EP0267948A1

EP0267948A1 - Separation method and apparatus

Info

Publication number: EP0267948A1
Application number: EP19870903672
Authority: EP
Inventors: Peter Donecker
Original assignee: Comalco Aluminum Ltd
Current assignee: Rio Tinto Aluminium Ltd
Priority date: 1986-05-26
Filing date: 1987-05-25
Publication date: 1988-05-25
Also published as: CN87104432A; WO1987007187A1

Abstract

Un appareil de séparation de particules est conçu pour séparer une substance particulaire sur la base de propriétés physiques différentes, telles que la sphéricité, la densité et la résilience. Les particules sont acheminées sous l'influence de la gravité dans un courant formant un rideau étroit sur une plaque de choc inclinée (9), destinée à renvoyer les particules en les déviant selon des chemins de déviation différents qui dépendent des propriétés physiques différentes. Le courant de particules déviées est séparé à l'aide d'une plaque de séparation réglable (10) et aboutit dans des régions collectrices (5, 6). Les cellules de séparation individuelles (1) sont de nature modulaire et peuvent être assemblées, afin de former une cascade permettant de produire des fractions variées de particules séparées selon les besoins.A particle separation apparatus is designed to separate a particulate substance on the basis of different physical properties, such as sphericity, density and resilience. The particles are conveyed under the influence of gravity in a current forming a narrow curtain on an inclined shock plate (9), intended to return the particles by deflecting them according to different deflection paths which depend on the different physical properties. The stream of deflected particles is separated using an adjustable separation plate (10) and ends up in collecting regions (5, 6). The individual separation cells (1) are modular in nature and can be assembled in order to form a cascade making it possible to produce various fractions of particles separated as required.

Description

"SEPARATION METHOD AND APPARATUS"

This invention is concerned with the separation of particulate materials utilizing properties inherent in particles to contribute to the separation process. The invention is particularly although not exclusively related to separation and classification of particulate materials on the basis of particle shape, resilience, size, magnetic susceptibility, electrical conductivity or like properties.

DESCRIPTION OF PRIOR ART Separation of particulate materials is currently carried out by a number of processes which rely on such properties as particle size, density and electromagnetic properties. Although generally effective for specific separation processes, prior art separation processes lack ready adaptability to differing particle properties and in general such prior art processes are difficult if not impossible to combine with other separation processes to enhance or selectively modify the separation of particulate materials. Many such prior art processes have been designed for the separation or classification of a particulate feedstock to achieve only a particular degree of separation or classification. Accordingly a feedstock may be subjected to many steps incorporating different separation or classification techniques to achieve a desired end result. Single pass separating or classifying devices for agricultural materials are described in US3587857, US3902457, AU8652892-A and NL8301221-A and devices for separating spherical objects are described in US3411626 and CS8400028-A.

A well known technique for sorting spherical particles utilizes a flat surface across which a mono-layer of particulate feedstock moves. This technique however is inefficient due to the need for a mono-layer and low particle velocity. Such techniques are exemplified in US3672500, US3464550 and DE-2701009-A. An alternative technique for sorting spherical material is described in SU831226A which relates to the use of a curved reflection surface to achieve separation.

US3680694 describes an apparatus utilizing properties of particle resilience to achieve separation but employs a different principle involving the resonant frequencies of the particles.

While all of the prior art devices and/or techniques may be useful as primary, intermediate or final steps in sorting, separating or classification of particulate material all suffer from one or more deficiencies which reduce efficiency of operation and adaptability in use.

Possibly the major disadvantage of prior art apparatus is that all require at least one moving part and some form of energy to operate the apparatus.

In virtually all prior art particle separation processes, there are considerable costs in energy and/or process material consumption as well as high capital costs in plant and equipment.

It is an aim of the present invention to overcome or alleviate at least certain of the problems associated with prior art particle separation processes and to provide a simple and inexpensive method and apparatus for separation of particulate materials on the basis of shape, resilience and other related properties.

BRIEF SUMMARY OF THE INVENTION According to .the invention there is provided a method of separating particulate materials, said method comprising the steps of:- allowing a particulate material under the influence of gravity to contact an impact surface whereby particles are deflected therefrom to follow respective deflection paths as a function of a physical property of each said particle; and, selectively splitting by splitting means at least one portion of said deflected particles into a respective collection region. Suitably the particulate material to be separated is directed from a feed source located above said impact surface and preferably the particulate material is fed in a controlled flow to said impact surface. Most preferably the particulate material is fed in a curtain-like stream. According to another aspect of the invention there is provided an apparatus for separation of particulate materials said apparatus comprising:- an impact surface adapted to deflect therefrom particles fed under the influence of gravity onto said impact surface whereby said particles are deflected therefrom to follow respective deflection paths as a function of a physical property of each said particle; and, splitting means to selectively direct at least one portion of said deflected particles into a respective collection region.

