Numerical Simulation Of Flow Characteristics Of Gas-solid Flow In Fluidized Bed

Energy-saving and environmental protection has become the two major themes inthe development of power industry. Circulating fluidized bed has been widely used inelectric power industry, with its advantages of high efficiency, low pollution and fuelused widely. Because of the characteristics of the fluidized bed itself, flow process withinthe bed is relatively complex. Studying the flow characteristics of gas-solid flow hasgreat significance for comprehensively understanding gas-solid flow in fluidized bed andlays foundation for the research of heat transfer, combustion and chemical reactions ofgas-solid in fluidized bed. With the rapid development of computer, numericalsimulation gradually is taken seriously, as a complementary and important method oftheoretical research and experimental research in the study of dense gas solid flow.The paper combined the discrete element method with computational fluiddynamics and established the mathematical model considering particle rotation toperform numerical simulation on flow characteristics of gas-solid flow in fluidized bed.Sequence diagram of particle axial and radial mixing process is obtained in thesimulation, which vividly shows the mixing process of particle in the bed. Quantitativeanalysis show that the axial mixing of particles is superior to radial mixing andimproving the velocity of fluidization air helps accelerate the mixing of particles in thebed. Radial mixing is more sensitive to the velocity of fluidization air than axial mixing.The gas velocity field, particle velocity field and the distribution of particle concentrationand particle average rotation speed is obtained in the simulation. The effect of particlerotation on particle velocity, bed expansion height and average void fraction and thefactors influencing the particle rotation speed is analyzed in the thesis. The simulationresults show that the rotation of the particles not only influences the movement of theparticles themselves but also has some impact on the flow field. The rotation speed of theparticles is not only concerned with the number of particle collisions, but it is also relatedto the intensity of collisions between particles. Particle separation characteristic ofdifferent density and diameter particles whose density and diameter is randomlygenerated at different superficial gas velocity is simulated. The results show that different density and diameter particles will appear the phenomenon of separation at lowsuperficial gas velocity. The degree of particle separation is weakened and the positionwhere particles occur obvious separation has been improved when the air inlet velocityincreases.