HYDRAULIC CLASSIFYING PROCEDURE AND MEANS

Abstract: Hydraulic classifying procedure and apparatus wherein particulate material transported by a liquid is divided in a centrifugal field established in a cylindrical, substantially vertical classifying space (1) into a fines product consisting of lighter particles, this product becoming separated in the centre of the centrifugal field, and a coarse product consisting of heavier particles, which is separated on the outer margin of the centrifugal field and descends in a spiralling flow conforming to the margin of the field, to the lower end of the classifying space. As taught by the invention, the coarse product is removed from the centrifugal field through an annular gap (3) formed on the lower end of the classifying space (1), using in aid a separate liquid flow conducted tangentially in relation to the centrifugal field and running tangentially to said gap. The coarse product may be removed together with the liquid flow to a hydrocyclone (10) which separates the coarse product, whereafter the liquid can be returned to the classifying process to serve as fluid medium in the classification taking place in the centrifugal field.

Description: HYDRAULIC CLASSIFYING PROCEDURE AND MEANS The present invention concerns a hydraulic classifying procedure wherein particulate material transported by a liquid is divided, in a centri-fugal -field established in a cylindrical, substantially vertical classifying space, into a fines product consisting of lighter particles, this product becoming separated in the centre of the centrifugal field, and into a coarse product consisting of heavier particles, this latter product being separated on the outer margin of the centrifugal field and descending in a spiralling flow following the margin of the field, to the lower end of the classi¬ fying space. The commonest means employed towards hydraulic classification of particulate material is the hydrocyclone, usually consisting of a cylindrical upper part and a conical lower part. The hydrocyclone divides the material to be classified into a fines product, which is removed through the top end of the cyclone, and a coarse pro¬ duct, which is removed from the lower end of the cyclone, i.e., through an aperture at the tip of the conical lower part. In addi¬ tion to the partly conical hydrocyclones mentioned, cyclones with level bottom have been used, in which separation of the fines and coarse products and their departure take place in substantially like manner. Moreover, such classifying means are knwon in which the coarse product is removed tangentially with the aid of a pas¬ sage commencing on the periphery or at the bottom of the means. The classifying carried out with said means of prior art is encum¬ bered by the drawback that the coarse product is removed by a liquid classifying fluid among which there is also finely divided matter contained in the material that is being classified and which, ideally, should end up among the fines product. Finely divided matter is removed along with the coarse product in at least equal prαprαtiαn as classifying fluid is removed, in other wards, the mare such matter is removed the higher is thus the ratio of coarse and fine product quantities. When the classification consti- tutes part of a wet grinding process, where optimally said ratio is about 100 tα 300%, the separation sharpness of classification carried out with means of prior art, that is the proportion of particles smaller than a given limit size contained in the material being classified which are successfully separated tα form the fines product, is typically only about 50%, and occasionally it is even less than 40%. The most commonly employed hydrocyclones have the further drawback that regulation αf said limit size during operation is nearly impossible. Hardly any ways of regulation are known other than regulating the size αf the coarse product removal aperture on the- lower end of the cyclone; even this is rarely applied, owing to practical difficulties. The object of the present invention is to devise a hydraulic clas¬ sifying procedure in which the above-mentioned drawbacks of the state of art are avoided and by which is obtained better separation sharpness than before, and controllab lity αf the classifying process. The procedure of the invention is characterized in that the coarse product is removed from the centrifugal field through an annular gap formed an the lower end of the classifying space, using as aid a separate liquid flow conducted tangentially in relation to the centrifugal field and which is tangential tα said gap. By using a pure liquid flow conducted tangentially in relation to the centrifugal field, one gains the effect that with the coarse product are entrained fewer, if any, finely divided particles having. a size belαw the fines limit size, than before. The amount of liquid flow can be adjusted tα be such that the liquid fluid supplied into the classifying process together with the material to be classified does not participate at ail in the removal of coarse product and, instead, in its entirety departs together with the fines. It is also possible to increase said liquid flow even fur¬ ther, whereby it can be applied in adjusting the limit size between the fines and coarse products. When necessary, the centrifugal field can be boosted with said liquid flow so that the coarse product is caused tα separate at a sufficient rate even in those instances in which the limiting size between the fines and coarse products is small. By the design of the invention, a secondary classification step has been created in the region of the annular gap, its operation being based on the fact that the velocity and direction, in the gap, of the separate liquid flow supplied tangentially in relation tα the centrifugal field determine that particle size of which the removal as coarse product, enforced by the centrifugal field, is possible. Since the coarse product has not yet, at this stage, finally de¬ parted from the first classifying step taking