Method and apparatus for separation using fluidized bed

Abstract

A gas is forced upwardly through a fluidization medium, such as sand, producing a fluidized bed which flows under the influence of gravity through an inclined trough. The separation of the side walls of the trough decreases in the direction of flow of the fluidized bed increasing the depth thereof. The apparent density of the fluidized bed is maintained substantially uniform, regardless of the increase in depth, by correspondingly increasing the pressure of the air forced through the medium in a manner corresponding to the depth thereof. A gas distribution plate beneath the fluidization medium having a higher resistance to the flow of gas than the layer of fluidization medium thereabove contributes to the maintenance of a substantially uniform apparent density in the fluidized bed despite variations in its depth. The fluidized bed will separate mixture of articles added thereto into a float fraction of articles having densities less than the density of the fluidized bed and a sink fraction of articles of correspondingly greater densities. Upper and lower layers of the fluidized bed entraining float and sink fractions of the mixture, respectively, are separated at the output end of the trough and cleaned of fluidization medium. The method and apparatus disclosed have demonstrated utility in the separation and sorting of agricultural products of all sizes and particularly of products greater than 5 millimeters in diameter.