EVAPORATION, in the chemical industry, consists in con verting a liquid into a vapour in order to remove it from solids dissolved in it. While in some instances this can be done in open kettles, it is customary to use closed units called evaporators, which may be single, duplex, triple or quadruple in assembly. When so grouped, they are known as "effects." Thus, a "triple effect" evaporator is common in the sugar industry, being used to concentrate syrup by the removal of water. Evaporators enable work to be done under partial vacuum, which both in creases the quantity of water that can be eliminated per pound of fuel used and also permits lower temperatures to be employed, the latter being important in handling some types of material. By maintaining a higher vacuum on each succeeding effect, the hot vapours from the preceding may be used to assist in heating the next effect in the series. Evaporators are of many types as to material employed in construction, means for increasing circu lation of the liquid being evaporated and means for discharging crystals drawn out of solution. The size is also variable, one of the largest in operation being some 3o ft. in diameter.
Some evaporators are continuous and others operate on the batch system. The "sugar pan" of the refinery, a single, large evaporator, is usually of the batch type, and in it the "sugar boiler" manipulates syrups of various concentrations to produce crystals of the desired size in the final stages of concentrating sugar from syrups of various origins.