Entrance effects at a multi‐orifice distributor in gas‐fluidised beds

Abstract

AbstractThe behaviour of multi‐orifice distributors in gas‐solids fluidised beds has been studied with particular regard to the height of the entrance effect and the mechanics of gas‐solids flow in the region immediately above the distributor plate.A model is proposed to predict the height of the entrance effect for a given distributor and gas‐solids system at various fluidising flow‐rates, and good agreement has been found with experiment. Experiments have been carried out with (a) a two‐dimensional air‐fluidised bed using three sizes of sand particles (dp: 137, 263, and 350 μm) and four distributors (orifice diameters: 0.001 m, 0.002 m; orifice spacings: 0.025 m, 0.05 m); and (b) a three‐dimensional air‐fluidised bed, 0.3 m square in cross‐section, using 350 μm sand particles on a distributor with 0.003 m diameter orifices at a spacing of 0.04 m.The principal factors influencing the height of the entrance effect were found to be the incipient fluidising velocity, mean particle size, orifice spacing and gas flow‐rate. The model has been used to estimate the minimum ratio of distributor pressure drop to bed pressure drop to bring about an even distribution of gas at the bottom of the bed.