Microwave reduction of iron ore with hydrogen

Abstract

An apparatus and method are provided for processing a metal oxide feed using microwave energy. The apparatus comprises a microwave cavity containing a solids passage of annular geometry through which the feed is advanced. A central structure extends along at least a portion of the solids passage and has a microwave-reflective surface arranged to redirect microwave radiation into the passage to improve heating uniformity. One or more microwave sources are coupled to the cavity to irradiate the feed, and a process gas circuit supplies gas to the passage for chemical processing of the feed. In one embodiment, the feed is advanced by a spiral guide forming part of the central structure within a cylindrical kiln. In another embodiment, the feed is fluidised in a toroidal bed chamber with a tangential gas inlet. The apparatus enables efficient and uniform microwave processing and reduction of metal oxide materials.

Description

[0001] MICROWAVE REDUCTION OF IRON ORE WITH HYDROGEN

[0002] TECHNICAL FIELD

[0003] This application claims priority from AU 2024903004 filed on 19 September 2024 and AU 2024903289 filed on 11 October 2024, the entire contents of which are hereby incorporated by reference.

[0004] BACKGROUND

[0005] Iron and other metals are conventionally produced from oxide ores in blast furnaces or rotary kilns. Blast furnace operation requires sintered or pelletised ore and metallurgical coke, and is associated with high operating temperatures, high energy consumption, and substantial carbon dioxide emissions. Alternative direct reduction processes employing hydrogen or natural gas have been developed, but these generally rely on externally heated reactors and face similar challenges of efficiency and uniformity.

[0006] Fluidised bed reactors have been used to process fine ores without pelletisation, but these reactors can be difficult to operate at scale due to issues of gas maldistribution, sticking and agglomeration of reduced particles, and instabilities in fluidisation behaviour. Rotary kilns and similar cylindrical reactors can continuously convey material, but heat transfer is often slow and non-uniform, requiring significant external energy input

[0007] The present application provides an alternative approach to process fine ores, without the need for pelletisation and proved equipment that allows a greater capacity of feed material while maintaining a sufficiently dense bed of material that can be directed through the processing reactor in less time with greater conversion efficiency. SUMMARY OF INVENTION

[0008] In a first form of the invention there is an apparatus for processing a metal oxide feed, the apparatus comprising:

[0009] • a microwave cavity defined at least in part by refectory walls;

[0010] • a solids passage of annular geometry within the cavity, the solids passage being configured to receive the metal oxide feed and to advance the feed along an annular path;

[0011] • a central structure extending along at least a portion of the solids passage, the central structure having a microwave-reflective surface arranged to reflect microwave energy within the microwave cavity;

[0012] • a transport mechanism configured to advance the feed along the solids passage, the transport mechanism comprising either: o a central spiral guide forming the central structure within a cylindrical kiln arranged to convey the feed through the solids passage without fluidisation; or o a toroidal bed chamber defined by chamber walls comprising an inner sidewall forming the central structure, an outer sidewall and a base, the inner sidewall, outer sidewall and base at least partly defining a toroidal volume for containing the metal oxide feed material;

[0013] • at least one microwave source coupled to the microwave cavity and arranged to communicate microwave radiation into the solids passage;

[0014] • a reducing gas circuit including a gas inlet and outlet in fluid communication with the solids passage;

[0015] • the apparatus reducing the metal oxide feed to a metallic product as the metal oxide feed advances through the solids passage.

[0016] In one embodiment, the transport mechanism configured to advance the feed along the solids passage is a toroidal bed chamber defined by chamber walls comprising an inner sidewall forming the central structure, an outer sidewall and a base, the inner sidewall, outer sidewall and base at least partly defining a toroidal volume for containing the metal oxide feed material.

[0017] In preference, the apparatus further includes a circulation fluid inlet arranged to introduce a fluidising gas.

[0018] In preference, the fluidising gas is introduced into the toroidal bed chamber with a velocity component tangential to the toroidal volume to fluidise and circulate the material within the toroidal volume.

[0019] In preference, the microwave-reflective surface is on an inner surface of the inner sidewall forming the central structure.

[0020] In preference, the microwave-reflective surface is on an inner surface of the outer sidewall.

