Managing Contaminated Animal and Plant Materials: Field Guide on ...

Description of a continuous dry-rendering systemAs shown in Figure 1, animal carcassesare received in temporary storage or rawmaterial bins (1), conveyed by a raw materialconveyor (2), <strong>and</strong> discharged across a magnet(3) to remove any ferrous metal contaminations.A raw material grinder (4) reduces the rawmaterial to a uniform particle size for h<strong>and</strong>ling<strong>and</strong> improved heat transfer in the cookingstep. The ground raw material is fed at acontrolled rate from a metering bin (5) into acontinuous cooker (6).The discharge is transported to a drainerconveyor (7). The drainer conveyor separatesthe liquid fat from the solids, which are thenconveyed from the drainer conveyor by adischarge conveyor (8).In the discharge conveyor, the solids fromthe drainer conveyor are combined with thesolids discharged from the settling tank (10)<strong>and</strong> from the decanter-type centrifuge (11).The solids from the discharge conveyorgo to the screw presses (9), which reduce thefat content of the solids to 10 to 12 percent.The solids that bypass the screw presses in theform of pressed cake go to the pressed cakeconveyor for further processing into meal.The fat removed in the screw presses goesto the pressed fat conveyor (12), which separatesthe large particles from the liquid fat <strong>and</strong>returns them to the discharge conveyor. Thefat from the pressed fat conveyor is pumpedto the settling tank (10). Fat discharged fromthe drainer conveyor (7) goes into the settlingtank (10).In the settling tank, the heavier bone <strong>and</strong>protein particles settle to the bottom, wherethey are discharged by the screw conveyor(not shown) into the discharge conveyor (8).Liquid fat from the settling tank is pumped215