place in the classi¬ fying space proper, said secondary classification influences the separation limit in such way that particles finer than the limit size which have been entrained will return to the classifying space, and by this route further to join the fines product. If the coarse product were brought into contact with the separate liquid flow removing it, only after it has departed from the classifying space proper, the result would merely be dilution of the coarse product flow. An embodiment of the invention is characterized in that the coarse product is separated from said separate liquid flow in a hydrocy¬ clone, whereafter the liiquid is returned to the classifying pro¬ cess tα serve as fluid medium in the classification taking place in the centrifugal field. The advantage gained is then that the liquid balance in the classi ication is not changed, compared with classi¬ cal hydrocyclone separation. This is of particular significance in solid material wet grinding processes, in which the solid matter content of the sludges which they produce i's usually strongly limited owing to further processing steps. The invention also concerns a means for hydraulic classification of particulate material by the procedure described above. The means comprises, as elements known in themselves, a cylindrical, substan¬ tially vertical classifying space, in which a centrifugal field can be established! a feed passage for supplying the material tα be classified and a liquid serving as fluid medium into the classify¬ ing spacel and removal apertures for removing the fines product consisting αf lighter particles, which separates in the centre of the classifying space, and the coarse product consisting of heavier particles, which separates on the outer margin of the classifying space and further separates in the form of a spiralling, descending flaw in the lower part of the classifying space. The means is char¬ acterized in that the coarse product removal aperture consists αf an annular gap an the lower end af the classifying space, and that with the means, at said gap, connects a passage which is tangential to the centrifugal field, so that in removing the coarse product one can utilize a liquid flow conducted through this separate passage and running tangentially to the gap. The invention is described in detail in the fo lowing with the aid of examples, referring tα the attached drawing, wherein: - Fig. 1 presents a hydraulic classifying apparatus according to the invention, Fig. 2 shows the lower part of the cylindrical classifying space belonging tα the apparatus αf Fig. 1, in section II-II as indicated in Fig. 1, Fig. 3 presents part of the classifying space of the apparatus in accordance with another embodiment of the invention, and Fig. 4 shows the classifying apparatus αf the invention, installed as a component in a grinding circuit. In Figs 1 and 2 is depicted a hydrffaulic classifying apparatus which divides particulate material composed of various-sized parti¬ cles and transported by a liquid, such as water for instance, into a fines product consisting of lighter particles and a coarse pro¬ duct consisting of heavier particles. This classification takes place in a vertical, cylindrical classifying space i in a centri- fugal field created by the tangential supply of material to be classified and αf liquid serving as fluid medium, this centrifugal field separating the fines product tα reside in the centre of the classifying space and the coarse product tα its outer margin. The material to be classified and the fluid are in spiralling rotary motion in the classifying space 1, this motion lifting n the centre αf the space the fines product to the removal aperture 2 located close tα the upper end αf said space, and on the outer margin of the space by gravity action urging the coarse product tα the coarse product removal aperture 3 in the lower part αf said space. The apparatus of Figs 1 and 2 comprises on the side of the cylin¬ drical classifying space 1, as essential components,- a feed passage 4 for material to be classified and for fluid medium, tangentially connecting with the upper end of the classifying space; a passage 5 for removing fines product and fluid conducting same, commencing at the removal aperture 2; a round closing plate ό in the lower part of the classifying space, this plate confining the coarse product removal aperture to be an annular gap 3 between this plate and the cylindrical wall of the classifying space; and horizontal passages 7a, 7b connecting tangentially with the lower end αf the classifying space for removal of the coarse product that has passed- through the gap, with the aid αf a separate liquid flow which runs tangentially tα said gap. The liquid flaw .coming through the passage 7a is supplied through the aperture 9a into the lower end of the classi¬ fying space, immediately under the annular gap 3, where it is set in spiralling motion conforming to the outer margin of said space and which is a direct continuation αf the spiralling motion present higher up, in the classifying space 1 proper, and it departs by the aperture 9b into the passage 7b. The passage 7a has been provided with a control valve, indicated in Fig. 1 with reference numeral 8. The liquid flow departing by the passage 7b transports the coarse product to a hydrocyclone 10, where the coarse product is separated tα gα to the removal aperture 11 at the conical end of the cyclone and the liquid, to the vertical removal passage 12 commencing in the upper part αf the cyclone. In Fig. 3 is depicted an embodiment αf the classifying apparatus which differs from that of Fig. 1 in the respect that the lower part 13 of the cylindrical classifying space 1 has been enlarged and on the boundary 13 between the wider lower part αf the space and the narrower part 14 thereabαve has been disposed a conical, vertically movable closing member 16. The size αf the arrnular coarse product removal aperture 3 between the closing member 16 and the classifying space 3 can be regulated in this embodiment with