APV Dryer Handbook - Umbc

fluid bed and are kept in
DRYER CHARACTERISTICS
motion by the rotor. As they
dry, the friable surface material
Drying medium Air
Inert Gas
is abraded by a combination
of attrition in the bed and the
Low humidity waste gas
mechanical action of the rotor.
Drying method Direct gas contact
Thus, a balanced fluidized
Inlet temperature Up to 1800°F (980°C)
bed is formed which contains
all intermediate phases
Flow Co-current
between raw material and
finished product.
Capacity Up to 10 tons per hour of
final product
Feed material Dilatent fluids
The dryer and lighter particles
Cohesive paste
become airborne in the drying
Filter cake
air stream and rise up the
Moist granules
walls of the drying chamber,
passing the end of the feed
Product residence time 5-500 seconds
screw and providing, in effect, a continuous back mixing action within the
heart of the dryer. At the top of the chamber, they must pass through the
classification orifice, which can be sized to prevent the larger particles from
passing on to the bag collector. These larger lumps tend to fall back into the fluid
bed to continue drying.
Air exiting from the bag collector (10) passes through the exhaust fan (12) and
is clean enough for use in a heat recovery system. Dried powder is discharged
continuously from the bottom of the bag collector through the discharge valve (11).
Two important features make the Spin Flash dryer suitable for products which tend
to be heat sensitive. First, the dry powder is carried away as soon as it becomes
light enough and therefore is not re-introduced into the hot air zone. Second, the
fluid bed consists mainly of moist powder which constantly sweeps the bottom and
lower walls of the drying chamber and keeps them at a temperature lower than
the dryer air outlet temperature. In addition to this self-cooling capacity, the lower
edge of the drying chamber directly above the hot inlet can be provided with
an auxiliary cooling ring.
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