Simulation Of Gas-solid Two-phase Flow In Bubbling Fluidized Bed By Lattice Gas Cellular Automata

The bubbling fluidized bed is a pre-reduction reactor in a fluidized ironmaking process,whose gas-solid two-phase flow problem is the core and difficult in the design,amplification and operation of the reactor.Due to the complex nonlinear interaction between the gas-solid two phases,the understanding of the typical flow laws in the bubbling fluidized bed,such as bubbles,coupling relationship between gas-solid two-phases etc.,is not sufficient and hinders the bubbling fluidized bed reaction application and process development.In view of these problems,based on the lattice gas cellular automata method,the gas-solid two-phase flow model is constructed,and the bubble phenomenon in bubbling fluidized bed is simulated,and then,the mechanism of gas-solid coupling is explored and verified on a single particle.The gas-solid two-phase flow model based on the lattice gas cellular automata method is a mesoscale model,and the conversion between model quantities and physical quantities is the basis of the construction and application of this model.To this end,based on the similarity principle,the basic quantities(i.e.length,time and mass)are obtained by the relationship of viscosity,sound velocity and density,and then the transformation relation of the derived quantities are obtained by dimension analysis.The rationality of the conversion relations are verified by the single-phase flow in a pipeline and gas-solid two-phase flow in bubbling fluidized bed.The gas-solid two-phase flow model consists of three parts: gas phase,solid phase(granular flow)and gas-solid coupling.On the basis of the lattice gas cellular automata of the gas model,the gravitational rule that characterize the surface tension between gas and solid are added.The granular flow model increases the rules of the lattice gas cellular automata,which characterize the grain gravity and dissipation characteristics,and the effectiveness of solid model was verified by the problem of unloading at the center of the free bed.In order to simplify the calculation of the interaction between gas and solid in dense granular systems,the spatial meshes of gas and solid phases are divided by the same scale,and the complex interphase coupling is replaced by the momentum exchange between heterogeneous particles.On the basis of this,the lattice gas cellular automata model of gas-solid two-phase flow is constructed.The gas-solid two-phase flow model was used to simulate the bubble phenomena in two typical bubbling beds(single nozzle and distribution plate).The simulation results show that the model can express the bubble generation and ascending process qualitatively,and the obtained bubble equivalent diameter has the same rule as the experimental and other methods.But with the rise of bubbles,the solid particles within the bubble are increased,bubble contour is not easy to identify,and the expansion of the bed is too large,these defects are related to the movement of the solid particles and are directly controlled by the coupling efficiency between gas and solid.This thesis attempts to improve these flaws,the boundary of the solid particles is projected onto the gas grid and a gas-solid coupling model of probability bounce is proposed,that is,the gas particles moving to the grain boundary react with a certain probability,and the momentum of the gas particles is accumulated and used for changes in particle motion state during the period.This improvement was first validated on a single particle,laying the foundation for further improvement of the simulation effect of the bubble.