WO2010046712A2 - A method and apparatus for the treatment of material with electromagentic radiation - Google Patents

A method and apparatus for the treatment of material with electromagentic radiation Download PDF

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Publication number
WO2010046712A2
WO2010046712A2 PCT/GB2009/051434 GB2009051434W WO2010046712A2 WO 2010046712 A2 WO2010046712 A2 WO 2010046712A2 GB 2009051434 W GB2009051434 W GB 2009051434W WO 2010046712 A2 WO2010046712 A2 WO 2010046712A2
Authority
WO
WIPO (PCT)
Prior art keywords
electromagnetic radiation
barrier
treatment
conveyors
generator
Prior art date
Application number
PCT/GB2009/051434
Other languages
French (fr)
Other versions
WO2010046712A3 (en
Inventor
Jans Przbyla
Sam Kingman
Steven Bradshaw
Original Assignee
The University Of Nottingham
E2V Technologies (Uk) Limited
University Of Stellenbosch
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The University Of Nottingham, E2V Technologies (Uk) Limited, University Of Stellenbosch filed Critical The University Of Nottingham
Publication of WO2010046712A2 publication Critical patent/WO2010046712A2/en
Publication of WO2010046712A3 publication Critical patent/WO2010046712A3/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C19/00—Other disintegrating devices or methods
    • B02C19/18—Use of auxiliary physical effects, e.g. ultrasonics, irradiation, for disintegrating
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B4/00—Electrothermal treatment of ores or metallurgical products for obtaining metals or alloys
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/78—Arrangements for continuous movement of material

Definitions

  • This invention relates to a method and apparatus for the treatment of material, in particular particulate material, with electromagnetic radiation.
  • the invention has particular, but not exclusive, application to the treatment of multi-phase material, such as ores, with electromagnetic radiation to cause differential expansion between the phases of the material resulting in weakening of the material at interfaces between different phases of the material.
  • Mined material may be treated with high field strength electromagnetic radiation by passing it along a conveyor which passes through a treatment zone where the material is exposed to electromagnetic radiation emitted by a microwave generator. It has been found however that especially when the mined material is multi-phased, coarse and granular, and where at least part of its composition is metallic, there is a tendency for the electromagnetic radiation (or electric field) to cause breakdown of the local gas in the form of plasma (arcing) or sparking within the bed of the material. If arcs travel to the electromagnetic radiation generator, damage can be caused to the generator and it may be rendered inoperable. Furthermore, formation of arcs between the material and walls of a chamber in which the material is treated can result in loss of energy or damage to the applicator and workload and therefore, a significant reduction in efficiency of the treatment process.
  • a method for treating material with electromagnetic radiation comprising providing a barrier between the material and an electromagnetic radiation generator arranged to emit electromagnetic radiation, the barrier arranged to prevent arcs, formed as a result of exposing the material to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator, and operating the electromagnetic radiation generator to expose the material to electromagnetic radiation.
  • sparks and arcs can limit the effectiveness of treatment and, if a spark or arc reaches the electromagnetic radiation generator, it can damage the electromagnetic radiation generator and render the system inoperable.
  • the provision of a solid barrier with appropriate dielectric properties means that dielectric breakdown of the gas may not spread to the electromagnetic radiation generator and, therefore, prevent damage being caused to the electromagnetic radiation generator by consequential sparks or arcs.
  • the barrier may have appropriate electrical insulating properties as a highly conductive barrier would stop the electromagnetic radiation from passing therethrough.
  • the barrier may have dielectric properties such that the barrier does not significantly alter the electromagnetic radiation passing therethrough.
  • the barrier may have a dielectric constant, ⁇ ' , of less than 5, preferably less than 3 and most preferably, less than 2 and a dielectric loss, ⁇ " , of less than 1 , preferably less than 0.1 , and most preferably, less than 0.01.
  • ⁇ ' dielectric constant
  • ⁇ " dielectric loss
  • the barrier may be arranged such that less than 10%, preferably less than 5%, and ideally less than 1%, of energy of the electromagnetic radiation is dissipated by the barrier. It may be that the barrier comprises reinforced rubber, or PVC, as these may have the necessary dielectric and/or attenuating properties.
  • the barrier creates a seal between the material and the electromagnetic radiation generator preventing dust from passing therethrough.
  • the barrier creates a seal to the dust it may prevent dust from creating and supporting paths for arcing between the material and the electromagnetic radiation generator.
  • the barrier may be arranged between the material and walls of a treatment chamber in which the material is exposed to electromagnetic radiation to prevent arcs from passing through the barrier to walls of the treatment chamber.
  • the barrier may be in the form of an enclosure around the material. As well as preventing arcing to the electromagnetic generator and the walls of the treatment chamber, such an enclosure may be beneficial in that it contains dust within a small area proximate to the material.
  • the method may comprise providing a substantially constant mass or volume of material per unit time to a treatment zone for treatment with electromagnetic radiation. This may result in substantially consistent results from the treatment of the material.
  • the material may comprise particulate material, for example particulate material as would obtained in a mining operation.
  • the method may comprise receiving loose particulate material at a first bulk density and packing the particulate material to a second, higher bulk density, the electromagnetic radiation generator being operated to treat the packed material with electromagnetic radiation.
  • the method may comprise providing an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation. This may be beneficial as increasing the packing density of the material may reduce the quantity of air in and around it, thus potentially reducing the frequency and severity of sparks and arcs. It is also known that more sparking and arcing occurs when the material has: i) angular surfaces, ii) differing dielectric properties, iii) varying particulate sizes, iv) varying temperatures, v) wide spatial distribution, vi) varying bulk densities.
  • the enclosure that retains the material at the second bulk density may also form the barrier to the electromagnetic radiation.
  • the enclosure is one or more closed containers, the material being packed at the second bulk density into the one or more closed containers before the material is treated.
  • closed containers may be used in a batch process.
  • the containers may be transported to a treatment zone by any means, such as conveyors, cranes, fork lift trucks, or the containers may remain in place and the electromagnetic generator and/or a waveguide for the electromagnetic radiation relocated such that the material in the container is treated with electromagnetic radiation.
  • the enclosure is one or more conveyors, in particular belt conveyors, on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the microwave generator.
  • the method may comprise placing the material on the belt conveyor, for example in an open zone of the one or more belt conveyors, and then closing the belt conveyors around the material before the material is passed through the treatment zone to retain the material at the second, higher bulk density. It may be that the material moves with a belt of the conveyor rather than relative to it. Movement of the material relative to the belt of the conveyor may imply that it has a relatively low packing density which, as discussed previously, may result in inconsistent treatment and/or encourage the formation of sparks and arcs.
  • movement of the material on the belt of the conveyor can result in segregation of the material on the belt, resulting in significant variation of the dielectric properties of the material being treated and consequently, variation in the results of the treatment.
  • Preventing, or at least reducing, movement of the material relative to the belt reduces the amount of segregation and therefore, reduces variations in the results of treatment.
  • the one or more conveyors may comprise two belt conveyors that cooperate together during part of their cycle to enclose the material. This may represent a relatively simple way to enclose the material travelling on a first conveyor. Additionally if both conveyors run on a loop, cooperating for only part of their complete rotation, this arrangement may allow for substantially continuous treatment of material.
  • the one or more conveyors may comprise a single belt conveyor that is wrapped around the material for part of its cycle to enclose the material.
  • At least one of the conveyors forms the barrier. This may provide a convenient way to provide the barrier, especially where both conveyors have appropriate dielectric properties such that arcs may be prevented from permeating beyond the enclosure created by the two conveyors. It may be that the one or more conveyors comprise a material that is resistant to abrasion. This may extend the life of the one or more conveyors, especially where the material is abrasive. Additionally it may help to prevent irregular areas forming on the surface of the conveyor which might form air pockets under the material and encourage the formation of sparks and arcs.
  • the barrier such as a belt of one or more of the conveyors, has a similar dielectric constant to the material to be treated. This may be advantageous because impedance mismatching may increase the likelihood of dielectric breakdown or system instability occurring.
  • the shape of at least one of the belts of the conveyors is determined by a series of rollers which also cause said at least one belt conveyor to pack the loose material to the second, higher bulk density.
