準二次元気系流動層中における粗大球の偏析挙動 (粗大球濃度の影響). (Japanese)

Segregation of Large Spheres in a Pseudo Two-Dimensional Gas-Fluidized Bed (Influence of Mass Fraction of Large Spheres). (English)

Gas-fluidized beds are used for the combustion and gasification of solid materials such as biomass pellets and municipal solid wastes. For the enhancement of fluidization and heat transfer, inert bed materials also exist in the beds. Because the characteristics of these raw and bed materials (particle size, shape and density) largely differ from each other, the fluidization of binary systems shows diverse and complex behaviors. In this study, segregation of binary mixtures with large size difference in a gas-fluidized bed is investigated numerically. For simplicity, we consider a pseudo two-dimensional bed and the spherical shape is assumed for both large and small solids. We focus on the influence of mass fraction of large spheres For small mass fraction case, the bed is well fluidized and a segregation occurs as we expected. When the mass fraction of large spheres becomes large, on the other hand, the bed is well fluidized at first, but it gradually and partially stops with the progress of segregation which induces the decrease of local mass fraction of large spheres. Defluidization is caused by the segregation of large spheres, which partially reduced the mass fraction of large spheres in the bed, preventing the bed to fluidize. The fluidization and segregation have a mutual influence. When the local mass fraction of large spheres is large, the bed becomes easier to fluidize because the local gas velocities increase in the gap between adjacent large spheres. We also found, even in the case local mass fraction of large spheres is large, the fluidization becomes difficult if the coarse spheres are not sufficiently surrounded by small particles. Although the local mass fraction of the large spheres has a great influence on the fluidization, the packing fraction of the smaller particles around the large spheres is also very important in the fluidization. [ABSTRACT FROM AUTHOR]

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