Fluid Bed Dryers

Puffer – popper – roaster – toaster – static, vibrating, through-the-bed, reverse fluid (Kontra-flo) dryers and coolers, from minimum to maximum throughput per hour.

Operation:
Fluid bed drying uses a heated gas to lift and maintain the feed in a fluidized state. Air is introduced into a wind box or plenum via a forced draft fan, and is distributed through a distributor plate of solid material via a perforated plate, nozzles, ceramic grid or other distribution medium. The bed attains fluid-like properties flowing and mixing. The fluidization provides intimate contact between each material particle and the gas stream creating an extremely efficient transfer device. Products that have large particle size variations, or high bulk densities can benefit a vibrating bed.

Feeding / discharge:
Manual, batch, automatic and continuous. Vibrators, screw feeders, rotary airlocks, double flap valves, gravity chutes

Feed Characteristics:
Liquids (only with appropriate technology), powders, granules, non friable agglomerates. Feed needs relatively consistent particle size. Very large particles present challenges. Low to high feed rates

Heat Source:
Steam, electrical, coal, liquid fuels, or gas

Exposure:
Mostly Direct. Flow is through the bed. Indirect systems (contact) available for certain products.

Residence time:
Controllable. Residence time can be altered by varying the feed and discharge rates. Bed depth can be varied.

Extraction:
Normally induced. Forced draft fans required for fluidization. Systems can have combustion, forced and induced draft fans for operation.

Dust Collection:
Cyclones, baghouses, scrubbers, Electrostatic precipitators. Systems require dust collection.

Control:
PLC, infrequently solid state controllers. System controls on discharge temperature. Can modulate energy and feed.

Benefits:
Very intimate contact with air/gas stream. Good mixing
Excellent transfer of energy
Gentle handling of product
Can be multi-zone units
Small real estate requirements
Low maintenance on static units
High temperature operation - can be refractory lined.
Unit can serve as an agglomerator (Roll tumble agglomeration)
Unit can have integral cooling section.

Limitations:
Loss of power will cause product to build up in wind chamber (back flow)
May cause size reduction due to attrition and impact
High energy costs for fans and dust collection
Dynamic forces from vibrating motion can require substantial structures.

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