The simplified flow diagram shows how multiple effect vapor compression distillation works. Feed enters the plant and is split into two streams. One stream enters the brine heat exchanger (Brine HX) where it is heated by cooling the hot brine leaving the plant. The other stream enters the distillate heat exchanger (Distillate HX) where it is heated by cooling the hot distillate leaving the plant. The pre-heated feed streams are then joined back into one stream and enter the first effect of the evaporator. Here, part of the feed is evaporated and the balance is pumped from the first effect and enters the second effect. Here again, part of the feed is evaporated and balance is pumped from the second effect and enters the third effect. This process is repeated until the fifth effect where the brine is taken out, cooled in the brine heat exchanger, and discharged from the plant. The vapor generated in the first effect flows in to the second effect and condenses on the cooler heat transfer surface there and is taken out as distillate. The heat released in condensing the vapor in the second effect is transferred across the heat transfer surface (slanted line) and causes the evaporation of the equivalent amount of water from the feed in the second effect. This process is repeated in the third, fourth, and fifth effects to produce distillate streams from each effect. The vapor generated in the fifth effect is taken out, compressed to raise its saturation pressure and temperature, and is then introduced to the condensing side of the first effect where it condenses on the heat transfer surface and is withdrawn as distillate. The condensate streams from each of the five effects are combined, then cooled in the distillate cooler and taken out of the plant.
Key points about vapor compression distillation systems:
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Overall heat transfer coefficient of the WFRD evaporator