Experimental study of exit effect on gas–solid flow and heat transfer inside CFB risers

Abstract

In two bench-scale cold circulating fluidized bed (CFB) risers with similar dimension but different cross section shape, the effect of different exit geometries on both gas–solid flow and heat transfer characteristics was investigated. The measured axial distribution of solid density and bed-to-probe heat transfer coefficient along the riser were found to have good correlation at certain superficial gas velocity and solid circulating flux. Abrupt exit can bring higher solid concentration and heat transfer coefficient near the exit, even in the whole riser. Due to combining effort of cavity and collision effect, solid concentration will first increase with projected height of the abrupt exit increasing. Then solid concentration will stay constant or even decrease when projected height increases over the maximum height particles can reach.Besides exit types and operating conditions, projected height of the abrupt exit, size and shape of cross section are all important factors affecting exit effect. In this paper, exit effect becomes more significant with a circular cross section than a rectangular one.