Compression heat recovery, also called vapor recompression, reuses vapors by raising their pressure and corresponding condensing temperatures. An evaporator operating at 140°F with 160°F steam condensation and a 20°F BPE need only raise the saturation pressure of the 140°F vapors (120°F due to the 20°F BPE) to 160°F. This amounts to a compression from 1.69 psia to 4.74 psia.
Where this compression ratio is less than about 2.4 to 1, mechanical
compression using electric motor driven compressors can be very economical. This is
called Mechanical Vapor Recompression (MVR).
Always consider mechanical vapor recompression in a new, pre-evaporator as
well, since much of the solvent can be removed before the BPE has risen very much.
Where the compression ratio is greater than about 4 to 1, steam jet (or thermocompressor) systems may be a better choice. This is usually referred to as Thermal Vapor Recompression.
These comparisons require significant experience and judgment. It's wise to consult manufacturers and process design professionals and to carefully review the site's energy and environmental issues.
