered questions, some facts were established and best-performance conditions were observed. The facts are that a vacuum can be formed on the outside of the screen, and the throughput capacity of the press easily went up 25% to 100% with vacuum conditions. The vacuum ranged from 8" to 42" water column (28" w.c. equals one psi). The best results where when we had the vent pipe open and the end of the drain hose submerged.

Dave DeWaard at DariTech in Washington is insistent that there must be an open vent line on the inlet hopper of the press in order obtain maximum capacity. Previously we thought the vent line was needed to let air out of the press on start-up. However it is now hypothesized that press capacity goes up with the vent line open because the recirculation line carrying manure back to the pit draws a vacuum in the inlet hopper, counteracting the vacuum in the drain line. An intermittent gurgling sound like a flushing toilet was heard from the press during our tests with an open vent line.


Why Separate Dairy Manure?

April 5, 2000                                                                                                                                                                                                          ISSUE #M5

The use of manure separators is practically unknown in many areas, while in other regions no dairy is without a device of some sort. There are reasons why this is true, and it is equally true that the trend is toward the expanded use of manure separators.

There are different justifications for the use of manure separators. Probably the strongest reason is to keep solids out of the manure ponds and to get the manure solids into a form that can be land applied without building a cake layer on the pasture or field. If un-separated manure is sent to the pond, tank or Slurrystore structure, settling can become a problem. This is especially true in flush barn ponds where a source of clarified water is requisite. The repeated cost of dredging a pond can be sufficient to justify installation of a separator.

Spraying the raw manure on a field or pasture is not a foolproof alternative. Flush barn farms usually need the recycled water. Besides, the wet manure can build up a mat layer so dense that grass will not grow through it. In contrast, composted manure solids are readily tilled into the soil, with strong benefits from fertilizer and organic addition.

There are areas where an altogether other justification exists for using a manure separator. Many farmers, especially in the north central States, use the composted manure as bedding for their cows. This represents a direct savings of cash that would be spent on sawdust, sand, ground paper, straw, or other bedding. (Farmers in other areas fear that, because of the climate, disease outbreak may occur with the use of manure bedding, so the practice is not used among them.)

Many other reasons are given for using a manure separator. In every county there is the story of the farmer who is getting rich raising worms in the compost, selling potting soil to nurseries, or selling bags of compost for $4.00 each. There is less discussion of the practice of blending press cake (which is mostly undigested feed, 50% protein) in the ratio of 5% for heifer and non-lactating cow ration.

Odor reduction is probably the greatest fringe benefit of using a manure press. However, environmental regulations have not reached the point of mandating the use of these machines.


Wobble Stick Switch

October 24, 2002                                                                                                                                                                                                    ISSUE #M25


The screws of screw presses used in manure are subject to abrasive wear. This wear does not occur in normal operation nearly as much as it does in a condition of "running dry". If a manure press is allowed to continue running when there is little or no cake being produced, the cake remaining in the machine becomes bone dry. This dry material, even without sand being present, is extremely abrasive. Because of this it is recommended that a wobble-stick switch be incorporated in the electrical control system.

The switch is mounted someplace below the cake discharge so that the wobble stick is in the path of the falling press cake. This is illustrated in the sketch below. The switch should be connected to a timer such that, if the switch does not detect activity for a while, like three minutes, the manure pump and press are shut down.

Shutting down the system when cake is not being produced is advantageous for several reasons:

1. Even though the press is not producing cake, as long as the screw is turning the flights are being worn down. In this stalled condition, the cake at the discharge remains stationary, tends to get very dry and even hot, and the amount of abrasion occurring to the circumference of the flights increases substantially.

2. If cake is not being produced, it is likely that the pit has been drawn down to where the capacity of the manure pump has been seriously reduced. This comes about because of the increased height that the manure must be pumped. (The pumped height is from the level of the pit to the inlet of the separator, not from the pump suction to the inlet of the separator.) It is time to shut down the system.

3. If very little cake is being produced, water on the inlet end of the screen will soak into the dry cake at the discharge. In this manner the lower portion of the plug at the discharge becomes sopping wet to the point where it breaks loose and flows out. The discharge door is held open by the dry material on the upper portion of the plug, and purging will begin. Shutting down the system before this happens can prevent the mess that comes with blowing the plug.

