Gas-Liquid-Solid Flow And Optimization Design Research Of Aeration Tank Driven By Inverted Umbrella Aerator

This paper is supported by the National Natural Science Foundation of China(51879122).Driven by the inverted umbrella aerator,the three-phase flow in the aeration tank is complex,including hydraulic jump,air mass entrainment and sludge particle settling.In this paper,experiments and numerical simulations on the gas liquid solid three-phase flow in the aeration tank are done,which provides the theoretical and practical basis for the research of this field.The main contents of this paper are as follows:1.Three-phase flow of the inverted umbrella aerator and sludge settling rate test benches are built.In this part,the sludge settling rates under different concentrations are measured,the settling model is established,the aeration performances of the inverted umbrella aerator under different rotational speeds,immersion depths and sludge concentrations are shown,the flow rate and sludge concentration of measuring points in the aeration tank are measured.The results show as follows:(1)The three common performance parameters of the aerator,the standard oxygen mass transfer coefficient,the standard transfer oxygen capacity and the standard aeration efficiency,are mainly affected by the rotating speed,the immersion depth and the sludge concentration.With the increase of speed,the three performance parameters are increased;with the increase of sludge concentration,the three performance parameters decreased;the immersion depth has an optimal value,which makes the three performance parameters reach the best.(2)Sludge sedimentation rate is strongly related to sludge concentration.With the increase of sludge concentration,the viscosity of sludge increases and the interaction between sludge particles increases,so the sludge sedimentation rate decreases.(3)In the aeration tank,the velocity near the impeller is larger,the turbulence degree is larger,and the ability to do work on sewage is stronger.The velocity of shallow water is greatly affected by the radial distance,while the velocity of deep water is hardly affected by the radial distance.(4)When the inverted umbrella aerator operates stably,the sludge concentration in the shallow water body varies greatly,and the sludge distribution in the deep water body is uniform.2.Mixture multiphase flow model and standard κ-ε turbulence flow model are used to simulate the three-phase flow in the aeration tank driven by the inverted umbrella aerator.The distribution characteristics,turbulent kinetic energy and turbulent dissipation rate of gas-liquid-solid three-phase flow with different sediment settling models are studied and compared with the experimental results.The results show as follows:(1)Compared with simulations of ignoring sediment settlement model and added Takács-double exponential sedimentation model,Vesilind exponential sedimentation model has a better unity with experiment.(2)The gas is mainly distributed in shallow water.Near the free surface,the interface between gas and other two surfaces is irregular.The sludge is evenly distributed in the aeration tank.(3)When the inverted umbrella aerator is running,the fluid on the left and right sides of the aeration tank is symmetrically distributed with the flow field axis as the symmetry axis,and forms the circulation vortex.When overlooking the liquid level,the impeller rotates counterclockwise,and the fluid rotates counterclockwise around the shaft.The flow velocity near the impeller of the aerator is larger,and with the increase of the distance from the impeller,the flow velocity gradually decreases,and the flow velocity reaches the maximum at the outer edge of the impeller.(4)The turbulent energy is larger than other regions.With the increase of depth,the turbulence degree of deep water gradually decreases,and the turbulent kinetic energy also decreases.(5)At the edge of the blade,the conversion between mechanical energy and kinetic energy is more intense,and the turbulent dissipation rate is larger at the edge of the blade.3.The aeration performance of the inverted umbrella aerator is improved by installing optimization device at the bottom of the aeration tank.Response surface method is used to establish the regression equation between the standard aeration capacity and the parameters such as the optimized device diameter,baffle height and gap width.The influence of each parameter on the aeration performance of the inverted umbrella aerator was analyzed,and the optimal parameters of the standard aeration capacity were obtained,and compared with the model before optimization.The results show as follows:(1)During the operation of the inverted umbrella aerator,the fluid in the tank is constrained by the wall of the optimization device,which makes a large number of fluid move to a deeper layer,and is promoted to a shallow layer through the optimization device,so as to speed up the oxygen mass transfer rate in the aeration tank.(2)With the increase of the optimized device diameter,the standard oxygenation capacity first increases and then decreases;With the increase of baffle height,the standard oxygenation capacity first increases and then decreases;With the increase of base width,the standard oxygenation capacity first increases and then decreases.(3)After optimization,the total transfer coefficient of standard oxygen increased by22.37%,and the standard aeration capacity increased by 22.37%.