Numerical Simulation Of Two-phase Flow Characteristics And Structural Optimization Design In Gas-solid Fluidized Bed

Gas-solid fluidized bed has been widely used in energy,chemical,pharmaceutical,petroleum,metallurgy and other industrial fields due to its own advantages.The phenomenon of particle agglomeration is common in the two-phase mixing process in a gas-solid fluidized bed.Taking some timely and effective control measures to avoid particle agglomeration from further forming lumps or agglomerations is of great significance for the stable operation of the fluidized bed reactor.In this paper,preliminary numerical simulation analysis is performed on coarser Geldart B particles?glass beads with an average diameter of 550?m?.The study found that the accumulation of particles in the gas-solid fluidized bed due to particle agglomeration severely reduces the gas-solid contact efficiency,thereby affecting mass and heat transfer in the fluidized bed.In order to weaken or even eliminate the accumulation phenomenon caused by particle agglomeration and fluidized dead zone in the fluidized bed,with the help of fluid dynamics simulation software FLUENT 19.1,the Euler two fluid model?TFM?method was used to study the fluidization performance of particles in a gas-solid fluidized bed filled with coarse Geldart class B particles from three aspects:height-to-diameter ratios,inlet gas velocity and distribution plate structure.First,the sensitivity analysis of the particle-particle collision particle-particle collision restitution coefficient e_ss was carried out in a two-dimensional fluidized bed.The influence of ess on the simulation results of axial time-average particle velocity,initial gas-solid phase mixing process,bubble size,bed expansion rate,etc.was studied.The research shows that under different height-diameter ratios,the influence of ess on the gas-solid fluidized bed numerical simulation results is not negligible,mainly reflected in the gas-solid two-phase mixing process.At the same time,the simulation error was analyzed in combination with the experimental data in the literature to determine the appropriate ess value for the subsequent numerical simulation of the fluidized bed.The study further developed three-dimensional numerical simulation of gas-solid fluidized bed,mainly from two aspects of height-diameter ratio and inlet gas velocity.The analysis of the two-phase mixing characteristics in the gas-solid fluidized bed at different height-diameter ratios showed that:when the height-to-diameter ratio H/D=1.5,in the middle region of the fluidized bed,the radial particle velocity and radial gas velocity distribution were relatively uniform and the fluctuation was smaller,the area of the dead zone formed by the particle agglomeration in the fluidized bed was smaller,and better gas-solid phase mixing was obtained.Therefore,under certain simulation conditions?same gas velocity and reactor inner diameter?,there was an appropriate height-to-diameter ratio to make the particle accumulation area in the fluidized bed smaller and the particle fluidization effect better.In addition,the study also investigated the two-phase mixing characteristics in the fluidized bed when the inlet gas velocities were the minimum fluidization velocities U_mf,3U_mf and 6U_mf,respectively.The research showed that the increase of the inlet gas velocity almost eliminated the accumulation of particles in the fluidized bed due to particle agglomeration,and the gas-solid phase can achieve more thorough mixing,significantly improved the fluidization quality of the particles.Finally,the characteristics of gas-solid two-phase mixing in a fluidized bed under the design of uniform and non-uniform distribution plates at different opening ratios??=0.15%,?=0.62%,and?=1.34%?were discussed respectively to study the performance of the distribution plate,the performance of the distribution plate was studied from the pressure drop of distribution plate,radial gas velocity and particle velocity.By comparing the fluidization effect of the particles above the distribution plate and inside the fluidized bed,the resulted show that with the increase of the opening ratios,the pressure drop of the distribution plate decreased significantly.When?=0.62%,compared with the non-uniformly distributed plates arranged in a circle,the uniform distribution of the square arrangement can significantly reduce the dead zone and channel flow formed by particle agglomeration in the fluidized bed,thereby improving the fluidized quality of particles,increasing the gas-solid contact efficiency and achieving the purpose of design optimization of the gas distribution plate structure.