  • the conveyors may shape the material to a desired formation prior to treating. If the conveyors are additionally responsible for increasing the packing density of the material, this packing operation may not need to be conducted by other apparatus.
  • the barrier may comprise a cover across an opening in the electromagnetic radiation generator through which the electromagnetic radiation is delivered. While, without the enclosure, this system would not necessarily confine sparks and arcs to a space proximate to the material, it may provide a relatively cheap and simple way of protecting the electromagnetic radiation generator.
  • the material is still collected into and retained with an increased packing density before treatment.
  • the advantages that may result from an increased packing density may still be available (e.g. potentially fewer sparks and arcs and more consistent treatment) .
  • the packing density of the material presented for treatment may still be provided so as to be substantially constant.
  • the method may comprise transporting the material through a treatment zone where the material is exposed to electromagnetic radiation at a predetermined speed.
  • the method comprises determining the predetermined speed from one or more properties of the material, such as dielectric constant, dielectric loss factor, conductivity and strength characteristics, for example, tensile strength, compressive strength and shear strength, of the material, and a packing density of the material and transporting the material at this determined speed.
  • the embodiment in which the material is transported on a conveyor may be convenient in that it may facilitate varying the speed of the process (and so the treatment) .
  • the method may comprise mixing the material with powder, liquid or a gel before it is treated.
  • the powder, liquid or gel may serve to fill gaps that would otherwise contain air. In this way sparking and arcing may be reduced.
  • Mixing the material with a liquid, such as water, may serve to help maintain the material at a higher packing density, especially where it is granular or particulate. This may help to prevent sparking and arcing and or increase the consistency of treatment. It may also reduce dust generation and liberation.
  • the electromagnetic radiation provided is in the form of microwaves or radio waves. Treatment with microwaves or radio waves may be particularly suitable for achieving particular results. Microwaves or radio waves may for example be particularly useful in producing differential heating in multi-phase materials. This may help to break down materials into their separate phases, perhaps therefore reducing the cost associated with subsequent comminution processes.
  • the method may comprise treating a multi-phase material with electromagnetic radiation such that the material experiences exposure to electromagnetic radiation for the order of 1 , and preferably Vz, second or less and for a short enough time to avoid causing substantial chemical changes to the phases of the material whilst causing differential thermal expansion between the phases of the material to cause weakening at interfaces between the phases.
  • the electromagnetic radiation has a high electric field strength to generate a power density of at least 10 3 Wm 3 , 10 8 Wm 3 , 10" Wm 3 , 10 10 Wm 3 , 10 11 Wm 3 , 10 12 Wm 3 , 10 13 Wm 3 , 10 14 Wm 3 or 10 15 Wm 3 and/or a frequency between IMHz and 10GHz.
  • High power treatments such as this may be particularly suitable for beginning to separate multiphase materials into their separate phases.
  • the time the material experiences exposure to electromagnetic radiation may of the order of (i) 1 second or less, (ii) 0.1 second or less, (iii) 0.01 second or less or (iv) 0.001 second or less.
  • the method may comprise transporting the material to be treated though a treatment chamber provided with choking structures to prevent leakage of the electromagnetic radiation from the treatment chamber.
  • These choking structures may be in the form of one or more castellations in the treatment chamber, extending away from the treatment zone, and may be provided with material that has a high attenuation for the electromagnetic radiation used to treat the material.
  • These choking structures may substantially prevent electromagnetic radiation from leaving the treatment chamber, particularly through its potentially open ends, through absorption of the electromagnetic radiation.
  • a circulator is provided to prevent reflected electromagnetic radiation from being reflected back to the microwave generator, from the treatment chamber. This may prevent reflected radiation from damaging the microwave generator.
  • a system for treating material with electromagnetic radiation comprising a electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in a treatment zone and a barrier between the treatment zone and the electromagnetic radiation generator, the barrier arranged to prevent arcs, formed in the treatment zone when the material in the treatment zone is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
  • the barrier may be an enclosure around the material. This may be beneficial in that it may contain dust and/or sparks and arcs within a small area proximate to the material. This may prevent unwanted dust and/or sparking and arcing in and around the treatment area and electromagnetic radiation generator. Furthermore, it may prevent the electromagnetic radiation from passing through to the walls of the system.
  • the system may comprise a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, the electromagnetic radiation generator arranged to treat the packed material with electromagnetic radiation.
  • the system may comprise an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation. This may be beneficial as increasing the packing density of the material may reduce the quantity of air in and around it, thus potentially reducing the frequency and severity of sparks and arcs. It is also known that more sparking and arcing occurs when the material has: i) angular surfaces, ii) differing dielectric properties, iii) varying particulate sizes, iv) varying temperatures, v) wide spatial distribution, vi) varying bulk densities.
  • Some or all of these factors may be reduced by increasing the packing density of the material so as to make it more homogenous. Additionally increasing the packing density of the material may mean that treatment of the material can be achieved more efficiently and in a more consistent manner, with more of the materials receiving similar levels of treatment with the electromagnetic radiation.
  • the enclosure that retains the material at the second bulk density may provide the barrier between the material and the electromagnetic radiation generator.
  • the enclosure is one or more closed containers, the material being packed at the second bulk density into one or more closed containers before the material is treated.
  • closed containers may be used in a batch process.
  • the enclosure is one or more conveyors, such as one or more belt conveyors, on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator.
  • the system may comprise a feeder for feeding material onto the belt conveyor, for example in an open zone of the one or more belt conveyors, and then closing the belt conveyors around the material before the material is passed through the treatment zone to retain the material at the second, higher bulk density.
  • the one or more belt conveyors may be arranged such that the material moves with a belt of the conveyor rather than relative to it. Movement of the material relative to the conveyor belt may imply that it has a relatively low packing density, which, as discussed previously, may result in inconsistent treatment and/or encourage the formation of sparks and arcs.
  • the one or more conveyors may comprise two belt conveyors that cooperate together during part of their cycle to enclose the material. This may represent a relatively simple way to enclose the material travelling on a first conveyor. Additionally if both conveyor belts run on a loop, cooperating for only part of their complete rotation, this arrangement may allow for substantially continuous treatment of material.
  • the one or more conveyors may comprise a single belt conveyor that for part of its cycle is wrapped round the material to enclose the material.
  • At least one of the conveyors forms the barrier. This may provide a convenient way to provide the barrier, especially where both conveyors have a sufficiently high dielectric strength and thickness such that arcs may be prevented from permeating beyond the enclosure created by the two conveyors. It may be that the one or more conveyors comprise a material that is resistant to abrasion. This may extend the life of the one or more conveyors, especially where the material is abrasive. Additionally it may help to prevent irregular areas forming on the surface of the conveyor which might form air pockets under the material and encourage the formation of sparks and arcs.
  • At least one of the conveyors has a similar dielectric constant to the material to be treated. This may be advantageous because impedance mismatching may increase the likelihood of dielectric breakdown occurring.
  • the packer may comprise a series of rollers that shape at least one of the conveyor belts to pack the loose material to the second, higher density. In this way the conveyors may shape the material to a desired formation prior to treating. If the conveyors are additionally responsible for increasing the packing density of the material, this operation may not need to be conducted by other apparatus.
  • the barrier may comprise a cover across an opening in a waveguide through which the electromagnetic radiation is delivered to a treatment zone from the electromagnetic radiation generator. While, without the enclosure, this system would not necessarily confine sparks and arcs to a space proximate to the material, it may provide a relatively cheap and simple way of protecting the electromagnetic radiation generator.
  • the material is still collected into and retained with an increased packing density before treatment.
  • the advantages that may result from an increased packing density may still be available (e.g. potentially fewer sparks and arcs and more consistent treatment) .
  • the packing density of the material presented for treatment may still be provided so as to be substantially constant.
  • the system may comprise a device for introducing powder, liquid or a gel into the material before it is treated.
  • the powder, liquid or gel may serve to fill gaps that would otherwise contain air. In this way sparking and arcing may be reduced.
  • Mixing the material with a liquid, such as water, may serve to help maintain the material at a higher packing density, especially where it is granular or particulate. This may help to prevent sparking and arcing and or increase the consistency of treatment.
