Numerical Simulation And Experimental Research Based On Outside Circulation Anaerobic Reactor

A lot of wastewater discharge has been an increasingly serious environmental problem as the rapid growth in world population and the rapid development of industrial technology.Anaerobic treatment is a biological treatment technology widely used for wastewater treatment which can achieve highly economical and energy recovery.Of these,anaerobic reactor is the key to anaerobic biological treatment technology.In this paper,the Computational Fluid Dynamics(CFD)Fluent software was used to a three-dimensional numerical simulation,and the OC anaerobic reactor was selected as the research subject.By changing the half-cone angle of the lower cone,the ratio of height to diameter of the reaction zone and the operating parameters to analyze the changes in the internal flow field,the structure optimization and optimal operating parameters of the OC anaerobic reactor were studied under the condition of the same processing capacity and the same volume of reaction zone.The simulation results were then verified by experiments.First of all,the steady-state numerical simulation of single-phase flow in OC anaerobic reactor was carried out,and the influence of the half-cone angle of the lower cone and the ratio of height to diameter of the reaction zone on the flow pattern of the reactor was studied by using the single factor method,so that the optimum structural parameters of the reactor were determined:the half-cone angle of the lower cone equals 45°,and the high-diameter ratio of the reaction zone H/D equals 5:1,and the influence of inlet flow rate on the operation capacity in the reactor under the optimal structure parameters,was investigated.The results show that when the inlet flow rate is 0.235 m/s and the reflux ratio is 26.74:1,the reactor has the best operating capacity.Then the numerical simulation of liquid-solid two-phase flow in OC anaerobic reactor was carried out.The simulation results with the average rising velocity(2m/h,3m/h,4m/h,5m/h,6m/h)of the reaction zone as a variable show that u increases from 2m/h to 6m/h,the liquid velocity increases correspondingly,the solid velocity decreases first and then increases,u=4m/h,granular sludge floats well in the OC anaerobic reactor,the reactor has the best processing capacity.The simulation results of different granular sludge properties are shown:d=2mm,the velocity of liquid-solid two-phase changes more slightly,and the sludge bed maintains a better floating trend,which enhances the reactor's processing capacity;?=1040kg/m3,it can increase the circulation rate and stability of OC anaerobic reactor.Then,using Na Cl solution as a tracer,and using residence time distribution method,the hydraulic characteristics of the average rising flow rate in different reaction zones of OC anaerobic reactors were studied experimentally.Results from experiment show u increases from 2m/h to 6m/h,V_d decreases from 22.8%to 7.2%;?_?~2 first increases from 0.094 to 0.123 and then decreases to 0.065;N first decreases from 10.6 to 8.1 and then increases to 15.4;D/?L first increases from 0.049 to 0.066and then decreases to 0.034.This combined result indicates that The OC anaerobic reactor has both full mixed flow and plug flow.When u=4m/h,the reactor is closer to full mixed flow.Finally,Comparative analysis through simulation and experiment shows that under a certain 6.2L/h processing capacity,the optimal operating parameters of the OC anaerobic reactor are the inlet flow rate of 0.235m/s and the reflux ratio of26.74:1.The simulation results are similar to the experimental results.It proves the feasibility of using simulation instead of experiment.It has certain guiding significance for the structure design,optimization and operation parameter selection of anaerobic reactors in the future.