[0021] In preference, the microwave source includes a waveguide configured to receive microwave radiation and to communicate the microwave radiation into the central structure toroidal volume, the waveguide comprising at least one microwave- transparent window formed in the inner sidewall, outer sidewall or the base; and wherein the inner sidewall comprises a microwave-reflective surface arranged to redirect microwave radiation into the toroidal volume to promote substantially uniform heating of the material.

[0022] In a further embodiment, the transport mechanism comprises a central spiral guide forming the central structure within a cylindrical kiln arranged to convey the feed through the solids passage without fluidisation.

[0023] In preference, wherein the spiral guide comprises a metallic or metallised reflective core with outwardly projecting spiral flights. In preference, the kiln is oriented substantially horizontally with a slight incline, or vertically with counter-current gas flow

[0024] In preference, water cooled coils surround the reactor.

[0025] In a further form of the invention, there is a method of reducing a metal oxide feed, including the steps of feeding a metal oxide feed into an annular solids passage defined between a central spiral guide and an inner wall of a cylindrical kiln; rotating the spiral guide and / or the kiln to convey the feed through the annular solids passage without fluidisation; irradiating the feed with microwave energy while contacting the feed with a reducing gas; and withdrawing a reduced metallic product from the kiln.

[0026] In another aspect, the invention provides a method of processing a metal oxide feed using microwave energy. The method involves introducing the feed into an annular solids passage within a microwave cavity and advancing the feed along the passage with a transport mechanism. As the feed progresses, it is irradiated by microwave energy supplied from one or more microwave sources, while a central structure having a microwave-reflective surface redirects microwave radiation into the passage to improve heating uniformity. A process gas, such as hydrogen, is introduced into the solids passage through an associated gas circuit, enabling chemical processing of the feed as it advances.

[0027] In one embodiment, the feed is conveyed through the annular passage by a spiral guide forming part of the central structure within a cylindrical kiln. In another embodiment, the feed is fluidised within a toroidal bed chamber defined by an inner reflective sidewall, an outer sidewall, and a base, with circulation gas introduced tangentially to establish fluidisation and circulation.

[0028] The process gas may be a reducing gas, such as hydrogen, allowing the metal oxide feed to be reduced to a metallic product. The spiral guide may be configured with a helical pitch in the range of 0.25 to 1 .5 times the diameter of the annular passage, providing controlled residence time. The microwave sources may operate at frequencies in the range of 0.9 to 3.0 GHz, and power may be dynamically adjusted in response to the stage of reduction of the feed material.

[0029] In certain embodiments, advancing the feed comprises fluidising the feed within a toroidal bed chamber defined by an inner sidewall forming the central structure, an outer sidewall, and a base.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the present invention will now be better understood and apparent to a person of ordinary skill in the art refereeing to the written description, by way of example only, in conjunction with the drawing, in which:

[0032] Figure 1 is a schematic view of a first form of the invention, showing a hollow central cylinder with spiral guide;

[0033] Figure 2 is a close up of Section A of figure 1 , showing the solid helical blades of the central cylinder with spiral guide;

[0034] Figure 3 is a close up of Section A of figure 1 , showing the helical blades with holes;

[0035] Figure 4 is a schematic view of a second form of the invention, being a fluidized bed reactor with central hollow cylinders in each of the fluidized beds;

[0036] Figure 5 is a close up of section B from figure 4, showing the hollow central section and

