3D Full-Loop Simulation of the Effect of Air Distribution on Gas-Solid Flow Uniformity in a Pilot-Scale CFB Apparatus

The primary air distribution in the wind box of a circulating fluidized bed (CFB) boiler is one of the important factors that influence the bed material fluidization and coal combustion efficiency. To investigate the air distribution on gas-solid flow characteristics and to improve the gas-solid flow uniformity in a CFB, three simulation cases were implemented based on a three-dimensional (3D) full-loop pilot-scale CFB apparatus. The furnace width is 1.137 m and the depth is 0.392m. In the simulation, the air distribution plate was replaced by a baffle that allowed air to pass through and prohibited the passage of particles. The air distribution plate was divided into two parts: a central region and a surrounding region. The resistance of the central region was set as 2.5 kPa, while the resistances of the surrounding region were set as 2.5, 2, and 1.5 kPa, respectively, in three simulation cases. The simulation results showed that when the resistances of the air distribution plate in the central and the surrounding region were the same, the air velocity near the air distribution plate in the wind box exhibited a saddle profile in width direction and an inverted U-type profile in depth direction. The particle volume fraction near the air distribution plate in the furnace showed a W-type shape profile in width direction and U-type profile in depth direction. With the decrease of surrounding region resistance of the air distribution plate, the average air velocity of the central region of the wind box near the air distribution plate decreased, while that of the surrounding region increased. Correspondingly, the particle volume fraction in the central region of the furnace increased, while that in the surrounding region decreased. The uniformity of particle volume fraction was the best when the resistance of surrounding region was 1.5 kPa.