Experimental Study And CFD Simulation Of Hydrodynamics And Mass Transfer Performance For WPA Structured Packings

Structured packing columns are widely used in many separation processes,because of the high capacity and efficiency.The performance of the structured packings has significant impact on the stability of the whole process,energy consumption,product purity and environment.In the pursuit of product quality and energy efficiency,the development of novel packings with low energy consumption and high efficiency is necessary and important.Based on the previous work,we focus on developing novel packings named WPA(wavelike poly-line arc),which are expected to hold high capacity and better efficiency.The hydrodynamics and mass transfer performance of novel packings were studied experimentally and numerically.In the simulation,we focus on the influence of surface texture on the hydrodynamics and mass transfer performance.The main work and results of this paper are shown as follows:1.According to the mechanism of fluid flow,WPA packings were designed.The top and bottom parts of the packing sheets were bent to be vertically smooth to avoid flow direction changes abruptly between two adjacent packing layers.The middle part of WPA packings was designed as linear and circular combination to increase turbulence of the flow and increase the gas-liquid contact time.2.In the water-air system,a cold model was employed to test the hydrodynamics and mass transfer of the WPA packings in a Φ500mm packings column.The results show that the relationship between the hydrodynamics and mass transfer performance and the specific surface area is in accord with the general rule.Moreover,the correlations of hydrodynamics and mass transfer for WPA packings were given.3.In order to verify the effect of structure on performance,comparisions were made with the performance of Mellapak 125X under the same test conditions.The results show the WPA packings hold higher capacity and better efficiency:compared with Mellapak 125X,the dry pressure drop deceased by 30%;wet pressure drop droped 20%～40%,and the percentage of decrease increased with the increase of liquid spray density;The flooding gas velocity increased 120%;The mass transfer efficiency of WPA 125 is higher in the liquid spray density range of 16.87 m3/(m2·h)≤L≤22.49m3/(m2·h);In he spray density range of 28.11 m3/(m2·h)≤L≤50.60m3/(m2·n),the mass-transfer efficiency of WPA 125 is almost the same as Mellapak 125X at lower gas velocity;With gas velocity increases,mass transfer efficiency is higher than that of Mellapak 125X.4.The influence of surface texture on the thickness of liquid film,the effective wetted area and liquid holdup is firstly connected with the whole tower pressure drop by using the multi-scale CFD method.In simulation procedure,the average thickness and effective wetting area are calculated using 2D and 3D unsteady VOF model.The pressure drop of the whole tower was simulated by using the porous medium model.The CFD results show the rough surface held a positive effect on both average film thickness and liquid holdup because of the accumulation of liquid at the trough.At the same time,the transverse diffusion of the liquid on the smooth surface caused the effective wetted area increased,but the difference of the effective wetted area was not as obvious as the average liquid film thickness and liquid holdup.The average relative deviations between the experimental data and the simulated results for wetted pressure drop on two surfaces are both about 10%.The deviation between the simulated results of smooth surface and experimental data of rough surface is about 20%.According to the focuses to determine whether the texture structure of the packing surface is ignored during the physical modeling.5.Based on the two phases flow CFD model,a mass transfer CFD model for desorption is presented.Through the analysis of flow field,it is verified that the WPA packing structure has a positive effect on mass transfer.At the same time,the mass transfer characteristics of the smooth surface and rough surface are studied.For low Reynolds number,mass transfer efficiency of smooth surface is approximately 20%higher than that of rough surface.For high Reynolds number,the smooth surface is only 5%above the rough surface.The surface of the packing can not be simply treated as a plane when the mass transfer CFD simulation is carried out,especially at low Reynolds number.6.The dry and wet pressure drop models for WPA packings were proposed.Structure factor was introduced in the dry pressure drop model,and the calculated data is equal to experimental data with a discrepancy less than 5%.The wet pressure drop model was based on the Delft mechanism model,and the Delft model is combined with the results of the CFD simulation.The relative deviation between the calculated values and the experimental values is about 10%.Then,the universality of the model was verified,and the model is applied to the packing in the literature.The relative deviation between the calculated data and the experimental data is within 10%.The model can provide theoretical surpport for the design of new packings.