WO1999003588A1

WO1999003588A1 - Disintegration apparatus

Info

Publication number: WO1999003588A1
Application number: PCT/GB1998/002090
Authority: WO
Inventors: Uri Andres
Original assignee: Imperial College Innovations Limited
Priority date: 1997-07-16
Filing date: 1998-07-16
Publication date: 1999-01-28
Also published as: GB0000892D0; AU8350498A; GB9714833D0; GB2342304B; GB2342304A

Abstract

A disintegration apparatus is described for disintegrating materials (for example, rock containing ore and minerals), by the application of high voltage electrical pulses. One aspect of the design is that first (18) and second (24) electrode walls are used to provide optimum contact with the rock, in order to provide electrical discharge at natural interfaces in the rock. Another aspect of the design is that at least one of the electrode walls is replaceable by another electrode wall having a different size of openings (22) to allow the end-size of the disintegration to be controlled. A further aspect of the design is that the opposite electrodes are non-parallel, and preferably form a convergent chamber. A yet further aspect of the design is that the rise time of the electrical pulses is no more than about 20 nanoseconds, in order to avoid energy wastage by conduction in the surrounding water.

Description

DISJ-NTEGRATION APPARATUS

This invention relates to the disintegration of material by the application of high voltage electrical pulses. The invention is especially suitable for disintegrating brittle materials having components with different electrical characteristics or different dielectric characteristics, but the invention is not limited exclusively to this. In one specific aspect, the invention is especially suitable for disintegrating rock for the extraction of native metal, metallic ores, industrial minerals and precious stones.

The electrical disintegration of brittle dilectrics (rock and ores in particular) was invented by Alexander Yutkin in Russia in the 1950s, in the form of an electrohydraulic technique (A. Yutkin, Electrohydraulic Effect, 55 pages, Mashgiz, Moscow, 1955). By discharging high voltage electrical pulses in water, in the vicinity of solids to be disintegrated, the shock waves, generated by the discharge, impact on the solid, and fragment it.

In the 1960s, at the Institute of High Voltage at Tomsk Polytechnic in Russia, a different technique of applying the high voltage electrical pulses was developed (A.A. Vorobiev and G.A. Vorobiev, Electrical Breakdown and Disintegration of Solid Dielectrics, Moscow, High School, 224 pages, 1966). Instead of discharging the electrical pulses in water, the high voltage pulses were applied directly to the material to be disintegrated. This technique was said to provide much better disintegration performance. In this technique, the material to be fragmented is contacted by two electrodes. The earthed electrode is a flat, usually perforated, sheet of metal, and the other electrode (usually the high voltage pulse electrode) is in the form of a rod. The rod may or may not be insulated. Although the method of direct contact of material is, in principle, more advantageous, the high energy consumption per unit of disintegrated material meant that this technique has not yet found significant commercial exploitation.

Reference is also made to GB-A-2,120,579 which describes a two-rod electrode system. This technique has been used at the Sandowana Mine in Zimbabwe for the commercial liberation of emeralds. It would be desirable to provide improvements to the known technology, in order to improve the disintegration performance of high voltage electrical pulse systems, and to make the techniques more attractive for commercial exploitation. In contrast to the prior art, one aspect of the present invention is to use first and second electrode walls between which an electrical field is generated when the high voltage pulses are applied.

Such an arrangement can enable discharges through the material at a far greater range of positions than an apparatus employing a rod electrode. When a rod electrode is used, it provides only one contact site to the material at which the electrical discharge must take place. In contrast, by using first and second wall electrodes, a far greater range of contact sites can be obtained.

The above feature is extremely important, because the discharge path of the electrical pulse, and the thermal/electrical breakdown of the material (evident by explosive disintegration of the solid material) generally takes place in the material along the interface or interfaces between different components of the material (especially components having different dielectric characteristics). The discharge path occurs in the areas of highest electrical field. These areas are located at the interfaces of, for example, mineral grains with different permitivity and electrical conductivity. It is this mechanism which can enable different components of the material to be liberated from each other. Therefore, the use of first and second wall electrodes (instead of rod electrodes) enables the discharges to occur at the optimum sites for disintegration or liberation (corresponding to the inter-component boundaries), instead of only at specific sites corresponding to the position of the rod electrode(s).