[0037] DESCRIPTION

[0038] As shown in Fig. 1 , the fine hematite ore is dried after coming from a filter unit and directed towards a rotary dryer 15. The dried hematite is mixed with alloying elements and fluxes in a mixer 40 before being fed to a hopper at the top of the reactor 80 (kiln) . Entry to the reactor 80 (kiln) is by a first rotary valve 90, in this instance, a bell valve. The reactor 80 is encased by a silica or alumina or ceramic vessel that is transparent to the microwave applied by water cooled copper pipes. The centre of the reactor 80 is occupied by a central spiral guide 170 with a hollow centre with a reflective surface on its outer surface to reflect the microwaves to the iron ore mass. The iron ore mass is guided by the spiral that has holes to allow hydrogen gas to pass through. The hollow centered spiral guide may be rotating or vibrating to ensure controlled even passage of the iron ore mass through the solids passage of the reactor (kiln). The iron ore passage and the microwave energy are controlled so that the reactor temperature is generally between 800-900°C, which is not sufficient to cause melting of the reduced iron ore. Hot hydrogen is introduced at the bottom of the reactor and it moves counter to the current or movement of the iron ore mass as it travels down the spiral guide. The iron powder exits the reactor by a second rotary 220 valve and enters a melting section where fine carbon can be added to increase the strength of the steel product. To ensure that there is no hydrogen left, this section may be operated under a slight vacuum. The molten iron transfers to an induction furnace where the slag can be separated from the pig iron. The pig iron is transferred to a converter where oxygen is blown through to make the steel of a specified composition. The steel can then be cast into billets or slabs ready for sale or for further processing to structural shapes as required.

[0039] Figure 1 in more detail, shows raw metal oxide feed material 10 entering a rotary dryer 15 through opening 21 . Rotation of the rotary dryer 15 agitates the metal oxide feed material, heat is applied to facilitate the removal of moisture and hydrogen, and / or oxygen, is introduced via conduit 22, hydrogen is a reducing gas and the hydrogen gas and raw metal oxide feed material are mixed together to form a premix being a hydrogen gas / raw metal oxide feed material stream.

[0040] The dried metal oxide feed material is then directed to a mixer 40 where alloying elements can be added, such as copper, silicon, manganese, magnesium, and nickel, each being selected in various amounts to achieve specific physical characteristics of the resultant mixed material, or fluxes. On completion of mixing in the mixer 40, the material is then directed via conduit 45 to a hopper 50 at the top of the reactor 80. A first rotatory rotary valve 90 is then operated to allow material to be added from the hopper 50 to the reactor 80 in a predetermined rate / amount.

[0041] The reactor 80 with microwave irradiation sources 82 operating together at between approximately 200 KHz and 400 KHZ, preferably around 250 KHz, which makes up the first heating zone, within which the material reactor 80 main chamber / reactor core 110 is heated to approximately 800°C - 900°C, which is below the melting point of the iron produced or the slag mixed with the iron ore feed. Water cooled copper pipes 79 surround the reactor 80 to prevent heat radiating outwardly from the reactor, in addition, the reactor is surrounded by a steel casing 120 to contain the hydrogen gas.

[0042] On a central axis of the reactor core 110 is a hollow central spiral guide 170, which includes a main central component 175 with an outer surface 176 and an inner surface 177, and a helical blade 180 located on the outer surface 176 of the main central component 175. The helical blade 180 can be a solid continuous helical blade around the outer surface 176 of the hollow central spiral guide 170 or blades arranged helically about the main central component 175. Hydrogen gas 200, preheated by heater 205, is forced into a lower section of the reactor 80 though the hydrogen conduit 207.

[0043] Fines, being dust of dried metal oxide material, as well as any water vapour or unreacted hydrogen gas, are directed out of the reactor 80 via conduit 87 to a cyclonic separator 88. Recovered solid material, being solid feed material, can be collected via 89 and directed to recycling into the system. Unreacted hydrogen gas and water vapour is directed out of the cyclonic separator 88 via conduit 91 , to a separator 101 , to separate out the unreacted hydrogen gas via 102, which can be recycled to either the rotatory drier 15 or the hydrogen source 200, and the water vapour separated via 103. As the metal oxide feed passes down through the reactor core, being subjected to microwave irradiation, the energy of the microwaves being emitted from the microwave emitting sources, is such that the temperature of the reactor is controlled to between approximately 800°C-900°C, which is sufficient to cause a reaction between the metal oxide feed and the hydrogen, but not sufficient to cause a melting of the iron ore undergoing reduction. This step is the reduction of the hematite by hydrogen where:

[0044] Fe2O3(hematite) Fe3O4(magnetite) ->FeO (wustite) Fe (iron).

