An evaporator is used to evaporate a volatile solvent, usually water, from a solution. Its purpose is to concentrate non-volatile solutes such as organic compounds, inorganic salts, acids or bases. Typical solutes include phosphoric acid, caustic soda, sodium chloride, sodium sulphate, gelatine, syrups, Kraft liquors 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, elutriating legs, filters or centrifuges. Examples of precipitates are sodium chloride, sodium sulphate, sodium carbonate and calcium sulphate. 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. The relatively pure condensed water vapour from many evaporators is recovered for boiler feed makeup, salt washing, salt dissolving, pump seals, instrument purges, equipment and pipeline washing and other uses.