Flow regimes and axial pressure profiles in a circulating fluidized bed

Abstract

The hydrodynamics and flow regime in fast fluidized beds of FCC and silica sand particles were determined in a Plexiglas column (0.1 m i.d. × 5.3 m high). The transport velocity ( U tr) was determined by the emptying time and flooding point determination methods. At a given solid circulation rate, solid holdups in the upper dilute region exhibit their maximum values with variation of gas velocities, where a dense region forms at the bottom of the riser. The gas velocity at which solid holdup in the upper dilute region exhibits a maximum value is defined as the fast transition velocity ( U FT). The fast fluidization regime can be divided into the fast transition region and the fully developed fast fluidization region. A demarcation line between the two regions is proposed. The fast transition velocity and the transition velocity ( U FD) to pneumatic transport have been correlated. The transition velocity of the fast fluidization region can be predicted by the choking velocity, U FD and U FT.