Method and apparatus for processing material using microwaves

Abstract

An apparatus for heating a microwave absorbent material comprises (a) a furnace having a microwave energy zone and (b) a conveyor for transporting microwave absorbent material through the microwave energy zone. The furnace comprises at least one module that forms at least a part of the microwave energy zone. The module is positioned above and on opposite sides of the conveyor and comprises a roof, side walls, and opposed ends. The opposed ends are configured to be coupled to an adjacent module in the microwave energy zone or to an adjacent section of the furnace. The module is configured so that it can be removed from the furnace and subsequently positioned in the furnace.

Description

[0001] METHOD AND APPARATUS FOR PROCESSING MATERIAL USING MICROWAVES

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method and an apparatus for heating a microwave absorbent material.

[0004] The invention relates particularly, although not exclusively, to:

[0005] (a) an apparatus that comprises a furnace, typically a linear hearth furnace, having a microwave energy zone, and a conveyor for transporting microwave absorbent material through the microwave energy zone, and

[0006] (b) a method of heating a microwave absorbent material in the furnace.

[0007] The present invention also relates particularly, although by no means exclusively, to a module for a furnace in which microwaves are emitted, typically a linear hearth furnace, with the module defining a microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace, with the module being configured to be removable from the furnace and to be subsequently positioned back in the furnace.

[0008] The term “microwave absorbent material” is understood herein to mean a solid substance comprising completely or in part a mined material that has been formed by a geological process. For the avoidance of doubt, the microwave absorbent material may be a blend of mined materials or even combinations of mined and non-mined material(s), may be in a loose or bound form, and / or may have already undergone some solid-state chemical or thermal process. It is not necessary that the microwave absorbent material in fact be particularly absorbent to microwaves on entry to the linear hearth furnace, only that it be readily absorbent to microwaves within the microwave energy zone.

[0009] The term “linear hearth furnace” is understood herein to mean a furnace that includes a lengthwise extending chamber with an inlet (feed) end at one end and an outlet (discharge) end at the opposite end and an endless conveyor that extends along the length of the chamber and carries material through the chamber from the inlet to the outlet ends for thermal processing in the chamber, with the conveyor returning to the inlet end from the discharge end and repeating the process of loading material on the conveyor to be transported through the chamber. Any hot gases arising in the furnace under operating conditions are contained therein and generally released only through purposefully provided gas ducting.

[0010] The term “microwave energy zone” is understood herein to mean a zone in the chamber of a furnace, such as a linear hearth furnace, in which microwave energy is delivered as part of the thermal processing of material passing therethrough and in which the microwave energy is at least substantially confined. For the avoidance of doubt, the microwave energy zone may not be the only zone in which thermal processing is carried out, and without limiting the foregoing, a furnace may have more than one microwave energy zone.

[0011] BACKGROUND

[0012] Mineral processing is required for delivering materials and goods that support an industrialised society, be the output therefrom merely for use as construction materials for building physical structures or as precursors for chemical processes that supply society with the finished goods that it needs or wants. Such processing to date has usually traditionally involved carbon intensive processes with a majority of such carbonaceous material used in or to support such processing eventually being oxidised to CO2 and discharged to the atmosphere. With the world seeking to reduce overall net emissions of greenhouse gases there is pressure on all processors to now find the means to make their products while minimising net emissions of greenhouse gases. In particular, there is pressure not to use or at least minimise as much as practical fossil fuels, such as coal or natural gas, in such processing that are effectively non-renewable and result in increased concentration of atmospheric greenhouse gases.

[0013] As an example, a majority of iron ore in the world is currently processed via the blast furnace route to produce molten iron (usually for onward processing thereafter to make steel), which is a technology that has existed since prior to the industrial revolution. Even with technology advances, the blast furnace currently still requires around 800kg of metallurgical coal for every tonne of iron produced and emits high levels of CO2, roughly 1.8-2.0 tonne CO2 per tonne of hot metal. The use of fossil fuels, in particular the requirement for coal (in the form of coke), is an essential feed material for a blast furnace to operate.

[0014] Thus, with an eye to the eventual replacement of blast furnaces, various alternative technical approaches are actively being pursued to make iron in a more environmentally friendly manner from a carbon use perspective; in particular through direct reduced iron (DRI) processes where the iron is reduced in a solid state.

[0015] One such proposal for producing DRI uses renewable biomass as a reductant and electromagnetic energy as a source of heat energy. The proposal is disclosed in International application PCT / AU2021 / 051398 in the name of the applicant. The application describes an invention for a process and an apparatus for direct reduction of iron ore in a solid state under anoxic conditions with biomass as a reductant and with electromagnetic energy as a source of energy where gases arising from reduction of the ore in the microwave delivery region (called therein a reduction zone) flow into an oxygen-available combustion zone where the iron ore may be initially heated from such combustion (a preheat zone), while still maintaining anoxic conditions in the reduction zone.

[0016] A further proposal for a process for direct reduction of iron ore in a solid state under anoxic conditions with biomass as a reductant and with electromagnetic energy as a source of energy might operate at scale is disclosed in International application PCT / AU2023 / 051350 in the name of the applicant. The application describes an invention for producing direct reduced iron under like conditions where there is additionally a transition zone between the preheat zone and the reduction zone where the material is compacted to form a more homogenised bed before it reaches the reduction zone and is exposed to electromagnetic energy. The disclosure in that application is incorporated herein by cross-reference.

[0017] The applicant has carried out further development work specifically on the microwave delivery regions disclosed in the inventions described in the above applications of the applicant to better establish how to effectively construct and operate a microwave energy zone within a linear hearth furnace for heating material, such as iron ore, at scale in an efficient manner.

[0018] The invention relates to the further development work.

[0019] The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere. It should also be understood that the number of skilled persons in the field of the invention in Australia and elsewhere is presently very small. SUMMARY OF THE DISCLOSURE

[0020] The present invention is based on consideration of a number of potentially conflicting demands for heating microwave absorbent material using microwave energy (whether as the only heating source or as one of a number of heating sources) in a furnace, such as a linear hearth furnace, in which there is a conveyor transporting a bed of material, such as iron ore and biomass, from an inlet (feed) end to an outlet (discharge) end, and in which microwave energy is supplied within a microwave energy zone of the furnace.

[0021] It is preferable from energy efficiency and equipment cost reasons that the microwave energy zone be as compact as possible. Inevitably, this means that access to the microwave energy zone is limited, and this creates difficulties when it is necessary to access the microwave energy zone to carry out maintenance.

[0022] It is also a requirement for any furnace in which microwaves are emitted that it be designed so that the microwave energy be contained therein.

[0023] There are exacting international standards for microwave emissions to avoid communication equipment interference issues. These emission levels are generally far lower than those required for human safety. Hence, the need for microwave energy confinement.

[0024] Microwave energy confinement can be challenging where the furnace is one in which the material to be heated is continually fed into the furnace, conveyed through a microwave energy zone of the furnace, and then discharged at elevated temperature.

[0025] The materials selection issues for the furnace increase as the processing temperature increases. This is particularly the case for processes operating at high temperatures, such as processes for producing DRI from iron ore. These issues include structural integrity, as well as gas and microwave containment. For example, where the microwave energy zone sees temperatures approaching or around 1000°C, only materials, such as heat-resistant stainless steel (e.g., SS310), can be used without providing substantial furnace cooling, which is undesirable as it reduces the efficiency of the furnace.

[0026] Further, every opening in the furnace structure for furnace components to penetrate the furnace structure and every joint in the furnace structure is a potential microwave energy leakage point, noting that the issues providing joints are further complicated by the need to allow thermal expansion and contraction of the furnace structure and furnace components as they heat up and cool. This is particularly relevant to the inside lining of the microwave energy zone where temperatures approaching or around 1000°C are experienced in processes for producing DRI from iron ore and, for example, the microwave delivery system apparatus in the microwave energy zone is made from metal.

[0027] Conventional expansion joints and compressible insulation are potential options to overcome some of these issues. However, such joints and openings are by their nature pathways for microwaves and therefore problematic.

[0028] For example, if a material used at such openings and joints or if a refractory material used to insulate the furnace is itself microwave absorbent, localised heating can occur, which can negate an intended purpose of placing the material there in the first place.

[0029] Complete sealing of such openings and joints through welding and the like is not practical, as it creates an ever increasing and compounding engineering exercise in addressing the thermal stresses created by rigid sealing.

[0030] Another challenge is to avoid unnecessarily creating impedance points for microwaves in any gaps between components of the furnace that may trigger electrical arcing, leading to excessive heating of such componentry or surrounding thermal insulation, while still ensuring that the microwave energy is contained to the desired zone.

[0031] Where the operating temperature of the furnace is reached, in part through microwave energy applied to the material in the furnace, gaps at expansion joints and the like cannot be assured to remain constant due to thermal expansion taking place as the furnace reaches it natural temperature equilibrium.

[0032] For many materials, the temperature at which they readily absorb microwave energy also changes with temperature and structure. Thus, in using microwave energy efficiently in a furnace for heating purposes, it can be necessary to have other separate heating means so that, for example, the material is first preheated. For efficiency, this means that the furnace may have to have multiple zones, with ideally the microwave energy largely contained to a designated microwave energy zone to minimise the number of potential microwave leakage points to be addressed.

