Optimization Of Mixing Scheme And Experimental Study Of Anaerobic Fermentation System Of Corn Stalk

Anaerobic fermentation is currently a more common way to rationalize the energy of corn stalk.In the actual operation of current biogas project,it is often operated in the way of continuous stirring,and due to its large size,it is difficult to investigate the internal flow state,which makes it difficult to determine the optimal speed of its operation.When operating below the optimal speed for a long time,the mixing state inside the fermentation reactor is not good,and the mixing state of solid-liquid phases inside the reactor is poor,resulting in uneven phase distribution,stratification and even accumulation inside the reactor,reducing the contact between microorganisms and materials,lowering the fermentation efficiency,and affecting the gas production efficiency,which greatly affects the stable operation of the system.And when the operating speed is higher than the optimal speed operation,although the internal material mixing efficiency is higher,but the cost of its operation is higher,which seriously affects the economy of the system operation.The use of intermittent stirring is a more effective way to ensure stable operation of the system while improving the operating economy.Therefore,in this experiment,the critical suspension speed of impeller for the reactor was predicted by CFD simulation based on the flow state inside the reactor and the orthogonal combination of intermittent periodic stirring was performed based on the predicted speed to obtain the speed combination that achieves the best engineering stability.（1）In this paper,a large biogas project in operation was investigated,and the reactor was physically modeled and meshed after scaled down,and the most appropriate mesh number in this simulation experiment was 3928848 by mesh independence verification.And then,using FLUENT software,the RNG k-εmodel was selected as the turbulence model,the Euler-Euler model as the multiphase flow model,and the wen-yu model as the traction model,combined with the regional adaption and patch function for the initial position of the straw particles,and the multiple reference system method was used to simulate the solid-liquid two-phase flow state during the inner stirring process of the reactor.（2）The scaled-down fermentation reactor was used as the target of the study,and multi-speed simulations were performed.The trends of three parameters,which were local particle concentration,standard deviation of concentration distribution,and axial velocity of the particles,were analyzed in the CFD simulation process.The critical suspension speed of impeller for the reactor,was determined based on the idiosyncratic points in the variation of the three parameters during the CFD simulation,which was 1.17 rps.At the same time,the results obtained from the empirical formula were compared with the results obtained from the simulation,and the reasons for the differences between the two were analyzed,and then the flow pattern inside the reactor was analyzed according to the concentration distribution and velocity distribution at different rotational speeds.（3）The critical suspension speed of impeller,which was calculated from CFD simulation,was used as a benchmark to conduct orthogonal combination tests with a variety of combinations for periodic intermittent stirring.The standard deviation of the concentration distribution and the power consumption were analyzed separately by ANOVA.The best combinations were r₁=90 rpm,t₁=15min,r₂=90 rpm,t₂=15 min,and r₃=70 rpm,t₃=15 min when homogeneity was used as the only response index.When economy was used as the only response index,its corresponding best combination is r₁=50 rpm,t₁=5 min,r₂=50 rpm,t₂=5 min,and r₃=50 rpm,t₃=5 min.Because of the differences between the two results,the ANOVA was performed on the basis of the already conducted ANOVA using the integrated scoring method for its system engineering stability,and the corresponding optimal combination was determined to be r₁=90 rpm,t₁=10 min,r₂=70 rpm,t₂=5min,r₃=70 rpm,t₃=5 min.Finally,this combination was finally determined through validation experiments to be the running combination that meets the optimal engineering stability of anaerobic fermentation.