Classifying – separating – and assorting solids – Fluid suspension – Gaseous
Patent
1986-12-31
1988-11-15
Basinger, Sherman D.
Classifying, separating, and assorting solids
Fluid suspension
Gaseous
209154, B04C 300
Patent
active
047847565
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a pneumatic classifying procedure wherein particulate material is, with the aid of centrifugal force, divided into a fine product consisting of lighter particles and a coarse product consisting of heavier particles and wherein the fine product is removed from the central part of the centrifugal field and the coarse product from its outer margin.
In pneumatic classifying of particulate material, prior art has employed, towards producing a centrifugal field causing classification, blowers setting the material in rotary motion, and mechanical rotors. The separation limit of such classification, that is the limiting size between fine particles and coarse product particles has usually been controlled by the aid of the rotational speed of the centrifugal field.
The coarse product can be separated, and removed from the centrifugal field, utilizing gravity when the separation limit of classification is large enough, about 50 .mu.m. When the separation limit goes down, what happens is that gravity is no longer sufficient to separate the coarse product from the classifying fluid rotating in the centrifugal field. In such cases the coarse product has been separated by removing, together with the product, the part of the classifying fluid accompanying it, to a separate coarse product cyclone. However, this method has the drawback that at the same time part of the fine product contained in the material will be entrained with the coarse product. Therefore the sharpness of separation will be poor in such classification, and it is progressively impaired, the finer the adjustment of the separation limit is made, by increasing the proportion of fluid flow going along with the coarse product.
The object of the present invention is to eliminate the drawback mentioned, by devising a classifying procedure by which better sharpness of separation than before is achieved and which is superior to procedures of prior art also as regards controllability of the process. The classifying process of the invention is characterized in that the coarse product is removed from the centrifugal field with the aid of a separate gas flow tangential to the centrifugal field.
The advantageous effect of the principle taught by the invention, i.e., of employing a separate gas flow which does not participate in the classifying process, is substantially based on the fact that said pure gas flow totally or partly replaces, in the coarse product removal, the classifying fluid rotating in the centrifugal field and containing fine product constituents of the material which is being classified. Thereby the entraining of fine product with the flow removing coarse product is minimized or entirely inhibited.
The gas employed towards removing the coarse product, from which the coarse product is separated in a cyclone, may advantageously be returned, after said process, to the classifying process to serve as fluid in the classification taking place in the centrifugal field.
The invention also concerns a means for classifying particulate material pneumatically, by the procedure just described. The means comprises, in a manner known in itself in the art, a classifying space in which a centrifugal field can be established; at least one feed passage for conducting material to be classified, and gas serving as fluid medium, into the classifying space; and exit apertures for removal of the fine product, consisting of lighter particles, from the central part of the classifying space and for removal of the coarse product, consisting of heavier particles, on the outer margin of the classifying space, and the means is characterized in that it has been provided with a passage which is tangential to the classifying space adjacent to the coarse product removal aperture so that the coarse product can be removed with the aid of a gas flow conducted through said passage.
In an advantageous embodiment of the invention, the size of the coarse product aperture opening into the passage which is tangential to the classifying space has been arranged to
REFERENCES:
patent: 1832256 (1931-11-01), Stebbins
patent: 3878091 (1971-04-01), Hukki
patent: 4248699 (1981-02-01), Hukki
Basinger Sherman D.
Larox Oy
Sotelo Jesus D.
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