AU2011200875A1 - Air classification of particulate matter - Google Patents

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "AIR CLASSIFICATION OF PARTICULATE MATTER" The following statement is a full description of this invention, including the best method of performing it known to me/us: 1 TITLE AIR CLASSIFICATION OF PARTICULATE MATTER FIELD OF THE INVENTION 5 This invention is concerned with classification of particulate matter by a curtain of air. The invention is concerned particularly, although not exclusively, with the classification of particles having a relatively low drag coefficient such as macadamia nuts. 10 BACKGROUND OF THE INVENTION In the macadamia nut industry, the farm gate price obtained by growers is dependent upon the quality of unopened nuts supplied to processors. As it is common for up to 10% of harvested nuts to have malformed, diseased or 15 otherwise unviable shrunken kernels, it is important that such unviable nuts are removed before delivery to a processor if the gate price or delivered price is to be maximized. Generally speaking, de-husked macadamia nuts are classified by a "Water Sorter" which distinguishes viable from non-viable nuts by density. 20 The "Water Sorter" in a simplistic sense comprises a water-filled vessel with convergently tapering walls forming an outlet port in the base of the vessel. Non-viable nuts with deformed or shrunken kernels float on the surface of the water while viable nuts sink to the outlet port where they are removed by a conveyor mechanism. 25 Whilst generally effective as a means of classifying macadamia nuts according to density, it has been found in practice that up to 40% of the nuts removed by flotation are in fact viable but will float due to differing levels of moisture and oil in the nuts. Another shortcoming of the "Water Sorter" is that the shells of the 30 macadamia nuts must be dried after classification before cracking. This adds substantially to handling and processing costs and can degrade the nut quality at least partially.

2 Still another disadvantage of the "Water Sorter" is the difficulty in maintaining hygiene standards in the process water due to the high level of oils and proteins leachable from the nuts which oils and proteins function as nutrients for airborne microorganisms. To reduce the risk of contamination 5 from such microorganisms, the body of water in the "Water Sorter" must be replaced frequently with a high wastage factor. In order to overcome the shortcomings of the "Water Sorter" classifiers, it has been proposed of recent times to utilize an air draft or "vacuum" air classifier. This device comprises a perforated roller conveyor which conveys 10 the de-husked nuts into a region of high velocity air passing upwardly through the conveyor to a suction hood located at a predetermined distance above the surface of the conveyor. Due to the high degree of sphericity of macadamia nuts and their relatively smooth outer skin, Stokes Law generally applies, as the airflow in which classification occurs is substantially laminar in nature. 15 Again, while generally effective for its intended purpose, the "vacuum" air classifier is really only suited to separation of nuts within a narrow diameter range as otherwise viable nuts having a smaller diameter can be swept into the suction hood along with larger unviable nuts with a lower mass or density. Accordingly, a preliminary sizing process is necessary to sort nuts into 20 discrete diameter ranges prior to classification in the "vacuum" air classifier. Other disadvantages associated with the "vacuum" air classifiers for macadamia nuts are high capital cost for classifier and size sorting machinery, large floor space requirements and high operational overheads which together generally preclude small growers from cost effective classification of their 25 macadamia nut crops. Accordingly, it is an aim of the present invention to overcome or ameliorate at least some of the disadvantages associated with prior art macadamia nut classifiers and otherwise to provide a convenient choice for users. 30 SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a method for 3 classification of particulate materials, said method comprising the steps of: directing, at a predetermined particle velocity, particulate material transversely through a curtain of gas, said curtain of gas being directed in an upright plane across a travel path of said particulate material; and, 5 collecting particles of material on opposite sides of at least one splitter located at a predetermined distance from said curtain of gas. If required, said particulate material may have a predetermined particle velocity applied thereto by a gravitational force. Suitably, said particulate material is directed towards said curtain of 10 gas along a downwardly inclined path. The particulate material may have a predetermined particle velocity applied thereto by a rotatable mechanism. If required, the gas may be temperature controlled. Suitably, the gas comprises air. 15 The curtain of gas may be variable in thickness. The curtain of gas may be directed at a predetermined gas velocity across said travel path of said particulate material. The curtain of gas may be directed in a plane at a predetermined angle relative to a direction of particulate material passing therethrough. 20 Suitably, the particles are classified by said splitter according to trajectory paths followed by said particles after emergence from said gas curtain. According to a further aspect of the invention, there is provided a method for the classification of particulate materials, the method comprising 25 the steps of: directing particulate material transversely through a curtain of gas by rotatably sweeping the material through the curtain of gas, the curtain of gas being directed in an upright plane across a travel path of the particulate material; and 30 collecting particles of material on opposite sides of at least one splitter located at a predetermined distance from the curtain of gas wherein the particles are classified by the splitter according to trajectory paths followed by 4 the particles after emergence from the gas curtain. According to yet another aspect of the invention there is provided an apparatus for classification of particulate materials, said apparatus including: a feed conveyor; 5 an elongate gas nozzle extending transversely adjacent an end of said conveyor; and, at least one splitter extending transversely of and spaced from said end of said conveyor, whereby in use, a predetermined particle velocity is applied to said particulate material by said conveyor before said particulate material 10 passes through a curtain of gas emerging from said nozzle at a predetermined gas velocity and whereby classification of said particles is effected by locating said at least one splitter at a predetermined position to separate particles according to trajectory paths falling on opposite sides of said at least one splitter. 15 The feed conveyor may comprise any suitable conveyor capable of imparting a forward motion to particulate material thereon. Suitably, the feed conveyor comprises an inclined surface across which particulate material flows under the influence of gravitational forces. If required, the feed conveyor is adapted to feed particulate material 20 through said curtain of gas at a predetermined velocity. The feed conveyor may include a rotatable sweep to impart a predetermined velocity to said particulate material. The elongate gas nozzle may comprise a plurality of spaced jets. Preferably, said elongate gas nozzle comprises a substantially 25 rectangular jet. If required, said gas nozzle may be adjustable to permit differing thicknesses of air curtain to issue therefrom. Preferably, said gas nozzle is adjustably mounted to permit direction of said gas curtain in a plane at a predetermined angle relative to a direction of 30 flow of particulate material through said curtain of gas. Suitably, said gas nozzle is coupled to a source of pressurized gas. Preferably, said source of pressurized gas is a rotatable fan powered 5 by a drive mechanism. Suitably, said at least one splitter comprises a wall member extending transversely of trajectory paths of particles emerging from said curtain of gas. If required, a collection hopper is coupled to a collection region located 5 on each side of said wall member. According to yet another aspect of the invention there is provided an apparatus for classification of particulate materials, the apparatus including: a feed conveyor; an elongate gas nozzle extending transversely adjacent an end of the 10 conveyor; and, at least one splitter extending transversely of and spaced from the end of the conveyor, whereby in use, a predetermined particle velocity is applied to the particulate material by a rotatable sweep located on the conveyor and the particulate material is thereby rotatably swept through a curtain of gas 15 emerging from the nozzle at a predetermined gas velocity and whereby classification of the particles is effected by locating the at least one splitter at a predetermined position to separate particles according to trajectory paths falling on opposite sides of the at least one splitter after emergence from the gas curtain. 20 BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully understood and put into practical effect, reference will now be made to a preferred embodiment illustrated in the accompanying drawings in which: FIG. 1 shows schematically a side elevation of a macadamia nut 25 classifier. While the description of the preferred embodiment is limited to a macadamia nut classifier, it should be understood that the invention is not so limited and can be applied to classification of a wide range of particulate materials including other species of nuts, moulded components, particulate 30 foodstuffs and the like where variations in mass and/or density are an indicator of product quality.