The feed source may comprise any suitable feeding apparatus such as a vibratory feeder, belt feeder or the like and may be adapted to allow the particulate material to fall as a thin curtain onto the impact surface.

The impact surface^"suitably comprises a plate-like element which may be planar contoured or textured or it may combine more than one of those features and preferably is angularly adjustable relative to the direction of flow of particulate material thereonto.

Associated with the impact surface there may be vibration means, heating means, a magnetic field, an electrostatic field, a fluid flow path or any combination thereof to assist in the separation process.

The impact surface may be comprised of any suitable material including but not limited to rigid materials, resilient materials, flexible materials. The impact surface material may be solid, porous or comprised of laminated members having different physical and mechanical properties. The impact surface may comprise a thin membrane-like member and the membrane impact surface may have adjustable tension means to vary the tension in the membrane.

Means may be associated with the impact surface to selectively vary the kinetic energy of particles contacting the impact surface. The splitting means suitably comprises at least one barrier between adjacent collection regions and said barrier may be adjustable to vary the position and/or area of one or more of said collection regions.

The splitting means may comprise one or more blade-like elements arranged transversely of a flow of particles directed from the impact surface to split said flow into portions each having particles of differing physical characteristics.

The splitting means may comprise fixed or angularly adjustable plate-like members which may be shaped, contoured or textured or combine more than one of those features.

Associated with the splitting means may be electrostatic and/or magnetic fields, vibration means, a fluid flow or any combination thereof to assist in the separation and/or splitting process.

The apparatus may comprise a plurality of separation units as described above, the collection regions of each unit communicating with respective feed zones of successive units whereby selectively split portions of a particulate feed material are subjected to further separation. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more clearly understood preferred embodiments of the invention will now be described with reference to the accompanying drawings in which FIG 1 shows schematically a separation unit;

FIG 2 shows a plurality of separation units connected to form a cascade;

FIGS 3 and 4 show an alternative embodiment of an apparatus according to the invention. FIG 5 shows a modular unit of the type shown in FIG 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG 1 the separation unit comprises a walled chamber 1 open at its upper end 2 and including sloping floors 3 and 4 respectively forming the floors of collection regions 5 and 6. Outlet ports 7 and 8 respectively are provided at the lower ends of floors 3 and 4.

Situated above the collection regions 5 and 6 is an impact surface 9 in the form of a plate-like member spanning the upper portion of the chamber 1.

A variable angle splitter blade 10 extends across the chamber 1 and is pivotably mounted on the apex of floors 3 and 4.

A particulate material is fed as a thin curtain onto surface 9 under the influence of gravity and depending upon such properties as sphericity, resilience, etc., the particles are deflected along differing deflection paths. some into collection region 5 and some into collection region 6. Depending on, say, the sphericity of the particles, the fraction collected in collection region 6 will comprise particles having a greater degree of sphericity than those collected in collection region 5. The splitter blade 10 is angularly adjustable to vary the effective area or opening associated with each collection area to provide a more precise split between the fractions. The splitting effect based on sphericity occurs because irregularly shaped or less spherical particles are statistically less likely to contact the impact surface with an orientation of the particle which might maximise the extent of particle deflection.

Depending upon the degree of separation required, either or both of the separated fractions removed from ports 7 and 8 may be recycled a number of times.

Rather than recycle fractions to obtain a greater degree of separation, units of the type shown in FIG 1 may be arranged in a cascade as shown in FIG 2. FIG 2 illustrates the modular nature of the invention wherein a plurality of units are stacked to form a cascade, the separated fractions of one unit being directed as a feed to successive units for further separation.

In the structure shown, outlet ports 20,21 of upper unit 23 are arranged as feed inlets respectively for lower units 24,25 which in turn feed inlets for units 26,27 and 28. The initial feed of particulate material is thus ultimately divided into four fractions collected in receptacles 29,30,31 and 32. Each of the impact surfaces 35 associated with each separation unit may be adjusted to the same inclination or depending upon the fractions to be separated the impact surfaces may have differing angles of inclination. Further, the impact surfaces may vary in surface contour, texture and/or construction. Similarly splitter bars 36 may be adjusted for separation of specific fractions. In addition to separation of particulate materials it will be readily apparent to a skilled addressee that the method and apparatus according to the invention may be applicable to^" classification of particulate materials according to one or more physical properties. In order to enhance the separative and/or classification capabilities of the method and apparatus according to the invention other influential techniques may be employed. For example, in the apparatus illustrated in FIG 1, the device may be rotated about an axis shown generally by axis b-b. In this manner the extent of deflection and/or the kinetic energy of the particles before or after deflection may be enhanced by centripetal forces on the particles.

