CFD-PBM Coupled Simulation Of Two Phase Flow In Coal Liquefaction Bubble Column Reactor

China's coal resources rank among the highest in the world,and it needs to consume a lot of coal every year.In the past,extensive use of coal often produced a lot of pollution.With emphasis on sustainable development,we need to make efficient and clean use of coal resources.Direct coal liquefaction and indirect coal liquefaction technology can convert coal into clean fuels and chemicals,which can alleviate the impact of oil supply safety issues on China's economic development and increase the efficiency of resource utilization.The reaction equipment in the coal liquefaction process is a bubble column reactor,which provides a multi-phase reaction site.The reactor has the advantages of good mixing performance,large production capacity,simple structure and easy operation.The safe and stable operation of the reactor is the key to the industrialization of coal liquefaction technology.Based on coal liquefaction technology,this paper studies the numerical simulation of multiphase fluid flow in a bubble columnFirst,an analysis is made of a breakup model that combines energy constraint and pressure constraint.The dimensionless breakup critical energy,collision breakup efficiency,collision frequency,and daughter bubble size distribution curve changes of the model are analyzed by Matlab programming.The predicted values of the dimensionless breaking rate and daughter bubble size distribution are compared with literature values.The results show that the dimensionless breakup rate and daughter bubble size distribution calculated by the breakup model are in good agreement with the experimental values.When the energy constraint and pressure constraint are combined,the model retains the characteristic that the dimensionless critical energy is large when the energy constraint bubble is relatively large.At the same time,due to the binding pressure constraint criterion,when the bubble is small,the dimensionless critical energy of bubble breakup no longer tends to zero,avoiding the problem of the bubble breakup rate tends to infinity when daughter bubble volumetric ratio approaches zero in Luo model.The daughter bubble size distribution of the model is "M" shaped.When the bubble diameter increases,the bubble breakup rate increases,and when the turbulent dissipation rate increases,the bubble breaking rate also greatly increases.With the increase of surface tension,the probability of equal breakup of bubble decreases,and with the increase of turbulence dissipation rate and bubble diameter,the probability of equal breakup of bubble increasesReasonably describing gas-liquid interaction force and daughter bubble size distribution is the key to accurately simulate the hydrodynamic parameters of the bubble column.After verifying the predicted value of bubble breakup rate and daughter bubble size distribution of the breakup model.For the gas-liquid system,the verified breakup model was implemented into the population balance model(PBM)and coupled with the Euler two-fluid model.The gas-liquid two-phase flow in a bubble column with an inner diameter of 0.44 m and a height of 2.43 m was simulated.The gas holdup and liquid axial velocity predicted by coupled model at different superficial gas velocities were compared with the experimental values Moreover,the effect of lift to model(prediction result)was investigated.The results show that,both gas holdup and liquid axial velocity is improved in radial distribution when the lift force is included.The simulation value of the CFD-PBM coupled model have a good agreement with the experimental data in low and high superficial velocity.Both the turbulent dissipation rate in the reactor and the interaction between the bubbles rise with an increase in superficial gas velocity,which makes the distribution range of bubble size widened.