Evaporation is a unit operation for solution concentration. By heating, the non-volatile components of the solution are boiled, causing a portion of the solute to vaporize and thus concentrating the solution.

All solutions evaporate in the evaporator, with the secondary steam generated not being reused; the solution does not pass through a second evaporator for concentration, meaning a single evaporator can complete the evaporation process, known as single-effect evaporation. The secondary steam produced in single-effect evaporation is not used for further material evaporation; it is simply removed during evaporation and not utilized. For single-effect evaporation, after issuing production orders and determining operating conditions, it is typically necessary to calculate the water evaporation volume, steam consumption, and heat transfer area of the evaporator.