Objective
The project relates to the erection of a full-scale production line for converting inedible offal and the like to meat-and-bone meal and animal fat by means of the wet pressing system.
The production line was designed for handling 10 tons raw materials per hour and the line was connected to an existing 5t/h experimental processing line, constructed and used in the preliminary R&D work.
The objective of the project was to design and construct the full-scale production line, to show feasibility of the process in full-scale operation, and to obtain key figures for the energy savings in the system.
During 1983 and the first quarter of 1984 the new equipment was bought and installed and the plant was commissioned. A number of problems was encountered and solutions sought. It was proven that the process - with minor modifications - was highly feasible in large scale operations. The expected capacity of 15 t raw materials per hour was slightly overestimated. During measuring a capacity of 13 t per hour was found.
First measurements of energy consumption took place in 1984, the final calculations being based on 20 production days, or a total of 460 production hours.Live steam was used in three places: indirect heating of the dryers, direct injection into the press liquid in order to increase the temperature to approx. 100 deg.C. before entering the tricanter, and to sterilization and refining of the fat. Heating of the press liquid was supplemented by flash steam. Heating of the coagulator took place by means of waste heat from dryers.
The amounts of live steam used was measuredand converted to kg oil using the figures for oil conversion in the KOFO boilers, i.e. 14.87 kg steam per kg fuel oil.
The following figures were obtained:
Dryers : 52.8 kg fuel oil per t water evaporated or 29.2 kg fuel oil per t raw materials.
Tricanter: 6.7 kg fuel oil per t water evaporated or 3.7 kg fuel oil per t raw materials.
Fat handling (theoretical figure): 0.6 kg fuel oil per t water evaporated
or 0.3 kg fuel oil per t raw materials.
Total oil consumption:
60.1 kg fuel oil per t water evaporated or 33.2 kg fuel oil per t raw materials.
Part of the heat in vapours from dryers which could not be utilized in the evaporator was sold to the local district heating system. A total of 310 Gcal was delivered during the measuring period, corresponding to 35 t of fuel oil.The fuel oil consumption during the measuring period was 196 t, which means that nearly 20% of the input energy was recovered and utilized for district heating purposes.
Similarly to the recording of steam consumption the consumption of electrical power was measured for various parts of the equipment.
The overall figures were: 125 kWh per t of evaporated water, or 69.1 kWh per t of raw materials treated.
Commercial potential is high and there are no real obstacles to a successful industrial development of the system. In fact, the wet pressing system, as marketed by Atlas Industries, is installed in three Danish plants with a rated throughput of nearly 85 t raw materials per hour in total. It is also installed in a German, an Irish and a US plant. Others are to follow. (The capacity of the wet pressing has continuously been increased since 1984, and the capacity is appr. 50 tons raw-materials par hour.)
The process is based on the discovery that it is possible at low temperature (50-60 deg.C. just above melting point of the animal fat) to separate nearly all fat and more than 60% of the water from the solids of the raw materials by means of a pressing process. This has made possible the design of a process with optimized use of the energy necessary for sterilization and removal of water, i.e. by evaporation of 80-90% of the water in the liquid phase from the press in a vacuum evaporator using waste energy from the drying of the solid phase from the press.
Technical system:
The experimental line with a capacity of 4-5 tons raw materials per hour was turned into a full-scale production line with a capacity of 13 t raw materials per hour by installation of extra equipment, the principal equipment thus being
2 hashers, 1 coagulator, 1 strainer screw, 2 twin screw presses, and 3 PCD-dryers, 2 tricanters and 1 3-stage waste heat evaporator.
Prebroken raw materials pass a magnet and ametal detector which in turn sort out magnetic material and materials containing non-magnetic metal. Freed of metal they are hashed to a size of less than 19 mm and indirectly heated with hot water to 60 deg.C. in a coagulator. They pass a strainer screw with adjustable hole size and are then pressed in a twin screw press, which divides the raw materials in two phases, a solid phase (press cake) containing 40-50% water and 4-7% crude fat on a dry matter basis, and a liquid phase containing fat, water and some solids. The liquid phase is heated to 100 deg.C. with live steam and passed through a 3-phase decanter (tricanter) which separates it into fat, stockwater and grax. The grax is returned to the coagulator, the fat is sent for refining and sterilization and the stick water containing 8% dry matter and 0.6% crude fat is pumped into the 3 stage waste heat evaporator for concentration. The concentrate containing 35% dry matter (8-9% fat in DM) is mixed into the press cake, which is dried in a plate contact dryer indirectly heated by live steam. The meal leaves the dryer at 110 deg.C. at which temperature sterilization is accomplished. The meal has a moisture content of
5-7% and a fat content of 7-8%. It is transported to milling by means of a pneumatic transport system. The dryer gases pass a scrubber where the particulates are removed from the vapours and a small proportion of the vapours is condensed. The scrubber liquid delivers hot water (90 deg.C.) to the coagulator via a heat exchanger. The gases then pass a heat exchanger where part of their energy is transferred to the district heating system. The gases finally serve as heating medium for stage I in the waste heat evaporator.
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DEM - Demonstration contractsCoordinator
8723 Loesning
Denmark