Pressure and apparent voidage profiles for riser with an abrupt exit (T-shape) in a CFB riser operating above fast fluidization regimes

Abstract

The influence of abrupt exit (T-shaped) configuration on the riser axial pressure profile in a large-scale circulating fluidized bed (CFB) is examined. A new analysis was developed to predict the axial voidage along the length of influence in the exit region with T-shape geometry. The exit region was characterized using non-dimensional analysis of the continuum equations (balances of masses and momenta) that described multiphase flows. In addition to deceleration length due to abrupt exit, the boundary condition for the solid fraction at the top of the riser and the fully developed regions, were measured using an industrial scale circulating fluidized bed (CFB) of 0.3m diameter and 15m tall. The operating factors affecting the flow development in the exit region were determined for three materials of various sizes and densities in core annular and dilute regimes of the riser. Performance data were taken from statistically designed experiments over a wide range of Fr (0.5–39), Re (8–600), Ar (29–3600), load ratio (0.2–28), riser to particle diameter ratio (375–5000), and gas to solid density ratio (138–1381). A series of correlations were developed to predict the voidage at the exit of the riser and length of influence due to the exit geometry. The correlations are based on gas and solid properties, operating conditions, and riser geometry.