Fluidized Bed

Definition - What does Fluidized Bed mean?

A fluidized bed consists of a fluid-solid mixture and exhibits fluid-like properties. It is considered a heterogeneous mixture of fluid and solid that can be represented by a single bulk density. The resulting phenomenon is called fluidization.

Fluidized beds are used for purposes like:

  • Fluidized bed reactors (types of chemical reactors)
  • Fluid catalytic cracking
  • Fluidized bed combustion
  • Heat or mass transfer or interface modification

Fluidized beds are also used for efficient bulk drying of materials. Fluidized bed technology in dryers increases efficiency by allowing for the entire surface of the object to be suspended and therefore exposed to the air.

Corrosionpedia explains Fluidized Bed

When a quantity of a solid particulate substance is placed under appropriate conditions to cause the solid/fluid mixture to behave as a fluid, a fluidized bed is formed. Fluidized beds are widely used in many modern technologies for efficient implementation of various physical and chemical processes. For example, drying of pharmaceutical powders and catalytic cracking of petroleum and coal combustion for generating electricity are commonly performed in fluidized beds.

In fluidized beds, the contact of the solid particles with the fluidization medium (a gas or a liquid) is greatly enhanced when compared to packed beds. This behavior in fluidized combustion beds enables good thermal transport inside the system and good heat transfer between the bed and its container.

Fluidized beds can be classified by their flow behavior:

  • Stationary or bubbling bed - Gas at low velocities is used and fluidization of the solids is relatively stationary.
  • Circulating fluidized beds (CFB) - Gases are at a higher velocity sufficient to suspend the particle bed.
  • Vibratory fluidized beds - Similar to stationary beds, but add a mechanical vibration to further excite the particles for increased entrainment.
  • Transport or flash reactor (FR) - At velocities higher than CFB, particles approach the velocity of the gas.
  • Annular fluidized bed (AFB) - A large nozzle at the center of a bubble bed introduces gas as high velocity.

One crucial parameter needed for the design of a fluidization operation is minimum velocity at which a bed of particles fluidizes. The details of the minimum velocity depend upon a number of factors, including the particles’:

  • Shape
  • Size
  • Density
  • Polydispersity
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