Square D offers wobble-stick switches and timers, as do many other companies. They can be bought through McMaster-Carr, Grainger, and Gulf Controls among others.

Wobble-Stick Switch

October 24, 2002                                                                                                                                                                                                 ISSUE #M25

The screws of screw presses used in manure are subject to abrasive wear. This wear does not occur in normal operation nearly as much as it does in a condition of "running dry". If a manure press is allowed to continue running when there is little or no cake being produced, the cake remaining in the machine becomes bone dry. This dry material, even without sand being present, is extremely abrasive.

Because of this it is recommended that a wobble-stick switch be incorporated in the electrical control system. The switch is mounted someplace below the cake discharge so that the wobble stick is in the path of the falling press cake. This is illustrated in the sketch below.

The switch should be connected to a timer such that, if the switch does not detect activity for a while, like three minutes, the manure pump and press are shut down.

Shutting down the system when cake is not being produced is advantageous for several reasons:

1. Even though the press is not producing cake, as long as the screw is turning the flights are being worn down. In this stalled condition, the cake at the discharge remains stationary, tends to get very dry and even hot, and the amount of abrasion occurring to the circumference of the flights increases substantially.

2. If cake is not being produced, it is likely that the pit has been drawn down to where the capacity of the manure pump has been seriously reduced. This comes about because of the increased height that the manure must be pumped. (The pumped height is from the level of the pit to the inlet of the separator, not from the pump suction to the inlet of the separator.) It is time to shut down the system.

3. If very little cake is being produced, water on the inlet end of the screen will soak into the dry cake at the discharge. In this manner the lower portion of the plug at the discharge becomes sopping wet to the point where it breaks loose and flows out. The discharge door is held open by the dry material on the upper portion of the plug, and purging will begin. Shutting down the system before this happens can prevent the mess that comes with blowing the plug.

Square D offers wobble-stick switches and timers, as do many other companies. They can be bought through McMaster-Carr, Grainger, and Gulf Controls among others.


Avocado Oil

May 20, 2016

A Vincent customer has built a successful business which produces avocado oil from distressed fruit. They process a couple hundred tons a day of windfall and packing house rejects, all black and soft.

The oil is extracted from the pulp, bottled, and sold as specialty cooking oil.

The process used is very similar to that used by producers of olive oil. The avocados are run through Italian 50 hp olive shredders and then fed into mixing tanks. GEA Westfalia describes this process as follows: "From there the flow goes to blanchers which stir the dough at 40/45 °C for one to two hours. Next it goes into a two phase decanter, separating oil+water and pomace."

The oil+water mixture is sent to bowl centrifuge to separate the oil.  This oil is cold pressed extra virgin, and it does not need to be refined.

Recently we were contacted by our customer because the KP-10 screw press we supplied a few years ago is too small for their current project. The goal is to remove additional moisture from the decanter sludge (they call it Pasta). The press liquor will be used as feedstock for a biogas digester.

Normally a screw press cannot remove any additional moisture from decanter sludge. However mixing press aid into a sludge occasionally enables the screw press to separate a significant amount of press liquor. As with olive sludge, avocado Pasta requires a heavy dose of press aid, from 6% to 20% by weight. We ran tests on the avocado, comparing rice hulls to cellulose fiber (ground wood). It looked like the use of cellulose fiber let the press separate twice as much press liquor as the rice hulls.

We were pleasantly surprised to see that a layer of oil floated up from the press liquor. This points us toward the selection of a high toque Series CP press instead of the more economical Series KP machines. It remains to be seen if this oil is suitable for recovery.

The liquor showed a fuzzy 10 Brix on my refractometer, so it might be usable as a feedstock for a biogas digester.

Samples from one of our trials showed 68% moisture in the as-received Pasta, 62% moisture after addition of press aid, and 56% moisture in the press cake.

It is anticipated that the press cake can be used either as a biofuel or animal feed. The presence of fiber from the press aid might enhance value as animal feed.

