Optimization Of Response Surface For Eddy Current Clarifier With Different Turbidity Based On FLUENT

In recent years,computational fluid dynamics（CFD）has been extensively studied in terms of flow field and particle trajectory in flocculation zone.The optimal operating parameter range of flocculation process can be determined based on the hydraulic parameters obtained from its numerical simulation results,and this parameter range can be used as the basis for designing the factor level of response surface optimization test.Therefore,in this paper,Fluent and response surface methodology were coupled to explore the flow pattern of the flocculation zone and the optimal process operating parameters when the eddy current clarifier treated water with different turbidity.Numerical simulation software Fluent is used to study different turbidity water under different reflux ratio and feed water flow flocculation area flow pattern and its parameters,flow field of study focuses on dealing with low turbidity（<30 NTU）,often turbidity,high turbidity（>100 NTU）water the optimal reflux ratio of inflow flow range,obtain different reflux ratio and feed water flow velocity,turbulent kinetic energy k,under the condition of effective energy consumptionε,velocity gradient G flow field parameters,such as,analyzing the change of the flocculation area flow field parameters curve and the hydraulic conditions,process operation parameters such as correlation,The flow pattern variation of the flocculation zone under different reflux ratios and influent flow rates was further revealed when the vortex clarifying tank treated water with different turbidity.Based on the optimal range of factor levels obtained from agitated coagulation test and numerical simulation,a three-level response surface optimization test with three factors（flow rate（flocculation time）,reflux ratio and dosage）was carried out to analyze the removal effect of turbidity,COD_Mnand UV₂₅₄when the eddy current clarifying tank treated water with different turbidity,and optimize the process operating parameters.1.Stirring and coagulation experiment:（1）The mass flow rate and average particle size of water with different turbidity were obtained,which provided data reference for FLUENT numerical simulation of inlet parameters of the Discrete Phase Model（DPM）.The mass flow rates at the inlet of DPM model under low turbidity（about 10 NTU）,normal turbidity（60-80 NTU）and high turbidity（about 200 NTU）conditions are 0.00001 kg/s,0.00006 kg/s and 0.00017 kg/s,respectively.The average particle size was 3.10 mm,7.9 mm and 10.7 mm,respectively.（2）The optimal dosage of PAC（polyaluminum chloride）under low turbidity,normal turbidity and high turbidity were 23mg/L,28mg/L and 32mg/L,respectively.The optimal dosage range was determined for response surface optimization test of eddy current clarifying tank for treating water with different turbidity.2.Numerical simulation of flow field:（1）The average velocity,turbulent kinetic energy k,effective energy consumptionεand velocity gradient G decrease with the increase of influent turbidity,and the head loss between the water inlet and the flocculation area increases with a small variation range.The influent turbidity has little influence on the flow disturbance effect of the eddy current reactor and the flow field parameters in the flocculation zone.（2）With the increase of reflux ratio,the average turbulent kinetic energy k,effective energy consumptionεand velocity gradient G in the flocculation area increase,and the turbulence intensity in the flocculation area increases.Taking the velocity gradient G(G=30-70 S^-1)of flow field parameters as the index,the optimal reflux ratio range was predicted to be 0.75～1.38 for the treatment of water flocculation with different turbidity in the vortex clarifying tank.（3）With the increase of the flow rate（flocculation time）,the average turbulent kinetic energy k,effective energy consumptionεand G value in the flocculation area and their change rate all increase.Taking the velocity gradient G value of flow field parameter as the index,the optimal flow range of eddy current clarifying tank for treating water flocculation with different turbidity is predicted to be 4.2～7.0 m³/h.3.Optimization of response surface process parameters:（1）Under low turbidity（about 10 NTU）condition,the influence of reflux ratio on the removal rate of pollutants in raw water is the most significant,followed by the flow rate,and finally the dosage.The interaction between flow and dosage was the most obvious,followed by dosage and reflux ratio,and finally by flow and reflux ratio.When the flow rate is 5.9 m³/h,the dosage of coagulant is 26.2 mg/L,and the reflux ratio is 1.25,the turbidity removal rate is87.05%,COD_Mnremoval rate is 67.29%,and UV₂₅₄removal rate is 55.24%.（2）Under the condition of constant turbidity（60-80 NTU）:the reflux ratio has the most significant effect on the pollutant removal rate in the raw water,followed by the dosage,and finally the flow rate.The interaction between reflux ratio and dosage was the most obvious,followed by dosage and flow rate,and finally the flow and reflux ratio.Combined with the predicted value of response surface optimization model and the repeatability test,the turbidity removal rate,UV₂₅₄removal rate and COD_Mnremoval rate are 95.36%,82.37%and 64.28%under the optimal conditions of flow rate of 6.4 m³/h,coagulant dosage of 32.5mg/L and reflux ratio of 1.07.（3）Under the condition of high turbidity（about 200 NTU）,the effect of reflux ratio on the removal rate of pollutants in raw water is the most significant,followed by the dosage,and finally the flow rate.The interaction between reflux ratio and dosage was the most obvious,followed by dosage and flow rate,and finally the flow and reflux ratio.Combined with the predicted value of response surface optimization model and the repeatability test,the turbidity removal rate,UV₂₅₄removal rate and COD_Mnremoval rate are 99.23%,95.03%and 71.42%under the optimal conditions of flow rate of 5.9 m³/h,coagulant dosage of34.8mg/L and reflux ratio of 0.8.（4）The optimum process parameters are obviously different for different turbidity water treatment by eddy current clarifier.High reflux ratio is more suitable for low turbidity water treatment,while low reflux ratio is more suitable for high turbidity water treatment.Compared with low turbidity water,the optimal amount of flocculant is larger in the treatment of constant turbidity and high turbidity water.The optimal influent flow of low turbidity and high turbidity water is smaller.