Research On Hydrodynamics And Mass Transfer Performance Of 2D High-stage Airlift Reactor

The internal loop airlift reactor(ILALR)was developed from the bubble column.ILALRs are advantageous in many fields with its simple structure,convenient operation,low power consumption.In addition,it does not need mechanical agitation.It has been widely applied in biochemical fermentation,chemical industry and wastewater treatment processes.However,because of the intrinsic complexities of multiphase flow,the flow and mass transfer are very complicated.The fluid mixing and mass transfer mainly focused on the gas-liquid separation zone in traditional ILALRs,which led to long mixing time and low-efficiency mass transfer.The multi-stage airlift loop reactor is used to improve the performance of the reactor;the draft tube is divided into three sections,which can greatly improve the mixing and mass transfer performance of the reactor.Screen internals were used in a two-dimensional two-stage internal loop airlift reactor.The influence of screens on the hydrodynamics and mass transfer characteristics in the two-stage ILALR,including gas holdup,mean bubble diameter,bubble rise velocity and volumetric mass transfer coefficient(K_La),have been experimentally investigated.It is found that screens can efficiently break bubbles up.Radial bubble velocity distribution is more uniform when screens being installed.Mean bubble diameter with smaller screen pores seems smaller and slightly increases with the increasing of superficial gas velocity U_g.A larger gas holdup and K_La can be obtained when a suitable screen was mounted.The variation trend of overall gas holdup and interfacial area a with U_g is similar.And a nearly constant liquid-side mass transfer coefficient(K_L)is found.The empirical correlations for the overall gas holdup and K_La have been proposed which fit the experiment data well.The gas-liquid two-phase flow in a two-stage ILALR has been studied by the software Fluent 15.0.The gas-liquid flow numerical model was built base on the Euler-Euler two fluid approach.The simulation results were compared with the data from our experiments.The numerical model shows a good agreement with the measured data on gas holdup.The simulation method is also used to study the structure of ILALR.The draft tubes and the screens are discussed.The CFD simulation can guide the reactor optimization and the scaling up of the reactors.