Cyclonic circulation regime

The chapter begins by describing how temperature and pressure affect parameters important for bubbling fluidized beds, and then discusses their effect on regime transitions, circulating fluidized beds, and cyclones. 

It is seen that for Geldart types A and B particles, fast fluidization requires superficial gas velocities approximately an order of magnitude greater than that for bubbling dense beds. In many applications of fast fluidization, the particles exiting top of the bed are captured by cyclones and recirculated for makeup injection at the bottom of the bed, hence this regime is also denoted as circulating fluidization, CFB. 

Fig. 10.9. A typical circulating fluidized bed combustor design [63]. The furnace (riser) is normally operated in the fast fluidization regime. The ash which is entrained from the furnace is separated from the flue gas in the cyclone. Most of the ash particles are sent into the siphon. The siphon is a small bubbling fluidized bed acting as a pressure lock. From the siphon the ash flows back into the riser. Reprinted with permission from Elsevier, copyright Elsevier 2007.

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