Evaluation of the turnover times of the bed particles and of the fine powders in a circulating powder-particle fluidized bed (CPPFB)

The bed turnover time decreased with increasing the size of fine powders to a certain level and then became almost constant with further increase of the size of fine powders. When the size of fine powders was larger than this critical size, neither the size nor the hold-up of fine powders affected the bed turnover time. The bed turnover time drastically increased with increasing the hold-up of fine powders for the cases of using very fine powders of 1.0 μm or smaller. On the other hand, the average turnover time of fine powders decreased with increasing the size of fine powders to a minimum at around 3.5 μm and then increased with increasing the size of fine powders. It also decreased with increasing the gas velocity and decreasing the hold-up of fine powders in the bed. The average turnover time of fine powders was several times larger than the bed turnover time at the same operating conditions.