Evaporation is one of the modern chemical unit operations, that is to vaporize and remove part of the solvent in the solution by heating to improve the concentration of the solution or create conditions for solute precipitation. Three-effect evaporator desalting method is a method to remove the inorganic salt in the waste liquid by evaporation using the concentration crystallization system.

Three-effect evaporator is composed of three evaporators connected in series. The low-temperature (about 90 ℃) heating steam is introduced into the first effect, and the waste liquid is heated. The generated steam is introduced into the second effect as the heating steam, so that the waste liquid in the second effect evaporates at a lower temperature than the first effect. This process is repeated until the last effect. The first effect condensate is returned to the heat source, and the other effect condensate is collected and output as desalinated water. One part of steam input can evaporate multiple times of water.

At the same time, the high-salt wastewater is concentrated from the first effect to the last effect in turn, and crystallized after reaching supersaturation at the last effect, thus realizing the solid-liquid separation of salt and wastewater.

During the treatment process of saline wastewater, the saline wastewater enters the three-effect concentration crystallization device, and is separated into desalinated water (desalinated water may contain trace low boiling point organics) and concentrated slurry waste liquid through the concentration crystallization process of three-effect evaporation condensation; Inorganic salts and some organic substances can be separated by crystallization and incinerated into inorganic salt waste residue; The concentrated waste liquid of non-crystalline organic matter can be treated by using drum evaporator to form solid waste residue and incinerate it; The desalinated water can be returned to the production system to replace the softened water for use.

Three-effect evaporator desalination method has the advantages of mature technology, wide range of wastewater treatment, small floor area, fast treatment speed, energy saving, etc. With the development of chemical industry, more and more high-salinity wastewater needs to be treated, and the application of three-effect evaporator desalination method will be more and more extensive.