Compression evaporation Thermocompression

Thermocompression Evaporators Thermocompression-evap-orator calculations [Pridgeon, Chem. Metall. Eng., 28, 1109 (1923) Peter, Chimin Switzerland), 3, II4 (1949) Petzold, Chem. Ing. Tech., 22, 147 (1950) and Weimer, Dolf, and Austin, Chem. Eng. Prog., 76(11), 78 (1980)] are much the same as single-effect calculations with the added comphcation that the heat suppied to the evaporator from compressed vapor and other sources must exactly balance the heat requirements. Some knowledge of compressor efficiency is also required. Large axial-flow machines on the order of 236-mVs (500,000-ftVmin) capacity may have efficiencies of 80 to 85 percent. Efficiency drops to about 75 percent for a I4-mVs (30,000-ftVmin) centrifugal compressor. Steam-jet compressors have thermodynamic efficiencies on the order of only 25 to 30 percent. 

It is impossible to arrive at generalized guidelines at the present time regarding the technoeconomics of steam compression by thermocompression (e.g., steam jet ejectors) versus mechanical recompression for steam-drying plants. The costs of installation of such systems are such that they should be considered only for large-scale continuous steam dryers, that is, those with evaporation capacities of 100 ton/day or higher. The steam compressors for such service are expected to cost over 500,000 (1990 estimate for North America). To this cost, one must add the costs of spares and maintenance. 

Seawater or brackish water is used for process applications or as potable water when fresh water is scarce. Six techniques are used for desalination. Five are evaporation processes multiple-effect thermocompression mechanical vapor compression once-through multistage flash and multistage flash with brine recirculation. The sixth process, reverse osmosis, uses membrane technology for desalination. 

Maintenance requirements could be listed in the following order, from lowest to highest maintenance thermocompression once-through multistage flash multistage flash with brine recirculation reverse osmosis multiple-effect evaporation mechanical vapor compression. Several factors are important ... 

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