Study On Gas-liquid Flow Process In A Rotating Packed Bed With Randomly Arranged Spherical Packing By CFD Simulation

Gradually eliminating environmental pollution by combining the development and research of green chemical technology has become a major direction for the future development of chemical industry.Chemical process intensification technology has attracted great attention in green chemical due to its advantages of reducing the occupied area of equipment and improving energy efficiency.In recent years,rotating packed bed(RPB)designed based on high gravity technology has shown remarkable strengthening effect on mass transfer and mixing,which has broad prospects in industrial application.With the development of computational levels and numerical models,Computational Fluid Dynamics(CFD)has become a tool with great potential in analyzing detailed fluid flow,designing and optimizing the structure of equipment internal components,etc.In this work,CFD simulation,theoretical analysis and experimental methods have been used in combination based on the previous research results.Taking the RPB with randomly arranged spherical packing as the research object,the gas flow and Newtonian,non-Newtonian liquid flow characteristics were studied,which provided theoretical guidance for the optimization of the internal components of RPB and the rational selection of operating parameters.Main conclusions are as follows:(1)A 3D geometric model of RPB with randomly arranged spherical packing was developed for the first time.The spherical packing model was consistent with the real packing structure.Realizable k-? turbulence model was used to simulate the gas flow characteristics.Results showed that the error between the simulated values and the experimental values of the total dry pressure drop of RPB was within ± 20%.The pressure drop of packing zone and tangential velocity increased with the increase of rotational speed,while the radial velocity,the pressure drop of the inner and outer cavity increased as gas flow rate increased.The higher values of turbulent kinetic energy were illustrated near the outer edge of the rotor,in which gas end-effect zone existed.In addition,a semi-empirical correlation based on the numerical simulation was proposed to predict the dry pressure drop of the packing zone in RPB combining the wall effect.The calculated values of the packing zone pressure drop were in agreement with simulated data.(2)A two-dimensional CFD model was developed to simulate the liquid flow characteristics of Newtonian fluids in the packing zone of RPB.The change of liquid flow pattern of the packing zone in RPB was analyzed and the influence of packing properties,operating parameters and liquid properties on liquid holdup and liquid specific surface area was studied.Results showed that the simulated results agreed with the CT images in the literature,which validated the rationality of the model.Liquid holdup increased as liquid flow rate and viscosity increased,while it decreased with the increasing contact angle,rotational speed and gas flow rate.Rotational speed,gas flow rate,and liquid flow rate could promote the increase of the liquid specific surface area,but the increasing in contact angle and viscosity would reduce the liquid specific surface area.(3)Based on the developed two-dimensional CFD model,taking the CMC solution system in the literature as the research object,CFD simulation of the non-Newtonian fluids flow characteristics in the packing zone of RPB was achieved by adding a user-defined non-Newtonian fluid shear-thinning model.Results showed that the flow patterns of Newtonian fluids and non-Newtonian fluids in the packing zone at the same apparent viscosity were relatively similar.With the increase of liquid flow rate and CMC concentration,the liquid holdup showed an increasing trend,but the liquid specific surface area decreased.The increasing rotational speed caused the decrease of the liquid holdup,but it had a significant promotion on the liquid specific surface area.The gas-liquid effective interfacial area increased with the increase of liquid flow rate,rotational speed and CMC concentration.However,when these three operating conditions continued to increase,the gas-liquid effective interfacial area growth rate would decrease or slow down.In addition,within a certain operating range,the correlation of gas-liquid effective interfacial area in the packing zone has been obtained by combining with CFD simulation data,and it could be found that the error was within±15%by comparing the predicted values with the CFD simulated values,which provided theoretical basis for the selection of operating conditions and further mass transfer research in RPB.