[0045] At the lower end of the reactor 80, the reduced iron powder (Fe) exits via a second rotatable valve 220 into a melting section 230, where fine carbon powder can be added to increase the tensile strength of the produced material. The material passing though the melting section is then directed to an induction furnace 300, the slag produced in the process being separated via 320, and the remaining crude iron material (pig iron) being separated via 330, for further processing into cast billets

[0046] As the outer surface of 176 of the central spiral guide 170 is reflective to microwave energy, incoming microwave energy from the microwave energy sources 82 is reflected back outward from the main central spiral guide 175, ensuring an improved even energy distribution to the metal oxide feed material as it passes along the length of the reactor 80. An example of a microwave reflective coating applied to the outer surface 177 is a coating containing metal based materials such as aluminum, graphene, metal based alloys. The central spiral guide 170 may also be constructed from a suitable microwave reflecting material, such as stainless steel.

[0047] A close up of a section of the reactor is shown in figure 2, showing the helical blades 180 of the central spiral guide 170, showing the hydrogen gas 245 that is being injected into the reactor 80 to pass through the helical screw blade180 and react with the metal oxide feed material, passing around the surfaces of the helical screw blade 180. Figure 3 shows a close of a section A of the helical blades, but where the helical blades 180 of the central spiral guide 170 can contain a plurality of openings 250, for example, slots, or holes, through the blades, to allow hydrogen gas 245 that is being injected into the reactor 80 to pass through the helical screw blade180 and have greater penetration into the metal oxide feed material, passing around the surfaces of the helical screw blade 180. Additionally, the openings in the helical screw blade prevent the formation of path of hydrogen travelling on an underside of the helical screw blade, providing for a greater mixing of the hydrogen with the metal oxide feed resulting in greater efficiency of reaction between the hydrogen and the metal oxide feed in the reactor 80.

[0048] In some embodiments, the central spiral guide 170 can be static, the metal oxide feed entering via the hopper is allowed to be directed by a static helical screw blade 180 to traverse around the reactor by gravity. In other forms, the central spiral guide 170 can be made to rotate around a central axis of the reactor at a predetermined speed, and / or the central spiral guide can be vibrated to assist a controlled and even movement of the metal oxide feed through the reactor core.

[0049] In some process it may be desirable to obtain an increased percentage of magnetite material being produced in the process, in which case an additional drying step may be required, as shown in figure 4.

[0050] Figure 4 shows the addition of magnetite feed material 411 into the rotary dryer 415. Similar apparatus shown in figure 1 . Rotation of the rotary dryer 415 agitates the magnetite feed material, heat is applied to facilitate the removal of moisture and hydrogen, and / or oxygen, is introduced via conduit 422, hydrogen is a reducing gas and the hydrogen gas and raw magnetite feed material are mixed together to form a premix being a hydrogen gas / raw magnetite feed material stream.

[0051] On completion drying in the rotatory dryer 415, the raw magnetite feed material is then directed via conduit 445 to a hopper 450 at the top of the reactor 500. A first rotatory rotary valve 510 is then operated to allow material to be added from the hopper 450 to the reactor 500 in a predetermined rate / amount. The reactor 500 with microwave irradiation sources 510 operating together at between approximately 200 KHz and 400 KHZ, preferably around 250 KHz, which makes up the first heating zone, within which the material reactor 480 main chamber / reactor core 520 is heated to approximately 800°C - 900°C, which is below the melting point of the iron produced or the slag mixed with the iron ore feed. Water cooled copper pipes 525 surround the reactor core 501 to prevent heat radiating outwardly from the reactor, in addition, the reactor is surrounded by a steel casing to contain the oxygen gas.

[0052] On a central axis of the reactor core 501 is a hollow central spiral guide 570, which includes a main central component 575 with an outer surface 576 and an inner surface 577, and a helical blade 580 located on the outer surface 576 of the main central component 575. The helical blade 580 can be a solid continuous helical blade around the outer surface 576 of the hollow central spiral guide 570.

[0053] Oxygen gas 580, preheated by heater 585, is forced into a lower section of the reactor 500 though the oxygen conduit 590. As with the helical blades shown in figures 2 and 3, the helical blades 580 can also include a plurality of openings (slot, holes) to allow gaseous oxygen to pass through and create a more efficient mixing of the raw magnetite feed material and the oxidizing gas (oxygen).