GEA Westfalia did alert us that in avocado skin there can be a product that the literature has named "persin". It is poisonous to some animals but not human beings.  Birds are especially sensitive to persin: try putting half an avocado in a cage with a bird inside.  As soon as the bird eats some of the peel, it will die.

Separately, Anderson International of Cleveland, Ohio has been contacted to see if oil can be separated from the avocado stones with their Anderson Expeller®. To date no results are available.


July 20, 2016

Carrageenan is a hydrocolloid which is a very popular food ingredient because of its gelling, thickening, and stabilizing properties. It is used in the production of toothpaste, salad dressing, and ice cream. Also, it is added to marinades and brines which are injected into meats, holding liquid for a juicier end product.

In a major test with carrageenan gel, we were working with the final product which had already had water separated from it with a belt press. That is the last step ahead of final drying. Vincent's goal in these tests was to see if a screw press could further dewater the cake from belt press.

Extensive testing was performed in the Tampa pilot facility. The entire operation can be seen on a YouTube video which averages 160 hits a month: Given that it is 27 minutes long, probably not many people watch the whole thing.

The material used for testing in these trials had 16% solids content. The best result achieved was press cake with 22-24% solids. It seems probable that the current design twin screw presses could achieve this with a reasonable throughput capacity. The savings in dryer fuel consumption would be very large. The increase from 16% to 22-24% solids represents removing 30% of the dryer's load.

[In another test with carrageenan from a different customer, our press cake came out with only 50% moisture. This had to be a different carrageenan, probably involving an alcohol process.]

Our first efforts were with a 6" twin screw press, the TSP-6. The carrageenan gel passed through the press with minimal water separation. So we piped in a McMaster Carr pressure multiplier. That took the air pressure on the discharge cone up from 5 to 10 bar. The press then forced more gel into the press liquor, but dewatering was still inadequate.

In an effort to clear the screen we tried an automatic reversing VFD program. The press ran continuously forward and backwards, hopefully breaking up the gel on the reverse turns. It didn't work.

Our second trial was with a Model KP-6 press with a perforated screen. It worked for only a while, and we saw that excessive fines were coming through the screen of the press.

Next we equipped that press with a fabric screen with openings of only 31 microns. This was achieved by fitting the fabric against a reinforcing layer of perforated stainless screen with 800 micron (0.033") holes. To prevent the fabric from being snagged by the flights of the screw, an inner layer of 800 micron perf was fit on the inside. While it worked, clear press liquor (water) was produced. However the layers of screening material soon plugged. We have never been able to overcome this problem despite a number of succeeding efforts with other materials.

Our third trial was with a laboratory Model CP-4 press. The press jammed almost immediately due to co-rotation of the material within the press. To prevent co-rotation, the inlet hopper of the press was pressurized with a 1,650 pound dead weight. This forced enough material through the press to show us how dry the carrageenan could be dewatered in a screw press. The video is almost comical at that point.

Our final test was back with the double screw Model TSP-6. The twin overlapping screws overcame the co-rotation problem. A characteristic of twin screw presses is that when material wants to co-rotate with one screw, the other screw forces the material to keep moving through the press.

Unfortunately little moisture removal was achieved. The material just could not be squeezed hard enough. Today we manufacture our twin screw presses with the screws further apart. This allows the shafts of the screws to be made in a conical form. The material being pressed is forced outward against the screen. Even at the time the video was made it was recognized that this would allow greater dewatering to be achieved.

Most of the presses used in these trials had wedgewire screens with slots which were 400 to 500 microns wide. Excessive fines came through these screens. However, when a slot width of 175 microns was used, the problem was solved.

Vincent would welcome the opportunity to demonstrate what can be done with a TSP press from our rental fleet.


May 19, 1997

An unusual application for a dewatering screw press is found in factories that produce fiberglass wool.  This insulating material is produced in continuous wide (20' or more) blankets.  The factory building we visited was long, over a quarter of a mile.  The wool is formed in a large chamber at one end, and it is either rolled or sheared into panels at the other end.  In between the two ends of the factory the material is coated with a binder resin that is baked on, and the material is then cooled to where it can be handled.

Once running, the equipment is only rarely shut down.  As the material comes from the chamber where the fibers are formed, it is white in color.  It turns to the familiar tan color only after the resin is baked.

