Fluid Bed
Processing - Fluid
Bed Drying
| Fundamentals
of fluid bed processing
Fluid
bed processing offers important advantages over other methods of drying
particulate materials.
Particle fluidization gives easy material
transport, high rates of heat exchange at high thermal efficiency while
preventing overheating of individual particles.
The properties of a given product are
determined from drying rate data, i.e. how volatile content changes with
time in a batch fluid bed operating under controlled conditions. Other
important properties are fluidization gas velocity, fluidization point
(i.e. the volatile content below which fluidization without mechanical
agitation or vibration is possible), equilibrium volatile content, and
heat transfer coefficient for immersed heating surfaces.
These and other data are applied in a
computational model of fluid bed processing, thus enabling dimensioning of
industrial drying systems.
Fluid bed drying is suited for powders,
granules, agglomerates, and pellets with an average particle size normally
between 50 and 5,000 microns. Very fine, light powders or highly elongated
particles may require vibration for successful fluid bed drying. |
Fluid bed processing involves drying, cooling,
agglomeration, granulation, and coating of particulate materials. It is ideal
for a wide range of both heat sensitive and non-heat sensitive products. Uniform
processing conditions are achieved by passing a gas (usually air) through a
product layer under controlled velocity conditions to create a fluidized state.
In fluid bed drying, heat is supplied by the
fluidization gas, but the gas flow need not be the only source. Heat may be
effectively introduced by heating surfaces (panels or tubes) immersed in the
fluidized layer.
In fluid bed cooling, cold gas (usually ambient
or conditioned air) is used. Conditioning of the gas may be required to achieve
sufficient product cooling in an economically sized plant and to prevent pick up
of volatiles (usually moisture). Heat may also be removed by cooling surfaces
immersed in the fluidized layer.
Agglomeration and granulation may be performed in
a number of ways depending upon the feed to be processed and the product
properties to be achieved.
Fluid bed coating of powders, granules, or
tablets involves the spraying of a liquid on to the fluidized layer under
strictly controlled conditions.
The NIRO Group offers a range of systems for
fluid bed processing. Continuous and batch dryers, coolers, agglomeration and
granulation systems are designed to operate in open cycle (involving water
evaporation) or closed cycle (involving mostly organic solvent evaporation). For
products posing a risk of dust explosion during processing, pressure shock
resistant designs, self-inertized and closed cycle systems are available.
Continuous fluid bed systems are supplied by NIRO, batch systems by Aromatic-Fielder.
- Chemicals
- Pharmaceuticals and Biochemicals
- Polymers
- Foodstuffs and Dairy Products
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