CFD Simulation Of Gas-liquid Flow And Mass Transfer Process In Bubble Column Reactor

The bubble column reactor is one of the most common and important multiphase flow reactors and has a wide range of applications in many fields.So far,people's understanding of the hydrodynamic behavior in the bubble column reactor is still insufficient.In-depth research and study of the bubble column reactor can provide theoretical basis and scientific guidance for the design,optimization,scale-up and operation of the reactor,which is of great significance.In this paper,based on the CFD-PBM coupling model,a three-dimensional CFD model of gas-liquid flow and mass transfer in the bubble column reactor is constructed to study the gas-liquid two-phase flow process and mass transfer process in the bubble column reactor.The main research results as follows:(1)Construct a three-dimensional CFD model of gas-liquid two-phase flow in the bubble column reactor,and study the gas-liquid two-phase flow process in the bubble column reactor.The results show that at lower superficial gas velocities,the simulated values of the single bubble size model and the PBM model are not much different,and the axial liquid velocity and axial gas velocity obtained by the PBM model are closer to the experimental values.When the superficial gas velocity is low,the coalescence and breakup between the bubbles are not obvious.When the superficial gas velocity increases,the gas-liquid two-phase flow pattern in the bubble column reactor begins to change from a uniform bubbling zone to a non-uniform bubbling zone.The change rule of radial distribution of the gas holdup and axial liquid velocity and axial gas velocity is similar,which increases with the increase of superficial gas velocity,while the gas-liquid interfacial area increases first and then decreases.When the superficial liquid velocity increases to a certain value,the gas-liquid two-phase flow direction changes.(2)Construct a three-dimensional CFD model of gas-liquid two-phase mass transfer in the bubble column reactor to study the gas-liquid two-phase mass transfer process in the bubble column reactor.Under different superficial gas velocities,the overall error of the simulation results and experimental data of the overall gas holdup and liquid volumetric mass transfer coefficient are within ±15%,and decrease with the increase of the superficial gas velocity.As the height increases,the gas holdup increases first and then decreases.The gas-liquid interfacial area decreases first and then increases in the central area of the bubble column,but does not change much in the near-wall area,while the liquid volumetric transfer coefficient decreases first and then increases.With the increase of the superficial gas velocity,the changes of gas holdup,gas-liquid interfacial area and liquid volumetric mass transfer coefficient are basically same,which are gradually increased.With the increase of the initial liquid phase height,the gas holdup diameter gradually decreases to a certain degree and then does not change.The gas-liquid interfacial area and liquid volumetric mass transfer coefficient increase first and then decrease.(3)Construct a three-dimensional CFD model of gas-liquid two-phase flow in the bubble column reactor,and study the influence of the turbulence model on the gas-liquid two-phase flow in the bubble column reactor.Successful application verifies the validity and accuracy of the WA turbulence model.The results show that the simulated values of the WA model generally show the best consistency with the experimental data.The turbulent kinetic energy deviation of the SST k-? model is the largest;as the height increases,the turbulent kinetic energy of the standard k-? model gradually decreases,while the WA and SST k-? models increase slightly.The change law of turbulent dissipation rate is similar to the change law of turbulent kinetic energy.The distribution trend of turbulent viscosity is relatively flat in the center area,and decreases rapidly in the near wall area.The turbulent viscosity of the standard k-? model is 2 to 3 times higher than that of the SST k-? and WA turbulent models.For the gas holdup,the radial distribution of the SST k-? and WA models is almost same,the standard k-? model is higher due to the increase of the bubble residence time.As the height increases,the gas holdup distribution becomes flatter.Based on the gas holdup and Sauter diameter,the value of the gas-liquid interfacial area calculated by the standard k-? model is the largest.