It is very important to choose different evaporator forms and evaporation processes

　　The evaporator forms include the film rising evaporator, falling film evaporator, natural circulation evaporator, forced circulation evaporator, scraper film evaporator, etc. when selecting, the evaporator can be determined according to the characteristics of different materials and the characteristics of various evaporators. The evaporator should be well matched, that is, to reduce the one-time investment and reduce the operating cost to a lower level, which is the choice of evaporation process. If multi-effect evaporator is used, membrane evaporator with low operating cost and low investment is selected as far as possible in process design, so as to minimize the use of natural circulation evaporator and forced circulation evaporator.

　　But in the process of evaporation crystallization, forced circulation evaporator is the evaporator form which must be selected. If the multi effect evaporator is used as far as possible, the four effect evaporator or three effect evaporator will be used. If the five effect or more effect is adopted, the one-time investment will increase a lot, but the operation cost is limited. Single or double effect is adopted, and one-time investment is less, but the operation cost will be very high.

　　When MVR evaporator is used, single stage or multi-stage can be considered. In the evaporation of salt containing wastewater, if the salt content of the material is low, in order to reduce the operation cost, the first stage can be considered to adopt membrane evaporation. For example, the falling film evaporator is adopted, and the forced circulation evaporator can be used for the second stage. This can greatly reduce the operating cost. For evaporation of some materials, the boiling point increases lower when the concentration is low and the boiling point is higher when the concentration is high. At this time, the combination of MVR evaporator and multi effect evaporator can be considered.