  • the electromagnetic radiation generator may emit electromagnetic radiation in the form of microwaves or radio waves. Treatment with microwaves or radio waves may be particularly suitable for achieving particular results. Microwaves and radio waves may for example be particularly useful in producing differential heating in multi-phase materials. This may help to break down materials into their separate phases, perhaps therefore reducing the cost associated with subsequent comminution processes.
  • the system may comprise a filter to prevent dust entering the electromagnetic radiation generator. This may help to prevent dust interfering with the component parts of the electromagnetic radiation generator and may also help to prevent the risk of arcs propagating inside the electromagnetic radiation generator.
  • a system for treating multi-phase material with electromagnetic radiation comprising a transporter for transporting the material through a treatment zone, an electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in the treatment zone, the electromagnetic radiation having a high enough field strength to cause differential thermal expansion between the phases of the material passing through the treatment zone to result in weakening of interfaces between the different phases of the material, and a barrier between the electromagnetic radiation generator and the treatment zone, the barrier arranged to prevent arcs, formed in the material during treatment with the high field strength electromagnetic radiation, from passing through the barrier to the electromagnetic radiation generator.
  • a system for the treatment of particulate material with electromagnetic radiation comprising a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, an electromagnetic radiation generator arranged to treat the packed particulate material with electromagnetic radiation and a barrier between the electromagnetic radiation generator and the packed material, the barrier arranged to prevent arcs, formed in the material during treatment with the electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
  • a computer for controlling a system according to any one of the second to fourth aspects of the invention, wherein the computer comprises a device to measure a property of the material and/or bulk density of material to be treated and arranged to adjust the transporter, packer and/or electromagnetic radiation generator to change the speed the material is transported through the treatment zone, the packing density of the material and/or a field strength or power of the electromagnetic radiation.
  • the computer comprises a device to measure a property of the material and/or bulk density of material to be treated and arranged to adjust the transporter, packer and/or electromagnetic radiation generator to change the speed the material is transported through the treatment zone, the packing density of the material and/or a field strength or power of the electromagnetic radiation.
  • This may allow the treatment to be adjusted depending on various known parameters of the material. For example dielectric properties, such a dielectric constant and dielectric loss factor, conductivity and strength of the material.
  • the power of the electromagnetic radiation or the degree of increase in the packing density to be initiated may be varied according to the composition of the material.
  • a data carrier having instructions stored thereon that, when executed by a processor of a computer, causes the computer to operate in accordance with the computer of the fifth aspect of the invention.
  • Figure 1 shows a schematic side view of an embodiment of the invention incorporating a second conveyor providing the barrier.
  • Figure 2 shows a schematic side view of an embodiment of the invention where the barrier is provided across an opening through which the electromagnetic radiation is delivered to a treatment zone.
  • the system comprises an electromagnetic radiation generator in this embodiment, a microwave generator 100 (containing for example a magnetron) and waveguide 102 that directs microwaves from the microwave generator 100 to a treatment zone 101 in a treatment chamber 104 through opening 103.
  • the generator may further comprise a circulator 130 that blocks reflected microwaves from passing back into microwave generator 100.
  • the microwave generator 100 may generate electric fields sufficient to achieve a power density of the order to 10 7 Wm 3 to 10 16 Wm 3 .
  • the treatment chamber 104 is a hollow duct with openings 105 and 107 at either end through which particulate material 112 is transported on a transporter, in this case a first conveyor 113.
  • the treatment chamber 104 includes several choking areas 106 in the form of a series of castellations, which reflect and stop the passage of microwaves along and out of the treatment chamber 104.
  • the choking areas may also contain microwave absorption formations 108 which are made from material that has a high attenuation for the microwaves generated by the magnetron 100.
  • the castellations may have a required shape and dimension to reflect microwaves back into the microwave chamber 104. The shape and dimension of the castellations may depend on the modes of the microwaves transmitted along the treatment chamber 104.
  • the first conveyor 113 comprises a belt 110 that passes through the treatment chamber 104 supported by rollers 111.
  • the belt 110 has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm to prevent arcs formed as a result of the treatment from passing through the conveyor belt 110.
  • the belt 110 has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e. does not vary by more than 10% over a temperature range of 150°C.
  • the belt 110 is also abrasion resistant for the material being transported, i.e. can be used continuously for an extended period of time, such as days, weeks or months without significant wear of the belt 110.
  • the belt 110 is reinforced rubber or PVC, but it will be understood that other suitable materials may be used.
  • the particulate material 112 is deposited onto the conveyor belt 110 by a feeder, in this case, hopper, 122.
  • the system also comprises a second conveyor 115 comprising a belt 114 supported by rollers 116.
  • the belt 114 of the second conveyor 114 has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm to prevent arcs formed as a result of the treatment from passing through the conveyor belt 114.
  • the belt 114 has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e. does not vary by more than 10% over a temperature range of 150°C.
  • the material of the second conveyor belt 114 also has a very low attenuation for the microwaves produced by the microwave generator 100, for example less than 1% of the energy of the microwaves is dissipated by the conveyor belt 114. This means that the microwaves applied through the opening 103 in the wave guide 102 can pass relatively freely through the second conveyor 114 so as to treat the material 112.
  • the belt 114 is also abrasion resistant for the material being transported, i.e. can be used continuously for an extended period of time, such as days, weeks or months without significant wear of the belt 114.
  • the belt 114 is reinforced rubber or PVC, but it will be understood that other suitable materials may be used.
  • the second conveyor 115 cooperates with the first conveyor 113 such that the belts 110 and 114 of the conveyors 113 and 115 form a seal around the material 112.
  • the rollers 111 and 116 have an outer circumference that is shaped to form the belts 110 and 114 of the conveyors 113 and 115 into a 'U-shaped' cross section (not shown) around the material 112.
  • both the belts 110 and 114 of the first and second conveyors 113 and 115 form a barrier to prevent arcs formed as a result of the treatment from passing through the second conveyor 114 and entering the wave guide 102.
  • the embodiment of Figure 1 is arranged to treat the material 112 with microwaves from the microwave generator 100.
  • Loose material 112 is poured onto the conveyor 113 at a first bulk density, the conveyor 113 moving the material towards the treatment chamber 104. Before the material 112 reaches the treatment chamber 104 it is enclosed by the belt 114 of the second conveyor 115.
  • the conveyor 113 and 115 act as a packer to pack the material together to increase the materials bulk density to a second higher bulk density.
  • the pressure the rollers 111 and 116 exert is adjustable to adjust the bulk density to which material 112 is packed.
  • the conveyors 113 and second conveyor 115 are arranged such that the belts 110 and 114 move at the same speed so as there is substantially no relative movement between the material 112 and either of the conveyor belts 110, 114 once the material 112 has been enclosed.
  • the quantity of air in the material is substantially decreased so as the frequency and severity of sparks and arcs may be reduced. This may achieved by the forces exerted by rollers 111 and 116, through a vacuum pump (not shown) or by mixing powder, liquid or a gel, in this embodiment water, into the material through device 117 that is connected to a source (not shown) of powder, liquid or gel.
  • the increase in the packing density of the material 112 also means that it is largely homogeneous both in density and composition.
  • the material 112 passes into the treatment zone 101 beneath the wave guide 102 it is treated with microwaves from the microwave generator 100, which pass through the second conveyor belt 114. Any sparks and arcs created in the material 112 as a result of the microwave treatment are contained between the conveyor belt 110 and the second conveyor belt 114.
  • the second conveyor belt 114 in particular acts as a barrier to sparks and arcs, preventing them from permeating inside the treatment chamber 104.
  • Microwaves that are scattered and not absorbed by the material 112 may be absorbed by microwave formations 108 in choking areas 106 or reflected by the structure of the choking areas 106 back into the treatment chamber 104. Following treatment the material 112 continues through the treatment chamber 104 until when outside the treatment chamber 104 the second conveyor belt 114 disengages with the conveyor 110 and the material may be further processed or collected as desired.
  • the system further comprises a controller in the form of a computer 120.
  • Computer 120 is connected to sensor array 121 for measuring properties of the material and/or the packing density of the material.
  • the computer receives signals from the sensor array 121 and determines from these signals an appropriate speed for the conveyors 113 and 115, a required force to be exerted by rollers 111 and 116 on the material and the required power and/or field strength of the microwaves emitted by microwave generator 100.
