Pneumatic classifier with grating

Claim 1

In an apparatus for classifying finely divided solid materials containing coarse and fine particles including: a. upright front and rear gratings between which a downwardly flowing stream of finely divided solid material is conducted in a zig-zag path, b. each grating including a plurality of vertically spaced horizontal beams alternating with horizontally disposed gas flow channels between adjacent beams of the front grating, said channels being provided by said beams, and a discharge outlet between adjacent beams of the rear grating, c. each beam of the rear grating being located back of a beam of the front grating and spaced therefrom to provide a portion of said zig-zag path, d. means for supplying gas to the channels in the front grating to flow transversely therefrom through the downwardly flowing stream of finely divided material and carry fines thereof through the respective opposite discharge outlets of the rear grating, e. each beam of the rear grating having a surface sloping toward and for directing the stream of finely divided material therefrom toward the beam next below the directly opposite beam of the front grating, f. each beam of the front grating including a portion projecting toward and adapted to direct the stream of finely divided material onto the sloping surface of the beam of the rear grating directly at its back, and g. means for separating fines from the gas flowing from the passageways of the rear grating, the improvements wherein h. oppositely positioned front and rear beams cooperate with each other to define a unit separator in said zig-zag path, the beams of the front grating having horizontal substantially parallel top and bottom surface areas extending toward said opposite discharge outlet of the rear grating, the resulting facing surface areas of adjacent beams of the front grating defining a channel therebetween which is narrow relative to the vertical height of a front beam, said narrow channel adapted to deliver a horizontal rearwardly-directed gas jet across and through said stream of material flowing into the adjacent unit separator and into the discharge outlet opposite said channel, i. the top of each beam of the rear grating is at a substantially lower level than the top surface area of the opposite beam of the front grating, j. adjacent beams of the rear grating defining a discharge outlet therebetween for the flow of gas carrying fine particles of the material of said stream and wherein k. the vertical distance between adjacent beams of the rear grating is substantially greater than that between adjacent beams of the front grating, thereby facilitating the flow of the gas of said gas jets through said stream of material and into and through the discharge outlets.