Fluidization characteristics in powder processing

Fluidization uniquely allows particulate solids to behave like fluids within a fluid stream. This phenomenon represents a special case of fluid-solids flow. During fluidization, fluid flow resistance occurs through the voids in a bed of solids. This resistance results from the total drag exerted by all the particles in the bed.

Fluidization characteristics in powder processing: Fluidized bed functions

Fluidization uniquely allows particulate solids to behave like fluids within a fluid stream. This phenomenon serves as a special case of fluid-solids flow. During fluidization, fluid flow resistance occurs through the voids in a bed of solids. This resistance results from the total drag exerted by all the particles in the bed.

Minimum fluidization velocity

Fluidization uniquely allows particulate solids to behave like fluids within a fluid stream. This phenomenon represents a special case of fluid-solids flow. During fluidization, fluid flow resistance occurs through the voids in a bed of solids. This resistance arises from the total drag exerted by all the particles in the bed.

The superficial gas velocity at which a bed of powder is just fluidized is the minimum fluidization velocity. You can characterize this state of incipient fluidization by measuring the pressure drop of a gas flowing through a packed bed.

At a specific gas velocity, bubbles begin to form. This velocity is known as the minimum bubbling velocity. As a bubble rises through the fluidized bed, it carries some solids with it. This action further influences the behavior of the mixture.

Fluidization Characteristics in Powder Processing: Solids Behaving as Fluids

De-aeration occurs when the fluidizing gas is suddenly stopped. The rate of bed de-aeration often indicates a material’s Geldart particle classification. Fast de-aeration suggests the material belongs to Geldart Group B, while slow de-aeration indicates it belongs to Geldart Group A.

You can also use de-aeration time as a design parameter for various powder handling applications. De-aeration tests can be performed under ambient or high-temperature conditions using air or inert gas as the fluidizing medium. These parameters describe the fluidization capability and floodability properties of the material being investigated.

Additionally, the fluidization setup can assess the potential wear of the material due to attrition. This assessment involves observing the release of fines from the bed or evaluating the intrinsically present fines that become fully airborne during fluidization.