[0054] Fines, being dust of dried magnetite material, are directed out of the reactor 500 via conduit 600 to a cyclonic separator 605. Recovered solid material, being solid magnetite feed material, can be collected via 610 and other unwanted material separated out are directed to waste.

[0055] As the magnetite feed material passes down through the reactor 500, being subjected to microwave irradiation from the microwave sources 510, the energy of the microwaves being emitted from the microwave emitting sources is such that the temperature of the reactor is controlled to cause a reaction between the magnetite feed material and the oxygen, to oxidise the magnetite to hematite: Fe3O4(magnetite) Fe2O3(hematite), which also converts ferrous iron (Fe2+) to ferric iron (Fe3+).

[0056] At the lower end of the reactor 500, the oxidized material exits via a second rotatable valve 650 into a melting section 660, then to an induction furnace 300, with the desired hematite material produce via oxidation being directed via conduit 680 to a mixer 690, where various alloying elements / fluxes can be added. After suitable mixing, the hematite material is then directed via conduit 691 into the hopper 692, and subsequently into the reactor 700. Reactor 700 is a reduction reactor involving the injection of hydrogen gas the reducing gas, similar to the reducing reactor of figure 1 .

[0057] On a central axis of the reactor core 720 is a hollow central spiral guide 770, which includes a main central component 775 with an outer surface 776 and an inner surface 777, and a helical blade 780 located on the outer surface 176 of the main central component 175. The helical blade 780 can be a solid continuous helical blade around the outer surface 776 of the hollow central spiral guide 770 or blades arranged helically about the main central component 775. Reactor 700 includes banks of microwave emitting sources 710 emitting microwave irradiation into the solids passage, where the feed material passes through, of the reactor core 720 heating the hematite feed material, causing it to react with the reducing gas (hydrogen) 750 being injected into a lower portion of the reaction 700.

[0058] Hydrogen gas 800, preheated by heater 805, is forced into a lower section of the reactor 700 though the hydrogen conduit 807. Fines, being dust of dried magnetite feed material, as well as any water vapour or unreacted hydrogen gas, are directed out of the reactor 700 via conduit 810 to a cyclonic separator 812. Recovered solid material, being solid magnetite feed material, can be collected via 815 and directed to recycling into the system. Unreacted hydrogen gas and water vapour is directed out of the cyclonic separator 812 to a separator 820, to separate out any unreacted hydrogen gas via 821 , and water vapour separated via 822. Figure 5, shows an additional reactor that realizes the same principle of a reflective central hollow core as shown in the preceding figures. The reactor 850 includes a modified fluidized bed in which a hollow cylinder is placed in the centre of the fluidised bed so that the fine iron ore (hematite) and incoming microwaves are concentrated. The cylinder may be made of silica, alumina or ceramic, or any other material capable of reflecting microwave energy, stainless steel is another suitable material, which can withstand the reduction temperatures within the fluidized bed. A preferable material is titanium metal. Alternatively, a silica, alumina or ceramic cylinder can be spiked or coated with a metal powder, such as titanium metal powder to effectively reflect any incoming microwave energy. As shown in figure 5, fine iron ore is fed at the top of the fluidised bed reactor, including any alloying elements and carbon particles via the hopper. Hot hydrogen gas is injected into the reactor, which fluidises the fine iron ore feed material, whilst microwave energy heats up the iron ore to the appropriate reaction temperature. For example, the iron ore can be heated to white hot with microwave frequency in the range of 250 to 500 Hz. The iron ore progresses from the top to the bottom of the fluidised bed reactor while hydrogen gas is introduced from the bottom of the fluidised reactor and leaves the reactor at the top, taking with it any water that that is formed during reduction of the iron ore feed material. Any fine solids are removed by a cyclone separator, and if valuable, these fine solids may be recycled or removed to waste as appropriate. The hydrogen - water stream removed from the top of the reactor is passed then through a condenser where water can be separated and discarded.

