Simulation And Performance Analysis Of Mechanical Vapor Recompression Evaporation And Crystallization System

Waste water is the result of population growth,industrial social development and fossil fuel exploitation The most chal enging problem in the world today is a large amount of highly concentrated wastewater that is extremely difficult to deal with.The high salinity of inorganic salt wastewater causes water pollution and makes soil degrade it difficultly.How to reduce its energy consumption,high efficiency and reach zero emission treatment requirements is the focus of current research.Mechanical vapor recompression technology（MVR）is currently considered to be one of the most efficient energy-saving technologies.At present,it has been applied to food industry,pharmaceutical industr y（amino acid concentration）,beverage industry（milk concentration）,wastewater treatment industry（organic wastewater,inorganic wastewater）,chemical engineering and other fields.The principle is that the secondary steam separated by the gas-liquid separator is adiabatica lly compressed by the compressor,so that the temperature of the secondary steam,the pressure rises,and the enthalpy value increases.Heating the solution in the evaporator tube as a heat source.Secondary steam condense into water.This paper is aimed at the characteristics that the solubility of sodium chloride wastewater does not change significantly with temperature.This paper design a treatment process based on mechanical vapor recompression technology.The chemical process simulation software（Advanced System for Process Engineering,Abbreviation Aspen Plus）is used to simulate the thermal performance of MVR system,which provides a theoretical gist for zero-emission of high-concentra t io n wastewater.First,using the chemical process simulation software Aspen Plus,The amount of sodium chloride treated is W=500kg/h,the raw material liquid mass fractionX₀=10%,the complete liquid mass fraction is X₁=20%,the evaporation temperature is 70°C,the heating steam temperature is 200°C.Compression ratio is 1.8.Amount of crystallization is 20.1kg/h as the original condition.Comparing the energy saving and economy between mechanica l vapor recompression evaporation crystal ization technology and low temperature three-effect evaporation crystal ization technology,it is proved that the MVR evaporation crystal ization technology is more advantageous than the low temperature three-effect evaporation crystal ization technology.Finally,By using the first-stage discharge concentration,evaporation temperature and compression ratio as independent variables,the evaporation water quantity,compressor power consumption,coefficient of performance,heat transfer temperature difference,and heat exchange area as the system performance indexes.Through analysis,it is concluded that as the first-stage discharge concentratio n increases,the amount of evaporated water increases,the power consumption of the compressor gradually increases,the heat exchange area of the first-stage evaporator gradually increases,and the heat exchange area of the secondary evaporator gradually decreases,but the total heat exchange area increases and the coefficient of performance（COP）remains basically unchanged.When the evaporation temperature increases,the amount of evaporated water increases linearly,the heat transfer temperature differe nce gradually increases,the power consumption of the compressor increases slightly,and coefficient of performance（COP）gradually decreases.When the compression ratio increases,the amount of evaporated water does not change,the heat transfer temperature differe nce increases linearly,the theoretical power consumption of the compressor increases linear ly,and total heat exchange area and heat exchange area of the primary and secondary evaporators gradually decrease,and coefficient of performance（COP）decrease exponentially.Low compression ratio and low evaporation temperature are beneficia to system energy saving.The lower the first-stage discharge concentration is beneficial to reduce costs.Through system optimization,the annual operating cost of the system is minimized when the evaporation temperature is 75°C and the compression ratio is 2.1.Considering the complexity of the industrial process,the compression ratio is increased by0.1 to the left and right,and the compression ratio of the system is preferably between 2.0and 2.2.Finally,the high-concentration wastewater is separated into solid salt and mother liquor by a crystallizer and a centrifuge.The salt removal rate of the solid salt reaches 100%,and the wastewater discharge amount is 0,which reachs the zero discharge requirement of the high-concentration wastewater.