Numerical Simulation Of Gas-liquid(Solid) Flow In Terephthalic Acid Reactor Using CFD-PBM Coupled Model

The p-xylene（PX）oxidation reactor is a key equipment of the PTA production process,which determines the product quality and production rate of PTA.The flow behaviors of the gas-liquid two-phase flow in the bubble column are very complicated,and the basic data related to the PX oxidation reactor is scarce.Therefore,it is a certain guiding significance for the design and scale-up of the PX oxidation reactor to study the gas-liquid two-phase flow characteristics and the variation of hydrodynamic parameters under the near industrial condition.In this paper,the influence of the mass concentration of acetic acid on the hydrodynamic parameters in the bubble column is investigated in the bubble column PX oxidation reactor through two-dimensional and three-dimensional CFD-PBM coupled model.The experimental data are obtained by differential pressure method,fiber optic probe and electrical resistance tomography measurement,and the simulation results are compared with the experimental values.Furthermore,the CFD-PBM coupling model is used to simulate the hydrodynamics in the heated and pressurized air-water system and the N₂-acetic acid system.The main results are as follows:The drag force model and the coalescence model are corrected by the surface tension term f（（?）₁/（?）₀）,and the modified model is used for numerical simulation in the acetic acid system with ambient temperature and ambient pressure.The simulation results of the hydrodynamic parameters are analyzed.The results show that when the mass concentration of acetic acid is in the range of 70%-80%,the average gas holdup has a maximum value.The predicted value of the average gas holdup is within±10%error,and the three-dimensional simulation results are in good agreement with the ERT experimental value.The modified model has better predictability in acetic acid systems with different mass concentrations.The drag force model is further optimized by introducing parameters of density,viscosity and surface tension,which is suitable for the heated and pressurized system.Through the optimized model,the influences of temperature,liquid properties and solid holdup on the average gas holdup and other hydrodynamic parameters are studied in the air-water system.The results show that the gas holdup increases with the increase of temperature,and decreases with the increase of solid holdup.The simulation results and the experimental values are basically in agreement within the error range of±10%.According to the research group’s breakup model,the model is further modified by viscosity and surface tension,and the influences of the modified breakup model on the gas holdup and other hydrodynamic parameters are investigated.The results show that,compared with Luo’s breakup model,Shi and Guo’s breakup models predicted value of the radial gas holdup is lower and the Wang’s breakup model predicted value of gas holdup is basically the same as that of Luo’s.Finaly,the influences of temperature and solid holdup on the average gas holdup and other hydrodynamic parameters in the heated and pressurized N₂ acetic acid system are studied.The results show that the gas holdup and other fluid mechanics parameters in the system are consistent with those in the air-water system,and the simulation results and experimental values of the gas holdup are also consistent within±10%of the error range.The average gas holdup and other hydrodynamic parameters of the N₂-acetic acid-TA system and the air-water-TA system are compared and analyzed.The results show that the average gas holdup in the N₂-acetic acid-TA system is higher,the small bubbles gas holdup is higher,and the bubble number density is higher.The gas-liquid phase area is increased,which is beneficial to the PX oxidation reaction process.