When selecting a dryer, it always is necessary to consider the final product form. When the degree of product attrition common to pneumatic and fluidized-bed dryer operation is unacceptable, continuous-band or "apron" dryers can provide an effective solution. These are widely used where moderately high rates of throughput on a continuous basis are called for. The most commonly used continuous-band dryer is the single-pass machine employing through-air circulation. Alternatively, and where there is limited floor space or a possible need for long residence time, multi-pass units are used with the conveyors mounted one above the other. In similar circumstances, another special type of multi-deck dryer can be used that employs a system of tilting trays so that the product is supported on both the normal working and the inside of the return run of the conveyor band. This arrangement considerably increases the residence time within the dryer and is particularly useful where the product has poor diffusional characteristics.
The method of airflow employed in these dryers is either vertically downward through the material and the sup-
Exhaust fan r
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