the aid of the positioning of said closing member. It is essential in the presented classifying apparatus of the invention that the removal of the coarse product through the pas¬ sage 7 with the aid of a liquid flow conducted tangentially in relation to the classifying space 1 and not partici ating in the classifying process prevents any finely divided material, which belongs to the fines product, from being intrained with the coarse, product. The liquid flow can be regulated by mens αf the control valve 3 in said passage, and the flow can be arranged to be such, for instance, that it takes care alone by itself of the coarse product removal, whereby the fluid coming into the classifying space 1 together with the material to be classified will in its entirety depart along with the fines product and there will be no fluid medium low in one direction nor in the other at. the coarse product removal aperture 3. It is also possible to adjust the flow coming through the passage 7 into the classifying space 1 tα be greater than the flow departing along with the coarse product, in which case part αf said liquid will go along with the fines pro¬ duct. It is possible by such regulation to enlarge or diminish the limit size αf the fines and coarse product particles. In Fig. 4 is presented a solid material grinding circuit comprising a classifying space 1 and a separator cyclone 10, which may both be as illustrated in Fig. 1. The material, consisting in part αf not previously processed material (reference numeral 17) and in part αf coarse product separated by the hydrocyclone 10 (reference numeral 11) is ground in the mill 18, and after grinding, the material is mixed together with water obtained from the cyclone 10 and it is fed by the aid αf the pump 19, tangentially, into the centrifugal field in the classifying space 1. The fines product separated by the classification departs from the process, while the water de¬ parting at the same time is replaced with a water flow introduced through the passage 7, this flow carrying the coarse product tα the separator cyclone 10 and, as has been stated, thereafter returning to serve as fluid medium in the classification taking place in the classifying space 1. The solid matter content of each particular flow has been entered in Fig. 4 as a percentage figure. It is obvious tα a person skilled in the art that different embodi¬ ments of the invention are not confined to the examples presented in the foregoing and that they may, rather, vary within the scape of the claims following below.

Claims: CLAIMS 1. A hydraulic classifying procedure wherein particulate material transported by a liquid is divided in a centrifugal field estab¬ lished in a cylindrical, substantially vertical classifying space (1) into a fines product consisting αf lighter particles, this product becoming separated in the centre of the centrifugal field, and a coarse product consisting of heavier particles, which is separated on the outer margin of the centrifugal " field and descends in a spiralling flow conforming to the margin of the field, tα the lower end of the classifying space, characterized in that the coarse product is removed from the centrifugal fie-ld through an annular gap (3) formed on the lower end of the classifying space (1), using in aid a separate liquid flow conducted tangentially in relation to the centrifugal field and running tangentially to said gap. 2. Procedure according to claim 1, characterized in that the coarse product is separated from said liquid flaw in a hydrocyclone (10), whereafter the liquid is returned to the classifying process to serve as fluid medium in the classification taking place in the centrifugal field. 4. A means for classifying particulate material by a procedure according to claim 1 or 2, said means'comprising a cylindrical, substantially vertical classifying space (1), in which a centri- fugal field can be established; a supply passage (4) for conducting •the material to be classified and the liquid serving as fluid medium into the classifying space; and removal apertures (2,3) for removing the fines product consisting of lighter particles, becom¬ ing separated tα reside in the centre αf the classifying space, and the coarse product consisting αf heavier particles, which separates on the outer margin αf the classifying space and further in the form of a spiralling, descending flow in the lower part of the classifying space, characterized in that the coarse product removal aperture (3) consists of an annular gap on the lower end of the classifying space (1), and that with the means connects at the site of said gap, a passage (7) tangential tα the centrifugal field so that in the coarse product removal can be utilized a separate liquid flow conducted through said passage and running tangentially in relation to said gap. 4. Means according to claim 3, characte ized in that the gap (3) has been produced by disposing at the lower end αf the cylindrical classifying space (1) a substantially round closing member (6,16) so that the gap is defined between the wall αf the classifying space and said closing member. 5. Means according tα claim 4, characterized in that the lower end (13) αf the classifying space (1) is widening and that the closing member (16) has been disposed to be movable vertically so that the size of the annular gap (13) can be regulated by moving the closing member. 6. Means according tα any one of claims 3-3, characterized in that the passage (7) removing the coarse product has been connected to a hydrocyclone (10) which Separates the coarse product from the liquid flow, and that the hydrocyclone has been connected over a connecting passage (12) and a pump (19) to the feed passage (4) of the classifying space (1) so that the liquid can be returned to the classifying process tα serve as fluid medium in the classification taking place in the centrifugal field.

Inventors: OVASKAINEN PERTTI, OVASKAINEN, PERTTI
Applicants: LAROX AG, LAROX OY
Application year: 1986
Main classification: B04C5
IPC codes: B03B5, B04C5, B04C9