Large quantities of hot water in the 130 to 140°F range are required for
scalding and plant cleanup. Waste energy is theoretically available from these
processes at about 120°F. In practice, much of it is usually inaccessible (i.e.,
entering multiple drains and contaminated with grease and other suspended
organic solids). Cooking or rendering is usually carried out at higher temperatures
up to about 250°F via steam heating, which can be reduced by recovering waste
heat in the vapors. (Please see Compression Heat Recovery for detail.)
A common and clean waste heat source is the energy rejected from the refrigerant compressor's discharge gas in the plant refrigeration system. Boiler feedwater or makeup water heating is usually the best heat use since relatively little condensate is returned.
In hog processes, waste heat is also available from the singeing exhaust and the inedible rendering process vapor. Modern plants typically recover the singeing exhaust energy via heat exchange.
Other energy cost reduction opportunities include:
