关键词: 气固流化床, 二元颗粒, 欧拉-欧拉多相流模型, 轴向分布, 径向分布

Abstract: In the fields of petrochemical and chemical engineering, some new processes involving the reactions of gas and catalysts with distinct functions and physical properties have been proposed. Since considerable physical properties difference in density, size and shape between two types of particles,the hydrodynamic behaviors of the binary mixture in the gas-solid fluidized bed are undoubtedly complex. This work presents a numerical investigation on the mixing and flow characteristics of binary particles (Geldart A particles and Geldart D particles) and gas in the bottom region of the gas-solid fluidized bed-riser coupling reactor. Considering the non-uniform structures in intermediate scale, the Eulerian-Eulerian multi-fluid model as well as the drag force model based on the energy minimization multi-scale (EMMS) are used. The axial distributions of bed density and pressure in the binary particle fluidized bed are investigated. By analyzing the turning points of these two parameters, the location of interface between the dense phase zone and the dilute phase zone is determined. The cross-sectional average solid holdup of Geldart A particles and Geldart D particles in the axial direction is also discussed. By comparing the parameter, the relative cross-sectional average solid holdup rates of the two types of catalysts, it is found that most Geldart D particles accumulate at the bottom of the bed in the axial direction. Furthermore, when the binary particle system is composed of coarse particles with low density and fine particles with high density, the distribution of the bed density in the bottom region of the bed layer is steady. In the radial direction, by analyzing the radial distributions of the local solid holdups of the two-solid phase, it is seen that both the Geldart A particles and the Geldart D particles tend to travel towards wall area. By introducing the new parameter, the local relative solid holdup, it is revealed that the Geldart D particle has a stronger tendency towards the wall compared to Geldart A particles.

Key words: gas-solid fluidized bed, binary particles, Eulerian-Eulerian multi-fluid model, axial distribution, radial distribution