Local solid particle behavior inside the upper zone of a circulating fluidized bed riser

Abstract

The solid phase behavior is studied in the upper zone of a circulating fluidized bed riser with glass particle of mean diameter 107 μm, using a Phase Doppler Anemometer. Superficial gas velocities U g > U c are investigated covering the turbulent and the fast fluidization regimes and this for three static bed heights ( H s = 50 mm, H s = 100 mm and H s = 150 mm). The results show that the mean axial particle velocity lateral profile shapes found parabolic for H s = 50 mm, devolve to a concave shape for H s = 100 mm and H s = 150 mm, creating a particles speeding zone between the core and the annulus zones. For both axial and transversal standard deviations of particle velocities in the core region, the values for the three static bed heights unite to form two stages of evolutions with U g, where the transition velocity between these stages is found associated to the appearing of a significant entrainment of solid particles. At this transition velocity, the transversal movement originally directed toward the center riser, undergo a change toward the wall beginning near the wall and spreading into a large part of the section riser with increasing U g. A discussion on the boundary between the turbulent and fast fluidization regimes is made based on these results.