APV Dryer Handbook - Umbc

eduction in liquid rate will result in insufficiently wetted powder and therefore,
weak agglomerates. Many designs rely on the product impacting the walls of the
agglomeration chamber to build up agglomerate strength. Other designs include
equipment for breaking large lumps into suitably sized agglomerates before the
final drying. Obviously, deposit formation will always be a concern in
agglomeration equipment as the process depends upon the creation of conditions
where the material becomes sticky.
Typically, equipment designs are complicated, probably reflecting the fact
that agglomeration actually is a complicated process. Despite the complexity
of the process, however, it is possible to carry out agglomeration by means
of comparatively simple equipment, which involves the use of a fluidized bed
for the re-wetting and particle contact phase. This approach provides the
following advantages:
1. There is sufficient agitation in the bed to obtain a satisfactory distribution
of the binder liquid on the particle surfaces and to prevent lump formation.
2. Agglomerate characteristics can be influenced by varying operating
parameters such as the fluidizing velocity, re-wet binder rate and
temperature levels.
3. The system can accept some degree of variation of the feed rate of
powder and liquid as the product level in the fluid bed is always constant,
controlled by an overflow weir. Thus, the re-wetting section will not be
emptied of powder. Even during a complete interruption of powder flow,
the fluidized material will remain in the re-wet section as a stabilizing factor
in the process.
4. By using fluid bed drying and cooling of the formed agglomerates, it is
possible to combine the entire agglomeration process into one continuously
operating unit.
5. Start-up, shut-down and operation of the fluid bed agglomerator are greatly
simplified due to the stabilizing effect of the powder volume in the
re-wet zone.
Proper implementation of a fluid bed agglomeration system requires detailed
knowledge of the fluidization technology. Fluidization velocities, bed heights, air
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