Study On Fluid Behavior And Structure Optimization In Multiliquid-inlet Rotating Packed Bed

As a process intensification technology for green chemical industry,high gravity(HIGEE)technology exhibits superior performance in molecular diffusion and gas-liquid mass transfer processes,and has been widely exploited in various industrial fields such as waste gas treatment.Rotating packed bed(RPB)is a kind of typical HIGEE device.Relying on high speed rotating packing,RPB can efficiently split and break up liquid,so as to improve gasliquid contact area and accelerate gas-liquid surface regeneration.Considering the fluid flow in the RPB is changeful,especially for the RPB with novel structure,it is necessary to adopt combined tools to reveal fluid flow behaviors more comprehensively.In addition,the gas and liquid flow behavior directly determines the gas-liquid mass transfer performance.Thus,the fluid research can further guide the structure optimization for RPB performance improvement.As a kind of novel RPB,Multiliquid-inlet rotating packed bed(MLI-RPB)has good characteristics of pressure reduction and mass transfer improvement as well as a good application prospect for gas-liquid absorption,due to its lack of partial packing and its multi-end effect zones.Inspired by the simulation concept of Digital Twin(DT),three dimensional(3D)printing technology is employed to realize the seamless connection between Virtual MLI-RPB for simulation and Real MLI-RPB for experiment.The combined method of experiment plus simulation provides comprehensive flow information of gasphase and liquid-phase in different zones of MLI-RPB,which are quantified to describe its properties of gas disturbance and liquid dispersion,etc.Computational Fluid Dynamics(CFD),as a supplementary means of fundamental research,can obtain details that cannot be conveniently observed in experiments.Also,as a reliable tool to guide structure optimization,it efficiently accelerates the innovation and development of product.The optimized internals of Virtual MLI-RPB is 3D-printed again to complete the interactive feedback with Real MLI-RPB,which obviously enhances its deep desulfurization.This approach of CFD simulation plus 3D printing realizes the digital accurate manufacturing for optimized structures of RPB,thus developing a research idea from efficient optimization to rapid prototyping.In summary,this work provides a strategy for comprehensive investigation of fluid flow behavior in RPB,provides a reference case for structure optimization of RPB and provides a DT model foundation of MLI-RPB for its wider engineering application in the future.The main research results are as follows:1.Three kinds of structure design for Virtual MLI-RPB were discussed including arrangement of vertical fibers,diameter ratio of packing rings and internals in the annular hollow zones.According to the Virtual MLI-RPB constructed by 3D modeling,the wire mesh packing of Real MLI-RPB is manufactured accurately and controllably via 3D printing technology.Firstly,the gas phase flow field in MLI-RPB was studied.On the one hand,pressure drop experiment was carried out on Real MLI-RPB,and the overall pressure drop and pressure distribution were studied.On the other hand,CFD simulation was carried out on Real MLI-RPB to obtain gas flow details that could not be obtained using porous media model such as velocity distribution and gas turbulence.The experiment and simulation are complementary to each other,and the gas flow behavior in MLI-RPB is studied comprehensively,which establishes a reliable method for the further optimization.2.Different from traditional manufacture tool,wire mesh packing can be more easily prototyped without basement disk via 3D printing,which makes it possible to visualize optically the liquid flow behavior in packing zone.On the one hand,the high speed photography experiment was carried out on the Real MLI-RPB.Macroscopic dispersion under a big shooting window was qualitatively observed using short focal length lens.Details of liquid flow out of packing zone were quantitatively observed using long focal length lens,including the droplet size and size distribution,droplet velocity and flight direction,etc.On the other hand,CFD simulation was carried out on the Virtual MLI-RPB,so that details of liquid flow in the packing zone were supplemented such as disintegration distance of liquid film.The liquid flow behavior in MLIRPB is studied comprehensively,which establishes a reliable method for the further optimization.3.Based on the simulation method established above,the internals were analyzed and compared,aiming to strengthen the gas-liquid surface renewal.Different internals have little influence on the macroscopic gas-liquid flow,such as overall pressure drop and liquid droplet behavior in outer cavity zone.Main difference is in the annular hollow zones between packing rings:On the one hand,the shear of gas phase between internals and the edge of three packing rings strengthened the turbulence in the gas phase,and the turbulent kinetic energy in the gap was increased by 2-5 times;On the other hand,repeated collision and fusion of droplets between internals and packing rings enhanced liquid dispersion,and the liquid holding capacity of the packing ring was increased by up to 20%.The comprehensive evaluation of A(0°,0°),C(-30°,-30°)and D(+30°,-30°)type internals is more conducive to gas-liquid surface renewal,which is mainly reflected in the disintegration of liquid film and the repeated collision and fusion of liquid droplet.It is expected to be conducive to improving the gas-liquid mass transfer performance of MLI-RPB.4.In the background of more and more strict standard for SO2 emission in China,the deep desulfurization performance of MLI-RPB was explored for industrial application.Using mixed solution of Na2SO3 and NaHSO3 as absorbent,the effects of pH value,sodium ion concentration,initial SO2 concentration,rotating speed,liquid flow rate,gas flow rate and liquid inlet mode on the desulfurization rate of MLI-RPB were investigated respectively.Referring to the simulation results about internals in the previous chapter,a new MLI-RPB reactor with low pressure drop and high desulfurization rate was developed through 3D printing feedback interaction,so that it could meet the engineering requirements at a lower rotational speed.Beseides,the experiment result is consistent with the simulation prediction,and further verifies the availability of the simulation optimization method in this study.5.With the help of CFD simulation plus 3D printing,this study developed an efficient strategy from accurate optimization to rapid manufacturing,which perfectly connected the virtual digital model with the actual application structure.It provides a combined research method for more comprehensive flow field information in RPB,shows a reference case for structure optimization of RPB,establishes a DT model basis for the engineering application of MLI-RPB,and expands the engineering guidance of CFD simulation for pilot RPB.