Product Description

A typical feeding method of multi-effect evaporators is forward feed, where both feed and steam are introduced in the first effect and the feed passed from effect to effect parallel to the vapor from the earlier effect. Feeding the steam results in the formation of a small amount of water vapor, which is used to heat the second effect. The vapor releases its latent heat and condense. The released latent heat would result in the formation of a smaller amount of vapor in the second effect. This process is repeated in subsequent effects, until the vapor temperature becomes close to the feed sea water temperature.

The forward configuration requires a pump for feeding of the dilute feed to the first effect. Since a vacuum usually maintained on the last effect, the liquid from one effect to the next effect could be transferred without a pump as the flow occurs in the direction of decreasing pressure. However, a pump is required to remove the concentrated product from the last effect. Forward feeding operation is helpful when the thick liquor or concentrated product may degenerate if exposed to high temperature.

Another feeding method in the multi-effect evaporators is called backward feed configuration. In this type of MEE, heating steam is fed to the first effect whereas feed enters at the last effect, i.e., the coldest effect and is pumped through the successive effects. The backward feeding requires a pump between each pair of effects to transfer liquid from lower pressure effects to higher pressure effects. Backward feed is commonly used when products are viscous and exposure to higher temperature increases the rate of heat transfer due to reduction in viscosity of the liquid.