Evaporators are classified into three types based on operating pressure: atmospheric pressure, pressurization, and depressurization. According to the motion of the solution in the evaporator, there are: ① circulation type. Boiling solution passes through the heating surface multiple times in the heating chamber, such as central circulation tube type, suspended basket type, external heating type, Levin type, and forced circulation type. ② One way type. Boiling solution passes through the heating surface in the heating chamber without circulating, and the concentrated solution is discharged immediately, such as rising film, falling film, stirring film, and centrifugal film. ③ Direct contact type. Heating medium and solution directly contact for heat transfer, such as immersion combustion evaporator. During the operation of the evaporation device, a large amount of heating steam is consumed. To save heating steam, multi effect evaporation devices and steam recompression evaporators can be used. Evaporators are widely used in chemical, light industry and other sectors.