  • the computer sends control signals to the rollers 111 , 116 to cause the rollers to adjust the speed of the conveyor belts 110 and 114 and/or the force applied to the particulate material by the rollers 111 and 116 and/or signals to the microwave generator 100 to change the strength/power of the microwaves.
  • the computer 120 may determine the appropriate values from a look-up table in memory (not shown) .
  • a microwave generator 300 is provided attached to a waveguide 302 to deliver microwaves to treatment chamber 304 which is a hollow duct with openings at either end. Attached to the end of the waveguide 102 forming a seal over its open end is a barrier 305 to prevent arcs formed as a result of the treatment from passing through it.
  • the barrier 305 is made of a material that has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm. The barrier has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e.
  • the barrier 305 does not vary by more than 10% over a temperature range of 150°C. It should be noted that the barrier 305 also has a very low attenuation for the microwaves produced by the microwave generator 300. This means that the microwaves applied by the wave guide 302 can pass relatively freely through the barrier 305.
  • the treatment chamber 304 includes several choking areas 306 in the form of a series of castellations. As with the first embodiment, the choking areas either contain microwave absorption formations 308 which are made from material that has a high attenuation for the microwaves generated by the magnetron 300 or reflect the microwaves back into the microwave chamber 304.
  • a conveyor 313 comprising a conveyor belt 310 that passes through the treatment chamber 304 is provided. The conveyor
  • the 310 comprises a substance that has appropriate dielectric properties to prevent arcs formed as a result of the treatment from passing through the conveyor 310.
  • the conveyor 310 is also abrasion resistant.
  • the material 312 On top of the conveyor belt is a material 312 to be treated, in this case the material 312 is granular.
  • the embodiment of Figure 2 is arranged to treat the material 312 with microwaves from the microwave generator 300.
  • Loose material 312 is poured onto the conveyor 310 which moves the material into the treatment chamber 304.
  • the material 112 passes into the treatment zone 301 beneath the wave guide 302 it is treated with microwaves from the microwave generator 100, which pass through the barrier 305. Any sparks and arcs created in the material 312 as a result of the microwave treatment are prevented from permeating inside the wave guide 302 by the barrier 305.
  • Microwaves that are scattered and not absorbed by the material 312 may be absorbed by microwave absorption formations 308 in choking areas 306.
  • the material 312 continues through the treatment chamber 304 until when outside the treatment chamber 304 it may be further processed or collected as desired.
  • barrier 305 need be provided to protect the wave guide 302.
  • the material 312 is shown passing through the treatment chamber 304 in a non-homogenous arrangement and without having had its packing density increased, in other embodiments an arrangement to increase homogeneity and or packing density of the material 312 may be provided.
  • the barrier 305 may be provided at other locations in or outside of the waveguide 302 as long as the barrier blocks sparks and arcs formed in the bed of material 312 from reaching the microwave generator 300.
  • the system may not comprise conveyors at all.
  • the particulate material could be packed into stand- alone closed containers, such as boxes, and then the containers placed in a treatment zone in which the material is exposed to microwaves.
  • the closed containers may provide a barrier to prevent sparks or arcs formed in the material during treatment with microwaves from passing to the wave guide/microwave generator.

Abstract

This invention concerns a method and apparatus for treating material with electromagnetic radiation. The method comprises providing a barrier between the material and an electromagnetic radiation generator arranged to emit electromagnetic radiation and operating the generator to expose the material to electromagnetic radiation. The barrier is arranged to prevent arcs, formed as a result of exposing the material to electromagnetic radiation, from passing through the barrier to the electromagnetic radiation generator. The method and apparatus are particularly suitable for the continuous treatment of granular material such as mined mineral material.

Description

A METHOD AND APPARATUS FOR THE TREATMENT OF MATERIAL WITH ELECTROMAGENTIC RADIATION
This invention relates to a method and apparatus for the treatment of material, in particular particulate material, with electromagnetic radiation. The invention has particular, but not exclusive, application to the treatment of multi-phase material, such as ores, with electromagnetic radiation to cause differential expansion between the phases of the material resulting in weakening of the material at interfaces between different phases of the material.
It is known to process, e.g. by milling, ores to extract a wanted mineral from unwanted surrounding rocks or minerals. It is also known (see patent application WO03083146) that pretreating mined materials with high field strength electromagnetic radiation before milling or grinding can facilitate later extraction of minerals from the mined material by weakening the material. Such pretreatment can reduce the energy and, therefore, the costs, associated with milling or grinding, which is very energy intensive.
Mined material may be treated with high field strength electromagnetic radiation by passing it along a conveyor which passes through a treatment zone where the material is exposed to electromagnetic radiation emitted by a microwave generator. It has been found however that especially when the mined material is multi-phased, coarse and granular, and where at least part of its composition is metallic, there is a tendency for the electromagnetic radiation (or electric field) to cause breakdown of the local gas in the form of plasma (arcing) or sparking within the bed of the material. If arcs travel to the electromagnetic radiation generator, damage can be caused to the generator and it may be rendered inoperable. Furthermore, formation of arcs between the material and walls of a chamber in which the material is treated can result in loss of energy or damage to the applicator and workload and therefore, a significant reduction in efficiency of the treatment process.
These problems are exacerbated by dust, (that arises from the general handling of the mined material) , in and around the treatment zone.
An additional problem is to be found in the uneven treatment of the mined material with the electromagnetic radiation. This problem is caused by the non-homogenous arrangement of the mined material on the conveyor and movement of the mined material relative to the conveyor as it passes through the treatment zone.
According to a first aspect of the invention a method for treating material with electromagnetic radiation comprising providing a barrier between the material and an electromagnetic radiation generator arranged to emit electromagnetic radiation, the barrier arranged to prevent arcs, formed as a result of exposing the material to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator, and operating the electromagnetic radiation generator to expose the material to electromagnetic radiation.
When the material is treated with electromagnetic radiation, high voltages may be created in voids in the material, which can result in sparks and arcs (dielectric breakdown of the gas surrounding the material) . Sparks and arcs can limit the effectiveness of treatment and, if a spark or arc reaches the electromagnetic radiation generator, it can damage the electromagnetic radiation generator and render the system inoperable. The provision of a solid barrier with appropriate dielectric properties means that dielectric breakdown of the gas may not spread to the electromagnetic radiation generator and, therefore, prevent damage being caused to the electromagnetic radiation generator by consequential sparks or arcs.
The barrier may have appropriate electrical insulating properties as a highly conductive barrier would stop the electromagnetic radiation from passing therethrough.
The barrier may have dielectric properties such that the barrier does not significantly alter the electromagnetic radiation passing therethrough. For example, the barrier may have a dielectric constant, ε' , of less than 5, preferably less than 3 and most preferably, less than 2 and a dielectric loss, ε" , of less than 1 , preferably less than 0.1 , and most preferably, less than 0.01. Such a low dielectric constant ensures that the barrier does not interfere with the electromagnetic wave and the low dielectric loss factor ensures that significant energy is not lost through heating of the barrier by the electromagnetic radiation. For example, the barrier may be arranged such that less than 10%, preferably less than 5%, and ideally less than 1%, of energy of the electromagnetic radiation is dissipated by the barrier. It may be that the barrier comprises reinforced rubber, or PVC, as these may have the necessary dielectric and/or attenuating properties.
It may be that the barrier creates a seal between the material and the electromagnetic radiation generator preventing dust from passing therethrough. The problem of dielectric breakdown of the gas, such as air, both in and around the material and in the electromagnetic radiation generator, is exacerbated by dust in the air. Dust may arise from the general handling and processing of the material especially where it is in a granular or particulate form. If the barrier creates a seal to the dust it may prevent dust from creating and supporting paths for arcing between the material and the electromagnetic radiation generator. The barrier may be arranged between the material and walls of a treatment chamber in which the material is exposed to electromagnetic radiation to prevent arcs from passing through the barrier to walls of the treatment chamber. For example, the barrier may be in the form of an enclosure around the material. As well as preventing arcing to the electromagnetic generator and the walls of the treatment chamber, such an enclosure may be beneficial in that it contains dust within a small area proximate to the material.