[0059] Any unreacted hydrogen can be recovered and directed towards a hydrogen storage tank or reuse as required. As the iron ore progresses to the bottom of the fluid bed reactor, it is reduced. There may be at least one fluid bed in the reactor, although in a practical sense, for commercial reasons, there may be three or more fluid beds in the reactor. The iron fines produced by the reduction are discharged at the bottom of the fluid bed reactor through a feeder and directed to an induction furnace where the steel fines are melted, including the slag and alloying elements. The molten steel may be treated in an oxygen converter before being cast into billets or slabs for sale. Turing to figure 5 in more detail, the fluidized bed with microwave energy, shows the reactor 855, having a stainless-steel casing 860. Fine iron ore (hematite) and alloying materials are fed in via conduit 865, with the star feeder 870, into the interior 875 of the reactor 855. The fine hematite ore from the hopper 851 may be pre-heated by electric heaters before feeding into the fluidized bed reactor 850. In the fluidized bed reactor 850, there are three fluidized beds, 880a, 880b and 880c, each fluidly coupled to its neighboring fluidized bed, and each of which have an operationally connected microwave generating unit 885a, 885b, 885c, which deliver microwave energy via the shell 890a, 890b, 890c, which is made from a suitable material, such as ceramic, alumina, silica, or engineered carbon, and contains the induction coils 895 and water-cooled copper tubing, sealed 900 against the side of the stainless-steel casing 320. Each area is appropriately insulated 905 and 910.

[0060] Each microwave generating unit 885a, 885b, 885c, generates microwaves at a frequency of between approximately 200 KHz to 400 Khz, with appropriate adjustments being made in relation to the particular hematite ore and the progress of reduction of the hematite ore as it progresses through the reactor.

[0061] The fluidized reactor of the present invention contains several beds with hydrogen fed at the bottom while the hot fine hematite ore is fed at the top and progresses downwards through down pipes to the bottom discharge of the fluidized bed reactor.

[0062] Hydrogen, created from Unipolar electrolysis of water, in accordance with US 10,314,316, is of a high purity with no CO2, is stored in the hydrogen storage tank 920, which is then compressed 925 and heated to a desired temperature approximately 1000°C via the heater 930 and directed by conduit 935 to a bottom 940 of the reactor 855. As the heated H2contacts the heated iron ore in chamber 880c, the iron ore (Fe2O3) is reduced to Fe with the byproduct of H2O. Un-consumed H2is than directed upwards to the chamber 880b, reducing iron ore in this chamber and again, any unconsumed H2is then directed upwards to the chamber 880a, where it is consumed in the reduction of the iron or being added in though the conduit 865.

[0063] Each of the successive fluidized beds, 880a, 880b and 880c, each of which have an operationally connected microwave generating unit 885a, 885b, 885c, then can reduce the iron ore with increased efficiencies and use of H2. In each of the fluidized beds, 880a, 880b and 880c, there is a hollow cylindrical member 950a, 950b and 950c respectively. The hollow cylindrical members 950 are substantially circular in shape creating a toroidal bed chamber (955a, 955b, 955c) defined by chamber walls comprising an inner sidewall of the reactor structure, an outer sidewall of the central hollow cylindrical member and a base, the inner sidewall, outer sidewall and base at least partly defining a toroidal volume for containing the metal oxide feed material. Incoming microwave energy from the microwave generating units 885a, 885b, 885c , passes through a microwave transparent material to enter the toroidal bed chambers 955a, 955b, 955c of each of the fluidized beds, 880a, 880b and 880c. The hollow cylindrical members 950a, 950b and 950c each have an outer sidewall facing into the toroidal chamber 955 the outer sidewall being made from or coated with a microwave reflecting material to create a microwave reflecting surface that redirects and redistributes microwave radiation from the microwave generating units 885 in the solids passage of the iron ore feed material to increase the uniformity of the microwave filed distribution, reduce dead zones or cold spots (uniform heating) within the toroidal bed chambers 955, and greatly enhance the energy efficiency by containing the microwave radiation within the active processing volume / zone, enhancing the reduction of the iron ore feed material (hematite) in the presence of hydrogen.