[0033] Another key requirement is for microwave energy within a microwave energy zone to be delivered into the microwave absorbent material as efficiently as possible. While it is possible to form a microwave energy zone within a furnace that is effectively a multimodal cavity in which the microwaves bounce around heating material that passes through from all directions, this is inefficient where significant heating is required in a short time frame. The best material to take up the microwaves and minimise exposure to microwave leakage from the microwave energy zone is the microwave absorbent material to be heated in that zone. Thus, it is highly desirable to create a well-defined energy pattern above and directed towards a top surface of a conveyor that transports material through a furnace, with a view to providing a minimum amount of heating across and along a bed of microwave absorbent material on the conveyor. The applicant has realised that this demand can potentially be accommodated using a plurality of microwave horns (described further below) or other suitable applicators placed in close proximity to a moving bed of microwave absorbent material, with the horns (or other suitable applicators) being arranged in a manner to form a regular field pattern.

[0034] Generally, microwave delivery systems for heating a material can be described as comprising three component parts, being a generator (with associated power supply), a transmission system (which typically includes a waveguide, and devices for tuning / impedance matching, etc.), and an applicator, referred to herein and defined as a “microwave outlet”. The generator produces microwaves, for example in a magnetron, at a set frequency. The transmission system receives the microwaves and transports them in a contained manner to the microwave outlet. Typically, the waveguide of the transmission system is formed from electrically conductive material or is surrounded by electrically conductive material. For example, the waveguide may be made of metal with a high conductivity such as copper, aluminium, brass, steel and sometimes has a conductive coating. The microwave outlet may be a horn or any other suitable component, which applies the microwave energy to the material to be heated within a resonant cavity that forms the microwave energy zone.

[0035] Conventionally, microwave horns and other suitable applicators (microwave outlets) are located at an end of a waveguide mostly in antenna / receiver situations (rather than typically in heating situations) and are positioned to transmit microwaves from the waveguide into a space in a directional manner. Typically, a horn is a flared metal waveguide, i.e. shaped like a horn. Typically, a horn comprises side walls that define the horn, with at least some of the side walls diverging outwardly with distance from an end of a waveguide so that the transverse cross-sectional area of the horn increases towards an outlet opening. Without such a horn, the typically small aperture of a waveguide (typically less than one wavelength) causes significant diffraction of the waves issuing from it, resulting in a wide radiation pattern without much directionality. Further, if a simple open-ended waveguide is used as an antenna, without a horn, the sudden end of the conductive walls causes an abrupt impedance change at the aperture, with the impedance step causing a waste of energy through a significant amount of energy being reflected back down the waveguide.

[0036] Having regard to the above considerations, in broad terms, the invention provides an apparatus for heating a microwave absorbent material, typically continuously, that comprises (a) a furnace, typically a linear hearth furnace, having a microwave energy zone and (b) a conveyor for transporting microwave absorbent material through the microwave energy zone, with the furnace comprising at least one module that forms at least a part of the microwave energy zone, with the or each module positioned above and on opposite sides of the conveyor, with the or each module comprising a roof, side walls, and opposed ends, with the opposed ends being configured to be coupled to an adjacent module in the microwave energy zone or to an adjacent section of the furnace, and with the module or at least one of the modules being configured to be removed from the furnace and subsequently positioned in the furnace.

[0037] When there are multiple modules that form at least a part of the microwave energy zone, each module forms a segment of the microwave energy zone.

[0038] When there is only one module in the microwave energy zone, it is still the case that the module forms a segment of the microwave energy zone.

[0039] The use of a module or modules (hereinafter “module(s)”) that can be removed from the furnace and subsequently positioned in the furnace is advantageous because it facilitates easy and convenient access to the microwave energy zone, for example to carry out maintenance work in the zone or to work on the module(s). The invention extends to situations where a module(s) is positioned back in the same location from which it was removed.

[0040] The invention also extends to situations where a module(s) is positioned in a different location from which it was removed.

[0041] The module(s) may be configured to be removed from the furnace and subsequently positioned in the furnace by being constructed to be able to be connected in a releasable manner to adjacent modules and / or to adjacent sections of the furnace in such a way that it is possible to lift or otherwise move the module clear of the furnace and lift or otherwise move the module into the same or a different position in the furnace with sufficient clearance to do so. A skilled person will appreciate that there is a range of structural connection options to do this.

[0042] By way of example, the or each module may comprise a lifting hook or other coupler to allow a crane or other lifting device to be coupled to and to lift and replace the module.

[0043] The use of the module(s) in the furnace generally and in the microwave energy zone of the furnace in particular creates thermal expansion and microwave containment issues, and these are discussed further below.

[0044] In this regard, the module may comprise:

[0045] (a) an inner member, typically a skin, typically a metallic inner skin, configured to reflect microwave energy within the microwave energy zone,

[0046] (b) an outer member, typically a shell, typically a steel shell, configured to be a structural member of the module, and

[0047] (c) a thermal insulator, such as a thermal insulating material, between the inner member and the outer member.

[0048] The term “structural member of the module” in the context of the outer member is understood herein to mean that the outer member is a major load bearing component of the module compared to the inner member and the thermal insulator. The invention is not confined to arrangements in which the outer member is the only load bearing component of the module. Those skilled in the art will know that the selection and thickness of the thermal insulating material will be based on a range of factors, including ensuring that any structural member of the module sees a temperature considerably less than the temperature within the furnace (in that section). As an example, where temperatures approaching or around 1000°C are seen inside the module (when the furnace is operating), typically the temperature that the structural member of the module sees will be less that 400°C, and ideally no more than around 200°C.

[0049] It is noted that there are alternative arrangements to that described in the preceding three paragraphs.

[0050] For example, the module may not have the above-described inner skin and may comprise an outer shell and a thermal insulator, with the outer shell being configured to reflect microwave energy within the microwave energy zone.

[0051] In a situation where there is only one module that forms at least a part of the microwave energy zone, typically, there is an axial gap between each end of the module and an adjacent section of the furnace to accommodate thermal expansion of the module in use of the microwave energy zone to heat material passing through the zone.

[0052] One or both of the adjacent modules may be configured so that each gap defines or comprises a choking structure that restricts microwave leakage through the gaps, while allowing the gap to continue to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passing through the zone.

[0053] In a situation where there is two or more than two modules that form at least a part of the microwave energy zone, with the modules being positioned successively along the length of the microwave energy zone, typically, there is (a) an axial gap between each pair of adjacent ends of the modules and (b) an axial gap between the ends of the first and the last module and adjacent sections of the furnace, to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passing through the zone.

[0054] The modules and / or adjacent sections of the furnace may be configured so that each gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passing through the zone.

[0055] Typically, each gap may “define” or “comprise” a choking structure because of the selection of:

[0056] - the geometry (i.e., dimensions) of the gap, or changes of direction of a pathway defined by the gap, or a section(s) of a pathway defined by the gap being formed primarily to increase impedance for microwaves.

[0057] The term “choking structure” is understood herein to mean a structure that restricts microwave leakage.

[0058] The modules and / or adjacent sections of the furnace may also be configured to form a gas seal for each gap.

[0059] The gas seal may comprise a bellows-type arrangement that extends across and closes the gap and is connected to adjacent modules or to a module and an adjacent section of the furnace and is configured to accommodate thermal expansion and contraction of the gap.

[0060] The module or at least one of the modules may comprise a plurality of openings.

[0061] There may be openings in any one or more than one of the roofs and the side walls of the module or at least one of the modules.

[0062] The module or at least one of the modules may comprise at least one microwave outlet for delivering microwave energy to the microwave energy zone.

[0063] The term “microwave outlet”, also known as “microwave applicator”, is understood herein to mean a metallic structure that extends into and delivers microwave energy into the microwave energy zone.

[0064] The microwave outlet may extend through one of the openings in the roof. For clarity, the microwave outlet as further described herein may include a portion of a waveguide that passes through the wall or roof of the module, and is not intended to be read down solely to the outlet component e.g. the horn, of the waveguide.

[0065] The microwave outlet may be supported externally of the roof and there may be a gap between the microwave outlet and the roof that allows relative movement to accommodate thermal expansion.

[0066] One or both of the roof and the microwave outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0067] The microwave outlet may be connected to and be supported by the outer member, such as the outer shell, of the roof and is not connected in a fixed way to the thermal insulator and the inner member, such as the inner skin, of the roof. As a consequence, the microwave outlet can move relative to these components (i.e., the thermal insulator and the inner member) and there is a gap between the microwave outlet and these components that allows relative movement to accommodate thermal expansion.

[0068] One or both of the inner member, such as the inner skin, of the roof and the microwave outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0069] Typically, each gap may “define” or “comprise” a choking structure because of the selection of:

[0070] - the geometry (i.e., dimensions) of the gap, or changes of direction of a pathway defined by the gap, or a section(s) of a pathway defined by the gap being formed primarily to increase impedance for microwaves.

[0071] The module may comprise at least one outlet for gas generated within the microwave energy zone to flow from the microwave energy zone.

