Fluidization Characteristics of Circulating Fluidized Bed Boilers

Abstract

The fluidization in the furnace of circulating fluidized bed (CFB) boilers is described. Data have been obtained from a 12 MWth CFB boiler and from literature. The bottom bed is bubbling rather than fast or turbulently fluidized as is often assumed. There is an extended splash zone above this bed, in which particles are thrown up by the bubbles and fall back onto the bottom bed. Other particles are carried further into the transport zone, initially as a saturated gas flow, but some particles move into the wall layers and the density decays towards the exit. The density of the transport zone is low, and the circulation rate is relatively seen small. Therefore, this flow is in a state of dilute-phase transport and not in the fast fluidization regime, such as is often claimed.