APV Dryer Handbook - Umbc

angles and nozzle position patterns. Powder movement is enhanced by the
vibration of the fluid bed unit and by the use of a special perforated air
distribution plate with directional air slots. A proper detailed design is vital
for trouble-free operation.
From the agglomeration zone, the powder flows into the drying area where
added moisture is removed by fluidization using heated air. In some instances,
more than one drying section is required, and in such cases, these sections are
operated at successively lower drying temperatures to reduce thermal exposure
of heat sensitive dry powders.
The final zone is for cooling, where either ambient or cooled air is used to cool
the agglomerates to a suitable packaging temperature.
During processing, air velocities are adjusted so that fine, unagglomerated
powder is blown off the fluidized layer. The exhaust air is passed through
a cyclone separator for removal and return of entrained powder to the inlet
of the agglomerator. When there are high demands for a narrow particle size
distribution, the agglomerated powder is passed through a sifter where the
desired fraction is removed and oversized and undersized material is recycled
into the process.
As with all re-wet agglomeration equipment, the operation must be performed
within certain operating parameters. Overwetting will lead to poor product
quality, while underwetted powder will produce fragile agglomerates and
an excessive amount of fines. However, fluid bed agglomeration does offer
a great degree of flexibility in controlling the final result of the process. The
characteristics of the formed agglomerate can be influenced by operating
conditions such as binder liquid rate, fluidizing velocity and temperature.
Typically, the fluid bed re-wet method will produce agglomerated products
with superior redispersion characteristics.
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