The method may comprise providing a substantially constant mass or volume of material per unit time to a treatment zone for treatment with electromagnetic radiation. This may result in substantially consistent results from the treatment of the material.
The material may comprise particulate material, for example particulate material as would obtained in a mining operation. The method may comprise receiving loose particulate material at a first bulk density and packing the particulate material to a second, higher bulk density, the electromagnetic radiation generator being operated to treat the packed material with electromagnetic radiation.
The method may comprise providing an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation. This may be beneficial as increasing the packing density of the material may reduce the quantity of air in and around it, thus potentially reducing the frequency and severity of sparks and arcs. It is also known that more sparking and arcing occurs when the material has: i) angular surfaces, ii) differing dielectric properties, iii) varying particulate sizes, iv) varying temperatures, v) wide spatial distribution, vi) varying bulk densities.
Some or all of these factors may be mitigated by increasing the packing density of the material so as to make it more homogenous. Additionally increasing the packing density of the material may mean that treatment of the material can be achieved more efficiently and in a more consistent manner, with more of the material receiving similar levels of treatment with the electromagnetic radiation.
The enclosure that retains the material at the second bulk density may also form the barrier to the electromagnetic radiation.
In one embodiment, the enclosure is one or more closed containers, the material being packed at the second bulk density into the one or more closed containers before the material is treated. Such closed containers may be used in a batch process. The containers may be transported to a treatment zone by any means, such as conveyors, cranes, fork lift trucks, or the containers may remain in place and the electromagnetic generator and/or a waveguide for the electromagnetic radiation relocated such that the material in the container is treated with electromagnetic radiation.
In another embodiment, the enclosure is one or more conveyors, in particular belt conveyors, on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the microwave generator. The method may comprise placing the material on the belt conveyor, for example in an open zone of the one or more belt conveyors, and then closing the belt conveyors around the material before the material is passed through the treatment zone to retain the material at the second, higher bulk density. It may be that the material moves with a belt of the conveyor rather than relative to it. Movement of the material relative to the belt of the conveyor may imply that it has a relatively low packing density which, as discussed previously, may result in inconsistent treatment and/or encourage the formation of sparks and arcs. Furthermore, movement of the material on the belt of the conveyor can result in segregation of the material on the belt, resulting in significant variation of the dielectric properties of the material being treated and consequently, variation in the results of the treatment. Preventing, or at least reducing, movement of the material relative to the belt reduces the amount of segregation and therefore, reduces variations in the results of treatment.
The one or more conveyors may comprise two belt conveyors that cooperate together during part of their cycle to enclose the material. This may represent a relatively simple way to enclose the material travelling on a first conveyor. Additionally if both conveyors run on a loop, cooperating for only part of their complete rotation, this arrangement may allow for substantially continuous treatment of material.
Alternatively, the one or more conveyors may comprise a single belt conveyor that is wrapped around the material for part of its cycle to enclose the material.
It may be that at least one of the conveyors forms the barrier. This may provide a convenient way to provide the barrier, especially where both conveyors have appropriate dielectric properties such that arcs may be prevented from permeating beyond the enclosure created by the two conveyors. It may be that the one or more conveyors comprise a material that is resistant to abrasion. This may extend the life of the one or more conveyors, especially where the material is abrasive. Additionally it may help to prevent irregular areas forming on the surface of the conveyor which might form air pockets under the material and encourage the formation of sparks and arcs.
It may be that the barrier, such as a belt of one or more of the conveyors, has a similar dielectric constant to the material to be treated. This may be advantageous because impedance mismatching may increase the likelihood of dielectric breakdown or system instability occurring.
It may be that the shape of at least one of the belts of the conveyors is determined by a series of rollers which also cause said at least one belt conveyor to pack the loose material to the second, higher bulk density. In this way the conveyors may shape the material to a desired formation prior to treating. If the conveyors are additionally responsible for increasing the packing density of the material, this packing operation may not need to be conducted by other apparatus.
Alternative or additional to the enclosure forming the barrier, the barrier may comprise a cover across an opening in the electromagnetic radiation generator through which the electromagnetic radiation is delivered. While, without the enclosure, this system would not necessarily confine sparks and arcs to a space proximate to the material, it may provide a relatively cheap and simple way of protecting the electromagnetic radiation generator.
It may be that even where the barrier is not provided in the form of an enclosure around the material, the material is still collected into and retained with an increased packing density before treatment. In this way the advantages that may result from an increased packing density may still be available (e.g. potentially fewer sparks and arcs and more consistent treatment) . It may additionally be that in this type of arrangement the packing density of the material presented for treatment may still be provided so as to be substantially constant.
The method may comprise transporting the material through a treatment zone where the material is exposed to electromagnetic radiation at a predetermined speed. In one embodiment, the method comprises determining the predetermined speed from one or more properties of the material, such as dielectric constant, dielectric loss factor, conductivity and strength characteristics, for example, tensile strength, compressive strength and shear strength, of the material, and a packing density of the material and transporting the material at this determined speed. The embodiment in which the material is transported on a conveyor may be convenient in that it may facilitate varying the speed of the process (and so the treatment) .
The method may comprise mixing the material with powder, liquid or a gel before it is treated. The powder, liquid or gel may serve to fill gaps that would otherwise contain air. In this way sparking and arcing may be reduced. Mixing the material with a liquid, such as water, may serve to help maintain the material at a higher packing density, especially where it is granular or particulate. This may help to prevent sparking and arcing and or increase the consistency of treatment. It may also reduce dust generation and liberation.
It may be that the electromagnetic radiation provided is in the form of microwaves or radio waves. Treatment with microwaves or radio waves may be particularly suitable for achieving particular results. Microwaves or radio waves may for example be particularly useful in producing differential heating in multi-phase materials. This may help to break down materials into their separate phases, perhaps therefore reducing the cost associated with subsequent comminution processes.
The method may comprise treating a multi-phase material with electromagnetic radiation such that the material experiences exposure to electromagnetic radiation for the order of 1 , and preferably Vz, second or less and for a short enough time to avoid causing substantial chemical changes to the phases of the material whilst causing differential thermal expansion between the phases of the material to cause weakening at interfaces between the phases.
It may be that the electromagnetic radiation has a high electric field strength to generate a power density of at least 103 Wm 3, 108 Wm 3, 10" Wm 3, 1010 Wm 3, 1011 Wm 3, 1012 Wm 3, 1013 Wm 3, 1014 Wm 3 or 1015 Wm 3 and/or a frequency between IMHz and 10GHz. High power treatments such as this may be particularly suitable for beginning to separate multiphase materials into their separate phases.
The time the material experiences exposure to electromagnetic radiation may of the order of (i) 1 second or less, (ii) 0.1 second or less, (iii) 0.01 second or less or (iv) 0.001 second or less.
The method may comprise transporting the material to be treated though a treatment chamber provided with choking structures to prevent leakage of the electromagnetic radiation from the treatment chamber. These choking structures may be in the form of one or more castellations in the treatment chamber, extending away from the treatment zone, and may be provided with material that has a high attenuation for the electromagnetic radiation used to treat the material. These choking structures may substantially prevent electromagnetic radiation from leaving the treatment chamber, particularly through its potentially open ends, through absorption of the electromagnetic radiation.
It may be that a circulator is provided to prevent reflected electromagnetic radiation from being reflected back to the microwave generator, from the treatment chamber. This may prevent reflected radiation from damaging the microwave generator.
According to a second aspect of the invention, there is provided a system for treating material with electromagnetic radiation comprising a electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in a treatment zone and a barrier between the treatment zone and the electromagnetic radiation generator, the barrier arranged to prevent arcs, formed in the treatment zone when the material in the treatment zone is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
The barrier may be an enclosure around the material. This may be beneficial in that it may contain dust and/or sparks and arcs within a small area proximate to the material. This may prevent unwanted dust and/or sparking and arcing in and around the treatment area and electromagnetic radiation generator. Furthermore, it may prevent the electromagnetic radiation from passing through to the walls of the system.
