Flow Field Numerical Simulation And Process Parameters Optimization Of Low Temperature Turbidity Water Treatment By Micro-Vortex Flocculation

Lake water and reservoir water,as sources of drinking water and backup water,play an important role in the urban water supply system of our country.They often show the characteristics of low temperature and turbidity in the cold winter area.Their flocculation process has the characteristics of large viscosity shear force,low concentration of particles,small particle size,strong hydrophilicity and low aggregation efficiency.The micro-vortex flocculation process with intellectual property rights of the project team is superior to the traditional flocculation technology in terms of flocculation efficiency and effluent quality,and has certain advantages in the treatment of low temperature and turbidity water.In this study,fluent numerical simulation analysis was carried out on the influencing factors of low temperature and turbidity water treatment by flocculation process,and the flow field rule of low temperature and turbidity water treatment by micro-vortex flocculation was revealed.Meanwhile,response surface test optimization was carried out on the low temperature and turbidity water treatment by micro-vortex flocculation process.The main research contents and conclusions are as follows:1.Study on the effect of factors on micro-vortex flocculation process by use of numerical simulation（1）Study on numerical simulation of micro-vortex flocculation reaction zone under different flocculation time,namely flow rate,was carried out.Flow fields under different flow conditions(i.e.flow rates of 2.0 m³·h^-1～10.0 m³·h^-1with step length of 0.1 m³·h^-1,corresponding to flocculation time of 60.0 min～10.2 min)at 5℃were simulated.The results are as follows.（1）Turbulent kinetic energy k,effective energy consumptionεas well as its change rate increase with the increasing flow rate Q,whereas the vortex scaleλand its change rate decrease with the increasing flow rate Q.（2）The flow rate Q,temperature（corresponding to kinematic viscosityν）as well as parameters of flocculation tank exert an impact of power function on turbulent kinetic energy k,which can be expressed as （?）The relationship between turbulent kinetic energy k and the rate of flow Q as well as the relationship between the vorticity scaleλand the rate of flow Q can be fitted ask（?）,respectively.（4）Based on the Kolmogorov micro-vortex theory,a better flow rate range fitted for the micro-vortex flocculation process has been preliminarily determined as about5.5m³·h^-1～7.5 m³·h^-1（corresponding to flocculation time of 18.5min～13.6 min）.（2）Study on numerical simulation of micro-vortex flocculation reaction zone at various temperatures was carried out.Flow fields at temperatures of 0℃～35℃with the step length of 1℃exemplifying the situation of fixed flow rate of 6.0 m³·h^-1（corresponding to the flocculation time of 17 min）was simulated.The results came to the following conclusion.（1）Turbulent kinetic energy and effective energy consumption decrease less with increasing temperature,while the vortex scale decrease significantly with increasing temperature.（2）The larger vortex scales generate at low temperature don’t match the smaller floc particles formed.Likewise,the smaller vortex scales generated at high temperature are not available for the larger floc particles.In the whole,neither can be more conducive to improving flocculation efficiency than at room temperature.（3）The relationship between turbulent kinetic energy k and temperature（corresponding to kinematic viscosityν）as well as the relationship between vortex scaleλand temperature can be fitted ask（?）,respectively,which further confirmed the positive relationship between k and（?）,as well as λ and （?）.The results combine the visualization of complex flow field with the theoretical formulas of key parameters of the flow field by use of numerical simulation,deeply interpreting the flocculation mechanism from the flow field perspective and providing theoretical guidance for engineering applications.（3）Study on numerical simulation of micro-vortex flocculation reaction zone with different suspended solids volume concentration was carried out.Exemplifying the condition of fixed flow rate of 6.0 m3·h-1（corresponding to flocculation time of 17 min）and fixed temperature of 5℃,flow fields with the suspended particle volume concentration of0.1%～1.0%（step length of 0.1%）were simulated using two-phase mixture model.（1）With the increase of the volume concentration of the suspended solids,the turbulent kinetic energy and the effective energy consumption increase gradually,and the vortex scale value decreases gradually.（2）In the simulation of solid-liquid two-phase flow,due to the addition of solid phase,the corresponding turbulent kinetic energy and effective energy consumption are lower than that of one-way flow simulation,and the vortex scale is larger,which reflects that when the vortex reactor is applied to the treatment of raw water containing solid,sludge deposition is easy to form at the bottom of the vortex reactor,which hinders the flow disturbance,reduces the turbulent kinetic energy and effective energy consumption,thus affecting the flocculation effect and effluent quality.2.Study on process parameters optimization for micro-vortex flocculation treatment of low temperature turbidity waterCombined with numerical simulation,the prediction of better flow range for micro-vortex flocculation process was proposed.Taking the flow rate,coagulant dosage and vortex reactor ratio as independent variables,turbidity,COD_Mnand UV₂₅₄removal rate as response values,using the Box-Behnken center combination design principle in design expert,the response surface analysis test of three factors and three levels was carried out,and the test data was analyzed by multiple regression fitting.（1）For turbidity removal,the influence of dosing ratio is more significant than that of coagulant dosage and flow rate,and it has a certain interaction with flow rate and coagulant dosage,and the three cooperate with each other to a certain extent.For the removal of COD_Mn,the dosage ratio is the most significant factor,the coagulant dosage is the significant factor,and the flow rate is the non significant factor.There is a significant interaction between dosage and coagulant dosage in the removal of COD_Mn.For the removal of UV₂₅₄,the significance order of the three factors is the same as COD_Mn.There is no obvious interaction between the coagulant dosage and flow rate for the removal of UV₂₅₄.The dosing ratio and flow rate,as well as the dosing ratio and coagulant dosage,both have a certain interaction.（2）The parameters obtained from response surface optimization were combined for 3times of repeatability verification test,the removal rate of verification test was close to the predicted value,and the predicted value of regression equation had a good fit with the test value.The best combination of parameters for the treatment of low temperature turbidity water by micro-vortex flocculation process are as follows:flow rate is 6.4 m³·h^-1,coagulant dosage is 26.8 mg·L^-1,and dosing ratio is 2（the first reaction chamber is a 3/5 ratio HJTM-2 vortex reactor+2/5 ratio HJTM-1 vortex reactor）.At this time,the removal rates of turbidity,COD_Mn,and UV₂₅₄are 85.48%,63.84%,and 55.37%,respectively.