The evaporation operation is to separate part of the solvent from the solution, and the amount of solute in the solution remains unchanged. Therefore, evaporation is a heat transfer process, and the heat transfer rate is the controlling factor of the evaporation process. The equipment used for evaporation belongs to heat exchange equipment. However, compared with the general heat transfer process, the evaporation process has its own characteristics, mainly in: ( 1 ) The boiling point of the solution rises : the material to be evaporated is a solution containing non-volatile solutes, as can be seen from Raoult’s law , At the same temperature, the vapor pressure of the solution is lower than that of the pure solvent. ( 2 ) Process characteristics of materials During the evaporation process, some properties of the solution change with the concentration of the solution. ( 3 ) Energy utilization and recovery : a large amount of heating steam is consumed during evaporation, and a large amount of secondary steam is generated by the vaporization of the solution .

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