Study On Hydraulic Characteristics And Optimization Of Modified Anaerobic Baffled Reactor (mABR) Based On CFD Simulation

The treatment efficiency of the modified anaerobic baffled reactor?mABR?is greatly affected by the hydraulic characteristics,and the upflow velocity and sludge concentration of the reactor are important parameters affecting the hydraulic characteristics in the reactor.The Euler multiphase flow model and the standard k-?model was introduced in this study to simulate the two-dimensional transient of the reactor by using the ANSYS16.0 Fluent software.On the basis of acidification of the refractory wastewater?solid-liquid two phase flow?and the gas production of high-concentration organic wastewater fermentation?gas-liquid-solid three-phase flow?at different upflow rates and different sludge concentrations,we explored the effects of the internal water flow rate and solid content?water occupation of sludge particles,%?on the characteristics of internal flow field and to further optimize the deficiency of the mABR reactor.The results show:?1?From the simulation results of two-phase flow,it can be seen that with the increase of the rising flow rate,the vortex flow in the reactor becomes more and more obvious,and the muddy water mixing efficiency is high,thereby improving the mass transfer effect of the microorganisms,and at the same time,the disturbance range of the rising water flow velocity.The same is true of change.At too low an upflow rate,there is a large solids content distribution?sludge accumulation?at the bottom of the reactor.The increase of the rising flow rate is conducive to raising the mud-water interface,promoting the mixing of muddy water and improving the mass transfer efficiency.However,the excessively high rate of up-flow will lead to the loss of sludge inside the reaction chamber and reduce the biomass retention capacity.Therefore,a reasonable rising speed is beneficial to improve the processing efficiency of the reactor and reduce the bottom dead zone.However,under the condition of too low sludge concentration?calculated according to the solid content?,the sludge distribution range in the reactor is not uniform,and too high concentration will cause the bottom of the reactor to accumulate or be lost.Therefore,when two-phase flow,the upflow rate and solid holdup ratio?sludge concentration?are v=2.0².5 m·h^-1 and 0.3(3 g·L^-1),1.5².0 m·h^-1,respectively.0.4(4 g·L^-1)hydraulic agitation and solid content distribution are good,so the operation of the reactor can be improved.?2?The difference between the three-phase flow and the two-phase flow is that biogas is generated at the bottom of the reactor.Because methane has a certain thrust to the sludge during the ascending process,the sludge layer can be compared to the two-phase flow,the three-phase flow,under the same conditions of the rising flow rate and the sludge concentration?solid content?.Raise to a higher position.Because the methane rise can cause agitation of the muddy water,at low rise velocity,the ascending water flow velocity is too small,the upper part of the upflow chamber has a significant effect on the gas agitation,and vortex is also generated.As the ascending flow rate increases,the rising water flow rate gradually increases,and the methane gas is taken out at a relatively block speed,so the stirring effect is getting smaller and smaller,but overall,the increase of the rising flow speed is more favorable.The mixing of muddy water increases the mass transfer efficiency between mud and water.Therefore,in the case of three-phase flow,the upflow velocity and sludge concentration are in the range of v=1.5².0 m·h^-1 and 3 g·L^-1,1.25 m·h^-11 and 4 g·L^-1,respectively.It is beneficial to the mixing of mud and water,so that the reactor is most efficient in removing pollutants.?3?Through the simulation of the two-phase flow and the three-phase flow of the mABR reactor,it is seen from the results that at the bottom of the reactor,regardless of the optimization of the operating parameters,there is a certain accumulation of sludge particles,which does not achieve the desired treatment effect.Therefore,the reactor was structurally optimized under the conditions of up-speed and sludge concentration of 2.0 m·h^-1 and 3 g·L^-1,respectively.After the optimization of the structure,it is very obvious that the distribution of eddy currents in the reactor is improved,and there is basically no accumulation of sludge at the bottom,and the distribution effect of the sludge in the reactor is good,and there is no large amount of pollution.Mud loss phenomenon.