The well-mixed drier

There are fwo fundamenfally different designs of fluidized bed the well-mixed bed and the plug flow bed. In addition, various combinations of fluidized bed drier may be used fo meef particular applications Kunii and Levenspiel (1991) illustrate a series of such designs (see Variations in fluidized bed drier design, below). 

The well-mixed drier has fhe disfinct disadvanfage of nof being able to dry particles to very low moisture contents because of fhe wide particle residence time distribution. In other words, some particles leave the bed immediately, having had no opportunity to dry and effectively bypass the bed some circulate within the bed for a long 

Reay and Allen (1982) assumed that the drying rate is dependent upon the capacity of fhe gas in the dense phase to absorb moisture and therefore that the drying rate is proportional to the difference between the partial pressure of wafer vapour in equilibrium wifh a moisture content X and the partial pressure p in the inlet gas which is in equilibrium with the equilibrium moisture content of the particles X. Therefore the drying rate at a moisture content X is given by 

Now because these authors further assumed a linear desorption isotherm, i.e. a linear relationship between the equilibrium partial pressure of wafer vapour and fhe solids moisfure content, it follows that 

Applying this relationship to drying curves obtained at two temperatures Ti and Tj, for a given change in moisture content AX, gives 

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