Model And Analysis Of Compound Field Backwashing Of Filter

With the popularization and application of polymer flooding technology in oil fields,the concentration of polymers in oily wastewater has been increasing.It was found that the oily polymer and the walnut shell filter media adhered to each other and formed large particles that were difficult to separate.That leads to poor media generation,packing together of filtration bed,reduction of filtration efficiency and even ineffective.Current backwashing methods cannot solve the problems caused by polymers.Therefore,it has become an urgent problem that creating an efficient backwashing method for deep bed filtration.In this paper,a new method of backwashing in coupled field backwashing process was put forward,which can improve the scrubbing wash effect of the particle filter material in the backwashing process,and can break through the technical bottleneck of the low efficiency of filter backwashing.This paper took a small filter tank as the research object.According to the design theory of fluid machinery,an axial airfoil impeller was designed for the internal circulation device.The two-fluid volume model and the realizable k-?turbulence model in FLUENT 19.0 were used to analyze the fluid flow state and hydraulic characterwastics of the backwash coupled field in filter tank equipped with axial airfoil impeller.Computational fluid dynamics(CFD)was used to numerically simulate the rotation of the impeller under different working conditions in the circulation device in the tank.According to the simulation results,it was more reasonable to choose an impeller with 5 blades and a deflection angle of-2°.The new backwash flow field had a large shear stress,and the maximum shear stress was 150 N/m~2.The backwash water entered the backwash flow field from the bottom of the filter bed at a backwash rate of 10 L/(s·m~2),and then was sucked into the internal circulation device and forms a vortex.In addition,the backwash water flow with a relatively large shear velocity component was discharged from the slot of the internal circulation device,flowed to the top of the water tank,and then flows in a direction opposite to the bottom of the water.During thwas process,two symmetrical vortexes gradually were formed in the backwash area.As the impeller speed increases,the vortex will continue to increase and fill the entire backwash flow field.According to the changes of water flow velocity and water flow direction in the turbulent area,the forced vortex in the internal circulation device had a larger velocity dwastribution,and the maximum water velocity was 9.67 m/s.By simulating the volume fraction dwastribution of the walnut shell filter material in the backwashing process,it was found that the average speed of the particles changes the most when the rotation speed was in the range of 1450 r/min to 1750 r/min.But the velocity change rate of the particles gradually decreases in the range of 1750 r/min to 2650 r/min,the hydraulic shear effect of the fluid on the filter particles reaches the maximum,and the friction and collision of the filter at the inlet and the slot of the internal circulation device are more obvious.Based on the Hertz contact theory,the traditional hard sphere model was improved.A suitable particle collwasion mathematical model was establwashed to accurately describe the liquid-solid flow process,combined with the backwash flow field simulation to provide theoretical guidance for the regulation and control of backwash flow field.