CFD-DEM investigation of heating process of coal tar pitch in packed and bubbling fluidized beds

To grasp the heating characteristics of coal pitch spheres in different bed structures, a 3D model for computational fluid dynamics-discrete element method (CFD-DEM) with coupled heat transfer was adopted to investigate the gas-solid flow and heat transfer characteristics in packed and bubbling fluidized beds. The following results were obtained: gas-solid flow and heat transfer structure, convective heat transfer intensity, heating rate and temperature uniformity under different flow regimes, the ratio of height to diameter, and the ratio of thickness to width. The results show that avoiding the local high-temperature particle region is less formed in bubbling fluidized beds compared with that in packed beds. When the ratio of height to diameter is greater than 0.95, it has little effect on the temperature rise of particles in the bubbling fluidized bed. The cooling time of the tracking particles in upper region increases with the increasing ratio of height to diameter, resulting in a larger temperature drop. The wall effect gradually decreases with the increase of the ratio of width to thickness, the rising velocity of bubbles and the kinetic energy of particles both increase, making the internal circulation rate of bed particles accelerate, the gas-solid temperature difference at the bottom of bed increases, and the heating rate of bed particles increases by about 24.2%. © 2020, Editorial Department of Journal of Southeast University. All right reserved.