Thermodynamic Analysis And Optimization Of Single Effect Mechanical Vapor Compression Seawater Desalination System(SEMVC)

Desalination technology is generated to solve the problem of shortage of freshwater resources and water pollution in the world.Although the technology has existed about two centuries,it has been valued by scientists both domestic and overseas.There are many methods of desalination technology,including distillation,crystallization and membrane.The technique of mechanical vapor compression distillation(MVC)is a kind of thermodynamic distillation,which is a kind of seawater desalination technology which only uses mechanical energy.This paper analyzes the current status and development trend of MVC,mainly studies the thermal performance of the system.Based on the first law of thermodynamics,a mathematical model is established to obtain the reasonable operation parameters of SEMVC.The effects of compression ratio,entropy efficiency,evaporation temperature of seawater and heat transfer temperature difference of evaporation and condensation process on system performance are discussed respectively,and the economy of the system is analyzed.The results show that the lower the compressor compression ratio,the higher the entropy efficiency and the lower the evaporation temperature can lead to the lower power consumption and the higher recovery rate of the system,and the influence of evaporation temperature is small when it range from 60? to 110?.Synthetically analyzing,the system running well when evaporating temperature in 85-95?,compression ratio control from 1.1 to 1.3,heat transfer temperature difference of 2-5?,water production of energy consumption in 9-12 kWh/m3.And a set of system design parameters are selected according to the analysis results.Exergy analysis mathematical model was established by the second law of thermodynamics.Combined with the data of parameters,discussed the compression ratio,entropy efficiency and evaporation temperature on the system efficiency of exergy utilization.The difference of thermal analysis and exergy analysis were discussed.Results show that the exergy efficiency of desalination process is 4.8%.Exergy loss mainly concentrated in the evaporator-condenser and the compressor,exergy loss coefficient of preheater and pump is small.The lower compression ratio,the higher entropy efficiency of compressor and the lower evaporation temperature can lead to the higher system exergy efficiency.The SEMVC plant can recycle waste heat fully and has high thermal efficiency,but the exergy efficiency of this technology is low.It's a breakthrough direction to improve the heat transfer performance by using high performance low pressure ratio of the compressor and choosing an appropriate evaporating temperature from the point of exergy loss.Finally,the equation of system performance is fitted,and the empirical evidence fitting equation of performance has certain accuracy and reference value.