As used herein the term "wall" is to be interpreted broadly to encompass any wall structure providing electrical conduction at possible conduction positions distributed on the wall. The wall may substantially entirely be conductive, or it may include conductive elements and intervening non- conductive elements. In one form, the electrode wall may comprise a plurality of elongate conductive bars arranged together to form a grill. In another form, the electrode wall may comprise a plurality of individual, relatively small conductive elements mounted in a non-conducting substrate, for example, in a grid pattern. The non- conduction substrate may itself be constructed as a plurality of individual insulators. The small conductive elements may be point-like, or they may be flat elements.

The wall electrodes may be impervious, for example, for very fine disintegration. However, it is preferred that at least one of the electrodes comprises a plurality of openings to enable the disintegrated material to pass therethrough. In many cases, both electrodes will comprise such openings.

The wall electrodes may have dimensions of up to several square metres, or more. The electrodes may be flat and parallel, or may be at an angle towards each other (i.e. converging or diverging). The electrodes may be arranged horizontally, vertically and may be flat or curvilinear.

In a second closely related aspect, the apparatus is configured to enable replacement, or adjustment, of one or more electrodes or wall(s), for deteπriining the size or sizes of openings in the electrode(s) or wall(s), respectively.

For example, the invention may provide an apparatus comprising at least one wall electrode, having a plurality of openings, dimensioned to allow the passage of particles therethrough of a size up to a first characteristic size. The apparatus is configured to enable replacement of the first electrode wall, by a second electrode wall having a plurality of openings dimensioned to allow the passage of particles up to a second characteristic size different from the first characteristic size.

With the above arrangement, the apparatus can be set to allow the passage of particles from the disintegration chamber, only once the material has been disintegrated to a certain particle size. For example, the particle size may be selected by employing the appropriate wall electrode having apertures for that particle size. This can allow the same apparatus to be "tuned" to suit variations in the same material being disintegrated, or to suit disintegration of a completely different material having a completely different component particle size.

This is important for the special case of recycling old reject material from previous mineral processing plants, where the particles already have dimensions below about 100 microns, and have to be disintegrated to achieve a finer particle size.

In the preferred embodiment, the wall electrodes comprise openings in the form of slots, the width of the slots defining the maximum size of particle able to pass through the slots.

In a closely related third aspect, the invention provides a non-parallel (i.e. convergent or divergent) arrangement of first and second electrode means in a disintegration apparatus. Preferably, the arrangement is convergent, the spacing between the first and second electrode means becoming smaller the further the material to be disintegrated travels. Such an arrangement can provide automatic compensation for the dirninishing size of the units of material, as the material is progressively disintegrated.

In a yet further closely related aspect, the invention provides for the generation of high voltage electrical pulses to be applied to a disintegration apparatus for disintegrating material, wherein each electrical pulse has a rise time of not significantly greater than about 20 nanoseconds. As defined herein, the rise time is the time for the pulse to reach about 80% of its maximum voltage magnitude.

In developing the invention, the inventor has appreciated that the use of pulses having a fast rise characteristic can provide significantly more efficient operation of the apparatus. In the period before the pulse has reached the threshold required for the electrical breakdown and disintegration, the energy in the pulse is simply wasted by conduction in the water. Since energy efficiency is a significant factor which is believed to have limited the commercial exploitation to date, such an improvement in energy efficiency can provide extremely important advantages. This has not been appreciated hitherto. In a yet further closely related aspect, the invention provides means for evacuating disintegrated particles from the, or a, disintegration chamber. For example, such means may be provided in the form of water (or other liquid) flow through the chamber. Additionally, or alternatively, the evacuation may be achieved by mechanical vibration of the materials in the chamber.

The purpose of the evacuation means is to improve the extraction of the fine particles from the chamber. The fine particles might otherwise become trapped, or not be in a suitable position, to pass through the openings, for example, in one or more of the electrodes.

Although the above aspects of the invention may be used independently, yet further advantages may be achieved by using two or more of the above aspects in combination.

