The Flow Pattern of Solid Particles in a Downcomer with an Orifice for Multi-Stage Fluidized Beds

Abstract

It is important to obtain the critical point for steady-state operation in the multi-stage fluidized bed with a downcomer attached to an orifice.
In this work the flow of solid particles in a downcomer was studied by use of a simple apparatus instead of a multi-stage fluidized bed. In the simple apparatus, the gas flow is the same as that in a multi-stage fluidized bed but the fluidized particles on a distributor are omitted.
It is found that the flow of solid particles in the downcomer with an orifice at the outlet end strongly influences the critical point. The flow pattern of solid particles in the downcomer was observed and recognized as moving-bed flow.
The critical point was investigated experimentally by using two kinds of solid particles (sand and spherical catalyst) and downcomers and orifices of five diameters. An empirical dimensionless equation of the critical point is proposed.