Flow Field Analysis And Structural Optimization Of An Expanded Granular Sludge Bed (EGSB) Reactor By Using CFD Simulation

Anaerobic treatment is a biological treatment technology which can achievewastewater treatment and energy recovery simultaneously. Anaerobic reactor as thekey treatment structure of anaerobic wastewater treatment system is becoming oneof the most popular directions of research areas in anaerobic treatment. Expandedgranular sludge bed (EGSB) is an efficient anaerobic reactor and has vast of appliedforeground and research value. The reaction process of anaerobic wastewatertreatment involves gas-solid-liquid phase’s reaction of physical, chemical andbiological. Nowadays, many studies mainly focus on the biological reactiondynamics and mass transfer process, however, the study of fluid characteristics arerarely. Besides, the design of anaerobic reactor mainly depends on the designmanual and some empiric formulas of relative standards, which has many problems.In order to optimize the design of reactor and develop the treatment performance, anadvanced technology should be developed to study the fluid characteristics ofreactor.Study object of the research is EGSB reactor, using computational fluiddynamics (CFD) to build mathematical model of reaction zone and three phaseseparation zone. The impact of water distribution system on the internal flow fieldas well as mass transfer and hydraulic characteristics were analyzed by solving themathematical mode, using experiment to validate models. The effect of three phaseseparator configuration on the internal flow field was analyzed by an existingmathematical model. The research can provide a certain theoretical basis andtechnical guidance for EGSB reactor design.The impact of water distribution system on the internal flow field wasinvestigated by using CFD simulation. The turbulent mass transport, liquid-solidmass transfer and hydraulic actions of the3-D space were analyzed in accordancewith the state of flow and the relative motion of liquid-solid. Under the same ratio α(the area percentage of hole) and different hole number, the ten hole could achievethe best turbulent mass transfer and liquid-solid mass transfer performance, whichcan enhance the flow scouring on granular sludge and develop the homogeneity ofsludge granules. Under the ten hole pattern, decreasing the ratio α to0.25%couldenhance the disturbance and turbulent mass transfer of lower part of the reactor.Besides, the relative velocity of liquid-solid was enhanced drastically; theliquid-solid transfer performance and the flow scouring on granular sludge weredeveloped obviously, while the homogeneity of sludge granules was decreased. Inaddition, under ten hole pattern, the vortex intensity at vertical direction, masstransfer, hydraulic action and the homogeneity of sludge granules were decreased when the delivered density in the center was high. Using pulse mode on waterdistribution could increase the flow rate of the inflow, besides, the inflow could bestopped before the relative velocity decreased drastically, which could enhance theliquid-solid mass transfer performance and hydraulic action.The impacts of three phase separator configuration on the internal flow fieldwere investigated by CFD simulation. The gas-solid separation performance ofgas-collecting hood and the flow state of settling zone and back seam were analyzed.The improved C-three phase separator could enhance the sedimentation efficiencyof settling zone and the driven force of the flow in back seam, develop theanti-impact ability of reactor under different conditions and improve the separatingcapacity effectively.