[0064] Figure 6 is a close up of section B from figure 5, showing a hollow cylindrical member 950b, with an outer side wall 960, inner side wall 965, base 970 and hollow chamber 975. The volume between the side wall 980 of the fluidized bed 880b and the inner side wall 965 of the hollow cylindrical member 950b creates the toroidal volume, being the toroidal fluidized bed volume 955b. Microwave energy generated from an operatively connected microwave generating unit 850b is delivered via the shell 890b into the toroidal fluidized bed volume 955b of the fluidized bed 880b, and the microwave energy (microwaves) heats the iron ore (hematite) in the presence of hydrogen. Microwaves 981 passing through the fluidized bed 880b are reflected 982 by the microwave reflecting surface on the outer side wall 960 of the hollow cylindrical member 950b back into the toroidal volume 955b of the fluidized bed 880b.

[0065] In the fluidized bed 880c, the final bed in this reactor embodiment, the molten material can be tapped and directed to the star feeder 881 and directed to the induction furnace 882, with unwanted slag material being tapped off via line 883 and molten steel being cast into billets via line 884, after oxygen conversion. The fine iron powder is melted by an induction furnace and blown with oxygen in a converter to remove any excess hydrogen but leaving only the carbon to make carbon steel and any alloying elements.

[0066] At the upper end 340 of the reactor 855, any unconsumed / unreacted H2is then tapped off and directed towards the solids separator unit 886, with any fine iron ore (hematite) exiting the reactor at the top passing through a cyclone separator to recover the fine solids and then through a magnetic separator operating at 14,000 gausses to recover more hematite fines, with any recovered solid material being separated off and redirected to be recycled vie line 887. Unconsumed / unreacted H2is then passed through a condenser unit 888, and any condensed water is removed via line 882 and H2is then passed via line 901 to the hydrogen storage tank 920.

[0067] In this present application, the heat is developed within the iron ore (haematite / magnetite) fines I feed material by the microwave energy, equipment such as reactor valves outside of the fluid bed reactor are not exposed to high heat and the possibility of hydrogen in embrittlement. The use of microwaves, with the hollow central core, allows for a safer heating process compared to conventional ways of externally heating the feed material and hydrogen. The invention provides apparatus for processing a metal oxide feed using microwave energy. In general, the apparatus comprises a microwave cavity defined at least in part by refractory walls, and a solids passage of annular geometry arranged to receive the feed and to advance it along an annular path. A central structure extends along the passage and has a microwave-reflective surface that redirects microwave radiation into the processing zone. One or more microwave sources are coupled to the cavity to deliver energy into the solids passage, while a process gas circuit with an inlet and outlet provides controlled gas flow through the passage.

[0068] In one form, the transport mechanism comprises a spiral guide forming part of the central structure within a cylindrical kiln, configured to advance the feed without fluidisation. In another form, the transport mechanism comprises a toroidal bed chamber defined by an inner reflective sidewall, an outer sidewall and a base, with a circulation fluid inlet arranged to introduce gas tangentially to fluidise and circulate the feed material. The central reflective surface improves microwave field distribution in both configurations, promoting uniform heating and efficient processing.

[0069] The invention also encompasses methods of processing a metal oxide feed using such apparatus. In the methods, the feed is introduced into the annular passage and advanced along it while being irradiated with microwave energy. Microwave radiation introduced into the reactor is reflected by a central reflective surface into the solids passage to improve field uniformity. A reducing gas, such as hydrogen, supplied into the passage to the reduction of metal oxides to metallic products. In one embodiment the feed is advanced by a hollow spiral guide within a cylindrical kiln; in another embodiment the feed is fluidised within a toroidal bed chamber having a hollow central section.

[0070] The apparatus and methods may employ reducing gases such as hydrogen. The spiral guide may be proportioned with a helical pitch relative to the passage diameter to provide controlled residence time, and the microwave energy may be supplied at industrial frequencies suitable to heat the feed material (hematite / magnetite). In all cases, the combination of an annular passage, a reflective hollow central structure, and integrated gas flow provides improved microwave energy utilisation, uniform heating, and efficient processing of metal oxide feedstocks compared with conventional systems.

[0071] As should now be evident, the present invention provides an iron-making method and a microwave iron-making furnace having a hollow central cylinder with microwave reflecting sides greatly increases the efficiency of the produced microwave energy to manufacture molten metal with high energy efficiency.

