Simulation On Hydrodynamics And Gas-Liquid Mass Transfer In Gas-Liquid-Solid Circulating Fluidized And Experiment In Expanded Bed

Gas-liquid-solid fluidized beds,as vital operating units in the engineering area,have been widely used in industrial application.In this work,hydrodynamics and gas-liquid mass transfer characteristics in the gas-liquid-solid circulating fluidized bed riser are systematically studied by numerical simulations.And experiment about hydrodynamics in gas-liquid-solid fluidized bed with small-particles is carried out to make preparation for studying the mass transfer characteristics.Based on ANSYS FLUENT^? 18.1 platform,the Euler-Euler-Euler method coupled with the Population Balance Model is applied to simulate the flow field and gas-liquid mass transfer characteristics in the gas-liquid-solid circulating fluidized bed,where the gas phase,the liquid phase and the solid phase（they were air,water and glass beads of 0.4 mm）are chosen as the Euler phases.How the Euler-Euler-Euler method coupled with the PBM is achieved through the flow field and the interphase interaction.Firstly,the bubble diameter is divided into 15 groups based on the PBM,and the Luo breakage model and the Lehr breakage model are compared in this work.It turns out that the bubble diameter distribution obtained from the Luo model is in double summit,which is inconsistent with reported experimental distribution in the literature.However,the bubble diameter calculated from the Lehr breakage model is in normal distribution and closer to the experimental data,thus it is selected in the following study.Secondly,the bubble diameter distribution predicted through the PBM is added into the adjusted drag model,which is compared with the normal drag model in terms of the radial distribution of the gas holdup,and it is revealed that the adjusted drag model can predict the radial non-uniform distribution better.Lastly,the effect of the superficial gas velocity,the superficial liquid velocity and the particle circulating rate on the gas holdup,solid holdup,the interfacial area,the gas-liquid mass transfer coefficient and the volumetric mass transfer coefficient is investigated.It is proved that the CFD-PBM coupled model can simulate the hydrodynamics and the gas-liquid mass transfer characteristics in the gas-liquid-solid circulating fluidized bed riser reasonably,but the effect of the particle circulating rate on the phase holdup and interfacial area need more adjustment.Besides,the experiment in the gas-liquid-solid fluidized bed（the diameter of particles is 0.6-0.8 mm）is carried out in terms of the hydrodynamics using the BVW-2 conductivity probe and immersion-type online multiphase measuring instrument.The effect of the superficial gas velocity and the superficial liquid velocity on the expended ratio,the ratio of transition length,bubble rising velocity and the phase holdup is studied in this work.It is discovered that compared with the superficial gas velocity,the superficial liquid velocity has stronger impact on the expended ratio.The ratio of the transition length keeps growing and then constant with the superficial gas velocity increasing,while it changes a little as the superficial liquid velocity increases.The average gas holdup and solid holdup increase linearly when the superficial gas velocity grows.But as the superficial liquid velocity increases,the average gas holdup barely changes and the average solid holdup decreases.All above research results can provide guidance for the design and scale-up of the gas-liquid-solid fluidized bed.