Fluidized beds - Mass and heat transfer

In a first part of the document [BE 8 255] , the main characteristics of divided solids, their classification, and the different gas-solid fluidization regimes accessible were presented. A set of data was provided concerning the characteristics of dense and circulating fluidized beds, and those of the auxiliary devices required for the proper operation of these technologies. The performance of fluidized beds as gas-solid and solid-solid mixers was also discussed.

The various possible applications of fluidized beds are then described.

Highly efficient mass and heat exchange can be achieved by direct contact between the high-surface-area divided solid and the fluidizing gas, or between the bed and the wall of an immersed exchanger. The fluidized bed is an open, practically isothermal volume, thanks to the high heat capacity of the solids compared with that of the gases, and the particle agitation and hydrodynamic mixing that renew the gas-particle and bed-wall contact surfaces.

This second part is devoted to the description of mass and heat transfer processes in fluidized beds. The main correlations for estimating gas-particle, particle-bed and bed-wall transfer coefficients are provided. These data are applied to the calculation of transfers in a wide range of devices, such as single- or multi-stage open exchangers, dryers or fluidized-bed boilers.