Thermal Performance Analysis And Optimization Of Multiple Effect Evaporation System

The principle of multiple effect evaporation(MEE)is to set multiple evaporators in the system,and the secondary steam generated in the evaporation process is reused as the heat source of the next evaporator to achieve the purpose of energy saving optimization.Multiple effect evaporation system has a wide range of applications in the preparation of pharmaceutical injection water,black liquid concentration and seawater desalination.Analyzing the thermal process of multiple effect evaporation can optimize the system structure and reduce energy consumption.At present,the research model of multiple effect evaporation system for preparation of injection water belongs to a relatively simple general model,which lacks the analysis of energy loss in the thermal process.In order to solve the problem of high energy consumption in the water production process of the multiple effect evaporation system for the preparation of injection water,the system modeling and thermal process optimization methods are studied in this paper.The main research contents are as follows :1.Based on mass balance,energy balance and heat transfer equation,the thermodynamic process model of multiple effect evaporation system for preparing injection water was established.The mathematical model of MEE system was programmed and simulated by using Matlab/Simulink module.By comparing the simulation results with the data collected by the operation of the multiple effect evaporation system engineering application equipment,the maximum error of the thermodynamic performance index is 6.71%,which verified the validity of the model.2.Matlab/Simulink module was used to simulate the thermal process of MEE system.The effects of industrial steam temperature,effects and preheating mode on the thermal performance of MEE system were analyzed,and the thermal loss caused by steam flow resistance was discussed.The research results show that : In view of the insufficient energy utilization of the final secondary steam in the multiple effect evaporation system applied in the current project,the thermal performance of the multiple effect evaporation system can be improved by using the mixed preheating method when the total number of effects is from five to ten,and it reaches the optimal value when the total number of effects is eight,and the gained output ratio(GOR)increases by 36.3%.Through the analysis of the steam flow resistance loss in the system,it is found that the steam resistance loss mainly occurs in the last two effects of the system.Reducing the secondary steam of the last two effects of the multiple effect evaporation system can effectively improve the energy utilization rate of the system.3.The experimental platform of three-effect evaporation system was designed and built to analyze the influence of thermal vapor compression(TVC)on the thermodynamic performance and water production economy of multiple effect evaporation system.Through the comparative test,it is found that the GOR and exergy efficiency of multiple effect evaporation system are increased by 26.7% and21% respectively by using TVC technology at the end effect secondary steam.Under the condition of the same water production,service time and equipment service life,the economic analysis of the experimental device is carried out.After the TVC technology is used,the total cost of water production in the system decreased by 6%.4.The thermal process of the multiple effect evaporation with thermal vapor compressor(MEE-TVC)system was further studied by using the Matlab/Simulink module,and the influence of the position of the steam ejector heat pump on the thermal performance of the system was discussed,and the multiple objective optimization of the six-effect MEE-TVC system was carried out.The results show that TVC technology can improve the thermodynamic performance of multiple effect evaporation system.In the six-effect MEE-TVC system,the GOR,thermal efficiency and exergy efficiency of the system increase first and then decrease with the position of the steam jet heat pump moving backward.Multiple objective optimization is carried out for the GOR,exergy efficiency and unit water production cost of the six-effect MEE-TVC system.Compared with the initial scheme,the unit water production cost of the optimized scheme decreases by 7%,and the GOR and exergy efficiency increase by 5.4% and 5.8%.It can be seen that the optimization method adopted in this paper can reduce the water production cost of the multiple effect evaporation system and improve the energy utilization rate of its thermal process,which has reference significance for the optimization design of the multiple effect evaporation system for injection water.