Alternatively or in addition to the abovementioned enhancement method, there may be applied across the region of the deflection paths of the particles an electrostatic or electromagnetic field. Electrostatic or electromagnetic fields may exist for example between the impact plate and the splitter bar or in planes parallel to or perpendicular to the deflection paths of the particles. In this manner magnetic susceptibility and/or electrical conductivity properties of particles may be employed in addition to other physical properties to effect separation and/or classification.

The separation/classification may be carried out in any suitable fluid medium or in vacuo. Such media may include air or in the event of potential explosion due to electrostatic discharge, an inert gas medium may be employed. For certain particles, liquids of varying viscosities may be employed. The fluid medium may be static or concurrent or countercurrent fluid flows may be utilized to control either the terminal velocities of particles contacting an impact surface and/or the deflection paths of the particles.

To further enhance separative capabilities, the impact surface may be vibrated to induce additional kinetic energy to the particles undergoing deflection. For certain particulate materials such vibration may be necessary to avoid adhesion of particles to the impact surface which adhesion may adversely affect separation capability.

For damp or sticky particles, the impact surface may be heated but in any event the impact plate may be cleaned periodically or continuously by diffusion of fluid therethrough or by brushing, scraping or wiping with a fluid jet. The impact surface may be planar or textured with projections of constant or varying frequency in terms of spacing or depth. In addition the impact surface may be curved to correct for the finite width of a falling curtain of particles. The curved surface may define portion of a circle, ellipse or paraboloid.

A further embodiment of the invention is illustrated in FIGS 3 and 4.

In FIG 3 a separation unit is formed by a rotating cylinder 30 having an inclined rotational axis. Fixedly mounted within cylinder 30 are a plurality of funnel-like members 31 each having an outlet port 32 aligned above an inclined impact surface 33.

As shown in FIG 4 the internal surface of cylinder 30 includes a plurality of lifting members 34 which serve to elevate a particulate material, introduced into the upper end 35 of cylinder 30, above the first funnel member 31a and to empty same into the mouth of the funnel as the cylinder rotates. Particulate material introduced into funnel 31a exists via outlet port 32 in a controlled manner to contact impact plate 33.

Portion of the particles are deflected further towards the outlet end 36 of cylinder 30 depending upon the physical characteristics of the mix of particles in the feed input. Similarly, another portion is not deflected to the same extent and this latter portion, when collected by lifting members, is less likely to be deposited in next funnel 31b. As the cylinder rotates a continuous separation occurs with particles having a predominant physical property emerging first at the outlet end 36 followed by gradually changing fractions of particles having differing physical properties.

The cascade arrangement of FIG 2 may be constructed from a plurality of modules having the general configuration of the unit of FIG 1. As shown in FIG 5 an end wall remote from the impact plate 9 may be removable where appropriate. The units are readily transportable to a site and the cascade may be constructed or the configuration thereof modified to suit the particulate material being separated, graded or classified. The cascade arrangement of FIG 2 may be constructed from a plurality of modules having the general configuration of the unit of FIG 1. As shown in FIG 5 an end wall remote from the impact plate 9 may be removable where appropriate. The units are readily transportable to a site and the cascade may be constructed or the configuration thereof modified to suit the particulate material being separated, graded_. or classified.

An example of particulate material which may be separated by such a process is alluvial sands which includes sand particles of varying shape and sphericity and plate-like flakes of gold. The more spherical sand particles emerge first followed by sand particles of irregular shape and finally the plate-like flakes of gold emerge. The present invention may be used in conjunction with prior art separation techniques either to provide an initial coarse feed separation or to provide a selective separation of emergent fractions.

In a further variation of the invention the particulate feedstock may be selectively coated with a coating material which affects the deflection characteristics of the individual particles.

In other variations the impact surface and/or the floors 3 and 4 of FIG 1 may be apertured to provide additional separation regions utilizing more conventional separation techniques. Accordingly it will be readily apparent to a skilled addressee that the method and apparatus according to the invention may be employed in the treatment of particulate materials for the purposes of:- shape classification; size classification; classification by co-efficient of restitution (resilience) ; classification and/or separation by other physical parameters including electrostatic properties and magnetic properties. Although the present invention has been described with reference to separation and classification of particulate materials on the basis of sphericity it will be nevertheless apparent that the invention is not so limited. By way of non-limitative example the present invention may be employed for:-

1. grading of proppants and frac sands;

2. sorting and grading of seeds; 3. separation and grading of abrasive grits;

4. separation and grading of gravel and sands;

5. sorting of mineral ores including mica, gold ore, mineral sands etc.

