Method of, and apparatus for, spiral air classification of solid particles in a gaseous carrier

Claim 3

A method as claimed in claim 1 wherein the suspension in the successive stages lie in parallel planes and the material passing together with the carrier medium out of one stage into the next subsequent stage is deflected by approximately 90* when viewed radially out of the direction of the said flow on passing out of the preceding stage.

Claim 4

A method as claimed in claim 2 wherein the flow of the suspension passing into the next subsequent stage is deflected again by approximately 90* when viewed radially out of the direction of the main flow in the region of transition between the preceding and the following stage on entering said following stage.

Claim 5

A method as claimed in claim 1 wherein the solid material particles are suspended in the carrier medium before being introduced into the first stage proper.

Claim 6

A multi-stage spiral air classifier for classifying solid particles suspended in a gaseous caRrier medium into at least three fractions of different particle sizes by providing a plurality of stages for separating part of the feed material as a coarse fraction in each stage, said classifier comprising separating means embodying at least two classification chambers disposed coaxially above one another and substantially in the form of annular discs, means for feeding said material and carrier medium into a first chamber, means for collecting a coarse fraction from the periphery of each of said chambers, means to pass material uncollected from said first chamber together with the carrier medium into a subsequent chamber for further separation of a coarse fraction from said material, said pass means comprising an annular opening defined between successive classification chambers for flow communication therebetween, said annular opening being disposed substantially coaxially with regard to said classification chambers providing an outlet aperture for the fine particles and the carrier medium from a first chamber and the material inlet for the successive chamber, and means for feeding at each subsequent stage additional carrier medium in the form of a spiral flow to the flow of material and carrier medium therein, said feeding means comprising an inlet for the additional carrier medium located at the periphery of said subsequent chamber.

Claim 7

A multi-stage spiral air classifier for classifying solid particles suspended in a gaseous caRrier medium into at least three fractions of different particle sizes by providing a plurality of stages for separating part of the feed material as a coarse fraction in each stage, said classifier comprising separating means embodying at least two classification chambers disposed coaxially above one another and substantially in the form of annular discs, means for feeding said material and carrier medium into a first chamber, means for collecting a coarse fraction from the periphery of each of said chambers, means to pass material uncollected from said first chamber together with the carrier medium into a subsequent chamber for further separation of a coarse fraction from said material, said pass means comprising an annular opening defined between successive classification chambers for flow communication therebetween, said annular opening being disposed substantially coaxially with regard to said classification chambers providing an outlet aperture for the fine particles and the carrier medium from a first chamber and the material inlet for the successive chamber, and means for feeding at each subsequent stage additional carrier medium in the form of a spiral flow to the flow of material and carrier medium therein, said feeding means comprising an inlet for the additional carrier medium located at the periphery of said subsequent chamber.

Claim 8

An air classifier as claimed in claim 5 wherein a cyclone separator for separating the finest fraction from the carrier medium is provided after the last classification chamber.

Claim 9

An air classifier as claimed in claim 5 wherein said feed means includes a pre-mixing chamber preceding the first classification chamber, a metering device, a blower, and an annular inlet passage connecting the pre-mixing chamber to the first classification chamber.

Claim 10

An air classifier as claimed in claim 5 wherein there are admission control means for the inlet for the additional carrier medium.

Claim 11

An air classifier as claimed in claim 5 wherein the air classifier has a multi-part casing and a lid which forms the upper boundary for each classification chamber.

Claim 12

An air classifier as claimed in claim 5 wherein each said means for feeding additional carrier medium comprising a ring of guide blades on its periphery.

Claim 13

An air classifier as claimed in claim 10 wherein the guide blades are mounted adjustably in the casing.

Claim 14

An air classifier as claimed in claim 5 wherein each said subsequent classification chamber is constructed in the form of a flat cylinder.

Claim 15

A spiral air classifier as claimed in claim 5 wherein the first classification chamber is constructed in the form of a flat cylinder.