This is a fully welded plate heat exchanger, a staged cooling device. It consists of three fully welded plate heat exchangers connected in series. The refrigerant, circulating water and ethylene glycol in each pipeline are used to cool the mixed solvent of dichloromethane in sections. The plate material is AISI 316L, without gasket. Three-stage heat exchange is a common form of heat exchange in the chemical industry and is the best solution for waste heat recovery.