Flow And Mass Transfer Study Of Gas-Liquid Reactor Based On CFD-PBM Coupled Model

Gas-liquid reactors are widely used in the petrochemical,environmental and biomedical fields.Different structures of gas-liquid reactors have significant differences in terms of operating conditions and effectiveness.It is important to improve the design and optimise the reactor to suit the actual operating conditions and parameters required for the different reactors.Computational fluid dynamics,as a convenient and reliable research method,has become an effective tool for studying gas-liquid reactors in recent years,providing a theoretical basis for the optimisation of experimental conditions and mass transfer studies of gas-liquid reactions.In this paper,the flow and mass transfer characteristics of gas-liquid two-phase flow in a mechanically stirred reactor are investigated and the Taguchi method is combined with computational fluid dynamics to optimize ten evaluation indexes of stirred reactors.Next,numerical simulations of airlift reactor were carried out to investigate the flow and mass transfer behaviour in the reactor,and the predictive performance of five mass transfer theoretical models for mass transfer in the airlift reactor was investigated.Finally,a stirred impeller structure was added to the airlift reactor to investigate the effect of stirring on the flow and mass transfer in the airlift reactor,and the prediction of mass transfer by the mass transfer theory models in the stirred airlift reactor was investigated.In this paper,the gas content and the volumetric mass transfer system in a gas-liquid stirred reactor are measured experimentally.Numerical simulations of the gas-liquid two-phase flow in the stirred reactor were established by CFD-PBM method,and parameters such as velocity vector,gas holdup,bubble size distribution and interface area in the reactor were analysed.A three-factor,three-level orthogonal experiment based on impeller type,aeration rate and agitation speed was designed using CFD in combination with Taguchi method,and process optimisation was carried out for P,α_g,a,k_la,α_g/P,a/P,k_la/P and three comprehensive evaluation indexes,respectively.The results show that axial flow impeller excel in reducing power consumption.Increasing the stirring impeller speed makes the greatest contribution to mass transfer enhancement.Increasing the gas flux reduces power consumption and increases mass transfer within a certain range,but not to a greater extent.For the airlift reactor,a numerical simulation method for CFD-PBM of the airlift reactor was established.The penetration model,slip velocity model,surface renewal stretch model,eddy cell model and rigid model were coupled with the numerical simulation,and the reliability of the computational model was verified by comparing literature data with simulation data.The silp velocity model has good predictive capability and its prediction points are basically located within±20%of the centre of the experimental value range.The penetration model with the surface renewal stretch model has a large prediction value.The eddy current model and the rigid model were small.In the stirred airlift reactor,the stirring of the impeller increases the dispersion of the gas phase in the reactor and can make the bubbles more uniform,effectively reducing the generation of large bubbles and promoting gas-liquid mass transfer.Five mass transfer theoretical models were compared for their ability to predict mass transfer in stirred airlift reactors.The results show that the penetration model,the slip velocity model and the surface renewal stretch model all have good predictive ability at larger k_la.Among them,the permeation theory model has the best prediction.The eddy cell model and the rigid model predicted too little.