6 DETAILED DESCRIPTION OF THE DRAWINGS The macadamia nut classifier 1 of FIG. 1 comprises a frame 2 supporting an inclined feed chute 3, an underpass outlet 4 for one grade of classified nuts and an overpass outlet 5 for another grade of classified nuts. 5 Underpass outlet 4 communicates with an underpass collection region 6 and overpass outlet 5 communicates with an overpass collection region 7. Between collection regions 6 and 7 is a splitter 8 in the form of a transversely extending wall. Adjacent the end of feed chute 3 is a rotatable roller 10 in the form of a 10 drive shaft 11 from which stiff bristles 12 extend radially. Drive shaft 11 is coupled to a variable speed drive motor (not shown). Located below the end of feed chute 3 is an elongate nozzle 13 extending transversely across a direction of feed of articles on feed chute 3. Nozzle 13 is coupled to a plenum chamber 14 in turn coupled to an outlet port 15 15a of a radial flow fan 15 powered by drive motor 16. In use, macadamia nuts (not shown) are metered onto feed chute 3 by metering apparatus (not shown) such as a vibratory conveyor, chain bar conveyor or the like to spread the feed of nuts generally across the width of feed chute 3. In this regard, the outer end of feed chute 3 may taper 20 convergently towards rotary brush 10 to assist in a generally even feed rate of nuts towards rotary brush 10. Feed chute 3 is inclined to enable the generally spherical macadamia nuts to roll under the influence of gravity towards brush 10 although a vibratory feed device (not shown) coupled to chute 3 could also be used. 25 With rotary brush 10 rotating at a desired speed, any nuts being engaged by the bristles 12 thereof are propelled tangentially by bristles 12 across the opening in nozzle 9 at a predetermined velocity. With fan 15 in operation, a narrow curtain of air emerges from nozzle 9 across the full width of chute 3 and at an angle of about 150 to 200 to the direction of travel of the 30 nuts. When nuts pass through the curtain of air they have imparted thereto an upright force by the curtain of air which upright force, in combination with 7 the delivery velocity from brush 10, has a resultant forward and upward force vector. Depending upon the density of the nuts, the less dense nuts are propelled upwardly such that their trajectory passes over splitter 8 into collection region 7 whilst more dense nuts have a lesser upright resultant 5 vector whereby the nuts either fall directly into collection region 6 or strike splitter 8 and then fall into collection region 6. The less dense nuts, typically unviable nuts, are directed to a collection hopper, drum or the like (not shown) via overpass outlet 5 while viable, more dense nuts are directed to a collection hopper, bagging machine or the like via underpass outlet 4. 10 In use it has been found that even with a fairly wide variation in nut diameters, the apparatus, once tuned, is highly selective in separating viable from non-viable nuts, apparently on the basis of momentum rather than merely density. It readily will be apparent to a person skilled in the art that many 15 modifications and variations may be made to the apparatus of the invention without departing from the spirit and scope thereof. For example, more than one splitter 8 may be employed to effect a size classification with macadamia nuts as well as to remove unviable nuts. Each splitter would then define separate collection regions in turn coupled to 20 respective outlet ports. Similarly, for fine tuning of the apparatus for macadamia nuts or otherwise for adaptation to other particulate products requiring classification, the angle of inclination of feed chute 3 may be adjustable, the speed of rotation of brush 10 may be selectively variable, the width and angle of inclination of nozzle 13 may be adjustable, the air velocity 25 issuing from nozzle 13 may be selectively variable and the height and spacing of splitters 8 may be selectively varied. It also will be readily apparent to a person skilled in the art that for macadamia nuts at least, the present invention offers a simple, inexpensive, compact yet elegant solution to the problems and shortcomings associated 30 with prior art "Water Sorter" and "Vacuum" air classifiers.

