Study on multi-effect mechanical vapor recompression systems used for the concentration of industrial high salt wastewater

Multi-effect mechanical vapor recompression (MVR) system is an effective technology for con-centrating industrial high-salt wastewater that has high boiling point elevation (BPE). To mini-mize the technical requirements of steam compressor, a superheat eliminator is incorporated in the multi-effect MVR system. By employing the Aspen Plus software, simulations are conducted to evaluate the performance of the modified single-effect to five-effect MVR systems in concentrat-ing calcium chloride solute from 5% to 30%. With the simulation results, impact of the number of evaporators and heat transfer temperature difference, along with the benefit of superheat elimina-tor are analyzed. This analysis aims to guide the optimal design of a multi-effect MVR device. It is concluded that the heat transfer temperature difference should not be higher than 9 degrees C for sys-tems with more than three evaporators. The addition of evaporators leads to higher pressure ratio of the compressor and increased consumption of fresh steam. The operation costs of two-effect system and three-effect system are similar. Furthermore, the benefit derived from the superheat eliminator, in terms of power and suction volume reduction, become more pronounced as the BPE increases. Incorporating energy-efficient devices for fresh steam generation can further facilitate the utilization of multi-effect MVR systems for high-salt wastewater concentration.