Embodiments of the invention are now described by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic section through a first embodiment of disintegration apparatus;

Figure 2 is a schematic section through a second embodiment of disintegration apparatus;

Figure 3 is a schematic representation of the layout for a further embodiment of disintegration apparatus;

Figure 4 is a schematic section illustrating an alternative construction of a wall electrode;

Figure 5 is a schematic section illustrating a first technique for removing disintegrated particles from the disintegration chamber;

Figure 6 is a schematic section illustrating a second technique for removing disintegrated particles from the disintegration chamber;

Figure 7 is a graph illustrating the characteristics of the electrical pulses; and

Figure 8 is a comparative table illustrating the results of different disintegration techniques. Referring to Figure 1, the disintegration apparatus 10 consists of a housing 12 which is divided into an upper chamber 14 and a lower chamber 16 by means of a first electrode wall 18. The upper chamber 14 is a disintegration chamber into which material to be disintegrated is loaded by means of a chute 20. The lower chamber 16 serves as a collection chamber for collecting the particles of material after disintegration. The first wall electrode 18 includes a plurality of openings (slots 22 in the present embodiment) through which the disintegrated material falls once it has been disintegrated to a suitable small particle size able to pass through the slots 22.

A second electrode 24 is positioned above the first electrode 18, for the creation of an electric field therebetween, when an electrical pulse is applied to one of the electrodes. In the present embodiment, the second electrode 24 is in the form of a wall electrode which extends from a position adjacent to the mouth region 26 of the upper chamber 14, to a narrow end region 28. The second wall electrode 24 is formed by a plurality of transverse conductive rods 30 joined by a conductive connector 32.

In use, the housing 12 is filled to a fill level 36 with a partially conducting medium, such as water (indicated by the fluid lines 38 in the upper and lower chambers). The material to be disintegrated is loaded using the chute 20, and a high voltage generator 40 is operated to generate high voltage electrical pulses. In this embodiment, the high voltage electrical pulses are applied to the second wall electrode 24, and the first wall electrode 18 is connected to earth.

The large surface area of both the first and second wall electrodes 18 and 24 provides a large range of contact positions with the material to be disintegrated. This provides a much greater probability that the high voltage pulses will be applied at an optimum position corresponding to the high concentration of the electrical field at the interface of different materials (for example, minerals) having different electrical characteristics. When the electrical discharge occurs, the material will thus tend to split along the interface, thereby separating the different components of materials. As the material is progressively disintegrated, the material forms particles which become progressively smaller. When a particle is generated having a sufficiently small end-size, the material is able to fall through the first electrode 18 into the lower collection chamber 16. Particles which do not yet have a sufficient size pass further towards the narrow end region 28 of the disintegration chamber. It will be appreciated that, at the narrow end, the electric field is stronger, and the smaller spacing between the electrodes can still provide intimate contact with the smaller particles, to provide the optimum direct-electrical- contact disintegration characteristics.

In the present embodiment, the first electrode 18 is designed to be replaceable. The electrode 18 can either be withdrawn through the mouth region 26, or a hatch could be provided to allow the electrode to be withdrawn through a wall of the housing 12. The electrode 18 can then be replaced by a further electrode having slots of a different characteristic size, to allow the end-size of the disintegrated particles to be controlled. This can enable the apparatus to be "tuned" to compensate for variations in the same material being disintegrated. Alternatively, it can allow the apparatus to be configured to disintegrate a completely different material. As an alternative embodiment, the size of the openings could be made to be controllable or adjustable.

Figure 2 shows schematically an alternative disintegration chamber formed by parallel (for example, horizontal) first and second electrodes 18a and 24a. In this second embodiment, the upper electrode 24a is generally solid, and the lower electrode 18a includes slots similar to those described above. The lower electrode 18a is formed of triangular shaped metal bars 42. The bars 42 are arranged with the tip 44 of each triangle pointing downwardly. Such a construction can avoid any tendency for the slots to become clogged, and is particularly suitable for slots having a very fine width (for example, less than 0.2 millimetres). As in the first embodiment, the lower electrode 18a is earthed, and high voltage electrical pulses are applied to the upper electrode 24a from a pulse generator 40a.

Figure 3 shows schematically the electrode layout for a yet further embodiment. In Figure 3, the first and second electrodes 18b and 24b define a convergent chute. The electrodes 18b and 24b both have apertures (for example slots) for allowing particles having a suitable small size to be discharged from the disintegration chamber. Material to be disintegrated is loaded into the mouth 46 of the chute, and the disintegrated material is collected from beneath the chute.

Figure 4 illustrates schematically an alternative construction of a wall electrode usable, for example, as the apertured first electrode 18. The electrode wall comprises an insulating substrate 53 having through holes 55 for allowing disintegrated material to pass through the wall. A plurality of individual electrode pins 57 project through the substrate 53 to form a distributed electrode matrix. In this embodiment, the tips 59 of the pins 57 stand proud of the substrate, but this is not essential. The spacing between the pins 57 may be typically about 10mm, but the spacing may be increased or decreased as desired. The rear ends of the electrode pins are connected together electrically by a conductor 61, for connection to earth or the high voltage signal generator.

