| The effect of wastewater treatment in an oxidation trench is influenced by the flow velocity distribution,flow field structure and gas volume distribution inside the trench.In this paper,numerical simulation of gas-liquid two-phase flow is carried out by CFD for two types of oxidation trench,bottom-exposed and surface-exposed,and multiphase flow motion is simulated by VOF method.The main conclusions are as follows:(1)In the model validation,the flow field morphology of the water column in an aeration lank with micro-porous aeration was simulated.Comparing the experimental phenomena tested in the literature,it was found that the results obtained from the numerical simulations basically matched the reality;by comparing the experimental real measurements as well as the graphs of the simulated monitored gas content,the error between the two was small and within the permissible range,which could prove the reliability of the chosen calculation model.(2)In the oval runway-shaped Orbal oxidation ditch,first optimize the air intake speed of the bottom holes,and analyze the effects of different bottom holes exposing air pores on the operation of oxidation ditch operation.When the intake speed reaches=0.070m/s,the flow field structure with z=2.5m and vertical axial section is significantly better than the first three schemes,and the distribution of gas volume scores is significantly improved,which is more conducive to sludge.The biochemical reactions of the particles and the mix of gas fluids improve the operating efficiency of oxide.(3)On the basis of the optimum inlet velocity of the bottom aeration hole,only the size of the differential pressure of the underwater pusher is changed to study the differences in the hydraulic characteristics and water flow structure inside the oxidation ditch under each scheme.The differential pressure of the underwater pusher is positively correlated with the overall gas volume fraction of the oxidation ditch,but when the differential pressure reaches a certain value,increasing the differential pressure does not have a significant effect on the improvement of the flow pattern in the oxidation ditch.In practical engineering,the differential pressure can be selected in conjunction with the energy consumption and normal operation needs.(4)In the optimization of the running parameters of the circular Orbal oxidation ditch,change the speed of the surface aeration device the aeration of the surface of the surface,comprehensively compare the gas volume score distribution of the three schemes,the speed distribution and the flow field structure.When reaching ω=6rad/s,it can not only improve the flow field structure in the oxidation ditch,reduce the energy loss caused by the vortex,but also improve the gas volume score in the oxidation ditch,improve the biochemical reaction efficiency of activated sludge,so this stage is determined by determining the stage The speed of the firing turntable should be greater than ω=6rad/s before it can achieve the ideal operating effect.(5)Surface aeration device has limited impact on the water flow field at the bottom of the oxidation ditch,so the underwater pusher is arranged in the oxidation ditch to improve the flow field structure in the oxidation ditch.The volume score in the oxidation ditch is positively correlated with the flow of the flower.When the 4 underwater flowers are arranged in the z=0.5m,the gas volume score is significantly higher than the first three types,and the increase is the largest.It shows that the increase in the number of flowers can effectively improve the gas distribution at the bottom of the oxidation ditch.In actual engineering,you can refer to this simulation result and combine the project to be optimized and improved. |
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