Flow behaviors in the downer of a large-scale triple-bed combined circulating fluidized bed system with high solids mass fluxes

Abstract

The flow behaviors in the downer of a large-scale triple-bed circulating fluidized bed (TBCFB) gasifier cold model, which is composed of a downer (φ 0.1m×6.5m), a bubbling fluidized bed (BFB, 0.75×0.27×3.4m3), a riser (φ 0.1m×16.6m) and a gas-sealing bed (GSB, φ 0.158m×5m), were investigated. Sand particles with a density of 2600kg/m3 and an average particle size of 128γm were used as bed materials. Solids mass fluxes were in the range 113-524kg/m2s. Average solids holdup in the developed region of the downer increased with increasing solids mass flux. The gas seal between the riser and the downer had a large effect on the solids holdup distribution in the downer. Compared with the solids holdup in the riser, a relatively low solids holdup was formed in the downer even at high solids loadings. A pressure balance model was set up to predict the solids mass flux for this TBCFB system. It was found that the static bed height in the GSB had a great effect on the solids mass flux. The possibilities of achieving a high density solids holdup in a downer were discussed. © 2011 Elsevier Ltd.