The system may comprise a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, the electromagnetic radiation generator arranged to treat the packed material with electromagnetic radiation. The system may comprise an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation. This may be beneficial as increasing the packing density of the material may reduce the quantity of air in and around it, thus potentially reducing the frequency and severity of sparks and arcs. It is also known that more sparking and arcing occurs when the material has: i) angular surfaces, ii) differing dielectric properties, iii) varying particulate sizes, iv) varying temperatures, v) wide spatial distribution, vi) varying bulk densities.
Some or all of these factors may be reduced by increasing the packing density of the material so as to make it more homogenous. Additionally increasing the packing density of the material may mean that treatment of the material can be achieved more efficiently and in a more consistent manner, with more of the materials receiving similar levels of treatment with the electromagnetic radiation.
The enclosure that retains the material at the second bulk density may provide the barrier between the material and the electromagnetic radiation generator.
In one embodiment, the enclosure is one or more closed containers, the material being packed at the second bulk density into one or more closed containers before the material is treated. Such closed containers may be used in a batch process.
In another embodiment, the enclosure is one or more conveyors, such as one or more belt conveyors, on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator. The system may comprise a feeder for feeding material onto the belt conveyor, for example in an open zone of the one or more belt conveyors, and then closing the belt conveyors around the material before the material is passed through the treatment zone to retain the material at the second, higher bulk density.
The one or more belt conveyors may be arranged such that the material moves with a belt of the conveyor rather than relative to it. Movement of the material relative to the conveyor belt may imply that it has a relatively low packing density, which, as discussed previously, may result in inconsistent treatment and/or encourage the formation of sparks and arcs.
The one or more conveyors may comprise two belt conveyors that cooperate together during part of their cycle to enclose the material. This may represent a relatively simple way to enclose the material travelling on a first conveyor. Additionally if both conveyor belts run on a loop, cooperating for only part of their complete rotation, this arrangement may allow for substantially continuous treatment of material.
Alternatively, the one or more conveyors may comprise a single belt conveyor that for part of its cycle is wrapped round the material to enclose the material.
It may be that at least one of the conveyors forms the barrier. This may provide a convenient way to provide the barrier, especially where both conveyors have a sufficiently high dielectric strength and thickness such that arcs may be prevented from permeating beyond the enclosure created by the two conveyors. It may be that the one or more conveyors comprise a material that is resistant to abrasion. This may extend the life of the one or more conveyors, especially where the material is abrasive. Additionally it may help to prevent irregular areas forming on the surface of the conveyor which might form air pockets under the material and encourage the formation of sparks and arcs.
It may be that at least one of the conveyors has a similar dielectric constant to the material to be treated. This may be advantageous because impedance mismatching may increase the likelihood of dielectric breakdown occurring.
The packer may comprise a series of rollers that shape at least one of the conveyor belts to pack the loose material to the second, higher density. In this way the conveyors may shape the material to a desired formation prior to treating. If the conveyors are additionally responsible for increasing the packing density of the material, this operation may not need to be conducted by other apparatus.
Alternative or additional to the enclosure forming the barrier, the barrier may comprise a cover across an opening in a waveguide through which the electromagnetic radiation is delivered to a treatment zone from the electromagnetic radiation generator. While, without the enclosure, this system would not necessarily confine sparks and arcs to a space proximate to the material, it may provide a relatively cheap and simple way of protecting the electromagnetic radiation generator.
It may be that even where the barrier is not provided in the form of an enclosure around the material, the material is still collected into and retained with an increased packing density before treatment. In this way the advantages that may result from an increased packing density may still be available (e.g. potentially fewer sparks and arcs and more consistent treatment) . It may additionally be that in this type of arrangement the packing density of the material presented for treatment may still be provided so as to be substantially constant.
The system may comprise a device for introducing powder, liquid or a gel into the material before it is treated. The powder, liquid or gel may serve to fill gaps that would otherwise contain air. In this way sparking and arcing may be reduced. Mixing the material with a liquid, such as water, may serve to help maintain the material at a higher packing density, especially where it is granular or particulate. This may help to prevent sparking and arcing and or increase the consistency of treatment.
The electromagnetic radiation generator may emit electromagnetic radiation in the form of microwaves or radio waves. Treatment with microwaves or radio waves may be particularly suitable for achieving particular results. Microwaves and radio waves may for example be particularly useful in producing differential heating in multi-phase materials. This may help to break down materials into their separate phases, perhaps therefore reducing the cost associated with subsequent comminution processes.
The system may comprise a filter to prevent dust entering the electromagnetic radiation generator. This may help to prevent dust interfering with the component parts of the electromagnetic radiation generator and may also help to prevent the risk of arcs propagating inside the electromagnetic radiation generator.
According to a third aspect of the invention there is provided a system for treating multi-phase material with electromagnetic radiation, the system comprising a transporter for transporting the material through a treatment zone, an electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in the treatment zone, the electromagnetic radiation having a high enough field strength to cause differential thermal expansion between the phases of the material passing through the treatment zone to result in weakening of interfaces between the different phases of the material, and a barrier between the electromagnetic radiation generator and the treatment zone, the barrier arranged to prevent arcs, formed in the material during treatment with the high field strength electromagnetic radiation, from passing through the barrier to the electromagnetic radiation generator.
According to a fourth aspect of the invention there is provided a system for the treatment of particulate material with electromagnetic radiation, the system comprising a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, an electromagnetic radiation generator arranged to treat the packed particulate material with electromagnetic radiation and a barrier between the electromagnetic radiation generator and the packed material, the barrier arranged to prevent arcs, formed in the material during treatment with the electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
According to a fifth aspect of the invention there is provided a computer for controlling a system according to any one of the second to fourth aspects of the invention, wherein the computer comprises a device to measure a property of the material and/or bulk density of material to be treated and arranged to adjust the transporter, packer and/or electromagnetic radiation generator to change the speed the material is transported through the treatment zone, the packing density of the material and/or a field strength or power of the electromagnetic radiation. This may allow the treatment to be adjusted depending on various known parameters of the material. For example dielectric properties, such a dielectric constant and dielectric loss factor, conductivity and strength of the material. The power of the electromagnetic radiation or the degree of increase in the packing density to be initiated may be varied according to the composition of the material.
According to a sixth aspect of the invention there is provided a data carrier having instructions stored thereon that, when executed by a processor of a computer, causes the computer to operate in accordance with the computer of the fifth aspect of the invention.
An embodiment of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:
Figure 1 shows a schematic side view of an embodiment of the invention incorporating a second conveyor providing the barrier.
Figure 2 shows a schematic side view of an embodiment of the invention where the barrier is provided across an opening through which the electromagnetic radiation is delivered to a treatment zone.
Referring first to Figure 1 , a system is shown capable of carrying out the invented process. The system comprises an electromagnetic radiation generator in this embodiment, a microwave generator 100 (containing for example a magnetron) and waveguide 102 that directs microwaves from the microwave generator 100 to a treatment zone 101 in a treatment chamber 104 through opening 103. The generator may further comprise a circulator 130 that blocks reflected microwaves from passing back into microwave generator 100.
The microwave generator 100 may generate electric fields sufficient to achieve a power density of the order to 107Wm 3 to 1016Wm 3.
The treatment chamber 104 is a hollow duct with openings 105 and 107 at either end through which particulate material 112 is transported on a transporter, in this case a first conveyor 113.
The treatment chamber 104 includes several choking areas 106 in the form of a series of castellations, which reflect and stop the passage of microwaves along and out of the treatment chamber 104. The choking areas may also contain microwave absorption formations 108 which are made from material that has a high attenuation for the microwaves generated by the magnetron 100. The castellations may have a required shape and dimension to reflect microwaves back into the microwave chamber 104. The shape and dimension of the castellations may depend on the modes of the microwaves transmitted along the treatment chamber 104.
The first conveyor 113 comprises a belt 110 that passes through the treatment chamber 104 supported by rollers 111. The belt 110 has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm to prevent arcs formed as a result of the treatment from passing through the conveyor belt 110. The belt 110 has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e. does not vary by more than 10% over a temperature range of 150°C. The belt 110 is also abrasion resistant for the material being transported, i.e. can be used continuously for an extended period of time, such as days, weeks or months without significant wear of the belt 110. In this embodiment, the belt 110 is reinforced rubber or PVC, but it will be understood that other suitable materials may be used.
