Citrus plants around the world are facing the same problem. The problem faced by these juicing plants is the disposal of orange peel. They are finding increased costs associated with landfill or with finding farmers willing to take the wet peel for animal feed. This is occurring at the same time as increased environmental regulations are being applied.
These plants are very small compared to the large scale operations in Florida and Brasil. That is, they generate a few tons per hour of peel, generally running only eight hours per day, as compared to 1,000 tons per day at the larger plants.
Because of the vast difference in scale the smaller plants cannot justify the investment associated with a highly efficient, full blown feedmill.
There is one solution that was popular among Florida's smaller processors in the 1960's. It is a "beginners" feedmill plant. It minimizes the capital expenditure at the expense of requiring more energy.
To understand this "beginners" plant, it is important to first understand how a large plant operates. In the large scale plants, peel moisture is removed in three independent operations:
- Firstly the peel is pressed to separate it into press cake and press liquor. This is a very energy efficient operation as the press horsepower is relatively low.
- The press liquor is evaporated in a waste heat evaporator. This heat exchanger evaporates water out of the liquor and leaves behind dissolved solids in a solution commonly called molasses. This water removal process is very economical: it requires no fuel because its energy source is the waste heat in the exhaust gasses leaving the dryer. The molasseses produced are then added back to the press cake.
- The press cake, with the added-back molasses, is dried in a rotating drum dryer. This is the least efficient of the three water removal devices. It requires about 1,600 BTU in the form of fuel oil or natural gas per pound of water removed from the peel.
In the process just described citrus peel, which starts at about 82% moisture, is dried down to 10 to 12% moisture. (This means that for every 100 pounds peel entering the peel bin, about 20 pounds of finished animal feed will result). As a final step the dried peel is pelletized in order to reduce its bulk. This is done in order to minimize transportation and storage costs.
The previously mentioned "beginners" process that may be economical for smaller processors calls for using only a dryer to remove all the moisture. This eliminates the need for investment in a dewatering press and a waste heat evaporator. In such a "beginners" plant we also recommend not investing in a pelleting mill and its associated pellet cooler.
To dry peel in this manner will require approximately 85 U.S. gallons of heavy fuel oil per short ton of feed produced. This compares to a range of 30 to 45 in Florida citrus plants. Thus we can see that the "beginners" plant has its lower capital investment being offset by higher operating costs.
The dried peel produced in this process is an excellent, palatable animal feed for dairy or cattle. Because of its low moisture content, it can be stored for prolonged periods with minimal spoilage.
The enclosed diagram shows the equipment required for drying the peel in this manner. One notable item is the reaction conveyor. It is necessary to add lime to the peel prior to drying; this is done in the reaction conveyor. The lime attacks the cells and releases the moisture so that it can rapidly and efficiently be evaporated in the dryer.
A frequent query has to do with incorporating a press into the cycle. The difficulty that arises involves what to do with the press liquor. The authorities will not accept it in the sewer system, and it can be used for irrigation purposes only if it is mixed with a great deal of water. (In heavy applications it kills the soil where land spreading is performed.)
Certain alcohol producers will buy the press liquor, stripped of d-limonene oil and concentrated to 50 Brix or more. It ferments readily and makes an excellent citrus alcohol. But how many small citrus processors have a nearby distillery?
Generally the only practical thing to do with press liquor is to run it through a steam or waste heat evaporator. A waste heat evaporator system generally costs almost as much as all of the rest of the feedmill put together. This investment becomes difficult to justify until all alternative methods of disposing of citrus peel have been exhausted.
CITRUS PEEL DRYING SYSTEM
Vincent Drawing C-91310 shows a citrus peel drying plant based on a Model 150 Dryer. The plant will dry approximately 19,000 pounds per hour of 82% moisture citrus peel, without the benefit of pressing or the use of a waste heat evaporator. The plant will produce approximately 3,800 pounds per hour of citrus peel dried to 10 to 12% moisture content.
The principal items, in their sequence in the production cycle, are as follows:
- Peel Bin. This vertical front peel bin, with hydraulically operated doors, is of carbon steel construction. A caged ladder to the top and a catwalk across the top are included. The unit is prefabricated and knocked down for shipment, to be welded together at the job site.
- Peel Bin Discharge Conveyor. Vincent will supply an ultra heavy duty conveyor, including three-bolt drilling, Gatke hanger bearings and a variable speed electric drive. This conveyor is of stainless steel construction, with a metering orifice plate. The peel bin is constructed with sufficient elevation such that the Discharge Conveyor can feed directly into the Peel Shredder.