[0072] The gas outlet may extend through another one of the above-described openings in the roof.

[0073] The gas outlet may be supported externally of the roof and there may be a gap between the gas outlet and the roof that allows relative movement to accommodate thermal expansion.

[0074] One or both of the roof and the gas outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0075] The gas outlet may be connected to and supported by the outer member, such as the outer shell, of the roof and not connected in a fixed way to the thermal insulator and the inner member, such as the inner skin, of the roof. As a consequence, the gas outlet can move relative to these components (i.e., the thermal insulation and the inner skin) and there is a gap between the gas outlet and these components that allows relative movement to accommodate thermal expansion.

[0076] One or both of the inner member of the roof and the gas outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0077] Typically, the gap may “define” or “comprise” a choking structure because of the selection of:

[0078] - the geometry (i.e., dimensions) of the modified gaps, or changes of direction of a pathway defined by the modified gaps, or a section(s) of a pathway defined by the gap being formed primarily to increase impedance for microwaves.

[0079] The furnace may comprise support members on both sides of the furnace for supporting the module or modules when positioned in the furnace. The support members may be side walls of the furnace.

[0080] Typically, the furnace further comprises a microwave choke positioned above the conveyor at an inlet to the microwave energy zone and / or at an outlet of the microwave energy zone for at least substantially preventing microwaves in the microwave energy zone passing beyond the choke(s).

[0081] The microwave choke may be an elongated metal section extending along a section of the furnace at or before the inlet to the microwave energy zone and / or at or after the outlet of the microwave energy zone.

[0082] The elongated metal section may form a downwardly facing channel positioned above and across the path of the conveyor through the section of the furnace.

[0083] The elongated metal section may comprise a plurality of chambers extending upwardly away from the conveyor and spaced along the section of the furnace that form a ‘corrugated’ baffle, with the number and dimensions and spacings of the chambers being based on characteristics of microwave energy in the microwave energy zone.

[0084] The microwave choke may comprise a microwave absorbent block of refractory material positioned above and across the path of the conveyor.

[0085] The microwave choke may be a module that can be positioned in and removed from the furnace as a unit.

[0086] Typically, there are at least two modules that form the microwave energy zone.

[0087] The module or at least one of the modules may have a plurality of the microwave outlets for delivering microwave energy to the microwave energy zone.

[0088] Typically, each module comprises a plurality of the microwave outlets arranged in a plurality of rows across a width of and along a length of each module.

[0089] Typically, each microwave outlet comprises horns. Typically, the horns in at least some of the rows in each module are offset laterally relative to the horns of at least some of the other rows - i.e., laterally relative to the direction of movement of material through the microwave energy zone.

[0090] Typically, the horns of each row in a module are offset with respect to the horns of successive rows.

[0091] Typically, each module having rows of horns has an even number of rows and an even number of horns in the rows.

[0092] Typically, the horns are sectorial pyramidal horns each with one pair of opposing sides being flared and the other pair of opposing sides being parallel.

[0093] Typically, a majority of sectoral horns in each pair of successive rows of horns in a module are placed to extend across a width of the conveyor with the shorter sides of such rectangular openings of the sectoral horns all aligned in one direction, as against a direction of movement of the conveyor through the microwave energy zone.

[0094] The invention is not confined to this orientation of the sectoral horns.

[0095] Where there is at least two or more modules, at least one module may be interchangeable with another and thus able to be inserted in different locations of the microwave energy zone.

[0096] Typically, the module comprising the plurality of the microwave outlets also comprises an outlet, typically in the roof, for removing hot gases generated in use from heating the microwave absorbent material in the microwave energy zone.

[0097] The present invention also provides, in broad terms, a removable module for a furnace, typically a linear hearth furnace, the module defining a microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace when positioned in the furnace, the module being configured so that when the module is positioned in a furnace with gaps between axially-spaced ends of the module and adjacent sections of the furnace or between axially-spaced ends of the module and adjacent modules to accommodate thermal expansion of the module in use of the furnace, each gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to accommodate thermal expansion of the module in use of the microwave energy zone.

[0098] The module may be configured to form a part of a sealed barrier that prevents hot gas exiting the furnace in an uncontrolled manner when the module is inserted into the furnace.

[0099] The module may be configured to form a gas seal for a gap between the module and an adjacent module or between the module and an adjacent section of the furnace when the module is inserted into the furnace.

[0100] The gas seal may comprise a bellows-type arrangement that, in use extends across and closes the gap and is connected to adjacent modules or to a module and an adjacent section of the furnace and is configured to accommodate thermal expansion and contraction of the gap.

[0101] The module may comprise a roof, downwardly extending side walls on opposite sides of the module, and opposed ends that define the microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace when positioned in the furnace.

[0102] The module may comprise:

[0103] (a) an inner member, such as a “skin”, typically, a metallic inner skin, configured to reflect microwave energy within the microwave energy zone,

[0104] (b) an outer member, such as a shell, typically a steel shell, configured to be a structural member of the module, and

[0105] (c) a thermal insulator, such as a thermal insulating material, between the inner skin and the outer shell.

[0106] The module may comprise a roof, downwardly extending side walls on opposite sides of the module, and opposed ends that define the microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace when positioned in the furnace.

[0107] Each of the roof and the side walls may comprise the inner member, such as the inner skin, the outer member, such as the outer shell, and the thermal insulating material.

[0108] The module may comprise a plurality of openings. There may be openings in any one or more than one of the roof and the side walls of the module.

[0109] The module may comprise a microwave outlet, which may be described as a microwave applicator, for delivering microwave energy to the microwave energy zone.

[0110] The microwave outlet may extend through one of the openings in the roof.

[0111] The microwave outlet may be configured to be supported externally of the roof and there may be a gap between the microwave outlet and the roof that allows relative movement to accommodate thermal expansion.

[0112] One or both of the roof and the microwave outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0113] The microwave outlet may be connected to and supported by the outer member, such as the outer shell, of the roof and not connected in a fixed way to the thermal insulator and the member, such as the inner skin, of the roof. As a consequence, the microwave outlet can move relative to these components and there is a gap between the microwave outlet and these components that allows relative movement to accommodate thermal expansion.

[0114] One or both of the inner member of the roof and the microwave outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0115] The module may comprise at least one outlet for gas generated within the microwave energy zone to flow from the microwave energy zone.

[0116] The gas outlet may extend through another one of the above-described openings in the roof.

[0117] The gas outlet may be configured to be supported externally of the roof and there may be a gap between the gas outlet and the roof that allows relative movement to accommodate thermal expansion.

[0118] One or both of the roof and the gas outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0119] The gas outlet may be connected to and supported by the outer member, such as the outer shell, of the roof and not connected in a fixed way to the thermal insulator and the member, such as the inner skin, of the roof. As a consequence, the gas outlet can move relative to these components (i.e., the thermal insulation and the inner skin) and there is a gap between the gas outlet and these components that allows relative movement to accommodate thermal expansion.

[0120] One or both of the inner member of the roof and the gas outlet may be configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

[0121] The module may be configured to be removed from the furnace and subsequently positioned in the furnace.

[0122] By way of example, the module may comprise a lifting hook or other coupler to allow a crane or other lifting device to be coupled to and to lift and replace the module.

[0123] As noted above, the module(s) may be configured to be removed from the furnace and subsequently positioned in the furnace by being constructed to be able to be releasably connected to adjacent modules and / or to adjacent sections of the furnace in such a way that it is possible to lift the module clear of the furnace and lift the module into the same or a different position in the furnace with sufficient clearance to do so. A skilled person will appreciate that there is a range of structural connection options.

[0124] The term “inner member” is understood herein to mean an internal member, typically an internal metal skin, of a module that acts as a reflective barrier to microwave energy within the microwave energy zone and, after a period of operation, approximates (at least on its surface) the temperature of the material passing through the microwave energy zone that has been heated by microwave energy within the zone, at least principally through radiation of energy from heated material.

[0125] Typically, the thermal insulation is transparent to microwaves.

