Simulation Study Of Two-Phase Flow Transfer Process In A Pulsed Sieve Plate Extraction Column

Liquid-liquid extraction usually refers to the mass transfer and separation process from the aqueous phase to the organic phase,which is an important unit operation in the chemical separation process with the technical characteristics of high efficiency extraction and fine separation,so it is widely used in many fields such as petrochemical industry,nuclear industry,wet metallurgy,pharmaceutical chemical industry and environmental chemical industry.Pulse sieve plate extraction column has become one of the most common extraction equipment in nuclear industry and other fields because of its large processing capacity,high efficiency,simple structure,and when dealing with highly radioactive and other harmful liquids,the pulse device can be far away from the tower,easy to maintain and easy to achieve protective shielding.How to improve the mass transfer separation efficiency of pulse sieve plate extraction column is the core problem in the design,scaling up and operation of this type of tower,the pure experimental study of the continuous phase and dispersed phase flow and mass transfer law in the tower to guide the optimization of the tower separation efficiency is subject to many constraints such as the complexity of the flow process,experimental conditions,etc.Therefore,the use of simulation methods to study and analyze the complex transfer process in the column can help to form a more comprehensive and accurate understanding of the extraction separation process in the column.Therefore,this paper couples a population balance model（PBM）considering droplet breakage and aggregation with a computational fluid dynamics（CFD）approach to investigate the CFD-PBM simulation of a two-phase system consisting of 30%TBP（tributyl phosphate）-n-dodecane-HNO₃ in a column.Firstly,a two-dimensional geometric model was constructed based on a reasonable simplification of the physical model of the pulsed sieve plate extraction tower,the initial and boundary conditions were determined,the mesh was divided,and then the model was solved and analyzed using Fluent software,and the following conclusions were obtained.（1）CFD-PBM simulations were performed using the Luo model,Lehr model and CT model as the source terms of the PBM model breakage and aggregation kinetics,and the droplet diameter distribution of the dispersed phase calculated using the Luo and Lehr models tended to be large droplets,while the droplet diameter distribution using the CT model was log-normal,and the relative deviation of the Sauter mean droplet diameter from the experimental results was12.56%,which was the smallest deviation among the three models;similarly,the hold-up of the dispersed phase simulated with the CT model also had the smallest relative deviation from the experimental results,which was 13.02%.（2）In CFD-PBM simulations,the drag coefficients were calculated using the Schiller-Nauman drag model and the Kumar-Hartland drag model,and the results of using the two different drag models showed that the average droplet diameter of Sauter obtained by using the Kumar-Hartland drag model was smaller and the relative deviation from the experimental results was only 8.28%.The simulated hold-up of the dispersed phase is also more consistent with the experimental results,with a deviation of only 5.54%.（3）Based on the above conclusions,the two-phase flow process in the tower was simulated by CFD-PBM with CT breakage and aggregation model and Kumar-Hartland drag model to obtain two-phase fluid dynamics information.The effect of the apparent velocity of both phases on the droplet diameter is small;the hold-up of the dispersed phase increases with the increase of the pulse velocity,and the increase of the apparent velocity of the dispersed phase is beneficial to improve the hold-up of the dispersed phase,while the change of the apparent velocity of the continuous phase has little effect on the hold-up.The apparent velocity of liquid flooding in the dispersed phase decreases with the increase of the apparent velocity of continuous phase liquid flooding,and the liquid flooding flux increases and then decreases with the increase of the pulse velocity,and there are extreme values.In conclusion,CFD-PBM simulations of two-phase flow processes in a pulsed sieve plate extraction column were conducted in this paper to obtain quantitative information on the two-phase fluid dynamics in the column and to summarize the laws between operating parameters and two-phase fluid dynamics characteristics,which can provide necessary theoretical guidance for the operation,design and optimization of pulsed sieve plate extraction columns.