Simulation Optimization And Experimental Study On Performance Of MVR System For High Salinity Wastewater

High salinity wastewater has the characteristics of large discharge,wide source,high salt content,complex composition,etc.Direct discharge will cause soil hardening,water eutrophication,and even threaten human life.How to treat high salinity wastewater with low energy consumption and high efficiency,and realize zero discharge and resource utilization,is a subject worthy of study.Mechanical Vapor Recompression（MVR）technology uses its unique secondary vapour recompression to achieve a continuous cycle of material evaporation,and is one of the most energy efficient evaporation processing technologies available.The thesis proposes a fractional crystallisation process of mechanical vapour recompression-evaporative crystallisation+cooling crystallisation to recover industrial grade Na Cl and Na2SO4 crystalline salts from wastewater,based on the characteristics of MVR technology to recover and utilise secondary potential;uses chemical process simulation software（Aspen Plus）to simulate and analyse the performance of the MVR fractional crystallisation system;builds a pilot plant platform to simulate industrial high-salt wastewater for testing to explore new ways of treating high-salt wastewater.Firstly,according to the characteristics of industrial high salt wastewater,the thesis proposes a separate crystallization process of mechanical steam recompression evaporation crystallization+cooling crystallization;According to the characteristics of sodium chloride and sodium sulfate in high salt wastewater,the specific idea of MVR fractional crystallization process is clarified:low temperature evaporation crystallization of Na Cl,high temperature evaporation crystallization of Na₂SO₄,cooling crystallization of mirabilite;With the help of the ternary system phase diagram of Na Cl-H₂O-Na₂SO₄,the crystallization temperature range of MVR fractional crystallization process is further refined,and DTB crystallizer is selected for crystallization operation.Based on the existing desulfurization wastewater simulation feed liquid data,Aspen Plus software is used to simulate and verify that MVR evaporation+cooling fractional crystallization process is feasible and more advantageous when the feed flow is 10000kg/h,the feed concentration is2.98%,and the evaporation scale（recovered condensate）is 9481kg/h.On this basis,the performance of MVR fractional crystallization system is analyzed for Na Cl with evaporation temperature of 70℃,vaporization fraction of 0.5 and compressor compression ratio of 1.8 to explore the feed concentration and evaporation capacity;COP,compressor power consumption,heat exchange and compressor compression ratio;The relationship between heat exchange area,evaporation capacity and evaporation temperature.The results show that low compression ratio and low evaporation temperature have more advantages in system energy saving.Finally,MVR evaporation+cooling crystallization test device platform was built to prepare mixed solutions containing Na Cl and Na₂SO₄to simulate industrial high salt wastewater for test.Prepare the solution according to the five proportions of m _{Na Cl}:m _Na2SO4=1:1,2:1,3:1,1:2 and 1:3,and conduct three tests respectively for each proportion.The test data shows that all the test groups can produce crystals with high purityand the crystalline products can meet the requirements of national standards;Consistent with expectations,the relationship between the grade of crystallization products and the proportion of initial reagents is not obvious,which further verifies that the MVR evaporation+cooling fractional crystallization process is feasible,providing a reference for the selection of treatment process for industrial high salt wastewater.