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

摘要： 在炼油/化工领域，一些新工艺涉及到两种功能/物性不同的催化剂颗粒与气相的混合及流动。本研究采用数值模拟的方法考察了Geldart A类和Geldart D类二元混合颗粒在气固流化床-提升管耦合反应器底部区域的流动特性。采用欧拉-欧拉多相流模型，考虑介尺度非均匀结构的影响，引入基于能量最小化多尺度原理的EMMS曳力模型，建立了气固流化床中二元颗粒的流动模型。通过分析二元颗粒体系的床层密度分布和床层压降分布的转折点，确定了密相区和稀相区的相交界面高度。沿床层轴向方向，通过对比床内两种颗粒的相对截面平均固含率，发现Geldart D类颗粒倾向于在床层底部运动；同时，大粒径/低密度颗粒和小粒径/高密度颗粒的二元颗粒体系的床层底部区域密度分布更稳定。沿径向方向，Geldart A类颗粒和Geldart D类颗粒均趋向边壁运动。定义相对固含率作为定量考察颗粒径向运动趋势的参数，发现Geldart D类颗粒较Geldart A类颗粒向边壁区域浓集的趋势更明显。

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