[0126] BRIEF DESCRIPTION OF THE DRAWINGS

[0127] The present invention is described further by way of example with reference to the accompanying drawings of a linear hearth, of which:

[0128] Figure l is a computer rendered image of an apparatus for producing, in this instance, direct reduced iron (DRI) from briquettes of a composite of iron ore fragments and biomass taken as a longitudinal section through the apparatus in accordance with an embodiment of the invention, with the apparatus comprising a linear hearth furnace and a conveyor for transporting the composite through the furnace, and with substantial sections of an outer housing of the furnace removed;

[0129] Figure 2 is a computer rendered image of a part of the microwave energy zone of the linear hearth furnace shown in Figure 1 showing a top view of four modules in accordance with an embodiment of the invention that form part of the linear heath furnace, each module comprising a plurality of microwave outlets and an outlet for gas generated in the furnace;

[0130] Figure 3 is a computer rendered image of a part of the microwave energy zone of the furnace shown in Figures 1 and 2 showing an underside view of the same four modules as in Figure 2, each having a series of microwave horns and an abutting microwave choke that sits above and across the conveying apparatus);

[0131] Figure 4 comprises Figure 2 and a simplified partial cross-section of a part of Figure 2 that shows a gap between two adjacent modules and an embodiment of a gas seal that closes the gap;

[0132] Figure 5 is a top view of one of the modules shown in Figures 2-4; Figure 6 is a cross-section along the line A-A in Figure 5;

[0133] Figure 7 is a cross-section along the line B-B in Figure 5;

[0134] Figure 8 is a schematic 3D drawing of two modules of the type shown in Figures 2-4 showing gaps / expansi on joints within and between such modules in accordance with embodiments of the invention;

[0135] Figure 9 is a more detailed drawing of a corner joint of one of the modules shown in Figures 2-4;

[0136] Figure 10 is a more detailed drawing of a side wall joint between the modules shown in Figures 2-4;

[0137] Figure 11 is a more detailed drawing of a roof joint between the modules shown in Figures 2- 4;

[0138] Figure 12 is a more detailed drawing of the joint at the base of one of the modules shown in Figures 2-4, including interaction with the conveyor, which in this instance is a structure having side walls;

[0139] Figure 13 is a more detailed drawing of an opening in one of the modules shown in Figures 2- 4 and a microwave outlet extending through the opening; and

[0140] Figure 14 is a more detailed drawing of an opening in one of the modules shown in Figures 2- 4 and a gas outlet extending through the opening.

[0141] DESCRIPTION OF EMBODIMENTS

[0142] What follows is generally a description of embodiments of the invention when applied to the Bioiron ™ process of the applicant’s group of companies, unless stated otherwise.

[0143] The Bioiron ™ process is a process for direct reduction of iron ore under anoxic conditions with biomass as a reductant and with microwave energy as a source of energy. Iron ore and biomass are microwave absorbent materials. The Bioiron ™ process is described in patent families in the name of the applicant, including the above-mentioned International applications PCT / AU2021 / 051398 and PCT / AU2023 / 051350, with the disclosure in these International applications being incorporated by cross reference.

[0144] The invention however is applicable to other applications for heating microwave absorbent material, for example calcining naturally occurring spodumene (an ore that contains a lithium material) where a phase change is sought from the a phase of naturally occurring spodumene to a P phase spodumene in the calcined material.

[0145] In addition, while a preheat zone is referenced in the description of embodiments of the invention, it is recognised that such an element may not be essential where there is a microwave absorbent material that is readily absorbent at room temperature. Such the material may be treated with microwaves immediately the material passes through the feed zone, i.e., it enters the microwave energy zone directly or after only having passed first through only a transition zone (as described later).

[0146] The microwave energy may be any suitable microwave frequency, but the current industrial frequencies of around 2450MHz, 922 MHz, 915MHz, 896 MHZ and 433MHz are of most interest. For example, in Australia and South Africa 922 MHz is the allocated frequency. In USA and Europe, 915MHz is the allocated frequency. In UK, 896 MHZ is the allocated frequency. A key requirement however is that the linear hearth furnace be designed so that such energy is contained within the furnace.

[0147] Figure l is a computer rendered image of part an apparatus for producing, in this instance, direct reduced iron (DRI) from a feed material in the form of iron ore fragments and biomass taken as a longitudinal section through the apparatus, with substantial sections of an outer housing of the furnace and an end section of the furnace removed and noting that the apparatus could be applied to any other microwave absorbent material and is not confined to iron ore fragments and biomass.

[0148] The apparatus partially shown in Figure 1 comprises a linear hearth furnace generally identified by the numeral 3 and a conveyor 5 for transporting the feed material through the furnace. The furnace 3 is configured for continuously producing DRI from the feed material, which is typically at least initially in the form of briquettes of a composite of iron ore fragments and biomass.

[0149] The furnace 3 comprises an inlet 7 for the feed material within a feed zone (not identified by a reference numeral) and an outlet (not identified by a reference numeral) for processed feed material within a discharge zone (also not identified by a reference numeral). The feed material forms a bed on the conveyor 5.

[0150] The furnace 3 also comprises, between the feed zone and the discharge zone, a preheat zone 11, a microwave energy zone 13 (for heating material with microwave energy), and a transition zone 15 between the preheat zone 11 and the microwave energy zone 13.

[0151] The transition zone 15 includes a compacting device 17 positioned a predetermined height above the conveyor 5 for compacting preheated feed material from the preheat zone 11. Typically, the compacting device 17 reduces the height of the bed of preheated feed material on the conveyor 5 as the conveyor 5 transports the material thereunder so that it presents a more homogenised as described herein bed of material as a result of compaction which is better suited to processing in the microwave energy zone 13.

[0152] The furnace 3 also comprises an outer housing 19, which is only partially shown in Figure 1 to allow other components of the furnace to be seen. The outer housing 19 defines an elongate chamber that includes the preheat zone 11, the transition zone 15, and the microwave energy zone 13. The outer housing 19 comprises a base (not identified by a reference numeral), opposed side walls (not identified by a reference numeral), and a roof 21 (extending over one part of the furnace 3, only).

[0153] In general terms, the outer housing 19 comprises structural components that support the outer housing, sheet metal components that enclose the zones, and thermal insulation components (as required in some zones).

[0154] The construction of the outer housing 19 for the zones 11, 13, 15 depends in part on the operating conditions in the zones 11, 13, 15. In general terms, a skilled person will be able to design and construct a suitable outer housing for the preheat zone 11 and the transition zone 15, and the following description does not include construction details for this reason.

[0155] The following description focuses on construction details for the microwave energy zone 13.

[0156] As noted above, minimising the extent to which microwave energy can “escape”, i.e., leak, from the furnace 3 is one consideration, and the design of the conveyor 5 that transports material through the apparatus, particularly the microwave energy zone 13, is an important factor in minimising microwave energy loss. This is complicated with potential operating temperatures varying from room temperature to well in excess of 1000°C, as is the case with the Bioiron™ process.

[0157] The conveyor 5 is configured to act as a barrier to microwave energy escaping the microwave energy zone 13 through the conveyor 5 as a consequence of the materials selection (typically steel) for manufacturing the conveyor 5 and a design of the conveyor 5. The conveyor construction is described in more detail in the specification of International application PCT / AU2025 / 050238 (which claims priority from Australian provisional application 2024900749, both in the name of the applicant) and the disclosure in the specification is incorporated by cross-reference.

[0158] In addition, as noted above, it is important to construct conveyor 5 and the furnace 3 to accommodate thermal expansion and contraction of the furnace structural and other components as they heat up and cool during operation of the furnace 3 and when the furnace 3 is not being used. This is a particular consideration given the elevated temperatures in the microwave energy zone when operating the Bioiron ™ process. This is also a particular consideration given the need to provide a gap so that there is no contact between the conveyor 5 and adjacent sections of the furnace as the conveyor 5 moves through the furnace 3.

[0159] In addition, as noted above, it is preferable from energy efficiency and equipment cost reasons that the microwave energy zone 13 be as compact as possible. Inevitably, this means that access to the microwave energy zone 13 is limited, and this creates difficulties when it is necessary to access the microwave energy zone to carry out maintenance. In view of the above considerations, in the embodiment of the apparatus shown in the Figures, the furnace 3 comprises:

[0160] (a) a plurality of modules 23 that define at least a part of the microwave energy zone 13 and, in effect, are part of the outer housing 19, with each module 23: a. being configured to be releasably coupled to an adjacent module 23 or to another adjacent section of the furnace 3 and to be removed from the furnace 3 (to allow access to the microwave energy zone 13 and to facilitate maintenance of the module 23) and subsequently positioned in the furnace 3 in the same or a different position, and b. comprising choking structures (not identified by a reference numeral in Figure 1 but shown in other Figures) that at least substantially prevent microwaves leaking from (i) gaps between the roof 41 and side walls 43 of the module 23, gaps between the module 23 and an adjacent module 23 and other adjacent sections of the furnace 3, and gaps between the conveyor 5 and the module 23 (which are necessary to allow the conveyor 5 to move relative to the modules 23) and (ii) openings in the module 23, for example openings in the roof of the module 23 for furnace components to penetrate the roof; and c. comprising gas seals to prevent gases in the furnace escaping the furnace; and

[0161] (b) microwave chokes 25 that are positioned at inlets and outlets of the microwave energy zone 13.

[0162] Figures 2-14 focus on embodiments of the modules 23 in accordance with the invention.

[0163] The purpose of each of the zones along the length of the furnace 3 shown in Figure 1 is as follows:

[0164] (a) the feed zone (not identified by a reference numeral) is configured to receive the feed material and form a bed of the feed material on the conveyor 5, with the feed material being supplied via the inlet 7 of the feed zone,

[0165] (b) the preheat zone 11 is configured for pre heating the material, in this case iron ore and biomass, and at least partly reducing iron ore and releasing volatiles in biomass and producing the preheated feed material, with the volatiles being combusted in the preheat zone, (c) the transition zone 15 between the preheat zone 11 and the microwave energy zone 13, with the compacting device 17 compacting the preheated material before it moves into the microwave energy zone 13,

[0166] (d) the microwave energy zone 13 for heating the preheated and compacted feed material further and, in this case reducing iron ore and forming DRI; and

[0167] (e) the discharge zone (not identified by a reference numeral) for discharging DRI from the furnace via the outlet (not identified by a reference numeral) of the discharge zone.

