Design And Research Of Multi-effect MVR System For High Salt Wastewater

With the rapid development of industry in China,a large amount of complex high-salt wastewater is discharged into the environment.If these high-salt wastewater cannot be properly treated,it will cause serious pollution to the existing water resources,and exacerbate the crisis of water scarcity.To solve the problem of industrial wastewater pollution and achieve sustainable economic development,zero liquid discharge(ZLD)is considered the best solution.However,the application of ZLD is limited by the high energy consumption and cost of solution concentration.In order to reduce the cost of ZLD process,this thesis combines the energy-saving advantages of multiple-effect evaporation(MEE)and mechanical vapor recompression(MVR)technology,fully considers the impact of boiling point elevation(BPE)of high-salt wastewater on energy consumption,proposes a multiple-effect MVR system scheme with a superheated eliminator,and designs a new two-effect split-flow MVR system.In this thesis,Aspen Plus software is used to simulate the performance and variable operating conditions of each multiple-effect MVR system,and the main research contents are as follows:(1)Using the physical property calculation method,the temperature rise characteristics of different high-salt wastewater are analyzed,and considering the technical characteristics of the steam compressor,a multiple-effect MVR system scheme with a superheated eliminator added to the suction port of the compressor is proposed,and one to five-effect MVR systems are designed.(2)The simulation models of each system are established using Aspen Plus software,and the simulation models are validated using experimental data from literature reports to prove the accuracy and reliability of the simulation models in this thesis.(3)Using the simulation research method,the energy consumption,operating costs,exergy destruction,thermal efficiency,and other aspects of multiple-effect MVR systems are analyzed under different BPE solutions,aiming at analyze the influence of BPE and the number of evaporators on system performance.(4)For the two-effect MVR system with the most market application potential,a new type of two-effect MVR system based on the technical characteristics of mature compressors in the existing market is proposed,and theoretical research and analysis are carried out.The results show that adding a superheated eliminator to the suction port of the compressor can effectively reduce the power consumption of the compressor.The exergy destruction analysis of the multiple-effect MVR system shows that the evaporator is the largest exergy destruction equipment.When the target concentration is less than 25%,the one-effect MVR system is the best choice for treating low BPE industrial wastewater.when the target concentration is more than 25%,the three-effect MVR system is the best choice for treating low BPE industrial wastewater from the perspective of power saving.Two-effect MVR system is recommended for the treatment of industrial wastewater with high BPE.The two-effect split-flow MVR system has the lowest compressor power,but it has the highest fresh steam consumption.The fresh steam has great influence on the gained output ratio(GOR)of the system.The GOR of the MVR system with high BPE calcium chloride solution is 18.9 when fresh steam is supplied by heat pump,which is 6.4 higher than that provided by boiler.With the development of steam generator technology such as solar energy and high temperature heat pump,the thermal performance advantage of multi-effect MVR system will become more apparent.