Considerable volumes of waste material are created.  Because of impurities, recycling is the exception.  Generally the dry waste is compacted in large industrial compactors. (Marathon is a supplier of these.)  The compacted material is landfilled.

The application for the Vincent press is to dewater waste at the beginning of the process.  The fine strands of fiberglass (angel hair) are formed by injecting molten glass through dies with tiny holes.  The extruded glass goes into a large chamber, surrounded by a hood, where it solidifies.  The hood walls are cooled with a water film, and the glass that hits the walls solidifies and is washed to a collection pit.

The water, fiberglass, and some glass particles the size of marbles accumulate in the pit.  This is pumped to shaker screens to remove a large part of the water.  The tailings from the shaker screens, amounting to only 200 pounds per hour each, were found to contain 90% moisture.  The high water content of the tailings presents a problem in that water drips from them as they are carried through the plant.  Also, they drip water when placed in the compactors along with the dry waste.

By running the tailings from the shaker screens through a screw press, we were able to remove one half to three quarters by weight as water.  This solved the dripping problem. A new problem created was that the water coming from the press contained a significant amount of ground glass.  This was created in the pressing action.  We feared that it would be abrasive; however, only the tan (baked) material is abrasive.

In our first testing, at Knauf Fiber Glass GMBH in Alabama, we were up against a Hycor Helixpress.  Both it and our CP-4 press had problems with the tailings bridging at the inlets to the presses.  This was solved by the addition of sluicing water (available from the shaker screens).

The 8" Hycor machine costs about $20,000 versus $12,000 for our CP-4 press.  In the end the Hycor unit was selected because it was better at passing chunks of glass and other
waste.  It was only later that we were able to resolve this problem in our press with the invention of the Sterile screw (see Pressing News #37).

Subsequently we learned of another identical application at Evanite in Oregon.  They were debating between buying an additional Oberlin machine for about $30,000, or a Hycor.  Their existing Oberlin, which they described as a semi-continuous belt press, produced press liquor with only 3 ppm solids and 45% press cake moisture.  In contrast, the Hycor they tested gave them 600 to 700 ppm in the pressate.  They could not accept the higher solids content in the wastewater, so they stuck with Oberlin.  Their objection to the Oberlin was primarily mechanical deficiencies which they were assured had been corrected.

We declined to test at Evanite because we knew our solids in the press liquor would be excessive.

The advent of the new KP presses gives us an excellent machine for the fiberglass application.  Bridging problems will be minimal because the press will grab anything that
will fall through the 8" pipe inlet.  Plus, the Sterile screw will not jam with large pieces of trash.  Cost is still an advantage as the KP-6 sells for the same as the CP-4.

The only remaining problem is ground glass in the press liquor.  This will have to be removed separately, probably by decanting in a pit.  After all, it is a screw press, not a filter press.

Issue 61



Full List of Applications

Food Waste

Energy: Digester Biogas, Cellulosic Ethanol, Biofuel


Pulp & Paper

Random and Miscellaneous


Fiber Filter

Plastics Recycling


Cooking Oil




Olive Oil

June 23, 2015

Olive oil production is a major industry, especially in countries such as Italy, Spain, Greece and Syria. Tunisia, Turkey, and Morocco are also significant producers. For many decades screw presses were used in this process, to separate the oil from the olive pulp. Today the use of decanters and centrifuges has taken over. GEA Westfalia and Alfa Laval are the principal suppliers.

The process starts when harvested olives are dumped into a trash removal machine and a washer. The trash (mostly leaves) is separated by air. The washer counts on the olives floating and the rocks sinking.

An in-line weigh scale is used as the olives are transported to storage bins. Different quality olives are separated into these bins.

From the storage bins the olives go to a small grinder which looks like a pellet mill. Inside it has a 1/4" perf screen through which the olives are crushed. This breaks the seeds into pieces.

This mass then goes to a ribbon blender which makes the olives into a pulp. To improve yield, steam is used to bring up the temperature a little bit.

This pulp is pumped to a horizontal decanter, 4000 rpm, which separates liquid from the pulp. Typically this is a two phase decanter, something introduced in the olive industry in the 1990's.

