The gas distribution plate is a key element i fluidization technology. It is designed to obtain optimum fluidization and powder movement during operation, and to prevent powder penetration through the plate on plant shut-down.

Fluidization
Fluidization is defined as an operation through which fine solids are transformed into a fluid like state through contact with gas. In the process of fluidization, an intense mixing between the solids and gas occurs, resulting in uniform condition of temperature, composition, and particle size distribution throughout the bed. Out of four basic components (a vessel, gas distribution plate, particulate solid and resource of gas), the gas distribution plate is considered the heart of the process.

Fluid bed drying
Fluid bed drying is the most widely used technique for drying food, dairy, and pharmaceutical powders and granulations. The unique features of the fluid bed’s excellent mixing capacity and high heat and mass transfer rates are highly dependent on the quality of fluidization resulting from the bubble characteristics of the fluidizing gas which to a large extent depend on the gas distributor design.

Meeting the design requirements
A fluid bed requires a distributor plate which supports the bed when it is not fluidized. It prevents particles from passing through and promotes uniform fluidization by distributing the fluidizing medium evenly. A wide variety of distributors can be used including drilled plates, nozzles, or bubble caps.

The main requirements for a distributor plate are to:

  • Promote uniform and stable fluidization
  • Minimize the attrition of bed particles
  • Minimize erosion damage
  • Prevent the flow-back of bed material during normal operation and on interruption of fluidization when the bed is shut down 
  • Minimum deviations in fluidizing velocity

Design highlights

  • Gas distributor plates are special perforated plates for distribution of process gas in a fluid bed.
  • The perforations are shaped as gills, which makes it possible to control the gas flow through the plate. 
  • The fluidizing velocity, and hereby the pressure drop over the plate, depends on the dimensions of the gills and the gill density (number of gills/area). It is possible to control the flow direction by altering the direction of the gills. 
  • The plate design is selected according to the product application, to obtain optimum fluidization and powder movement during operation and to prevent powder penetration through the plate on plant shutdown. 
  • All plates feature special directional perforations that secure lenient powder handling, ability to handle fat-containing powders, and achieve a self-emptying characteristic.

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