6. grading of tennis balls or other sporting balls;

7. sorting and grading of shot;

8. grading of fertilizer pellets;

9. grading of grinding media;

10. grading of metal and ceramic powders; 11. grading of ball bearings;

12. sorting of shells from nuts e.g., macadamia nuts;

13. grading of catalyst pellets;

14. quantification and qualification of shape distribution in particulate materials. EXAMPLES Example 1 (Comparative)

A quantity of ceramic beads having diameters in the range 0.85 to 1.18mm was tested to ascertain by conventional means the "sphericity" of the beads. Sphericity is expressed as the ratio of the mass of substantially spherical particles to the mass of the particulate feedstock

Sphericity was determined by passing the ceramic beads across an inclined vibrating plate and collecting at an appropriate position that fraction of particles which rolls freely across the plate surface relative to the remaining fraction. Sphericity of the particles was determined to be 47% by this method. Example 2 The same sample of ceramic beads employed in comparative Example 1 was then introduced into a "cascade" sorting apparatus as shown schematically in FIG 2 of the accompanying drawings.

The beads were well rounded but varied in sphericity.

The cascade employed for this test comprised ten modules of the type illustrated schematically in FIG 1 and the feed rate was optimized at 500 kg/metre width per hour. The sorted beads were then collected as five fractions, each of which fraction was weighed and tested for sphericity. The results are set forth in Table 1 as follows:-

Table 1

Fraction Number % Weight Sphericity

1 16. 8 74 % 2 30.2 55 % 3 33. 5 40 % 4 16. 1 27 % 5 3. 4 23 %

00. 0

The results set forth in the table above clearly demonstrate the effectiveness of the apparatus according to the invention to selectively sort, separate and classify particles on the basis of sphericity. The apparatus with appropriate modification is believed to be equally applicable to sorting separately or classifying particulate materials on the basis of other physical properties such as density, resilience, shape etc.

Claims

1. An apparatus for separation of particulate materials, said apparatus comprising:- a separating means including an impact surface adapted to deflect therefrom particles fed under the influence of gravity onto said impact surface whereby said particles are deflected therefrom to follow respective deflection paths as a function of a physical property of each said particle; and, at least one splitting means to selectively direct at least one portion of said deflected particles into a respective collection region.

2. An apparatus as claimed in claim 1 comprising a plurality of separating means, the respective collection regions of each separating means communicating with a respective feed zone of a successive separating means whereby selectively split portions of a particulate feed material are subjected to further separation.

3. An apparatus as claimed in claim 1 or claim 2 including means to feed a particulate feedstock as a thin curtain onto said impact surface.

4. An apparatus as claimed in claim 3 wherein said impact surface comprises a plate-like element, said plate-like element being planar, contoured or textured or any combination thereof.

5. An apparatus as claimed in claim 4 wherein said impact surface is angularly adjustable relative to the direction of flow of particulate material thereonto.

6. An apparatus as claimed in claim 5 including means to selectively vary the kinetic energy of particles contacting said impact surface.

7. An apparatus as claimed in claim 6 wherein said splitting means comprises at least one barrier between adjacent collection regions, said at least one barrier being adapted to selectively vary the position and/or area of one or more of said collection regions.

8. An apparatus as claimed in claim 7 wherein said splitting means comprises one or more blade-like elements arranged transversely of a flow of particles directed from the impact surface to split said flow into portions each portion having particles of differing physical characteristics.

9. An apparatus as claimed in claim 8 wherein said one or more blade-like elements are angularly adjustable.

10. A method of separating particulate materials, said method comprising the steps of:- allowing a particulate material under the influence of gravity to contact an impact surface of a particle^' separation means whereby particles are deflected therefrom to follow respective deflection paths as a function of a physical property of each said particle; and, selectively splitting by splitting means at least one portion of said deflected particles into a respective collection region associated with said particle separation means.

11. A method as claimed in claim 10 wherein particles collected in a collection region of a particle separation means are directed under the influence of gravity to contact respective impact surfaces of one or more particle separation means to undergo successive separation steps said particles being successively deflected to follow respective deflection paths as a function of a physical property of each said particle; and, successively selectively splitting by splitting means at least one portion of said deflected particles into a respective successive collection region.

12. A method as claimed in claim 10 or claim 11 wherein particui-ite material to be separated is fed in a controlled flow onto said impact surface.

13. A method as claimed in claim 12 wherein said particulate material is fed in a thin curtain-like stream.