Claims

CLAIMS1 . An apparatus for processing a metal oxide feed, the apparatus comprising:• a microwave cavity defined at least in part by refectory walls;• a solids passage of annular geometry within the cavity, the solids passage being configured to receive the metal oxide feed and to advance the feed along an annular path;• a central structure extending along at least a portion of the solids passage, the central structure having a microwave-reflective surface arranged to reflect microwave energy within the microwave cavity;• a transport mechanism configured to advance the feed along the solids passage, the transport mechanism comprising either: o a central spiral guide forming the central structure within a cylindrical kiln arranged to convey the feed through the solids passage without fluidisation; or o a toroidal bed chamber defined by chamber walls comprising an inner sidewall forming the central structure, an outer sidewall and a base, the inner sidewall, outer sidewall and base at least partly defining a toroidal volume for containing the metal oxide feed material;• at least one microwave source coupled to the microwave cavity and arranged to communicate microwave radiation into the solids passage;• a reducing gas circuit including a gas inlet and outlet in fluid communication with the solids passage;• the apparatus reducing the metal oxide feed to a metallic product as the metal oxide feed advances through the solids passage.

2. The apparatus of claim 1 , wherein the transport mechanism configured to advance the feed along the solids passage is a toroidal bed chamber defined by chamber walls comprising an inner sidewall forming the central structure, an outer sidewall and a base, the inner sidewall, outer sidewall and base at least partly defining a toroidal volume for containing the metal oxide feed material.

3. The apparatus of any one of the above claims, wherein the apparatus further includes a circulation fluid inlet arranged to introduce a fluidising gas.

4. The apparatus of any one of the above claims, wherein the fluidising gas is introduced into the toroidal bed chamber with a velocity component tangential to the toroidal volume to fluidise and circulate the material within the toroidal volume.

5. The apparatus of any one of the above claims, wherein the microwave- reflective surface is on an inner surface of the inner sidewall forming the central structure.

6. The apparatus of any one of the above claims, wherein the microwave- reflective surface is on an inner surface of the outer sidewall.

7. The apparatus of any one of the above claims, wherein the microwave source includes a waveguide configured to receive microwave radiation and to communicate the microwave radiation into the central structure toroidal volume, the waveguide comprising at least one microwave-transparent window formed in the inner sidewall, outer sidewall or the base; and wherein the inner sidewall comprises a microwave-reflective surface arranged to redirect microwave radiation into the toroidal volume to promote substantially uniform heating of the material.

8. The apparatus of claim 1 , wherein the transport mechanism comprises a central spiral guide forming the central structure within a cylindrical kiln arranged to convey the feed through the solids passage without fluidisation.

9. The apparatus of claim 8, wherein wherein the spiral guide comprises a metallic or metallised reflective core with outwardly projecting spiral flights.

10. The apparatus of any one of the above claims, wherein, the kiln is oriented substantially horizontally with a slight incline, or vertically with counter-current gas flow11. A method of reducing a metal oxide feed, including the steps of feeding a metal oxide feed into an annular solids passage defined between a central spiral guide and an inner wall of a cylindrical kiln; rotating the spiral guide and / or the kiln to convey the feed through the annular solids passage without fluidisation; irradiating the feed with microwave energy while contacting the feed with a reducing gas; and withdrawing a reduced metallic product from the kiln.

12. A method of processing a metal oxide feed, the method comprising:• introducing the feed into a solids passage of annular geometry within a microwave cavity;• advancing the feed along the solids passage using a transport mechanism;• irradiating the feed with microwave radiation supplied from at least one microwave source coupled to the cavity;• reflecting microwave radiation into the solids passage from a central structure having a microwave-reflective surface; and• introducing a process gas into the solids passage through a process gas circuit in fluid communication with the solids passage, wherein the feed is processed as it advances through the solids passage.

13. The method of claim 12, wherein advancing the feed comprises conveying the feed through the solids passage by means of a spiral guide forming part of the central structure within a cylindrical kiln.

14. The method of claim 12, wherein advancing the feed comprises fluidising the feed within a toroidal bed chamber defined by an inner sidewall forming the central structure, an outer sidewall, and a base.

15. The method of claim 12, wherein the process gas is a reducing gas.

16. The method of any one of claims 12 to 15, wherein the feed is reduced from a metal oxide to a metallic product during irradiation.

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