The centrate is screened and then pumped to a bowl style centrifuge. This separates the flow into three fractions: water, oil, and sludge.

Typical installations of this equipment are rated at 100,000, 150,000, and 250,000 kilos of olives per 24 hour day.

The oil goes to gravity decanter tanks followed by a final membrane filter. Virgin olive oil is the result. The tank bottoms are pumped back to a centrifuge, for oil recovery.

The yield is about one kilo of oil from six kilos of olives. This varies with green and black (ripe), along with other factors.

The pomace from the decanters goes to a de-stoner machine which separates almost 90% of the pit pieces from the pomace. This pomace is shipped off-site to a hexane solvent recovery plant to get out the residual oil. This is the lowest quality olive oil. In Spain it is called lampante, lamp oil.

The pits are sold as boiler fuel. They have only about 22% moisture content. Frequently some are burned in a small boiler to make steam to heat the facility. A small amount of steam is used in the ribbon blenders.

A few years ago Vincent had a foray into this industry, working with GEA Westfalia. The goal was to separate additional liquid from the pomace from the decanters. This liquid is rich in polyphenols, a class of pharmaceutical organic chemicals valuable because of antioxidant properties. There was also a possibility that the pomace could be made into animal feed.

As is always the case, the screw press could not separate liquid from decanter pomace. However, by dosing with cellulose fiber press aid, the screw press was made to work. There was about a 50/50 split between press cake and press liquor.

If the pomace was a couple weeks old, natural enzymatic reaction had released liquid which could be separated as press liquor. In the case of pressing fresh pomace, it was necessary to first add hydrated lime to react the pomace ahead of the screw press. Either way, press cake with only 40% moisture content could be produced.

Unfortunately the process did not pencil out. It is one more case of a technical success but a commercial failure.

Issue #274

Scrap Gel Caps

March 9, 2012

Pharmavite is a very large nutraceutical firm whose products are marketed under the Nature Made trade name.  Owned by Otsuka Pharmaceutical in Japan, Pharmavite has its manufacturing operations in San Fernando, California.

Pharmavite uses a Vincent screw press in an unusual application.  The press recovers the valuable pharmaceutical contents from scrap gel capsules.  They refer to our press as the reclaim machine.

Scrap gel caps fall in two main categories: (1) Brittle ones due to over-drying; these are easy to break and drain.  And, (2) normal gummy ones which have been rejected due to failing an assay test. 

Since the contents of the gel caps are being recovered, the machine must be fully sanitized between each batch of gel caps.  During the testing period an evaluation was made between a passivated glass bead finish and having the machine electro-polished.  Vincent had never had one of our presses electro-polished, but now we have found a local source in the Tampa area.

Pharmavite's goal is to recover 85% of the fluid in the gel caps.  All of them have an oil based liquid inside, so they have a long shelf life without the need for refrigeration.  They are stored in mini-bulk bags, on pallets.  The bags containing scrap are red-tagged.

A switch from bovine gel caps to porcine gel caps was made because of mad cow disease.  Now there is a push to go on to pectin (i.e., plant, not animal) gel caps.

Vincent's screw presses came to Pharmavite's attention through our sales rep, Jeff Rubak, SPM Sales Inc.  Jeff's 's main line is Quadro.  The Quadro's are emulsifiers which are used to blend pharmaceutical powders into oil before being injected into the gel caps.

The press used in this application is a Model CP-6.  It has an unusual feature in the Series CP machines, a rotating cone.  This was found to be indispensable for satisfactory operation.  Also, a sixth pair of resistor teeth was added to serve as spin-stops.  High discharge cone pressures are required to break the capsules, along with a tight fit between the cone and the cake discharge spout.  Half pitch flighting in the inlet hopper, along with a high speed gearbox, provide the best possible feeding into the press.


From 50 to 200 kilos per hour of gel caps are pressed.  Recovery ranges from 75% to as much as 97% of the pharmaceutical content of these gel caps.  Reduced screw rpm and throughput have been employed in order to get higher liquid recovery.

A nitrogen purge feature was added to the press because some gel caps use fish oil.  This might tend to spoil if exposed to oxygen.  Vincent supplied covers fitted with edge seals for this purpose.


Issue 243