Stable Operation Condition for a Spouted Bed Equipped with a Moving Bed Downcomer with an Orifice

Abstract

The smooth transfer of solids from upper stage to lower stage through a downcomer is important for a stable operation of multi-stage spouted beds. Behavior of gas and solids in a moving bed downcomer, which is fitted with an orifice at the bottom, under negative pressure gradient has been investigated experimentally for a spouted bed operation, using Geldart D particles as bed materials. For this study, a downcomer has been installed in a one-stage spouted bed.
As the results, the limits of operating conditions for a stable operation of a spouted bed with a downcomer were determined experimentally. The limits were influenced by the pressure drop across the spouted bed at the minimum spouting, length of the downcomer and the pressure gradient of the moving bed in the downcomer. Also, the range of the operating conditions for stable operation was extended with decreasing the bed depth of the spouted bed. In addition, based on experimental observation, the moving bed flow pattern changed from stable flow to intermittent flow as the gas pressure gradient in a moving bed downcomer increased and the fact could be explained by the solids discharge model which expresses the gas and the particles flow in the vicinity of the orifice.