- Liming System. A Vincent VL-450 Hydrated Lime Proportioning System, mounted on a fabricated steel base, is included. The lime hopper, sized to hold one and a half bags of lime, is installed adjacent to the shredder. An auger from this hopper adds approximately 1/2% by weight of hydrated lime to the peel as it leaves the peel bin.
- Peel Shredder. A Vincent VS-180 Shredder is included. This horizontal rotor machine reduces the peel mostly to a range of 1/4" to 3/4", with a minimum of fine material. It is of the thin, rigid blade design, as contrasted to the hammer mill concept. All contact parts are of stainless steel. The blades, which are fixed, cut the material before it is discharged through the perforated screen. The shredder housing is hinged so as to allow ease of washing, inspection, and changing the screens. In operation the housing fits folded onto the chute that feeds the shredder, assuring a tight fit. The rotor turns in only one direction; however, the blades can be reversed to give double life.
- Reaction Conveyor. Shredded peel drops directly into a slightly inclined Reaction Conveyor. This conveyor is sized to allow approximately 10 to 12 minutes dwell time. It is of carbon steel construction and features a notched blade screw. The chemical reaction between the lime and the peel that occurs in this conveyor is required in order to break down the cell structure of the peel so that moisture can be better removed in the drying operation.
- Elevating Conveyor. Limed peel from the Reaction Conveyor is elevated to the Dryer Feeder by this stainless steel conveyor. Also, recycled material from the second pass of the dryer is mixed with the limed peel in this conveyor. The design is such that, if required, material can be dropped back into the inlet of the reaction conveyor.
- Dryer Feeder. This screw conveyor receives peel from the Elevating Conveyor and feeds it into the Dryer. This is a stainless steel screw feeder fitted with a companion flange matched to the dryer throat. It has a variable speed drive to control the process feed rate.
- Burner. The burner will require up to 150 U.S. gallons per hour of fuel oil. The burner package is suppled with dampers and valves and a steam heater for the oil. The burner is capable of burning optional lighter fuel oils, or natural gas. It comes with the required combustion air blower.
- Furnace. Vincent will supply a Model VF-150 refractory lined furnace consisting of a carbon steel shell mounted on a fabricated steel base. It is designed to receive and mix recirculated exhaust gasses from the Dryer discharge in order to control the gas temperature entering the Dryer. The firebrick lining is supplied and installed by the customer.
- Return Elbow. There is a 180º Elbow between the Furnace and the Dryer so as to minimize the possibility of overheating peel in the Dryer.
- Controls. Vincent supplies a solid state programmable controller that modulates combustion and monitors the flame. Control of the combustion rate is through a sensor mounted at the inlet to the third pass of the dryer. This is required for precise control of product quality.
- Model 150 Dryer. This is a Vincent triple pass dehydration unit with an insulated, stationary outer drum. The unit includes recycle conveyors so that partially dried material can be extracted at the end of the second pass and mixed with the incoming material. This is especially important for the proper drying of unpressed citrus peel. The drum is carried on machined steel tires, mounted on an expansion type steel base with cast steel machined trunnions. The rotor is driven by a chain and sprocket system with a speed reducer. The base frame can be bolted to a 6" concrete slab without any special foundations; this saves installation costs.
- Separation System. The Vincent low level entry cyclone separator, ductwork, dampers, and stack are supplied. This system assures gentle handling of the dried peel. A motorized air lock and carbon steel screw conveyor are used to move the peel from the separation chamber to the cooling reel and bagger. A radial blade exhaust fan with its drive are also included.
- Cooling Reel. The Vincent Model 525 Cooling Reel gently cools the dried peel with an action similar to that of a large diameter clothes drier. Ambient air is drawn counter- current through the unit to achieve an evaporative cooling effect. Cooling is required in order to prevent the phenomena of re-heating of the stored peel. In the cooling process, evaporation results in a further reduction of moisture content of about 1%. The unit comes complete with a fan, dust collector, duct work, supports, and electric motors.
- Bagging System. This system includes an surge hopper and a semi-automatic weighing and bagging unit. This unit consists of a hold/weighing bin with an adjustable discharge, a weight indicator, a bag holder, and a compact Fischbein sewing head. The take-away belt, belt trays and motor and drive are included.