Numerical Simulation Study On The Position Distribution And The Optimization Of The Optimization Of The Aeration Of The Oxidation Trench Thruster

Oxidation ditch plays an important role in the treatment of sewage at present,but there are some problems such as low flow velocity and serious sludge deposition in the oxidation ditch.The flow field structure,velocity field distribution and gas volume fraction of the mixed liquid in the oxidation ditch are important factors affecting the sewage treatment effect.The pusher selected in this paper is a 0 thickness differential pressure pusher.In addition,the capacity of liquid aeration in oxidation ditch is also an important factor for the hydraulic characteristics and suspended solids deposition in oxidation ditch,which directly affects the operation efficiency of oxidation ditch.In view of these phenomena,on the basis of previous research of ox.idation ditch,based on the N-S equation and RNG k-ε model as the turbulence model,VOF is used as the multiphase flow model to track the free water surface.In this paper,the oxidation ditch model of a sewage treatment plant in Qinhuangdao city is simulated by numerical simulation.According to its model structure,five types of pushers and two different aeration modes are proposed.Based on the simulation results,the distribution of flow field and velocity and the hydraulic characteristics of the oxidation ditch are compared,and the following conclusions are drawn:(1)In the model validation,the simulated and measured values are basically in agreement.,thus proving the reliability of the selected mathematical model.The influence of oxidation ditch bend makes a certain range of reflux area appear on the right side of the baffle.The flow turbulence near the underwater thruster is stronger,the velocity near the middle partition wall is lower,and the edge velocity of the bank wall is larger.(2)The low speed area of the flow is mainly concentrated near the central wall at the outlet of the bend due to the structural changes of the straight channel and the bend,and the low velocity at the bottom is also the common point.The optimal arrangement of the position d/L=0.64 of the pusher in five working conditions is determined according to the comparison of flow field and velocity.Under the same pressure difference,the oxidation ditch of working condition 4(d/L=0.64)is more favorable to sewage treatment.The results have some reference significance for optimizing the structure and cost control of oxidation ditch.Under the premise that the whole structure of the oxidation ditch is invariant,changing the distribution position of the pusher can effectively increase the flow distribution and velocity of the oxidation ditch,reduce the probability of sludge deposition,and solve the reflux problem at the exit of the bend.(3)Comparing the micropore aeration and surface aeration on the bottom of the oxidation ditch,it can be found that the aeration mode has little effect on the flow field structure of the oxidation ditch,and the vortex phenomenon is easy to appear near the bend and the driving force of the pusher and the friction force of the pool wall.The microporous aeration method can prolong the mixing time of water vapor at the bottom of the oxidation ditch,increase the flow rate and gas content of the whole liquid,make the flow rate distribution more uniform,and the better the mixing effect of the gas-liquid two-phase,which is more favorable to the mass transfer of the gas-liquid two-phase.(4)Microporous aeration reduces the dead zone rate at the bottom of the oxidation ditch,improves the unfavorable conditions of the bottom water flow,reduces the probability of settling the suspended matter in the sewage,and effectively improves the efficiency of the sewage treatment in the oxidation ditch.