Design and Analysis of Multi-Effect Mvr Systems Dealing with Solutions of High Boiling Point Elevation

Abstract

The thermal-based multi effect MVR evaporation system is an effective technical method to reduce the cost of wastewater treatment systems that can realize zero liquid discharge (ZLD). A single-effect and the other four multi-effect MVR systems with only one steam compressor are designed. A superheat eliminator is added at the suction line of the compressor of each system. Additional fresh steam is supplied for the operation of multi-effect MVR systems. Models of each MVR system is established suing Aspen Plus software and the model of single-effect MVR system is verified with reported data. The calcium chloride solution is taken an example of solutions of high boiling point elevation. Performance of the five MVR systems are simulated. On the base of simulation results, the energy analysis, economic analysis, exergy analysis and the thermodynamic efficiency analysis were carried out. It is concluded that the single-effect MVR system has the highest operating cost, but its gained output ratio (GOR MVR ) is the biggest. Smaller heat transfer temperature difference in each evaporator results in less energy consumption and higher exergy efficiency of all MVR systems. As the operating cost of the four multi-effect MVR are very close, two-effect MVR system is a preferable selection. The multi-effect MVR system combined with new energy devices will be the design optimization direction of the thermal-based ZLD technology in the future.

Keywords: multi-effect, mechanical vapor recompression (MVR), boiling point elevation (BPE), gained output ratio (GOR）