Studies Of Liquid Flow Behavior And Mass Transfer Performance In A Rotating Packed Bed With Constant Cross-sectional Area

As one of the typical process intensification technologies,high gravity technology relies on the high-speed rotation of porous packing in a rotating packed bed（RPB）to produce the high gravity environment,which can accelerate the renewal of gas-liquid interface via disintegrating liquid,then intensifying the mass transfer process.Packing is the core component of an RPB,and its structure is closely related to the fluid flow bahavior and mass transfer performance.The conventional mesh packings formed by the coiling meshes with constant porosity have an increasing cross-sectional area along the radial direction,which negatively affects the fluid flow behavior and mass transfer performance.Therefore,the idea of developing the new type of packing with controllable cross-sectional area was innovatively put forward in this study,targeting at the widely adopted mesh packing in RPBs.The novel mesh packing with constant cross-sectional area was innovated.The strategy of“computational fluid dynamics（CFD）simulation+three-dimensional（3D）printing+experimental feedback”on structure optimization has been adopted.In detail,the packing geometry was optimized from two aspects of“main geometry”and“structural unit”.The main results are as follows:（1）Aiming to improve the global liquid distribution,the mesh packings with different structures and controllable cross-sectional area were designed and precisely fabricated via using 3D printing technology.The mass transfer performance of those mesh packings were systematically evaluated via chemical absorption of the Na OH-CO₂ system and physical desorption of the H₂O-O₂ system,resperctively.Results indicated that the concentric mesh packing,of which vertical fibers could be arrayed as stagger as possible between adjacent mesh layers to enhance the probability of liquid breakup.Thus,the concentric mesh packing exhibited higher a_e and k_La_e than the coiled one.Additionally,the concentric mesh packings with constant cross-sectional area along the radial direction improved the mass transfer performance.In detail,it exhibited 25.5%and 14.7%higher of a_e and k_La_e than those of the coiled one.According to the dimensionless analysis,the correlations for prediction of a_eand k_La_e,considering previous and current data,were respectively established with acceptable deviations.（2）The structural unit—“fiber cross-sectional shape（CSS）”of mesh packing was further optimized for the purpose of regulating the liquid flow pattern,aiming at controlling the liquid flow behavior and liquid elements size.In view of the fact that the initial liquid distribution in the entrance region of the packing zone significantly affects the liquid dispersion inside the entire packing,the flow behavior of liquid jet impacting on rotating single-layer meshes was studied,with a consideration of the impacting positions on both the vertical and horizontal fibers.The effects of various fiber CSSes on liquid flow pattern and dispersion characteristics were clearly illustrated by visualization and CFD simulation.The typical liquid flow pattern and dynamic dispersion mechanism were qualitatively analyzed.The curved surface allowed liquid to flow around fiber and converge again,then generated liquid ligaments and films perpendicular to the rotational axis.The sharp edges of quadrangular fiber hampered separated liquid to converge,thus generating liquid films parallel to the rotational axis.Additionally,the droplet diameter and liquid distribution were quantified.The mesh composed of vertical quadrangular fiber and horizontal elliptical fiber outperformed the mesh with circular fibers in controlling the liquid flow patterns and intensifying liquid dispersion.（3）In view of the fact that the liquid flow patterns including droplets,ligaments,and films formed in entrance region of the packing zone are differ from the initial liquid jet,thus the liquid flow behavior were futher clarified after fully developed in the entair packing zone.The liquid flow characteristics in synthetically optimized multi-layer mesh packing with constant cross-sectional area were studied via high-speed camera in an RPB.The liquid flow patterns and transitions in the new packing（V_QH_E）and its counterpart（V_CH_C）were analyzed,respectively.The d and u of liquid droplet inside RPB were studied.Results indicated that the average diameter and velocity of droplet in V_QH_E were lower that those in V_CH_C.According to the dimensionless analysis,the correlations for prediction of droplet diameter and velocity were established based on the data of this work.The deviations between predicted values and experimental values were less than±20%.（4）Based on the understanding of liquid flow patterns and dispersion properties in various packings,it can be speculated that V_QH_E with optimized fiber CSSes has the great prospect to alleviate the blockage of mesh packing caused by sulfur generation in desulfurization.Hence,the H₂S removal with chelated iron solution was investigated in an RPB.The results indicate that V_QH_E exhibited superior H₂S removal efficiency and mass transfer performance than V_CH_C.The H₂S removal efficiency of V_QH_E could reach up to 99.3%under the experimental operations.The V_QH_E obtained larger mass transfer cofficient by 25.9%than that of V_CH_C.The sulfur adhesion on the packing surface after continuous operation was observed.A less amount of solid sulfur was deposited on V_QH_E,leading to a smaller mass increase ratio than that of V_CH_C.As a consequence,V_QH_E with optimized fiber was an integration of strengthening H₂S removal efficiency and alleviating blockage.The novel PRB with constant cross-sectional area exhibits prospects in the systems confronted with blockage caused by solid products.