GB1391892A - Method of and apparatus for the pneumatic classification of finely divided solids - Google Patents

Abstract

1391892 Pneumatic classifiers MURSKAUSKONE OY 26 Sept 1972 [27 Sept 1971] 44511/72 Headings B2H and B2P A pneumatic classifier for finely divided solids, e.g. cement, talc or kaolin, comprises a housing 1; means 6 to produce a circulation of classifying air within the housing; means 2 for feeding material to be classified to the housing; primary dispersion means 7 located within the housing at a given reference level and using part of the classifying air to effect dispersion of the material therein in a primary dispersion zone 12 in the housing; a horizontal centrifugal classifier 8 located in the housing above said reference level and connected to the primary dispersion zone; secondary dispersion means 18 located within the housing below the said reference level and using the remainder of the classifying air to effect dispersion, in a secondary dispersion zone 21 in the housing, of solids settling out by gravity from the primary dispersion zone, the secondary zone 21 being in communication with the primary zone 12 and with the centrifugal classifier 8; a cyclone 3 connected to the centrifugal classifier 8 to collect the final fine product; and a hopper 4 connected to the secondary dispersion zone 21 to collect the final coarse product. The classifying air consisting of clean air derived from the cyclone 3 via a pipe 5 is circulated through the housing by a blower 6. Part of the air is fed past a control flap 14 through an ejector 7 to which the feed channel 2 is connected so that the solids are dispersed in air in the zone 12. The fraction of solids entrained in the air stream flows via guide plates 13 into the horizontal classifier 8 which is of the cyclone type and from which the fine product is discharged with air through an opening 16 tangentially connected to cyclone 3 while coarse middlings with some fines are returned via a discharge slot 17 to the zone 12. The fraction of solids settling out by gravity from the zone 12 down a funnel 20 are redispersed by the ejector-like means 18 into the zone 21 in which the coarse product settles downwards and is collected in the hopper 4 and the fines are entrained with the air upwards via a channel 22 into the classifier 8. In a modification, Fig. 2 (not shown), the classifier 8 is connected in series with a second classifier of the same type disposed at a higher level. The coarse middlings from the second classifier are directed either to the primary dispersion zone 12 or to a separate collecting hopper and the fines pass with the air into the cyclone 3. Secondary dispersion means in the form of rows of grid bars are disposed downstream of the ejector 7. In Fig. 3, a rotating dispersion drum 29 having circumferentially spaced rods is disposed downstream of ejector 7 and upstream of a stationary dispersion grid 30. The centrifugal classifier 8 consist of a horizontal rotary drum 31 made of spaced parallel rods or, as shown, of triangular shaped ribs.