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<br />.... <br />co <br />-l <br />o <br /> <br />VI VAPOR COMPRESSION-VERTICAL TUBE EVAPORATOR- <br />MULTISTAGE FLASH PROCESS <br /> <br />Vapor compression (VC) distillation is a well established desalting <br /> <br />process that is particularly applicable to requirements for compact, low <br /> <br />capacity desalting plants. It has been used extensively for small capacity <br />marine applications and for several land-based desalters in the range of <br /> <br />20,000 to 1 mgd. <br /> <br />In its simplest form, the process consists of a single effect <br />vertical tube evaporator with brine boiling inside the tubes or flashing <br />above the tubes. The steam produced is pressurized and heated with a <br /> <br />mechanical compressor, then condensed on the outside of the vertical <br /> <br />tubes, thereby boiling more brine and producing desalted product water. <br /> <br />Most of the energy required by the process is used in the vapor <br /> <br />compressor, and only a small amount of additional heat is required to <br /> <br />offset losses from the equipment. Thus, the key economic factors in <br /> <br />the p~ocess are the vapor compressor driver and the cost of its required <br /> <br />fuel. <br /> <br />The process efficiency can be increased by adding more evaporator <br /> <br />effects, increasing the brine temperature or flow rate, improving process <br />waste heat recovery, and recovering heat from the brine blowdown and <br /> <br />product water s:treams. There are, of course, cost and physical limita- <br /> <br />tions on each of these process variables, and an economic balance must <br /> <br />be made for the lowest water cost, <br /> <br />Recent conceptual changes originally made in the VTE and the MSF <br />28 29 . <br />processes' have been app11ed to the VC process and have greatly <br /> <br />improved it. It has been proposed that the improved heat transfer <br /> <br />41 <br /> <br />.c,,,, <br /> <br /> <br />,'~ <br /> <br />\- <br />