[0168] The conveyor 5 is an endless conveyor having a metallic material base that moves through the chamber of the furnace 3 from the feed zone to the discharge zone and transports material that is at least initially in the form of briquettes (in this example) through the chamber from the feed zone and discharges DRI in the discharge zone and then returns to the feed zone to be re-loaded with additional briquettes.

[0169] The furnace 3 also comprises an assembly (not identified by a reference numeral) for supporting and moving the conveyor 5 through the chamber. The assembly may be any suitable assembly. A skilled person would be able to select an appropriate assembly for any given situation, and the following description does not include construction details for this reason.

[0170] The furnace also comprises a transfer pipe 27 for transferring bulk gas flow from the micro wave energy zone 13 to the preheat zone 11.

[0171] The furnace 3 also comprises a flue gas outlet 65 in the preheat zone 11 for discharging hot gases produced in the furnace by heating and / or combustion within the furnace 3.

[0172] The apparatus also comprises a microwave system for supplying microwave energy to the microwave energy zone 13 that heats microwave absorbent material, in this case, iron ore (which may be partly reduced) and residual biomass material form the preheat zone 11 and reduces ore to DRI.

[0173] The feed zone (not identified by a reference numeral) of the furnace 3 includes an inlet 7 in the form of a feed chute configured to continuously feed microwave absorbent material (iron ore and biomass, compacted into briquettes) into the feed zone via the inlet to form a relatively uniform bed of microwave absorbent material on the moving conveyor 5 in the feed zone of the chamber, while restricting outflow of furnace gases via the inlet 7.

[0174] The term “relatively uniform bed of microwave absorbent material” is understood herein to mean a relatively uniform layer covering the base and typically having a consistent ‘bed’ thickness, at least length ways, i.e., in the direction of material within the furnace 3. This does not however mean that material has to be stacked in anything more than a random way on the base, noting that in some embodiments this may be desirable.

[0175] The discharge zone (not identified by a reference numeral) of the furnace 3 is configured to discharge processed DRI from the microwave energy zone 13 via an outlet in the form of a discharge chute (not identified by a reference numeral), while restricting the inflow of gases into the microwave energy zone 13 of the chamber. The discharge zone includes an enclosed discharge chute that has a downwardly directed opening that has a flow control valve that can be selectively operated to allow microwave absorbent material to flow through the opening. It is important to limit the amounts of oxygen-containing gases flowing back into the microwave energy zone 13 as DRI is pyrophoric when hot. Regardless of whether the processed material is DRI or another material, it is desirable to limit significant gas flow from the discharge zone back into the microwave energy zone 13 to avoid excessive dust make, which is detrimental to the efficient heating of microwave absorbent material in the microwave energy zone 13.

[0176] The preheat zone 11 of the furnace 3 has a plurality of air or oxygen-enriched air fed burners (not identified by a reference numeral) for generating heat by burning combustible gases in a top space of the preheat zone 11. The burners are spaced along the length of the preheat zone 11. The optimal spacing can be determined by a skilled person for any given operating conditions, such as the amount and type of any combustible material and the amount and type of microwave absorbent material.

[0177] The combustible gases generated in the furnace 3 may include, for example, combustible gases originating within the furnace from: volatiles in combustible material, such as biomass, moving through the preheat zone 11 ; and combustible gases, such as CO, generated by reduction of microwave absorbent material, such as iron ore in:

[0178] (i) the preheat zone 11 ; and

[0179] (ii) the microwave energy zone 13, with the combustible gases generated in the microwave energy zone 13 flowing from that zone 13 to the preheat zone 11, mainly through transfer pipe 27.

[0180] Alternatively, or in addition, there may be combustible gases supplied to the burners in the preheat zone 11 depending on the material being preheated and / or operating conditions in the furnace. Where there is no combustible material within or associated with the microwave absorbent material that is feed into the feed zone of the furnace combustible gases will need to be supplied to the burners in the preheat zone 11 or an alternative heating means found.

[0181] In use, the microwave energy zone 13 of the furnace 3 is typically an anoxic environment with heat provided solely by microwaves. Such microwaves heat the preheated iron ore and biomass.

[0182] As is described further below, the microwave system for supplying microwave energy to the microwave energy zone 13 comprises (a) a source of microwave energy i.e., generators with associated power supply (not identified by a reference numeral), transmission systems (which typically include waveguides and devices for tuning / impedance matching, etc.), with waveguides in the form of ductwork that transfers microwaves, and (c) applicators, i.e., microwave outlets, connected to waveguides and configured to transfer microwaves into the microwave energy zone 13.

[0183] With particular reference to Figures 1-4, each module 23 includes a plurality of the microwave outlets 31 (in the form of horns 35) and short sections of waveguides 33 located in a top space of the microwave energy zone 13.

[0184] The microwave energy may have any suitable microwave frequency and vary by country, but the current industrial frequencies of around 2450MHz, 915MHz, 443MHz and 330 MHz are of most interest. The horns 35 are pyramidal horns, more particularly sectoral horns as can best be seen in Figure 3.

[0185] The horns 35 are arranged in rows and positioned so that in use outlets 37 of the horns 35 (see Figures 3 and 8) are in close proximity to a bed of preheated, compacted iron ore and biomass passing through the microwave energy zone 13 at any point in time. A person skilled in the art would be able to determine a suitable spacing between outlets 37 and the bed in any given situation.

[0186] The rows extend across a width of a section of the microwave energy zone 13 within a module 23 or a series of modules 23 and along a length of the section (again within a module 23 or series of modules 23) above a top surface of the material carried on the conveyor 5.

[0187] The described section may be any suitable length and any suitable width.

[0188] The horns 35 are not in contact with each other at outlets 37 and there are gaps between the horns 35 at such location.

[0189] The horns 35 are defined by side walls 39a, 39b that are typically formed from metal sheet material.

[0190] The horns 35 are rectangular in transverse section and are formed with one pair of opposing side walls 39a being wider than the narrower side walls 39b. The side walls 39a are flared walls and diverge with distance from the waveguides 33. In use, this produces a fan-shaped microwave beam, which is narrow in the plane of the flared side walls 39a and wide in the plane of the other side walls 39b. The flaring may be in the E-plane (electric field) or Id- plane (magnetic field) direction to form a rectangular opening at its output end.

[0191] The horns 35 in each row are placed across the width of the conveyor 5 so that the shorter sides walls 39b are parallel with the direction of moment of the conveyor 5 within the microwave energy zone 13.

[0192] The horns 35 are arranged and configured so that the cumulative effect of the field patterns of the horns is to maximise the homogeneity of treatment of the material on the conveyor 5. It is noted that the invention is not confined to the above-described structure and arrangement of the microwave outlets 3, and a skilled person would be able to design alternative embodiments for any given situation.

[0193] The compacting device 17 in the transition zone 15 is in the form of a driven roller.

[0194] The compacting device 17 of the furnace 3 is provided to break-up and compact material on the conveyor 5 as it moves through the transition zone 15 from the preheat zone 11 to the microwave energy zone 13 so that it presents a more homogenised and uniform height bed of material which is better suited to processing with microwave energy in the microwave energy zone 13. The compacting device 17 does this by applying a downward force onto material and thereby breaking and compacting by reducing the height of material passing through the gap between the compacting device 17 and the conveyor 5. It is noted that there may be a combination of surface and profile and range of densities in the bed. Typically, the bed is a high density packed bed.

[0195] In use of the apparatus, hot gases generated in the microwave energy zone 13 flow into and through the preheat zone 11 from the microwave energy zone 13 via the transfer pipe 27 counter-current to the direction of movement of material on the conveyor 5 through the furnace from the inlet to the outlet.

[0196] The counter-current flow of gas from the microwave energy zone 13 into the preheat zone 11 is caused by a higher gas pressure in the microwave energy zone 13 compared to gas pressure in the preheat zone 11. While such pressure effect will be largely caused by the suction effect of a required exhaust fan linked to a dust extraction (baghouse) system at the atmosphere discharge end of the process the higher gas pressure is also the result of several structural and operational factors in the described embodiments of the apparatus of the invention.

[0197] The counter-current flow of gas from the microwave energy zone 13 to the preheat zone 11 transfers combustible gases, such as CO, that are generated in reactions that reduce iron ore in the microwave energy zone 13 to the preheat zone 11. The combustible gases in the gas flow from the microwave energy zone 13 are combusted by the plurality of air or oxygen- enriched air fed burners spaced along the length of the preheat zone 11. In use, the conveyor 5 transports material that is initially in the form of briquettes (not identified by a reference numeral) of iron ore and biomass successively and continuously through the zones in a sequential manner and eventually circles back in its endless pathway so that each portion of the refractory or metallic base material of the conveyor 5 eventually presents itself at the feed zone to be loaded with more briquettes. Preferably, the refractory or metallic base material has residual heat from the chamber when the conveyor 5 returns to the feed zone.

[0198] In use, hot gases generated in the linear hearth furnace 3 are discharged as a flue gas via the flue gas outlet 65 in the preheat zone 11.