Claims (20)

1. A method for the classification of particulate materials, the method comprising the steps of: directing particulate material transversely through a curtain of gas by rotatably sweeping the material through the curtain of gas, the curtain of gas being directed in an upright plane across a travel path of the particulate material; and collecting particles of material on opposite sides of at least one splitter located at a predetermined distance from the curtain of gas wherein the particles are classified by the splitter according to trajectory paths followed by the particles after emergence from the gas curtain.

2. A method as claimed in claim 1 wherein the particulate material has a predetermined particle velocity applied thereto by a gravitational force and the rotatable sweep.

3. A method as claimed in claim 1 or claim 2 wherein the particulate material is directed towards the curtain of gas along a downwardly inclined path.

4. A method as claimed in any preceding claim wherein the gas is temperature controlled.

5. A method as claimed in any preceding claim wherein the gas comprises air.

6. A method as claimed in any preceding claim wherein the curtain of gas is variable in thickness.

7. A method as claimed in any preceding claim wherein the curtain of gas is directed at a predetermined gas velocity across the travel path of the particulate material.

8. A method as claimed in any preceding claim wherein the curtain of gas is directed in a plane at a predetermined angle relative to a direction of particulate material passing therethrough.

9. An apparatus for classification of particulate materials, the apparatus including: a feed conveyor; 9 an elongate gas nozzle extending transversely adjacent an end of the conveyor; and, at least one splitter extending transversely of and spaced from the end of the conveyor, whereby in use, a predetermined particle velocity is applied to the particulate material by a rotatable sweep located on the conveyor and the particulate material is thereby rotatably swept through a curtain of gas emerging from the nozzle at a predetermined gas velocity and whereby classification of the particles is effected by locating the at least one splitter at a predetermined position to separate particles according to trajectory paths falling on opposite sides of the at least one splitter after emergence from the gas curtain.

10. An apparatus as claimed in claim 9 wherein the feed conveyor comprises an inclined surface across which particulate material flows under the influence of gravitational forces.

11. An apparatus as claimed in claim 9 or 10 wherein the elongate gas nozzle comprises a plurality of spaced jets.

12. An apparatus as claimed in claim 9 or 10 wherein the elongate gas nozzle comprises a substantially rectangular jet.

13. An apparatus as claimed in any one of claims 9 to 12 wherein the gas nozzle is adjustable to permit differing thicknesses of air curtain to issue therefrom.

14. An apparatus as claimed in any one of claims 9 to 13 wherein the gas nozzle is adjustably mounted to permit orientation of the gas curtain in a plane at a predetermined angle relative to a direction of flow of particulate material through the curtain of gas.

15. An apparatus as claimed in any one of claims 9 to 14 wherein the gas nozzle is coupled to a source of pressurized gas.

16. An apparatus as claimed in claim 15 wherein the source of pressurized gas is a rotatable fan powered by a drive mechanism. 10

17. An apparatus as claimed in any one of claims 9 to 16 wherein the at least one splitter comprises a wall member extending transversely of trajectory paths of particles emerging from the curtain of gas.

18. An apparatus as claimed in claim 17 wherein a collection hopper is coupled to a collection region located on each side of the wall member.

19. A method for classification of macadamia nuts substantially as hereinbefore described with reference to the accompanying drawings.

20. An apparatus for classification of macadamia nuts substantially as hereinbefore described with reference to the accompanying drawings.