Numerical Simulation Of Micro-vortex Flocculation Process And Optimization Of Key Operating Parameters Based On Fluent

Flocculation plays an important role in conventional water treatment process.The design and operation of flocculation process play an important role in water treatment process.Therefore,it is necessary to study the optimization of flocculation process.The micro-vortex flocculation process with intellectual property rights of East China Jiaotong University is superior to the traditional flocculation process in terms of water yield and treatment effect in engineering application,but there is randomness in the selection of its technological parameters.For example,the size of micro-vortex reactor and water hole is randomly set,and the key operating parameters such as flocculation time are not optimized,which is very disadvantageous to the treatment effect of micro-vortex flocculation process.Therefore,this paper uses Fluent software to simulate the micro-vortex flocculation process,and explores the influence of different micro-vortex reactor,water hole,flocculation time and temperature on the micro-vortex flocculation process.Combining with pilot test,the relationship between flow field evaluation index,floc performance parameters and effluent water quality index is established,which provides a new idea for the optimization of key operation parameters of micro-eddy flocculation process.The main results of this paper are as follows.1.Numerical simulation of flow in micro-vortex flocculation process with different structural parameters（1）Numerical simulation of flow in micro-vortex flocculation process with different micro-vortex reactorThe vortex velocity gradient,turbulent kinetic energy distribution and energy dissipation distribution in the vertical shaft of two kinds of micro-vortex reactors,HJTM-1 and HJTM-2,were simulated and analyzed at water temperature of 20℃and intake flow rate of 6 m³/h.The effective range of action of the two kinds of micro-vortex reactors was determined.The results show that the turbulent kinetic energy and energy dissipation of the two types of micro-vortex reactors are flat compared with those of HJTM-1 and HJTM-2.Mean and maximum values are larger,and the effective range is larger.Therefore,HJTM-2 type micro-vortex reactor will be more conducive to improving the collision probability of floc particles.（2）Numerical simulation of flow in micro-vortex flocculation process with different size of water hole（length,width and location）Effects of the structure size of the water hole（length is L,width is B and location is H）on flow field of micro-vortex flocculation processThe orthogonal numerical simulation of L,B and H in the water hole was carried out under the water temperature of 20℃and the inflow flow rate of 6 m³/h.Turbulence kinetic energy and energy dissipation were taken as the evaluation indexes.The results show that for the effects of turbulence kinetic energy and energy dissipation in the flow,the order of factors is as follows:B>L>H,the width B has a highly significant influence on the turbulence kinetic energy,and the energy dissipation is a significant effects factor.Length L has a significant effect on turbulence energy and a non-significant effect on energy dissipation.The effect of location away from mud bucket H on turbulent kinetic energy and energy dissipation is not significant;the optimum working condition is working condition 1,that is,which is 160 mm in length,110 mm in width and 55 mm in position..2.Numerical simulation of flow in micro-vortex flocculation process with different operation parameters（1）Numerical simulation of flow in micro-vortex flocculation process with different flocculation timeWhen the flocculation time is 10 min to 52 min,the turbulent kinetic energy is1.37×10-4m²/s²⁶.81×10-6m²/s²,the energy dissipation is 9.10×10-5m²/s³¹.14×10-6m²/s³,and the scale of vortex is 0.32⁰.97 mm.Turbulence kinetic energy and energy dissipation are related to flocculation time.The correlation equation between turbulence kinetic energy and flocculation time isk（28）0.0121t^-1.919,correlation coefficient R² is 0.99992,the correlation equation between energy dissipation and flocculation time is?（28）0.0698t^-2.8436,correlation coefficient R² is 0.99996,and the correlation equation between vortex scale and flocculation time is?（28）0.0157t（10）0.1870,correlation coefficient R² is 0.9898.（2）Numerical simulation of flow in micro-vortex current flocculation process with different water temperatureWhen the water temperature is between 5℃and 30℃,the turbulent kinetic energy is4.13×10^-5m²/s²³.69×10^-5m²/s²,the energy dissipation is 1.61×10^-5m²/s³¹.34×10^-5m²/s³,and vortex scale is 0.773 to 0.481 mm.The results show that the turbulent kinetic energy,energy dissipation and vortex scale decrease with the increase of temperature,and the influence of temperature on vortex scale is obvious.2.Optimization test of operation parameters of micro-vortex flocculation process（1）Effect of flocculation time on floc equivalent particle size,effluent turbidity and COD_MnThe results of pilot-scale experiments under different flocculation time showed that with the increase of flocculation time,the floc equivalent particle size,turbidity removal rate and COD_Mnn removal rate increased first and then decreased.When flocculation time was 20.7minutes,the floc equivalent particle size reached the maximum of 0.606 mm.At this time,turbidity removal rate and COD_Mnn removal rate were the highest,94.3%and 78.4%respectively.（2）The relationship between relative deviation（absolute value of the difference between vortex scale and equivalent particle size）and effluent turbidity and COD_Mnn removal rateCombined with pilot-scale experiment and numerical simulation,the results show that the turbidity and COD_Mnn removal rate of effluent are significantly correlated with relative deviation.The relationship between turbidity removal rate and relative deviation is as follows:correlation coefficient R² is 0.9223,the relationship between COD_Mnn removal rate and relative deviation is as follows:correlation coefficient R² is 0.8922.The smaller the relative deviation,the higher the removal rate of turbidity and COD_Mn.Numerical simulation of flocculation plant structure parameters by Fluent software provides a theoretical basis for optimizing the structure of micro-vortex reactor and micro-vortex flocculation plant;simulation of flocculation process operation parameters establishes the correlation between flocculation time and flow performance parameters;Combiningwithpilot-scaletestandanalysis,theflocculationkeyoperation parameter-flocculation time is optimized.The micro-vortex flocculation process provides theoretical basis and practical reference,which is of far-reaching significance to further promote the application of the process and the development of its theory and technology.