[0199] The briquettes may be manufactured by any suitable method. By way of example, measured amounts of iron ore fines and biomass and water (which may be at least partially present as moisture in the biomass) and optionally flux is charged into a suitable size mixing drum (not identified by a reference numeral) and the drum rotated to form a homogeneous mixture. Thereafter, the mixture may be transferred to a suitable briquette-making apparatus (not identified by a reference numeral) and cold-formed into briquettes. Briquettes for the Bioiron process would typically be around 20 cm3in volume and contain 30-40% biomass (e.g., elephant grass at 20% moisture). A small amount of flux material (such as limestone) may be included, with the balance comprising iron ore fines.

[0200] The physical structure of the DRI at the end of the process is not critical. The physical structure may be friable and break easily or it could resemble a robust 3D “chocolate bar”.

[0201] With reference to Figures 1-4, the modules 23 that at least partially define the microwave energy zone 13 are arranged end-to-end along the length of the microwave energy zone 13.

[0202] As noted above, the modules 23 are configured to be releasably coupled together to allow modules to be removed from the furnace 3 and to be repositioned in the furnace in the same or a different position in the furnace. The coupling may be any suitable coupling. A skilled person would be able to design a suitable coupling for any given situation.

[0203] Removal of modules 23 is typically required to allow access to the microwave energy zone

[0204] 13 for maintenance and to the module 23 for maintenance. Efficient removal and placement of a replacement module 23 is important to minimise operational downtime.

[0205] Each module 23 is constructed to be able to be lifted from a position in the furnace 3, clear of the furnace 3, and to be moved to another location for maintenance work, etc, and then lifted back to the same or another position in the furnace 3.

[0206] Typically, each module 23 includes lifting points that can be coupled to a crane hook(s).

[0207] Thermal expansion and contraction considerations mean that there are axial gaps 53 between adjacent modules 23 or between a module 23 and an adjacent section of the furnace 3.

[0208] As a consequence, one or both of the adjacent modules 23 is configured to form a gas seal for each gap to prevent loss of gas from the furnace.

[0209] With reference to Figure 4, the gas seal comprises a bellows-type arrangement 67 that extends across and closes the gap 53 and is connected (a) to adjacent modules 23 or (b) to a module 23 and an adjacent section of the furnace 3 and is configured to accommodate thermal expansion and contraction of the gap 53. The bellows-type arrangement 67 may be any suitable construction and be made from any suitable material that accommodates thermal expansion and contraction while functioning as a gas seal.

[0210] It is noted that Figure 4 is a simplified Figure that focuses on the gas seal and does not include other details such as a choking structure that minimises leakage of microwaves form the micro wave energy zone 13 through the gap 53.

[0211] Each module 23 comprises a roof 41, downwardly extending side walls 43 configured to be outboard of opposite sides of the conveyor 5, and opposed ends 45.

[0212] Each module 23 comprises:

[0213] (a) an inner member 47, typically a skin, typically a metallic inner skin, configured to reflect microwave energy within the microwave energy zone 13,

[0214] (b) an outer member 49, typically a shell, typically a steel shell, configured to be a structural member of the module 23, and

[0215] (c) a thermal insulator 51, such as a thermal insulating material, between the inner member 47 and the outer member 49.

[0216] The thermal insulating material is ideally itself transparent to microwaves so that it does not heat up through any microwave penetration. An example of such a thermal insulating material which is for temperatures around 1000°C is Morgan Superwool Prime®’ which is a low bio persistence fibre having a medium dielectric constant, with low microwave loss, composed of around / S”18SiCh and l / 3rdCaO.

[0217] As described above, each module 23 comprises a plurality of waveguides 33 and microwave outlets 31 in the form of horns 35.

[0218] Each module 23 also comprises at least one gas outlet 85 for gases generated in the microwave energy zone 13. In the embodiment shown in the Figures, the gas outlets 85 are connected to the transfer pipe 27 (Figure 1).

[0219] The outlet(s) 85 can be a part of the gap 53 that is formed between adjacent modules23 and / or specifically designed gas opening(s) in the module 23.

[0220] Each module 23 includes openings 55 in the module roof 41, and the waveguides 33 and the gas outlet(s) 85 extend through the openings 55.

[0221] The waveguides 33 and the gas outlet(s) 85 are supported externally of the modules 23. and there are gaps 57 between the module roof 41 of each module 23 and the waveguides 33 and gaps 59 between the module roof 41 and the gas outlet(s) 85.

[0222] As noted above, minimising the extent to which microwave energy can “escape”, i.e., leak, from the furnace is an important consideration for furnace design from a safety perspective, and

[0223] - the design of the microwave energy zone 13 is an important factor in minimising microwave energy loss from the furnace, and operating a process in a furnace that has a conveyor 5 that moves through the microwave energy zone 13 and comprises fixed side walls (in relation to the moving conveyor) presents a particular challenge for minimising leakage of microwaves from the micro wave energy zone 13.

[0224] Usually, as shown in Figures 1-8, there will be more than one module 23 containing the microwave outlets 31, with such modules 23 having a plurality of the microwave outlets 31 both in a line across the modules, i.e., forming multiple rows across a section of the furnace, and as multiple rows along a module 23, i.e., along a section of the length of the furnace 3.

[0225] The top view of a module 23 shown in Figure 5 is a good illustration of the arrangement of multiple rows of microwave outlets 31 and the relative positions of the microwave outlets 31 and the gas outlet 85.

[0226] The cross-section views in Figures 6 and 7 provide more details of the structure of this embodiment.

[0227] This arrangement of multiple rows of microwave outlets 31 is driven by a productivity objective.

[0228] Individual power outputs of commercially available microwave generators are limited, but the wider the furnace 3 can be within practical physical limits, the higher the potential productivity from a throughput point of view for processing microwave absorbent material.

[0229] Thus, it is likely that there will be a plurality of the microwave outlets 31 placed above and across the conveyor 5 simply to maximise microwave absorbent material throughput at the desired temperature.

[0230] Once this approach is followed there will be natural ‘hot spots’ created across any conveyor, where material will receive more energy (as against at the edges of the microwave outlets which present parallel to the movement of the conveyor). The corresponding cooler areas between such ‘hot spots’ arise because care has to be taken to avoid microwave outlets crosscoupling and thereby interfering with each other’s performance.

[0231] Thus, to compensate for this, at least one other row of microwave outlets 31 will be placed behind a first row in a laterally offset position to try an equalise out the ‘hot spots’ through being laterally off-set to the microwave outlets proceeding them. The efficiency of this approach can be maximised through using sectorial pyramidal horns with one pair of opposing side walls 39a being wider side walls and the other pair of opposing side walls 39b being narrower side walls.

[0232] This can lead to the need for an even number of rows with each such row having a matching number of microwave outlets 31, but without some further adjustment in the heating pattern, this of itself is not sufficient. While a majority of each pair of consecutive rows of sectoral horns 35 can be placed across the conveyor 5 with the shorter side walls 39b all aligned in one direction, it may be desirable to rotate at least some of the microwave outlets 31, at a 90- degree angle, to get a more uniform heating pattern.

[0233] It may also be desirable to have modules 23 that are interchangeable with one another so that heating patterns can be adjusted or changed. Changes may be desirable for different microwave absorbent materials and / or for variations in feed grades. Likewise, it may be desirable to have modules 23 that are effectively ‘blanks’ that can be inserted between modules that hold the microwave outlets. This could be to allow time for heat within particular microwave absorbent material (arising from the application of microwaves) to better homogenise before applying further microwave energy.

[0234] Typically, modules 23, when inserted into the furnace 3, rest on side walls (not identified by a reference numeral) that form part of a base structure of the furnace 3. This is due to a number of considerations. First is to keep the mass of the modules 23 reasonable given they must be lifted into place. Secondly, as it is usual for the conveyor 5 in the furnace 3 to return to the inlet end by passing directly under the conveyor 5 as it moves to the outlet end. With such a conveyor 5, particularly given the temperatures involved, there is a need to have supporting axles and the like that pass through the walls of the furnace 3. Thus, it is desirable that the module 2 or series of modules 23 sit above such componentry.

[0235] Such module 23 or series of modules 23 that, with the conveyor 5, form the microwave energy zone 13 need to be choked (from a microwave perspective).

[0236] This is achieved at the entry and exit ends of the microwave energy zone 13 by the microwave chokes 25 shown in Figure 1. Each choke 25 is in the form of a pair of elongated metal sections that form a plurality of parallel downwardly facing channels 61 along a section of conveyor 5, one at each end of the microwave energy zone 13, that are above and to the sides of the material on the conveyor 5.

[0237] The chokes 25 are formed to substantially prevent microwaves emitted in the microwave energy zone 13 passing beyond the chokes 25.

[0238] The dimensions and numbers of the channels 61 are selected having regard to the microwave frequencies in the microwave energy zone 13. The microwave chokes 25 form a ‘corrugated’ baffle. When the rectangular metallic channels 61 are suitably selected, this has the effect of reflecting most of the microwave energy back into the microwave energy zone 13 (although some will be absorbed into the bed of material on the conveyor 5 as it passes through the chokes 25). While such chokes 25 can be effective on their own, it is desirable that there be a microwave absorbent block of refractory material (not identified by a reference numeral) positioned above and across the path of the conveyor 5. This absorbs any residual microwave energy.