In the above embodiments, at least one of the electrodes is apertured, to allow the fully disintegrated material to exit from the disintegration chamber. However, in other embodiments, neither electrode might be apertured. In that case, a downstream exit grill would be provided to allow separation of disintegrated material from the non-disintegrated material after leaving the disintegration chamber.

In the first and third embodiments illustrated above, the material to be disintegrated generally moves through the disintegration chamber under gravity. However, additional propulsion may be provided, for example, by mechanical vibration. Such propulsion would be needed, for example, for the second embodiment. Although not shown explicitly in the foregoing embodiments, it is preferred that means be provided for releasing, or evacuating, the disintegrated particles, so that the particles can escape from the disintegration chamber. On such technique is illustrated, for example, in Fig. 5, where the same reference numerals represent features described in earlier embodiments. In order to evacuate the disintegrated particles, water is circulated through the disintegration chamber. On one side of the disintegration chamber 14 is the collection chamber 16. To the other side of the disintegration chamber 14 is a water inlet 47. Water is pumped around the circuit by means of a pump 48. The flow of high pressure water in the disintegration chamber 14 urges any small disintegrated particles to pass through the openings in the electrode 18, and to pass into the collection chamber 16. The fine particles are filtered out of the water flow by a filter 49, before the water returns through the pump 48. It will be appreciated that other open-circuit or closed-circuit means for generating a flow of liquid through the disintegration chamber may be used as desired.

As an alternative to the liquid flow evacuation, Fig. 6 illustrates a mechanical vibration arrangement for "shaking" the fine disintegrated particles, so that they can escape from the disintegration chamber 14. In Fig. 6, the earthed electrode 18 sits as a movable floor which is driven by a mechanical driver (shown schematically at 51). The electrode 18 might be movable vertically and/or horizontally, as desired. The effect of the vibrations is to enable the fine disintegrated particles to migrate towards the electrode 18 and the openings therein. If desired, the disintegration chamber, rather than merely the electrode wall 18, could be vibrated.

If desired the vibration technique could be combined with the liquid flow technique illustrated in Fig. 5.

Figure 7 illustrates the voltage waveform of the pulses generated by the pulse generator 40 in the above embodiments. The pulse waveform is indicated generally by the reference numeral 50. As can be seen in Figure 6, the pulse has a fast rising characteristic, with a rise time of no more than about 20 nanoseconds. Such a fast rise characteristic is extremely desirable, as it reduces the amount of energy wasted before the pulse reaches the discharge threshold 52. Before the discharge threshold is reached, the energy of the pulse is wasted by conductance through the water in the discharge chamber. Once the discharge threshold 52 is reached, there is sufficient voltage to generate a conductive path through the material to be disintegrated. The threshold voltage will depend on the characteristics of the material being disintegrated, and can vary widely from one material to another.

In Figure 7, the broken line 54 represents a comparative pulse having a slower rise characteristic. The area under the line 54 (before it reaches the discharge threshold 52) represents the amount of energy wasted. It can be seen that such a slower rise characteristic results in considerably higher energy wastage, leading to less efficient disintegration.

Generally, for mineral disintegration and/or liberation from rock, pulse voltages in the range of 100 kv - 200 kv are used. The energy, per pulse, supplied by the pulse generator is controlled depending on the electrical and mechanical properties and size of the material being disintegrated, and on the desired end-size after disintegration. For particles having a size in the range of 100 μm - 10 mm, an energy of between 300 and 500 joules is typical. For particles having a size less than 100 μm, a pulse energy of between 3 and 10 joules is more appropriate, about 5 joules being typical.

Figure 8 illustrates a comparison between the results of mechanical disintegration techniques, and electrical pulse application techniques, for producing mineral concentrates for iron extraction from hematite and magnatite. The mechanical techniques consisted of milling and tumbling the material to crush it to a fine particle size in a conventional manner. The electrical discharge technique was tested using the apparatus illustrated in Figure 1.

