Method and apparatus for blending fine and cohesive powders in a

Abstract

A mixture of fine and cohesive powders is blended to complete homogeneity in a nuclear-safe bubbling-bed fluidized bed blender having an improved fluidizing grid. The blender includes a generally vertically-oriented slab-shaped, nuclear-safe mixing vessel having a fluidizing grid disposed at one end of the vessel. The fluidizing grid comprises a linear array of generally downwardly-directed, pyramidal-shaped hoppers each having walls converging into a conically-shaped opening. A plurality of ball valves are employed, one such valve being disposed at the bottom of each hopper. The rotary closure member of each of the ball valves includes a first set of gas orifices for directing a flow of fluidizing gas upwardly in a divergent swirl-shaped pattern along the walls of each of the hoppers. In one embodiment a second set of fluidizing gas orifices for directing a flow of fluidizing gas downwardly into the apex of each of the hoppers is also provided. During blending, fluidizing gas is supplied to the first set of orifices, or to a combination of the first and second sets of orifices, in an amount sufficient to cause bubbles of fluidizing gas to rise through the mixture of powders and emerge from the top surface of the powders until a homogeneous blend of powders is achieved.