Food Waste

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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

 

CORN WET MILLING

 

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 wet corn 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

Coffee

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

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.

Fish

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

Garbage

August 20, 2003, Revised November, 2010                                                                                                                                                              ISSUE #141

GARBAGE
(ANIMAL FEED AND BIOFUEL)

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

Mushrooms

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

Mushrooms

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:

SUMMARY OF TEST RESULTS:

ALL BUTTONS -->
ORIGINAL CP-4 BUTTONS
KP-6 WITH ROTATING CONE
KP-6 WITH TAPERED SHAFT
SECOND PRESSING IN CP-4
PRESSING CAKE WITH 3% LIME
STEAM INJECTION IN CP-4
MOISTURE CONTENT AS FED INTO PRESS PRESS CAKE PRESS LIQUOR
9-Oct
18-Oct
18-Oct
18-Oct
18-Oct
18-Oct
93%
93%
93%
91%
87%
93%
91%
92%
90%
88%
74%
89%
95%
94%
95%
94%
94%
95%

 

Issue 258

 

Okara

May 25, 2009                                                                                                                                                                                                       ISSUE #211
                                                                                                             OKARA

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, www.laitram.com. 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