Numerical Simulation Of Gas-Liquid Flow Behavior In Bubble Columns Using CFD-PBM Coupled Model

Gas-liquid bubble column is widely used in petrochemical industry,environmental engineering and other fields because of its unique advantages.The study of gas-liquid flow behavior in bubble columns has been one of the hotspots in this field.Due to many chemical processes operated under high pressure conditions and organic solvent systems,it is important to accurately predict the flow state of gas-liquid two phases and the variation of hydrodynamics parameters for the design,scale-up and optimization of the pressurized bubble column.Numerical simulations of gas-liquid two phase flow were presented in a pressurized bubble column with an inner diameter of 0.3 m and a height of 6.6 m on the Fluent 15.0 platform.The experimental data as comparative analysis was obtained using conductivity probe,electrical resistance tomography(ERT),and differential pressure method under operating pressure of 0.5-2.0 MPa,and the superficial gas velocity of 0.12-0.32 m/s.The effects of pressure,liquid properties on the fluid dynamics parameters in the bubble column were investigated.The main results are as follows:Based on the preliminary numerical simulation work of the research group,three drag models of bubble swarms based on CFD simulation are proposed.Model A adds the gas holdup of large bubble and small bubble to Roghair's drag model of bubble swarms,and further optimizes the model parameters by using the density correction term;Model B considers the small bubble and the liquid phase as dense phase and the large bubble as the dilute phase.A simplified scheme based on Buffo and Roghair's drag model of bubble swarms is proposed;Model C is a Dual-Bubble-Size(DBS)drag model based on the Energy Minimization Multi-scale(EMMS)concept.CD/db is simplified to the relationship between the density correction term pg/pg,0 and the superficial gas velocity Ug.The simulation results show that the three drag models of bubble swarm have good predictability for the gas holdup in the bubble column.On the basis of the interphase force,the population balance model(PBM)is further coupled to CFD model for the evaluation of the bubble size distribution in the bubble column.The effects of the initial bubble size,the different group of bubble,coalescence coefficient,bubble breakup model on the bubble behavior are discussed.The experimental results showed that the fluid mechanics parameters are sensitive to the coalescence model under the experimental operating conditions.Therefore,the density correction term and the gas holdup of large bubble are introduced into the Luo's coalescence coefficient to optimize the bubble coalescence model.It is found that the optimized bubble coalescence model has better accuracy for the prediction of bubble size in the bubble column.The optimized CFD-PBM coupled model was used to simulate the different systems of bubble column,such as the mixed solvent-air system with SEBS-1650 and cyclohexane(to investigate the influence of liquid viscosity),and the mixture of oleic acid and water-air system(to investigate the influence of liquid surface tension).This model is further improved,and the optimized model has good predictability for the influence of different liquid properties on the gas holdup in the bubble column.