Rendering is the breaking down of animal cells by mechanical and thermal
action, permitting the separation of raw fat from cellular material. Animal scraps
are rendered to produce oil, grease, tallow, and meal. Rendering is the most
energy-intensive operation in the entire meat processing industry.
Rendering operations, as typically practiced, involve processing poultry or animal by-products and converting them to tallow or meal. The tallow is used by the chemical industry in the manufacture of fatty acids and other chemicals used in the soap industry. Edible meal, on the other hand, is recycled back to the birds or animals as part of their nutritional diet.
Each raw material - whether it is beef, poultry, fish, etc. - contains a high percentage of moisture and requires slightly different processing. In general, an indirectly heated cooker is used to heat the raw material to evaporate the water. In most cases, clean boiler steam at up to 125 psig is used as the heat input to the cookers. Cookers may be either batch-operated or continuously operated; most new cookers are of the continuous type.
The recovery of contaminated waste vapor from a continuous rendering cooker is a good application for the open cycle heat pump.
