Research And Application Of Mechanical Vapor Recompression System For Treating High Concentration Saline Wastewater

High concentration saline wastewater is a kind of common wastewater in industry.The direct discharge of these wastewater into the environment will cause environmental pollution and ecological damage,and some inorganic salts in high concentration saline wastewater also have the value of recycling and reuse.Therefore,how to recycle and treat them through reasonable technological route and low-cost process to reduce high concentration saline content.Then to reduce the environment destroys and achieves certain economic benefits,which has important research value.Mechanical vapor recompression evaporation system?MVR?is a technology that uses mechanical compression to compress the secondary vapor,raise the temperature and pressure of the secondary vapor,increase the enthalpy and then use it as a heat source.This technology improves the thermal efficiency of the system by recycling the latent heat of the secondary steam which was previously discarded.In view of the characteristics of high energy consumption in the treatment of high concentration saline wastewater,this dissertation explores the treatment process based on mechanical vapor recompression evaporation technology.Through process simulation and experimental research,the working characteristics of MVR system of high concentration saline wastewater and the influence of operation parameters for coefficient of performance are explored.The low energy consumption and low-cost process of treating high concentration saline wastewater is realized.Firstly,the MVR process was simulated with water as the medium,and the simulation accuracy was verified by pilot test.The results show that the simulation results are in good agreement with the pilot test results.The relationship between coefficient of performance and compression ratio,coefficient of performance and operating pressure,compression ratio and temperature rise of secondary steam,outlet temperature and compression ratio of compressor,supplementary water volume and compression ratio,evaporative water volume per unit energy consumption and compression ratio,operating pressure and evaporative water volume per unit energy consumption,motor power and compression ratio,steam condensation heat release and compression ratio in MVR evaporation process were investigated.The optimization of operation parameters lays a foundation for wastewater treatment.Because the actual wastewater is high concentration saline wastewater,which is different from ordinary water in nature,and its concentration and boiling point directly affect the accuracy of simulation,the basic data of ammonium sulphate and sodium sulphate wastewater are determined through small-scale experiments.Based on the measured basic data,the process simulation of ammonium sulfate wastewater treatment was carried out.The simulation results were in good agreement with the pilot test results.On this basis,the process design of single-effect mechanical vapor recompression system for wastewater with 3500 kg·h^-1 treatment capacity and40.5%?wt%?ammonium sulfate content was carried out.The boiling point elevation value was set at 13?,and the steam flow rate of compressor was 2200 kg·h^-1.The actual operation results show that the compressor power consumption of evaporating water per ton is 40.1 kW·h.Compared with the original stripping and distillation process,the cost is reduced by 68%,and the product quality meets the requirements of first-class products.In addition,according to the results of parameter optimization,when the compression ratio is less than 2,the coefficient of performance increases rapidly with the reduction of compression ratio.A hierarchical compression MVR model of ammonium sulfate was built and simulated.The results show that the energy consumption of the compressor can be reduced by 23.4%compared with single-stage compression.In addition,the MVR evaporation system of hierarchical compression was designed for the sodium sulfate wastewater with a flow rate of 11500 kg·h^-1 and a mass fraction of 16%.A hierarchical compression MVR system combined with falling film evaporation and forced circulation evaporation was adopted.After actual operation,the compressor power consumption of evaporating water per ton was 25.1kW·h,and the product quality met the requirements of Class II qualified products.Through the study of MVR evaporation energy-saving process for high concentration saline wastewater,the low-cost recovery goal was achieved,and it has certain economic benefits.Through salt recovery of high concentration saline wastewater,the discharge of wastewater meets the requirement of entering downstream wastewater treatment plant.The research results have reference value for similar treatment of high concentration saline wastewater.