Solids circulation and attrition rates and gas bypassing in an internally circulating fluidized bed

Solids circulation and attrition rates and gas bypassing in an internally circulating fluidized bed (ICFB) were studied. The bed materials used were mixtures of silica sand and calcium particles. The effects of the superficial gas velocities in the annulus and the draft tube, average diameter of the calcium particles, and geometry of the draft tube on the solids circulation and attrition rates and gas-bypassing fractions were investigated. It was found that the solids circulation rate first increased with increasing superficial gas velocity in the annulus and then leveled off. It also increased with increasing superficial gas velocity in the draft tube and the orifice diameter. However, it decreased with increasing average diameter of the calcium particles. When the draft tube height increased from 25 to 35 cm, a minimum solids circulation rate occurred at 30 cm. Moreover, when the inner diameter of the draft tube increased from 3 to 5 cm, a maximum solids circulation rate occurred at 4 cm. Gas-bypassing fractions depended primarily on the solids circulation rate, superficial gas velocity in the draft tube, and state of solids packing and bed height in the annulus. The attrition rate initially depended on the solids circulation rate and the extent of collisions among the particles, and it would then reach a steady state. Therefore, the characteristics of the calcium particles were the most important factors affecting the attrition rate in ICFB. Finally, an empirical correlation equation for the steady-state solids circulation rate proposed in this study could match the experimental results.