Study Of Gas-Liquid Two-phase Flow Characteristics In An Airlift Loop Reactor

Airlift loop reactors(ALR)have been widely applied in chemical and biotechnological industries due to their special advantages.How to design an airlift reactor with high performance and realize the operation optimization of airlift reactors are based on exploring the flow characteristics in the reactor.In this paper,the cold model experiment and CFD simulation were combined to study the effect of internals and operating conditions on the gas-liquid flow in the reactor.The experiment results show that:the gas holdup and liquid velocity increase with the increasing superficial gas velocity;when the draft-tube diameter increases,the gas holdup and riser liquid velocity increase,the downcomer liquid velocity decreases;due to the sieve plates in riser,the bubbles size decreases,the amount ofbubbles increases,the distribution condition of gas phase improves;the gas holdup increase and the liquid velocity decrease when the amount of sieve plate increases,and two sieve plates are more efficient;the gas holdup decrease and the liquid velocity increase when the aperture ratio of sieve plate increases.The cold model ALR was then investigated by CFD to validate the simulation methods and the simulated results agree well with the experimental data.Following the validation,CFD was extended to study the industrial cyclohexane oxidation ALR.The simulation results indicate that the key hydrodynamic parameters for the circulation flow are the liquid circulation velocity and liquid circulation flux.The increasing liquid circulation flux in the downcomer enhances the gas phase entrainment in the draft-tube,while the increasing liquid circulation velocity in the riser reduces the riser gas holdup.With a constant reactor diameter,the gas holdup and liquid circulation flux increases with the increasing cross-sectional area ratio of downcomer to riser.The draft-tube with a horn-mouth can efficiently enhances the gas-liquid separation at the reactor top.Within a certain range,the axial position height of the draft-tube can influence the circulation driving force and resistance loss in the reactor.The gas holdup increase and liquid circulation velocity decrease with the decreasing orifices diameter of the gas distributor.With a higher superficial gas velocity,the effect of the internals on the flow characteristics in the reactor will be more obvious,the gas-liquid two-phase flow will be also more unstable.