Research On The Fouling Mechanism Of Heat Exchanger In The Process Of Industrial Salinity Wastewater Treatment

The efficient recovery and recycling of salt water from coal chemical industry has become an im portant measure to save industrial water resources and promote the development of green chemical industry.However,the treatment of scaling in the relevant heat exchange equipment in the process flow has greatly increased the process operating cost,and has become a bottleneck problem that limits the safe and stable operation and development of the process.Therefore,it is of extremely important theoretical value and practical significance to study the mechanism of fouling process of heat exchange equipment in the process of treating salt water in coal chemical industry.In this paper,coal chemical salt water is taken as the research object,an experimental device is designed and built,and the fouling growth process of the positive solubility single salt Na2SO4 and the mixed salt of Na2SO4 and NaCl on the heat exchange surface of the double-tube heat exchanger is studied by numerical simulation The crystallization and scaling process of CaC03 on the heat transfer surface of the double-tube heat exchanger is described.The fouling phenomenon of positive solubility salt usually occurs on the wail surface where the surface temperature is lower than the fluid temperature.The effect of inlet temperature,inlet flow velocity and solute mass ratio on the fouling deposition process of Na2SO4 and its mixed salt(Na2SO4+NaCl)on the cold surface was studied by the fouling thermal resistance method.The experimental results show that the fouling thermal resistance gradually increases with the increase of solution temperature before the solubility inflection point of sodium sulfate;after the solubility inflection point of sodium sulfate,the fouling thermal resistance gradually decreases with the increase of solution temperature;the results show that the fouling thermal resistance decreases with the increase of the inlet flow velocity of the solution,which indicates that the fouling process is controlled by chemical kinetics;the fouling rule of mixed salt is similar to that of pure salt,the main reason is that Na2SO4 is the main deposit(91.1,wt%)through the XRF analysis of the fouling samples,and the higher the content of NaCl in the solution,the smaller the fouling thermal resistance due to the existence of the common ion effect.Based on the results of the deposition process of CaCO3 on the double-pipe heat exchanger surface,through the establishment of physical model and mathematical model of crystallization fouling process,and the input of relevant experimental process parameters and result parameters,the numerical simulation of the crystallization fouling process of CaCO3on the heat exchanger surface is carried out by using FLUENT and coupling UDF.The simulation results show that:due to the lack of particles fouling model in the mathematical model,therefore,the simulation value is generally smaller than the experimental value,but has the same trend as it;the mass deposition rate and fouling thermal resistance increase with the increase of solution concentration or solution temperature or heat surface temperature;the fouling thermal resistance decreases with the increase of flow velocity,indicating that the fouling process is controlled by chemical kinetics;the fouling thermal resistance decreases with the increase of flow diameter.The research in this paper provides theoretical basis and guidance method for the sediment prevention and inhibition process of heat exchanger,supports and solutions for the development of relevant wastewater treatment process,and lays a research foundation for the subsequent development of multi-species and multi-component fouling growth prediction model.