[0239] To allow for ease of removal each microwave choke 25 is constructed as a module and as such can be inserted in the linear hearth furnace 3 to form part an integral part of the furnace 3. This also aids in installation of modules 23 in the microwave energy zone 13 by creating space for modules 23 to be moved sideways within the zone to facilitate removal and placement of modules 23.

[0240] Usually, a relevant module 23 will abut each microwave choke 25 via having outer steel shell section that meets at least the outer surface of the relevant abutting microwave choke 25 on three sides of its channel structure in a contiguous manner. Typically, the microwave choke 25 will be itself a lower height structure than that of a module 23. As such, the relevant module 23 will abut an adjoining microwave choke 25 by having an outer steel shell that extends across the conveyor in a vertical manner and extends in a downward direction to meet the top outer surface of the adjoining microwave choke 25. Typically, each microwave choke 25 abuts a different module 23. Figures 2 and 3 have adjoining microwave chokes 25.

[0241] For each module 23 to work effectively as part of the microwave energy zone 13, it is preferred that the module 23 has a metallic inner skin 47 with a generally microwave reflective inwardly-facing surface so that any microwaves hitting it are reflected back toward the microwave absorbent material as it passes through the microwave energy zone 13. While an inwardly-facing outer shell 49 of a module 23 could be reflective, this is not particularly efficient and creates challenges.

[0242] In order to contain heat generated in the microwave energy zone 13 and maintain structural integrity of the module 23, the thermal insulator 51, such as a thermal insulating material, is applied to the inwardly-facing part of the outer shell 49 of the module 23 between the inner skin 47 and the outer shell 49. If that insulator material is microwave absorbent, then extra heat passes to the outer shell 49. While there are refractory materials (like alumina) and / or insulation materials that are generally transparent to microwaves, i.e., the microwaves pass through without substantially heating the material, they can be quickly become ineffective where dust from the microwave absorbent material (such as iron ore and biomass) forms on their outer surface. The dust by its nature will absorb the microwaves and heat up, potentially resulting in thermal runaway. Thus, the microwave energy is not reflected back, and its heating value is at best partly lost.

[0243] As noted above, operating the furnace 3 at different temperatures in different zones, with different materials used to construct the furnace (including the modules 23), using modules 23 in the high temperature microwave energy zone 13, and providing openings in the furnace for components such as waveguides 33 and gas outlets 85 means that the furnace construction has to take into thermal expansion and contraction of material using in the construction of the apparatus. Gaps, and joints used to accommodate the gaps, created by addressing thermal expansion issues need to be protected from becoming ready pathways for microwaves, and thereby points of unintended heating, whether through being an impedance point prone to arcing or containing material that is itself microwave absorbent.

[0244] The joints and gaps that exist in the module 23 and between adjacent modules 23 are illustrated in Figure 8, which is a schematic 3D drawing of two modules 23 showing the gaps / expansi on joints within and between such modules 23.

[0245] Typically, with reference to Figure 8, at a minimum there will be a gas outlet gap 59 (where hot gases are vented from the roof 41 of the module 23 via a gas outlet 85) and a number of microwave energy input means gaps 57 (where the microwaves pass through the roof 41 of the module 23 in waveguides 33).

[0246] There will also be joints and gaps at the base of the module 23 and at the side walls 43 of the module 23, where the module 23 contacts other furnace structure. More particularly, with reference to Figure 8 but also noting Figures 9-14, each module 23 is formed to contribute to restricting microwave energy passing through:

[0247] (a) gaps 53 between the ends of adjacent modules 23,

[0248] (b) gaps 69 between the side wall and the roof of each module (“corner joint gap”),

[0249] (c) gaps 71 between the side walls of adjacent modules (“side wall gap”),

[0250] (d) gaps 75 between each module side wall and a conveyor side wall (“module base wall gap”), and

[0251] (e) gaps 81 between each module side wall and a base of the furnace (also “module base wall gap”), in the series of modules 23 in the microwave energy zone 13.

[0252] The gaps 53, 57, 59, 69, 71, 75, 81 are necessary to accommodate thermal expansion of the modules 23 in use of furnace.

[0253] In order to restrict microwaves leaking from the gaps 53, 57, 59, 69, 71, 75, 81 :

[0254] (a) each module 23 and / or adjacent sections of the furnace 3 are configured so that each axially-spaced gap 53 between the modules 23 and adjacent sections of the furnace defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion of the modules 23 in use of the microwave energy zone 13 to heat material passing through the zone, and

[0255] (b) each module 23 defines or comprises a choking structure that restricts microwave leakage through the other gaps 57, 59 and gaps 75 between the conveyor 5 and the module 23.

[0256] Typically, each gap may “define” or “comprise” a choking structure because of the selection of:

[0257] - the geometry (i.e., dimensions) of the gap, or changes of direction of a pathway defined by the gap, or a section(s) of a pathway defined by the gap being formed primarily to increase impedance for microwaves.

[0258] The choking structure may be any suitable form.

[0259] For example, typically the module 23 is formed with a flange(s) 63 or other structural elements that facilitate forming the gap(s) with a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap(s).

[0260] The following Figures 9-14 include examples of choking structures.

[0261] Figure 9 is a more detailed drawing of an upper section of the module 23 at an internal comer of (a) the module roof 41 and (b) the module side wall 43 in the microwave energy zone 13. There is a gap 69 between the metallic inner skin 47 of the module roof 41 and the metallic inner skin 47 of the side wall 43 of the module. The gap 69 is defined by a flange 63 that extends downwardly from the metallic inner skin 47 of the module roof 41 into the microwave energy zone 13, parallel to the metallic inner skin 47 of the module side wall 43. The gap 69 is necessary to allow for thermal expansion of the metallic inner skins 47. The gap 69 provides a pathway for microwave energy to leak from the microwave energy zone 13. The flange 63 is formed so that the gap has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap 69.

[0262] Figure 10 is a more detailed drawing of side walls 43 of adjacent modules 23. The Figure shows a gap 71 between the side walls 43. The gap 71 is defined by a flange 63 that extends from the side wall 43 of one module parallel to and spaced inwardly of a section of the side wall 43 of the adjacent module 23. The gap 71 is necessary to allow for thermal expansion of the metallic inner skins of the side walls 43. The gap 71 provides a pathway for microwave energy to leak from the microwave energy zone 13. The dimensions of the flange 63 and the width of the gap 71 are selected so that the gap 71 has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap 71.

[0263] Figure 11 is a more detailed drawing of the roofs of adjacent modules 23. The Figure shows the gap 53 between the modules 23. It is noted that the above-described gas seal is not shown in the Figure to simplify the Figure. The Figure also shows that the outer shell 49 of the module roof 41 includes a flange 63 that extends above the gap 53 and overlaps a platform 83 of the adjacent module roof 41. The flange 63 and the platform 83 are spaced apart and define a gap 73 that provides a pathway for microwave energy to leak from the microwave energy zone 13. The flange 63 and the platform 83 are spaced apart so that the gap 73 has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap.

[0264] Figure 12 is a more detailed drawing of a part of a lower section of the module 23 and an adjacent section of the microwave energy zone 13.

[0265] With reference to Figure 12, a base of the side wall 43 is spaced above a base 79 of the furnace 3 so that the metallic inner skin 47 of the side wall 43 can expand downwardly in use of the apparatus and, therefore, there is a gap 81 between the base of the side wall 43 and the base 79 of the furnace 3. The metallic inner skin 47 includes a flange 63 that extends downwardly and partially closes the gap 81.

[0266] With further reference to Figure 12, the conveyor 5 is spaced inwardly from the side wall 43 so that the conveyor 5 can move freely and not contact the side wall 43 and, therefore, there is a gap 75 between the upwardly extending conveyor side wall 77 and the metallic inner skin 47 of the side wall 43.

[0267] The gap 81 and gap 75 provides a pathway for microwave energy to leak from the microwave energy zone 13.

[0268] A choking structure in the form of a so-called G-seal choke 65 is positioned in the gap 81 to prevent microwaves passing through the gap 81. In addition, the flange 63 is formed so that the gap 75 has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap 75 before it reaches the G-seal choke 65.

[0269] Figure 13 is a more detailed drawing of an opening 55 in the roof 43 of one of the modules 23 shown in Figures 1-4 and an upper section of the horn 35 of a microwave outlet 31 extending through the opening 55. There is a gap 57 between the inner skin 47 of the roof 41 and the upper section of the horn 35 to accommodate thermal expansion. The horn 35 includes a flange 63, which may also be described as a collar, that is provided so that the gap 57 has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap 57.

[0270] Figure 14 is a more detailed drawing of an opening 55 in the roof 41 of one of the modules 23 shown in Figures 1-4 and the gas outlet 85 extending through the opening 55. There is a gap 53 between the inner skin 47 of the roof 41 and the gas outlet 85 to accommodate thermal expansion. The gas outlet 85 includes an outwardly extending flange 63, which may also be described as a collar, that is provided so that the gap 53 has a suitable geometry, pathway, or impedance section that restricts microwave leakage through the gap 53.

