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Feed
Vapors
Steam
Product
Figure 13.3 Forced falling film evaporator.
Various systems for using these commercially available evaporators have
been developed to minimize energy consumption. Three of the most com-
monly used evaporation systems are:
• The multiple effect evaporation plant (MEE) plant.
• The MEE plant using a thermal vapor recompression (TVR) system
• Evaporation with mechanical vapor recompression (MVR).
Key aspects of these three evaporation systems are outlined in the following
sub-sections.
13.3.2 Multiple Effect Evaporation
Multiple effect evaporation, or MEE, involves structured sequencing of the
evaporators, with the number of evaporators or effects commonly restricted
to four, unless another specific design is required. The salient features are:
• A multiple effect evaporator is an apparatus that efficiently uses the heat
from steam to evaporate water.
• In a multiple effect evaporator, water is boiled in a sequence of vessels,
each of which is at a lower pressure than the last.
• As the boiling point of the water decreases with pressure, the vapor pro-
duced in one vessel can be used to heat the next vessel.
• Only the first vessel requires a source of external heat.
