Recompression staged evaporation system

A method and system for recapturing and utilizing low grade energy in the form of low pressure vapors generated in an industrial evaporation process. A prime mover drives a screw compressor and concurrently provides heat at several levels which is utilized in a staged evaporation system in accordance with the requirements of the stages of the system. The screw compressor recompresses the contaminated vapors to a pressure and temperature sufficient to evaporate the major fraction of moisture to be removed in the industrial evaporation process.

What is claimed is:

1. For use in combination with a rendering cooker having a plurality of stages and a hollow central shaft passing through selected stages of said plurality of stages, a system for upgrading and re-using low grade, contaminated steam generated by said cooker in evaporating water from raw materials comprising:

a screw compressor connected to said cooker and operable to compress low grade contaminated steam received from at least one of said selected stages to a relatively high pressure and temperature;

fluid jackets surrounding said selected stages of the cooker;

means for passing steam received from said screw compressor serially through said central shaft and at least some of said fluid jackets to heat said raw materials and to purge non-condensable gases from said central shaft;

a prime mover connected to, and operable to drive, said screw compressor;

means for producing hot water or steam from energy in the exhaust gases of said prime mover; and

means for delivering said hot water or steam to at least one of said fluid jackets.

2. A method of utilizing energy efficiently in a cooker of a rendering system in which steam is used to heat raw materials to remove moisture from said materials comprising:

in a screw compressor, compressing low grade, contaminated steam liberated in the heating of raw materials in said cooker to produce steam of relatively high pressure and temperature;

passing said steam of relatively high pressure and temperature through a hollow central shaft of said cooker and then through a first fluid jacket surrounding a first portion of said cooker to heat said raw materials and to sweep non-condensible gases out of said shaft;

generating hot water or additional steam by heat exchange with exhaust gases of an engine drivably connected to said screw compressor, said hot water or additional steam having a higher temperture than the steam output of said screw compressor; and

directing said hot water or additional steam to a second fluid jacket surrounding a second portion of said cooker to further heat and remove moisture from said raw materials.

3. A system as defined in claim 1 wherein said prime mover is a gas engine.

4. A system as defined in claim 1 wherein said prime mover includes cooling apparatus through whcih coolant flows, and said system further includes means for transferring heat from said coolant to one of said stages.

5. A system as defined in claim 1 including means connected between the inlet of said screw compressor and at least one of said selected stages for removing a portion of the solid particulates from low grade steam passing to said screw compressor and returning said removed particulates to said cooker.

6. A system as defined in claim 1 wherein said selected stages comprise a first evaporation stage for receiving steam of relatively high pressure and temperature from said screw compressor, and a second evaporation stage for receiving steam or hot water produced from energy in the exhaust gases of said prime mover, said second evaporation stage operable at a higher temperature than said first evaporation stage.

7. A method as defined in claim 2 further including recoverng heat from a coolant in said engine and using said recovered heat to preheat said raw materials.