On top of the conveyor belt 110 is the material 112 to be treated. The particulate material 112 is deposited onto the conveyor belt 110 by a feeder, in this case, hopper, 122.
The system also comprises a second conveyor 115 comprising a belt 114 supported by rollers 116. The belt 114 of the second conveyor 114 has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm to prevent arcs formed as a result of the treatment from passing through the conveyor belt 114. The belt 114 has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e. does not vary by more than 10% over a temperature range of 150°C. It should be noted that the material of the second conveyor belt 114 also has a very low attenuation for the microwaves produced by the microwave generator 100, for example less than 1% of the energy of the microwaves is dissipated by the conveyor belt 114. This means that the microwaves applied through the opening 103 in the wave guide 102 can pass relatively freely through the second conveyor 114 so as to treat the material 112.
The belt 114 is also abrasion resistant for the material being transported, i.e. can be used continuously for an extended period of time, such as days, weeks or months without significant wear of the belt 114. In this embodiment, the belt 114 is reinforced rubber or PVC, but it will be understood that other suitable materials may be used. The second conveyor 115 cooperates with the first conveyor 113 such that the belts 110 and 114 of the conveyors 113 and 115 form a seal around the material 112. To achieve this, the rollers 111 and 116 have an outer circumference that is shaped to form the belts 110 and 114 of the conveyors 113 and 115 into a 'U-shaped' cross section (not shown) around the material 112. In this embodiment, both the belts 110 and 114 of the first and second conveyors 113 and 115 form a barrier to prevent arcs formed as a result of the treatment from passing through the second conveyor 114 and entering the wave guide 102.
In use the embodiment of Figure 1 is arranged to treat the material 112 with microwaves from the microwave generator 100. Loose material 112 is poured onto the conveyor 113 at a first bulk density, the conveyor 113 moving the material towards the treatment chamber 104. Before the material 112 reaches the treatment chamber 104 it is enclosed by the belt 114 of the second conveyor 115. In enclosing the material 112, the conveyor 113 and 115 act as a packer to pack the material together to increase the materials bulk density to a second higher bulk density. In particular, the pressure the rollers 111 and 116 exert is adjustable to adjust the bulk density to which material 112 is packed. The conveyors 113 and second conveyor 115 are arranged such that the belts 110 and 114 move at the same speed so as there is substantially no relative movement between the material 112 and either of the conveyor belts 110, 114 once the material 112 has been enclosed.
Once the packing density of the material 112 has been increased, the quantity of air in the material is substantially decreased so as the frequency and severity of sparks and arcs may be reduced. This may achieved by the forces exerted by rollers 111 and 116, through a vacuum pump (not shown) or by mixing powder, liquid or a gel, in this embodiment water, into the material through device 117 that is connected to a source (not shown) of powder, liquid or gel. The increase in the packing density of the material 112 also means that it is largely homogeneous both in density and composition.
As the material 112 passes into the treatment zone 101 beneath the wave guide 102 it is treated with microwaves from the microwave generator 100, which pass through the second conveyor belt 114. Any sparks and arcs created in the material 112 as a result of the microwave treatment are contained between the conveyor belt 110 and the second conveyor belt 114. The second conveyor belt 114 in particular acts as a barrier to sparks and arcs, preventing them from permeating inside the treatment chamber 104.
Microwaves that are scattered and not absorbed by the material 112 may be absorbed by microwave formations 108 in choking areas 106 or reflected by the structure of the choking areas 106 back into the treatment chamber 104. Following treatment the material 112 continues through the treatment chamber 104 until when outside the treatment chamber 104 the second conveyor belt 114 disengages with the conveyor 110 and the material may be further processed or collected as desired.
In the embodiment shown in Figure 1 , the system further comprises a controller in the form of a computer 120. Computer 120 is connected to sensor array 121 for measuring properties of the material and/or the packing density of the material. The computer receives signals from the sensor array 121 and determines from these signals an appropriate speed for the conveyors 113 and 115, a required force to be exerted by rollers 111 and 116 on the material and the required power and/or field strength of the microwaves emitted by microwave generator 100. In response to making these determinations, the computer sends control signals to the rollers 111 , 116 to cause the rollers to adjust the speed of the conveyor belts 110 and 114 and/or the force applied to the particulate material by the rollers 111 and 116 and/or signals to the microwave generator 100 to change the strength/power of the microwaves. The computer 120 may determine the appropriate values from a look-up table in memory (not shown) .
Referring now to Figure 2, a variation on the embodiment discussed above is shown. Like parts are referred to with like reference numerals in the series 300. A microwave generator 300 is provided attached to a waveguide 302 to deliver microwaves to treatment chamber 304 which is a hollow duct with openings at either end. Attached to the end of the waveguide 102 forming a seal over its open end is a barrier 305 to prevent arcs formed as a result of the treatment from passing through it. The barrier 305 is made of a material that has a dielectric constant of about 2, a dielectric loss factor of about 0.01 and a thickness of approximately 1 cm. The barrier has the property that the dielectric constant of the belt remains stable over a range of temperatures, i.e. does not vary by more than 10% over a temperature range of 150°C. It should be noted that the barrier 305 also has a very low attenuation for the microwaves produced by the microwave generator 300. This means that the microwaves applied by the wave guide 302 can pass relatively freely through the barrier 305.
The treatment chamber 304 includes several choking areas 306 in the form of a series of castellations. As with the first embodiment, the choking areas either contain microwave absorption formations 308 which are made from material that has a high attenuation for the microwaves generated by the magnetron 300 or reflect the microwaves back into the microwave chamber 304. A conveyor 313 comprising a conveyor belt 310 that passes through the treatment chamber 304 is provided. The conveyor
310 comprises a substance that has appropriate dielectric properties to prevent arcs formed as a result of the treatment from passing through the conveyor 310. The conveyor 310 is also abrasion resistant.
On top of the conveyor belt is a material 312 to be treated, in this case the material 312 is granular.
In use the embodiment of Figure 2 is arranged to treat the material 312 with microwaves from the microwave generator 300. Loose material 312 is poured onto the conveyor 310 which moves the material into the treatment chamber 304. As the material 112 passes into the treatment zone 301 beneath the wave guide 302 it is treated with microwaves from the microwave generator 100, which pass through the barrier 305. Any sparks and arcs created in the material 312 as a result of the microwave treatment are prevented from permeating inside the wave guide 302 by the barrier 305. Microwaves that are scattered and not absorbed by the material 312 may be absorbed by microwave absorption formations 308 in choking areas 306.
Following treatment the material 312 continues through the treatment chamber 304 until when outside the treatment chamber 304 it may be further processed or collected as desired.
It will be appreciated that in this embodiment only a relatively small barrier 305 need be provided to protect the wave guide 302. It should also be noted that although in this embodiment the material 312 is shown passing through the treatment chamber 304 in a non-homogenous arrangement and without having had its packing density increased, in other embodiments an arrangement to increase homogeneity and or packing density of the material 312 may be provided. Furthermore, it will be understood that the barrier 305 may be provided at other locations in or outside of the waveguide 302 as long as the barrier blocks sparks and arcs formed in the bed of material 312 from reaching the microwave generator 300.
The invention is not limited to the above described embodiments but includes modifications and alterations as would be apparent to the man skilled in the art. For example, the system may not comprise conveyors at all. For example, the particulate material could be packed into stand- alone closed containers, such as boxes, and then the containers placed in a treatment zone in which the material is exposed to microwaves. In such an embodiment, the closed containers may provide a barrier to prevent sparks or arcs formed in the material during treatment with microwaves from passing to the wave guide/microwave generator.

Claims

1. A method for treating material with electromagnetic radiation comprising providing a barrier between the material and a electromagnetic radiation generator arranged to emit electromagnetic radiation, the barrier arranged to prevent arcs, formed as a result of exposing the material to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator, and operating the electromagnetic radiation generator to expose the material to electromagnetic radiation.
2. A method according to claim 1 , wherein the barrier has appropriate dielectric properties such that the barrier does not significantly alter the electromagnetic radiation passing therethrough.
3. A method according to claim 2, wherein the barrier has a dielectric constant, ε' , of less than 5
4. A method according to claim 2 or claim 3, wherein the barrier has the property that the dielectric constant does not vary by more than 10% over a temperature range of 150°C.
