Introduction

With the development of the chemical, pharmaceutical, papermaking and other industries, high-concentration refractory wastewater has always been a difficulty in wastewater treatment. The use of evaporation technology to treat high-concentration wastewater mainly uses the boiling point difference between water (solvent) and pollutants (solute), and the process of separating the solvent from the solute by controlling the surface or internal gasification of the wastewater at a certain temperature and pressure . After evaporation, pollutants with high boiling points are left in the evaporation residue, while water with low boiling points is discharged as a condensate. According to the principle of evaporation, only when the difference between the boiling point of the pollutant and the water is large, the separation effect will be better. Otherwise, the pollutants will evaporate directly and become part of the condensate, or azeotrope with water and enter the condensate, which will cause the COD of the effluent to rise. Therefore, a suitable condensate treatment process must be adopted for specific wastewater to make the effluent of the sewage treatment system meet the requirements.

At present, the evaporation equipment used in wastewater treatment includes multi-effect evaporator and mechanical compression evaporator.

Multi-effect evaporation principle

        In industrial production, in order to reduce heating steam consumption, multi-effect evaporation can be used. Multi-effect evaporation connects multiple sets of evaporators in series, except that the first-effect evaporation uses fresh steam from the plant area as the heat source, and each subsequent effect evaporation uses the secondary steam generated by the previous stage as the heat source for heating. Therefore, the multi-effect evaporation is significantly reduced The consumption of heating steam is reduced. In addition, except for the last-effect evaporator, the secondary steam generated by each stage of evaporation will be discharged as condensed water after being used as a heat source in the heating chamber of the subsequent stage, thereby greatly reducing the consumption of cooling water.