Circulating fluidized beds

This chapter describes the key characteristics and the key operating parameters, such as superficial gas velocity and solids circulation flux, of circulating fluidized beds (CFBs). It illustrates the nonuniformity of radial profiles of solids distribution in the CFB, as well as mixing of solids and gases in the CFB. Axial and radial distributions (profiles) of the various parameters are often used to characterize the hydrodynamics and reactor performance inside risers, including solids holdups, gas and particle velocities, etc. The chapter discusses the reactor performance of CFBs and the effect of reactor diameter on CFB hydrodynamics. Compared with conventional low-velocity bubbling and turbulent fluidized bed reactors, CFB reactors offer several key advantages. These advantages are achieved at the expense of some reduction in heat transfer coefficients between heat transfer surfaces and the bed (or suspension) and somewhat greater temperature gradients than in dense beds.