Three Dimensional CFD Modeling Of Gas-liquid Flow And Mass Transfer In Rotating Packed Beds

Rotating Packed Bed(RPB),which is a new kind of mass transfer equipment,uses centrifugal force generated by rotation to increase contact area between gas phase and liquid phase and then to enhance mass transfer efficiency.RPB has been successfully applied into synthesis for nanometer materials,absorption of the volatile components from organic matters,desorption of oxygen from oil field by water injection and so on.It is important for the design and optimization of its structure to study the characteristic of hydrodynamics and mass transfer in RPB,which can extend the industrial application of RPB.Therefore,this work adopted the combination of experiment-method and simulation-method.On one hand,we utilized experiment-method to summarize the characteristic of hydrodynamics and mass transfer.On the other hand,we made use of computational fluid dynamics(CFD)software,to obtain the characteristic of hydrodynamics and mass transfer performance,which can reveal process mechanism and save the time and energy.This study utilized water-nitrogen system to respectively investigate the characteristic of dry and wet bed pressure drop for two types of packing(ball packing and wire packing)in a RPB.At the same time,water deoxygenation process by pure nitrogen was established to study the characteristic of mass transfer in a Rotated Random ball-packing Bed.Based on the experiment,a three dimensional gas-liquid flow and mass transfer model was established,which investigated the effects of gas flow,rotational speed and other operating conditions on pressure drop,liquid holdup and mass transfer performance.Main conclusions were as following:1 The experimental results of polytetrafluoroethylene ball packing and wire packing indicated that the dry bed pressure drop of two packings is positively related to gas flow rate and rotational speed.Under the condition of gas-liquid ratio 16-125,wet bed pressure drop of the two packings were measured and the values were obviously affected by gas flow rate but almost independent on liquid flow rate.Wet bed pressure drops are all a little bigger than dry bed pressure drops.Compared with that of wire packing,the dry bed pressure drop of random ball packing is higher and the wet bed pressure drop is lower than that of wire packing.2 The mass-transfer experimental results of water deoxygenation process for random ball packing revealed that under the condition of gas-liquid ratio 2-14,desorption efficiency is up to 95%.The desorption efficiency is higher when the gas flow rate,liquid flow rate and rotational speed increase.Mass transfer coefficient increases with the increase of various operating conditions,and the value ranges from 0.10 to 0.40.Gas flow rate has little influence on mass transfer coefficient.3 The porous medium model and actual ball-packing model were established to study the flow characteristics of gas phase.The simulated results which are obtained by the adoption of standard k-? turbulence model are in agreement with the experimental results with deviation within±20%in the condition of lower rotational speed and lower gas flow rate.Moreover the simulated results which are obtained by the adoption of realizable k-s turbulence model are in agreement with the experimental results with deviation within±20%in the condition of lower rotational speed and higher gas flow rate as well as higher rotational speed.The result of simulation provides basis for the selection of appropriate turbulent model.At the same time,the validity of the model is proved which can lay the foundation of gas-liquid two-phase flow study.4 A three dimensional geometrical model of gas-liquid countercurrent rotating packed bed was established.In the gas-liquid flow and gas-liquid mass transfer simulation Euler-Euler model was applied.The simulated results indicate that the trend characteristic of wet pressure drop is the same with those of the experiment data.Gas flow rate has little influence on liquid holdup,but when rotational speed increases,liquid holdup decreases.A three dimensional real packing model for gas-liquid mass transfer was firstly established.The results of simulation showed the process of deoxygenation from the liquid phase to the gas phase which provided the idea for further research.