Study On Performance Of Water Pump Forced Circulation Equalization Basin Based On CFD Numerical Simulation

Water quality fluctuation(WQE)is one of the common problems in the process of sewage treatment.Excessive WQE will lead to substandard effluent quality and worse or even collapse of the follow-up biochemical treatment system.In view of the influent WQE in the process of sewage treatment,when the influent mass flow and influent fluctuation period(T)were certain,the rectangular wave was used as the fluctuation type,the equalization process of water pump forced water quality equalization basin(WPFWQEB)was numerically simulated via Fluent software and the equalization function coefficient(y)was introduced,and then the effects of inlet conditions such as different reflux ratio(s)and structural parameters such as the height of reflux distribution pipe(h),the number of reflux distribution holes(m)and the diameter of reflux distribution holes(d)on the equalization effect of the WPFWQEB were analyzed.At the same time,the numerical simulation results were verified by the verification test.And the paper drew the following conclusions:(1)The non-equipment equalization basin itself had a certain equalization capacity,but with the increase of inflow fluctuation period,the equalization effect of the non-equipment equalization basin would gradually decrease.When T was 60min,the equalization function coefficient could reach 0.80;As T increased to 120min,k value dropped sharply to 0.60,and the change range of k value was 33.3%.In the subsequent verification test,it was found that when T increased to 120min,the actual k value dropped to 0.55,indicating that the T is one of the main factors affecting the equalization performance of the equalization basin.The longer the influent fluctuation period,the worse the equalization performance.(2)s was the main factor affecting the equalization effect of the WPFWQEB.When h=200mm,m=8 and d=16mm,with the s increased from 0.16 to 1.00 in the"rapid growth area",k increased from 0.72 to 0.82,and the fitting equation k=0.6985+0.1275s;Then,s entered the"slow growth area"and continued to increase to 6.00,the value of k increased to 0.92,and the fitting equation k=0.7831+0.03729s-0.002547s~2;It could be concluded that the larger the s value is,the better the equalization effect is,but when s>1,the growth range of k value becomes slower.If it is necessary to improve the equalization effect of the equalization basin,s should be selected first.(3)In a certain range,the height of reflux water distribution pipe,the number and diameter of reflux water distribution holes are not the main factors affecting the equalization performance of WPFWQEB.When h varied from 50 mm to 350 mm,k fluctuated from 0.81 to 0.84,and the variation range was only 3.7%;When the height of the reflux water distribution pipe was 350mm,the water mixing and water flow velocity in the water outlet area were enhanced because the reflux water distribution pipe was close to the water outlet,and the value of the k increased slightly(0.84).When m or d was too large,it would lead to insufficient effluent kinetic energy of each water distribution hole,resulting in poor equalization effect of the equalization basin.When m was 4～22 and d was 8mm～32mm,the corresponding variation ranges of equalization function coefficient k were 2.40%and 3.75%.Considering the factors such as energy consumption,structural complexity,construction difficulty,cost and equalization effect,it is recommended to set the reflux water distribution pipe at the middle and high part of the basin body;The number of reflux water distribution holes is 6～10;It is better to control the ratio of d to the diameter of reflux hole at 0.27～0.67.(4)In the verification test,it was proved once again that the reflux ratio is the main factor affecting the equalization performance of the WPFWQEB,while other structural parameters have limited influence on the equalization performance of the equalization basin.The experimental equalization performance variation law of parameters such as reflux ratio,height of reflux water distribution pipe,number of reflux water distribution holes and diameter of reflux water distribution holes is highly consistent with the variation law shown by numerical simulation.The relative average deviation of k value was controlled within 4.88%,7.23%,4.88%and 4.88%respectively,which showed the feasibility of numerical simulation applied to the study of equalization performance of WPFWQEB,proved that the evaluation method of equalization function coefficient is scientific.