Define the Fluidized Dryers?
Fluidization occurs when a flow of fluid upwards through a bed of particles (ranging from fine powders to particulate foods such as diced carrots) reaches sufficient velocity to support the particles without carrying them away in the fluid stream. The bed of particles then assumes the characteristics of a boiling liquid, hence the term fluidization. The fluid responsible for fluidization may be a gas or air the choice of which will confer different properties on the fluidizing system.
Fluidized bed dryers can be used for either of the following situations:
a) Finish or final drying of products partially dried by other techniques; for example, blueberries dried osmotically are then dried at 170°C for 4 minutes in a high temperature fluidized bed.
b) Drying foods completely - examples of this include the drying of grains, soybeans, peas, beans and vegetables.
The complete drying of foods in fluidized beds may be carried out either by the use of a "high temperature short time" process or by a more gradual process at a lower temperature. Delicate fruits such as blueberries are dried by the HTST process (170°C for 8 minutes), whereas oil seeds are dried over a longer period of time (55-65°C for 4 hours). This longer, cooler process is required so that the quality of the oil and the germination characteristics of the grain are not affected.