In Figure 8, the left hand column of each table illustrates the particle size range, and the right hand column indicates the amount of SiO₂ impurity in the particles on average. It is clearly evident that the electrical discharge technique results in less impurities, this advantage becoming more noticeable for small particle sizes. This can enable purer iron to be extracted, leading to a much higher quality of the iron itself.

The electrical pulse discharge techniques described above have also been employed in the separation of precious stones, including diamonds and emeralds, from surrounding rock. This has produced extremely high quality precious stones, with very little splitting, or damage to the precious stones. In other words, the disintegration takes place along the interface between the surface of the precious stones and the rock surrounding them.

Although the techniques have been described above in the field of mineral extraction from rock, the principles of the invention can be applied in numerous other fields, in particular, the disintegration of concrete, particularly with steel reinforcement members, the disintegration of electronic scrap material (to enable precious metals and other materials to be recovered), and the disintegration of vegetables in agriculture.

It will be appreciated that the foregoing description is merely illustrative of preferred forms of the invention, and that many modifications may be made within the scope of the invention. Although features believed to be of particular importance are defined in the appended claims, the applicant claims protection for any novel feature described herein and/or illustrated in the drawings whether or not emphasise has been placed thereon.

Claims

1. Apparatus for disintegrating material by application of a high electrical voltage, the apparatus comprising a region for receiving the material to be disintegrated, and first and second spaced apart electrode walls located in, or adjacent to, said region, wherein, in use, the high voltage electricity is supplied to generate an electric field between the electrode walls.

2. Apparatus according to claim 1, wherein the first electrode wall is removable, the apparatus further comprising a third electrode wall positionable in place of the first electrode wall.

3. Apparatus for disintegrating material by the application of high voltage electricity, the apparatus comprising at least one electrode wall having openings therein for allowing disintegrated material on to a first predetermined particle size to pass through the openings, the apparatus being configured to allow replacement of the electrode wall by a second electrode wall having openings to allow the passage therethrough of disintegrated material of up to a second particle size different from the first particle size.

4. Apparatus according to any preceding claim, wherein the electrodes are generally non-parallel.

5. Apparatus for disintegrating material by the application of high voltage electricity, the apparatus comprising a region for receiving the material to be disintegrated, and first and second electrode means positioned in, or adjacent to, said region, wherein the spacing between the first and second electrode means varies with position in said region.

6. Apparatus according to claim 4 or 5, wherein the arrangement of the electrodes is convergent, the spacing between the first and second electrode means becoming smaller the further the material to be disintegrated travels in said region.

7. Apparatus according to any preceding claim, wherein at least one of the electrodes comprises a wall having openings therein to allow the passage of disintegrated material therethrough.

8. Apparatus according to claim 7, wherein the openings comprise slots.

9. Apparatus according to any preceding claim, further comprising means for imparting movement to the disintegrated particles in the disintegration chamber to facilitate separation of the disintegrated particles from the material to be disintegrated.

10. Apparatus for disintegrating material by application of a high electrical voltage, the apparatus comprising at least one separation wall having openings therein for allowing disintegrated particles of a sufficiently small size to pass therethrough to separate from relatively larger particles, the apparatus further comprising means for imparting movement to the particles to permit the smaller particles to move towards the openings.

11. Apparatus according to claim 9 or 10, wherein the movement imparting means comprises means for creating a flow of liquid.

12. Apparatus according to claim 11, wherein the liquid flows through the openings.

13. Apparatus according to claim 9, 10, 11 or 12, wherein the movement imparting means comprises means for mechanically vibrating the particles.

14. Apparatus according to claim 13, wherein the wall having the openings therein is movable to vibrate particles in contact therewith.

15. Apparatus according to any preceding claim, further comprising means for generating electrical pulses to be applied to the first and second electrodes.

16. Apparatus according to claim 15, wherein the pulse generator comprises means for generating pulses having a rise time of not significantly greater than about 20 nanoseconds.

17. A pulse generator for use with disintegration apparatus for disintegrating material by the application of high voltage electricity, the generator comprising means for generating electrical pulses having a peak voltage greater than about 50 kilovolts, the pulses having a rise time of not significantly greater than about 20 nanoseconds.

18. Apparatus for disintegrating material by the application of high voltage electrical pulses, the apparatus comprising a region for receiving material to be disintegrated, first and second electrode means positioned in or adjacent to said region, and a pulse generator for generating electrical pulses to be applied to at least one of the electrodes, the pulses having a rise time of not significantly greater than about 20 nanoseconds.