Hydrodynamics Optimization In A Two-stage Internal Loop Airlift Reactor

Internal loop airlift reactors(ILALRs)have been widely used in chemical industry,but multi-stage ILALRs are not widely used in actual industry.Therefore,it is necessary to conduct deeply research on the hydrodynamics and mass transfer characteristics of multi-stage ILALRs.In this study,a contraction-expansion guide vane(CEGV)is combined with a twostage internal loop airlift reactor(TSILALR).It is expected that the CEGV will be able to generate local circulation flows at each stage in the TSILALR.A computational fluid dynamics(CFD)simulation is conducted to evaluate the performance of the CEGV in the TSILALR.The bubble size distribution and turbulence flow properties in the TSILALR are considered in the CFD simulation by using the population balance model and RNG k-ε turbulence model.The CFD model is validated against the experimental results.The streamlines,flow pattern,bubble size distribution,and axial liquid velocity in the TSILALRs with and without the CEGV are obtained by CFD simulation.The performance of the CEGV in the TSILALR,in terms of the hydrodynamic properties,is discussed.The addition of CEGV in the TSILALR effectively generates local circulating flows in each stage,inhibits the back mixing of the liquid phase,and produces a concentration gradient in the first and second stages.In addition,the effects of superficial gas velocity and width of the CEGV on the flow field in the TSILALR are presented.By comparing the hydrodynamic properties of the TSILALR without CEGV,it is found that the average gas holdup of the first stage and the second stage of the TSILALR increases,the average axial liquid velocity decreases,and the bubble size distribution becomes wide.With the increase of the width of the CEGV,the axial liquid velocity decreases gradually,and the bubble size distribution becomes wider and forms a bimodal distribution.The orthogonal experimental design method is used to investigate the influence of CEGV and superficial gas velocity on the reversed liquid flow rate and pressure drop.The optimal CEGV with the minimum pressure drop and the minimum reversed liquid flow rate were obtained by multi-objective optimization.