Drier design

Dryers are different in characteristic from distillation columns and evaporators in that the heat is added and rejected over a large range of temperature. Changes to drier design can be directed by the plus-minus principle. 

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). 

Previous w orkers concerned with the conveying function of rotary driers have generally given primary consideration to determining the time of passage. It was believed that the holdup in the drier was of vital importance in the drier design. Work on this problem was presented by Sullivan et al. (S15) and Smith (Sll, S12). 

It would be possible to construct a freeze-drier incorporating features designed to minimise the risks of environmental contamination and in 1972 Parker and Smith described the construction of a laboratory drier designed to freeze-dry pathogens.However, economic constraints inevitably result in adapting commercially available freeze-driers to reduce the risks when processing hazardous agents. 

---