5. A method according to any one of claims 2 to 4, wherein the barrier has a dielectric loss, ε" , of less than 1
6. A method according to any one of the preceding claims, wherein the barrier is arranged such that the electromagnetic radiation passing through the barrier is attenuated by less than
10%.
7. A method according to any one of the preceding claims wherein the barrier comprises reinforced rubber or PVC or a material having similar dielectric properties.
8. A method according to any preceding claim wherein the barrier creates a seal between the material and the electromagnetic radiation generator preventing dust from passing therethrough.
9. A method according to any one of the preceding claims, comprising providing a substantially constant mass or volume of material per unit time for treatment with electromagnetic radiation
10. A method according to any one of the preceding claims, wherein the barrier is further arranged between the material and walls of a treatment chamber in which the material is exposed to electromagnetic radiation to prevent arcs from passing through the barrier to walls of the treatment chamber.
11. A method according to claim 10, wherein the barrier is in the form of an enclosure around the material.
12. A method according to claim 10 or claim 11 , wherein the enclosure is one or more closed containers,
13. A method according to claim 10 or claim 11 , wherein the enclosure is one or more conveyors on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator.
14. A method according to claim 13, wherein the one or more conveyors are belt conveyors and the method comprises placing the material on a belt of one of the conveyor and then closing one or more belts of the conveyors around the material before the material is passed through the treatment.
15. A method according to claim 14, wherein the material moves with the conveyor belt rather than relative to it.
16. A method according to any one of claims 13 to 15, wherein the one or more conveyors comprise two belt conveyors that cooperate together during part of their cycle to enclose the material.
17. A method according to any one of claims 13 to 16, wherein the one or more conveyors comprise a material that is resistant to abrasion.
18. A method according to any one of claims 13 to 17, wherein at least one of the conveyors has a similar dielectric constant to the material to be treated.
19. A method according to any one of claims 1 to 9, wherein the barrier comprises a cover across an opening in the electromagnetic radiation generator through which the electromagnetic radiation is delivered.
20. A method according to any one of the preceding claim, comprising transporting the material through a treatment zone where the material is exposed to electromagnetic radiation at a predetermined speed.
21. A method according to claim 20, comprising determining the predetermined speed from one or more properties of the material and/or a packing density of the material and transporting the material at the determined speed.
22. A method according to any one of the preceding claims, wherein the material comprises particulate material and the method comprises receiving loose particulate material at a first bulk density and packing the particulate material to a second, higher bulk density, the electromagnetic radiation generator being operated to treat the packed material with electromagnetic radiation.
23. A method according to claim 22, comprise providing an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation.
24. A method according to claim 23, wherein the enclosure for retaining the material at the second bulk density also forms the barrier to the electromagnetic radiation.
25. A method according to claim 24, as dependent through to claim
12, comprising packing the material at the second bulk density into the one or more closed containers before the material is treated.
26. A method according to any one of the preceding claims, wherein the method comprises mixing the material with powder, liquid or a gel before it is treated.
27. A method according to any one of the preceding claims, wherein the electromagnetic radiation is provided in the form of microwaves or radio waves.
28. A method according to any one of the preceding claims, comprising treating a multi-phase material with electromagnetic radiation such that the material experiences exposure to electromagnetic radiation for the order of Vi second or less and for a short enough time to avoid causing substantial chemical changes to the phases of the material whilst causing differential thermal expansion between the phases of the material to cause weakening at interfaces between the phases.
29. A method according to any preceding claim wherein the electromagnetic radiation has a frequency between IMHz and 10GHz.
30. A method according to any preceding claim where a circulator is provided to prevent reflected electromagnetic radiation from being travelling back to the electromagnetic radiation generator.
31. A system for treating material with electromagnetic radiation comprising a electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in a treatment zone and a barrier between the treatment zone and the electromagnetic radiation generator, the barrier arranged to prevent arcs, formed in the treatment zone when the material in the treatment zone is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
32. A system according to claim 31 , wherein the barrier has a dielectric constant, ε' , of less than 5.
33. A system according to claim 31 or claim 32, wherein the barrier has the property that the dielectric constant does not vary by more than 10% over a temperature range of 150°C.
34. A system according to any one of claims 31 to 33, wherein the barrier has a dielectric loss, ε" , of less than 1
35. A system according to any one of claims 31 to 34, wherein the barrier is arranged such that the electromagnetic radiation passing through the barrier is attenuated by less than 10%.
36. A system according to any one of claims 31 to 35 wherein the barrier comprises reinforced rubber or PVC or a material having similar dielectric properties.
37. A system according to any one of claims 31 to 36 wherein the barrier creates a seal between the material and the electromagnetic radiation generator preventing dust from passing therethrough.
38. A system according to any one of claims 31 to 37, comprising a treatment chamber in which the material is exposed to electromagnetic radiation and the barrier is further arranged between the material and walls of a treatment chamber to prevent arcs from passing through the barrier to the walls of the treatment chamber.
39. A system according to claim 38, wherein the barrier is in the form of an enclosure around the material.
40. A system according to claim 38 or claim 39, wherein the enclosure is one or more closed containers.
41. A system according to claim 38 or claim 39, wherein the enclosure is one or more conveyors on which the material is transported though a treatment zone where the material is exposed to electromagnetic radiation emitted by the electromagnetic radiation generator.
42. A system according to claim 41 , wherein the one or more conveyors comprise two belt conveyors that cooperate together during part of their cycle to enclose the material.
43. A system according to claim 41 or claim 42, wherein the one or more conveyors comprise a material that is resistant to abrasion.
44. A system according to any one of claims 41 to 43 , wherein at least one of the conveyors has a similar dielectric constant to the material to be treated.
45. A system according to any one of claims 41 to 44, wherein the packer comprises a series of rollers that shape at least one of the conveyors to pack the loose material to the second, higher density.
46. A system according to any one of claims 31 to 37, wherein the barrier comprises a cover across an opening in the electromagnetic radiation generator through which the electromagnetic radiation is delivered.
47. A system according to any one of claims 31 to 46, comprising a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, the electromagnetic radiation generator arranged to treat the packed material with electromagnetic radiation.
48. A system according to claim 47, comprising an enclosure that retains the packed material at the second bulk density during treatment with electromagnetic radiation.
49. A system according to claim 48, wherein the enclosure provides the barrier between the material and the electromagnetic radiation generator.
50. A system according to any one of claims 31 to 49 comprising a device for introducing powder, liquid or a gel into the material before it is treated.
51. A system according to any one of claims 31 to 49, wherein the electromagnetic radiation generator emits electromagnetic radiation in the form of microwaves or radio waves.
52. A system for treating multi-phase material with electromagnetic radiation, the system comprising a transporter for transporting the material through a treatment zone, an electromagnetic radiation generator arranged to deliver electromagnetic radiation to the material in the treatment zone, the electromagnetic radiation having a high enough field strength to cause differential thermal expansion between the phases of the material passing through the treatment zone to result in weakening of interfaces between the different phases of the material, and a barrier between the electromagnetic radiation generator and the treatment zone, the barrier arranged to prevent arcs, formed in the material during treatment with the high field strength electromagnetic radiation, from passing through the barrier to the electromagnetic radiation generator.
53. A system for the treatment of particulate material with electromagnetic radiation, the system comprising a packer for receiving loose particulate material at a first bulk density and packing the material to result in packed particulate material at a higher, second bulk density, an electromagnetic radiation generator arranged to treat the packed particulate material with electromagnetic radiation and a barrier between the electromagnetic radiation generator and the packed material, the barrier arranged to prevent arcs, formed in the material during treatment with the electromagnetic radiation emitted by the electromagnetic radiation generator, from passing through the barrier to the electromagnetic radiation generator.
54. A computer for controlling a system according to any one claims 31 to 51 , wherein the computer comprises a device to measure a property of the material and/or bulk density of material to be treated and arranged to adjust the transporter, packer and/or electromagnetic radiation generator to change the speed the material is transported through the treatment zone, the packing density of the material and/or a field strength or power of the electromagnetic radiation.
PCT/GB2009/051434 2008-10-24 2009-10-23 A method and apparatus for the treatment of material with electromagentic radiation WO2010046712A2 (en)

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