Investigation On Mixing And Mass Transfer In Multistage Internal Airlift Loop Reactor

A simple multistage internal airlift loop reactor(MIALR),which has been widely employed in the chemical industry,was designed and investigated.The influences of interstage height and superficial gas velocity in the MIALR on the performance of the mixing and mass transfer were inspected.Three typical regimes,i.e.,abnornal,transition and regular regimes,in the MIALR were observed and proposed in this work for the first time.There were two critical superficial gas velocities impacted by the interstage height in the MIALR for the flow regime transition,and two mathematical models were proposed here for the prediction of flow regimes.It was indicated from the results that a higher superficial gas velocity was desired for reaching a regular regime when the interstage height of the MIALR increased.In addition,the respective gas holdups in the riser and the downcomer would be promoted if there was an increment of the interstage height in the MIALR.The gas holdups in the riser and the downcomer at the third stage were the highest at the same conditions,and those at the first stage were the lowest among the three stages in the reactor.Moreover,the higher the interstage height,the higher the circulating liquid velocity in the downcomer was.The highest circulating velocity in the downcomer was measured at the first stage,and the lowest value was obtained at the third stage.Finally,a reduction of mixing time was gained when the interstage height increased,while an increase of volumetric mass transfer coefficient was obtained at the same conditions.Additionally,the slurry hydrodynamics was measured in this work,and the average concentrations of sand in the MIALR were 1%,1.5%,and 2%,respectively.The influences of sand concentration and superficial gas velocity in the MIALR on the performance of the mixing and mass transfer were inspected.Three typical flow regimes,i.e.,abnornal,transition and regular regimes,in the MIALR were observed.It was found that only in the regular regime can all the sand circulate without depositing on the bottom.As the concentration of sand increases,the critical superficial gas velocity for the flow regime to change from the transition regime to regular regimes one increases.Meanwhile,the gas holdups in the risers and downcomers of the MIALR decrease,and so do the circulating liquid velocity and volumetric mass transfer coefficient decreases.In addition,the mixingtime increased with the increase of the solid concentration in the reactor.With the same sand concentration and superficial gas velocity,the gas holdup is largest in the third stage,and the gas holdup is smallest in the first stage.As for the circulating liquid velocity,it is largest in the third-stage,and smallest in the first stage.Therefore,a guideline for the scientific design,scale up and operation of this kind of industrial MIALRs was provided in this work,and it has great value for science and application.