TRANSITION FROM TURBULENT TO FAST FLUIDIZATION

Based on eight transition criteria, at least two types of transition velocities are identified for the demarcation of the transition from turbulent to fast fluidization. The "critical velocity," U se , corresponds to the significant entrainment of particles from the bed, beyond which a circulating fluidized bed operation becomes essential. The "transport velocity," U tr , defines the transition to fast fluidization based on the axial solids concentration profiles. Below this velocity, a distinct interface exists between a top dilute region and a bottom dense region. Above U tr , the variation of voidage with height becomes relatively smooth. U tr is found to be a function of measurement location and riser height, as well as gas and particle properties.