Numerical Simulation Of Gas-liquid Flow In A Pressurized Bubble Column Using The CFD-PBM Coupled Model

Bubble columns are widely used in chemical,energy,environmental and biological industries with the advantages of simple structure,large capacity,easy operation,adequate heat and mass transfer,and small bed pressure drop.And many processes are conducted under high pressure.It is of great significance for the design,scale-up and optimization of pressurized bubble column to predict the flow status of gas-liquid flow and various fluid mechanics parameters under pressurized conditions.The numerical simulation of gas-liquid flow is studied in a pressurized bubble column based on FLUENT15.0 platform.Meanwhile,the model parameters are modified according to the experimental data from Qin(2012),and the influence of pressure and other conditions on the hydrodynamic behavior of the bubble column is investigated.The main results are as follows:First,the electrical resistance tomography(ERT)is compared with the traditional test technique(differential pressure method,conductivity probe method)using the average gas holdup.The average gas holdup at Pane 1 and Plane 2 of pressure bubble column increases with the increase of superficial gas velocity and the results of the three test techniques are basically consistent.This verifies the reliability of ERT tested in pressurized bubble columns.Meanwhile,the CFD-PBM coupled model is applied to simulate the gas-liquid flow in a pressurized bubble column.The effect of operating pressure on the cross-sectional gas holdup and profile gas holdup were investigated.The cross-sectional gas holdup contours and time-series diagrams measured by ERT were compared with the simulation results.The results showed that the results measured by the electrical resistance tomography techniques were in good agreement with the calculated results of computational fluid dynamics,which can enable stable measurement of hydrodynamic parameters in pressured bubble column.It was further demonstrated that ERT technique was feasible for visualization and real-time measurement of gas-liquid two phase flow in the pressurized bubble column.Secondly,on the basis of the Roghair bubble group drag force model,the correction of the density term ?g/?0 is performed according to the cold model experimental data(Qin 2012).The modified bubble group drag model was used to investigate the effect of pressure on the hydrodynamic parameters.The results show that as the pressure increases,the radial gas holdup increases and the bubble rise velocity decreases.And the simulation results are in good agreement with the experimental results.Therefore,it can be shown that the numerical simulation using the modified bubble group drag model can effectively predict the influence of different pressure on the hydrodynamic behavior of the gas-liquid flow in pressured bubble column.Finally,in order to analyze bubble coalescence and breakup under pressurized conditions,the CFD model was coupled with population balance model(PBM).And the density correction term ?g/?0 is introduced into the Luo bubble coalescence model.The modified CFD-PBM coupled model was used to investigate the effect of pressure and superficial gas velocity on the hydrodynamics parameters.The simulation results were in good agreement with experimental data(Qin 2012).With the increase of operating pressure and superficial gas velocity,the gas holdup of small bubbles gradually increases,and the gas holdup of large bubbles changes little.Meanwhile,the modified CFD-PBM coupled model was applied to nitrogen-water system and air-acetic acid system.In the two systems,the average gas holdup increased with the apparent gas velocity,and the simulation results were basically consistent with the experimental values.