Patent GB-1257901-A (GB)
IPC: B07B4/02
Filed: 1970-01-07
Abstract: 1,257,901. Pneumatic classification of solids. PARKANO OY. 7 Jan., 1970 [9 Jan., 1969; 25 Feb., 1969], No. 854/70. Headings B2H and B2P. A mixture of finely divided solid materials is graded by dropping the mixture in a vertical stream past a plurality of vertically spaced, substantially horizontal gas streams such that material of less than a first predetermined size is carried laterally out of the vertical stream by the gas streams, thereafter constraining the gas streams to flow upwardly whereby only particles of material which are less than a second smaller predetermined size remain entrained in the gas streams. As shown in Figs. 1a and 2, gas from a blower is fed through regulating means 11 into a front space 12 of a housing 9 of a grading unit and flows as horizontal streams through narrow channels 2 between vertically spaced horizontal beams 1 and through similar channels formed between vertically spaced beams 3 covered by cutter blades 4. The beams 1, 3 define a gap through which the material to be graded falls from a feed hopper 10. Means may be provided to move the beams 1, 3 so as to alter the size of the gap. The material may be subjected to the action of one or more gas jets in the hopper 10 to facilitate its dispersion. The coarse particles are retained by funnel-shaped spaces 6 formed between respective beams 1, 3 and collect into a receptacle 17. The remainder of the material is entrained by the gas streams into a rear space 13 in the housing where a sloping wall 14 causes the gas streams to undergo an upward change of direction whereby only fine particles remain in the gas stream and pass therewith through an opening 15 into a cyclone 16 where they are separated from the gas which is returned to the suction side of the blower, whereas medium-sized particles fall down to the bottom of the space 13 into a receptacle 18. In other arrangements, Figs. 1b and 1c (not shown), instead of the beam-and-cutter combination 3, 4, one or two vertical rows of inclined blades are provided. In a further modification, Fig. 3 (not shown), the housing is provided with a vertical rear wall in front of which are arranged, in the space 13, horizontally spaced vertical partitions, the lower edge of each partition being below that of the partition in front thereof. The various gas streams are deflected upwardly through the channels which are formed between the partitions and which open into a chamber at the top of the housing, the chamber being in communication with the inlet of a cyclone. In Fig. 4, groups of vertically spaced grading units 21 connected in series by collecting and feeding channels 25 are arranged in a circular array and are fed with ground cement clinker from a cement mill via a belt conveyer 37, a disc feeder 22, a distribution channel 23 and distribution tubes 24. Air is fed to the units 21 from a common reservoir 26 via distribution tubes 27. The final coarse products from the lowermost grading units are collected together in a cone 36 and returned to the cement mill for further grinding. The fine product from each grading unit is recovered from the associated cyclone 28, the cyclones of each group of grinding units having a common discharge tube 34 leading to transfer means 35 for the fine product. Air collecting tubes 30 for the cyclones 28 lead to a main suction tube 29 connected to one or more blowers 31 which circulate the air back to the reservoir 26. Some of the circulating air is sucked via a side tube 38 attached to each tube 30 into a dedusting unit.