An evaporator is used to evaporate a volatile solvent, usually water, from a solution. Its purpose is to concentrate non-volatiles solutes such as organic compounds, inorganic salts, acids and bases. Typical solutes include phosphoric acid, caustic soda, sodium chloride, sodium sulfate, gelatin, syrups and urea.

In many applications, evaporation results in the precipitation of solutes in the form of crystals, which are usually separated from the solution with cyclones, settlers, wash columns, elutriation legs or centrifuges. Examples of precipitates are sodium chloride, sodium sulfate, sodium carbonate and calcium sulfate. The desired product can be the concentrated solution, the precipitated solids, or both.

In some applications, the evaporator is used primarily to recover a solvent, such as potable water from saline water. In any case, the relatively pure condensed water vapor from many evaporators is recovered for boiler feed makeup, salt washing, salt dissolving, pump seals, instrument purges, equipment washing, line washing and other uses.

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