CFD simulation investigation of heat transfer characteristics in a downer bed with side nozzle
In the process of coal pyrolysis,the gas-solid flow and heat transfer behavior in the downer bed with side nozzle play a crucial role in its reaction performance.A heat transfer model considering three heat transfer mechanisms:gas-coal,gas-char convective heat transfer,and coal-char collision heat conduction,was constructed using char as the heat carrier through computational fluid dynamics CFD simulation.A detailed investigation was conducted on the effects of operating parameters such as char density,particle size,and gas velocity on the flow behavior and heat transfer characteristics in a downer bed,in order to provide some qualitative guidance for the promotion and optimization of downer beds.The results indicated that reducing the char density,particle diameter,and gas velocity was beneficial for improving the solids holdup of coal particles.The influence sensitivity to coal heating process from high to low was:char density＞gas velocity＞particle diameter.In the process of heat transfer,a char density of 900kg/m3,particle diameter of 0.4mm,and gas velocity of 10m/s,were most favorable operating conditions for gas-solid phase convective heat transfer and coal-char collision heat conduction.Among them,gas-char convection heat transfer was dominant,followed by gas-coal convection heat transfer,and collision conduction of coal-char accounts for a relatively small proportion.
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