(152b) Modeling of dense particle flow in the annulus of spouted beds with draft tube

Spouted beds provide good gas-solid contacting for coarse, irregular granular materials that conventional fluidized beds have some problems to hand for. However, the behavior of slow dense flow of granular solids in the annulus of spouted bed is still not well understood. In this work, an axi-symmetrical granular flow model based on the Mohr-Coulomb analysis is used to predict the stress and velocity distributions in the annulus of a spouted bed with draft tube. Coulomb's criterion, which is widely used in soil mechanics, provides the basis for the analyses. A new idea of the determination of stress discontinuities using the method of characteristics (MOC) is proposed, and then the stress and velocity equations are solved using MOC. The results show the details of stress variations which have never been investigated before. The method of differential slices, an approximate method, gives a very close prediction to MOC in active state zones, but has great differences with MOC in passive state zones. The velocity directions have a sudden change at each discontinuity, thus velocity jumps along the radial coordinate that has not been observed in the experiments are predicted. The calculated velocities are consistent with the experiments on an average.