Dense-phase fluidized beds cyclones

Bed components in a dense-phase fluidized bed include the gas distributor, cyclone, dipleg, heat exchanger, expanded section, and baffles, as shown in Fig. 9.4. The basic function of each component in a fluidized bed is described in the following. 

A dense phase fluidized bed generally consist of a gas distributor, a cyclone, a dipleg, a heat exchanger, an expanded section, and baffles [44]. A schematic representation of a dense phase fluidized bed reactor is shown in Fig 10.3. 

As the gas velocity is increased beyond 17 a point is reached at which the particles are transported out of the bed altogether either in dense-phase or in dilute-phase pneumatic transport the velocity at which this occurs is called the transport velocity, C/tr- In order to maintain a constant inventory of particles in the bed at velocities in excess of 7tr it is necessary to recycle them via external cyclones and a standpipe, a geometry known as a circulating fluidized bed. A comprehensive review of the literature on circulating systems has been given by Grace et al. (1997), and the subject is also dealt with in Chapter 19 of this handbook. 

Fluidization occurs in stationary (segregation of bed and free board), turbulent (circulating fluid bed), and forced dense-phase (transport reactor) mode. All systems require hot gas cyclones either to recycle entrained particles back into the fluid bed or just to separate them from the product gas. 

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