[0271] The above-described microwave chokes shown in Figures 8-14 are typically designed such that, for the particular frequency of applied microwaves, the choking structures together with the overall structure of the module(s) 23 restrict the passage of such microwaves through the gaps by a factor of a least 100 (20 dB), typically a factor of at least 1000 (30 dB).

[0272] Many modifications may be made to the embodiments described in relation to the Figures without departing from the spirit and scope of the invention.

[0273] By way of example, the invention is not confined to the microwave system for supplying microwave energy to the microwave energy zone 13 shown in the Figures, including the particular arrangement of the microwave outlets 31 (in the form of horns 35) shown in the Figures.

[0274] By way of example, the invention is not confined to the particular form of the choking structures described above on pages 36 onwards in relation to the flanges 63, and the invention extends to any suitable “choking structures” as this term is understood in functional terms to mean a structure that can restrict microwave leakage through gaps. The information provided above is a sufficient basis for a skilled person to be able to design a suitable “choking structure” in any situation.

[0275] By way of further example, the invention is not confined to the particular form and arrangement of the microwave horns 35 and the invention extends to any suitable microwave outlets.

Claims

CLAIMS1. An apparatus for heating a microwave absorbent material comprising (a) a furnace having a microwave energy zone and (b) a conveyor for transporting microwave absorbent material through the microwave energy zone, with the furnace comprising at least one module that forms at least a part of the microwave energy zone, with the or each module positioned above and on opposite sides of the conveyor, with the or each module comprising a roof, side walls, and opposed ends, with the opposed ends being configured to be coupled to an adjacent module in the microwave energy zone or to an adjacent section of the furnace, and with the module or each module being configured to be removed from the furnace and subsequently positioned in the furnace.

2. The apparatus defined in claim 1 wherein the module comprises an inner skin configured to reflect microwave energy within the microwave energy zone, an outer shell configured to be a structural member of the module, and a thermal insulator between the inner skin and the outer shell.

3. The apparatus defined in claim 1 or claim 2 wherein, when there is only one module that forms part of the microwave energy zone, and there is an axial gap between each end wall of the module and an adjacent section of the furnace to accommodate thermal expansion of the module in use and of the microwave energy zone to heat material passing through the zone.

4. The apparatus defined in claim 3 wherein one or both of the adjacent modules is configured so that each gap defines or comprises a choking structure that restricts microwave leakage through the gaps, while allowing the gap to continue to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passing through the zone.

5. The apparatus defined in claim 1 or claim 2 wherein, when there is two or more than two modules that form the microwave energy zone, with the modules being positioned successively along the length of the microwave energy zone, there is (a) an axial gap between each pair of adjacent end walls of the module and (b) an axial gap between the end walls of the first and the last module and adjacent sections of the furnace, to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passingthrough the zone.

6. The apparatus defined in claim 5 wherein the modules and / or adjacent sections of the furnace are configured so that each gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion of the modules in use of the microwave energy zone to heat material passing through the zone.

7. The apparatus defined in any one of the preceding claims wherein the module or at least one of the modules has a plurality of openings through its structure.

8. The apparatus defined in claim 7 wherein the module or at least one of the modules comprises at least one microwave outlet for delivering microwave energy to the microwave energy zone.

9. The apparatus defined in claim 8 wherein the microwave outlet(s) extends through openings in the roof of the module(s).

10. The apparatus defined in claim 8 or claim 9 wherein the microwave outlet is supported externally of the roof and there is a gap between the microwave outlet and the roof that allows relative movement to accommodate thermal expansion.

11. The apparatus defined in claim 10 wherein one or both of the roof and the microwave outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

12. The apparatus defined in claim 8 or claim 9 wherein the microwave outlet is connected to and supported by the outer shell of the roof and not connected in a fixed way to the thermal insulation and the inner skin of the roof and, as a consequence, the microwave outlet can move relative to these components (i.e., the thermal insulation and the inner skin) and there is a gap between the microwave outlet and these components that allows relative movement to accommodate thermal expansion.

13. The apparatus defined in claim 12 wherein one or both of the inner skin of the roof and the microwave outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

14. The apparatus defined in any one of claims 7 to 13 wherein the module comprises at least one outlet for gas generated within the microwave energy zone to flow from the microwave energy zone.

13. The apparatus defined in claim 12 wherein the gas outlet extends through another one of the openings in the roof.

14. The apparatus defined in claim 13 wherein the gas outlet is supported externally of the roof and there is a gap between the gas outlet and the roof that allows relative movement to accommodate thermal expansion.

15. The apparatus defined in claim 14 wherein one or both of the roof and the gas outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

16. The apparatus defined in claim 15 wherein the gas outlet is connected to and supported by the outer shell of the roof and not connected in a fixed way to the thermal insulation and the inner skin of the roof and, as a consequence, the gas outlet can move relative to these components (i.e., the thermal insulation and the inner skin) and there is a gap between the gas outlet and these components that allows relative movement to accommodate thermal expansion.

17. The apparatus defined in claim 16 wherein one or both of the inner skin of the roof and the gas outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

18. The apparatus defined in any one of claims 3 to 17 wherein each gap “defines” or“comprises” a choking structure because of the selection of- the geometry (i.e., dimensions) of the gap, or changes of direction of a pathway defined by the gap, or a section(s) of a pathway defined by the gap being formed primarily to increase impedance for microwaves.

19. The apparatus defined in any one of the preceding claims wherein the furnace comprises support members on both sides of the furnace for supporting the module or modules when positioned in the furnace.

20. The apparatus defined in any one of the preceding claims wherein the furnace comprises a microwave choke positioned above the conveyor at an inlet to the microwave energy zone and / or at an outlet of the microwave energy zone for at least substantially preventing microwaves in the microwave energy zone passing beyond the choke(s).

21. The apparatus defined in claim 20 wherein the microwave choke comprises an elongated metal section extending along a section of the furnace at or before the inlet to the microwave energy zone and / or at or after the outlet of the microwave energy zone.

22. The apparatus defined in claim 21 wherein the elongated metal section forms a downwardly facing channel positioned above and across the path of the conveyor through the section of the furnace and comprises a plurality of chambers extending upwardly away from the conveyor and spaced along the section of the furnace that form a ‘corrugated’ baffle, with the number and dimensions and spacings of the chambers being based on characteristics of microwave energy in the microwave energy zone.

23. A removable module for a furnace, the module defining a microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace when positioned as a part of the furnace, the module comprising a roof, downwardly extending side walls on opposite sides of the module, and opposed ends that define the microwave energy zone of the furnace or at least a part of the microwave energy zone of the furnace when positioned as a part of the furnace, the module being configured so that when the module is positioned with gaps between axially-spaced ends of the module and adjacent sections of the furnace orbetween axially-spaced ends of the module and adjacent modules to accommodate thermal expansion of the module in use of the furnace, each gap defines or comprises a choking structure that restricts microwave leakage through the gap into the internal body of the module, while allowing the gap to accommodate thermal expansion of the module in use of the micro wave energy zone.

24. The module defined in claim 23 configured to form a gas seal for each gap between the module and an adjacent module or between the module and an adjacent section of the furnace when the module is inserted into the furnace.

25. The module defined in claim 23 or claim 24 comprises an inner member, such as a skin, typically, a metallic inner skin, configured to reflect microwave energy within the microwave energy zone, an outer member, such as a shell, typically a steel shell, configured to be a structural member of the module, and a thermal insulator, such as a non-absorbing microwave thermal insulating material, between the inner skin and the outer shell.

26. The module defined in claim 25 wherein each of the roof and the side walls comprise the inner skin, the outer shell, and the thermal insulating material.

27. The module defined in any one of claims 23 to 26 comprising a plurality of openings that pass through the inner kin, the outer shell, and the thermal insulating material.

28. The module defined in any one of claims 23 to 27 comprises a microwave outlet for delivering microwave energy to the microwave energy zone.

29. The module defined in claim 28 wherein the microwave outlet extends through one of the openings in the roof.

30. The module defined in claim 29 wherein the microwave outlet is configured to be supported externally of the roof and there is a gap between the microwave outlet and the roof that allows relative movement to accommodate thermal expansion.

31. The module defined in claim 30 wherein one or both of the roof and the microwave outlet is configured so that the gap defines or comprises a choking structure that restrictsmicrowave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

32. The module defined in claim 29 wherein the microwave outlet is connected to and supported by the outer shell of the roof and not connected in a fixed way to the thermal insulation and the inner skin of the roof and, as a consequence, the microwave outlet can move relative to these components and there is a gap between the microwave outlet and these components that allows relative movement to accommodate thermal expansion.

33. The module defined in claim 32 wherein one or both of the inner skin of the roof and the microwave outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

34. The module defined in any one of claims 23 to 33 wherein the module comprises at least one outlet for gas generated within the microwave energy zone to flow from the microwave energy zone.

35. The module defined in claim 34 wherein the gas outlet extends through another one of the openings in the roof.

36. The module defined in claim 35 wherein the gas outlet is configured to be supported externally of the roof and there is a gap between the gas outlet and the roof that allows relative movement to accommodate thermal expansion.

37. The module defined in claim 36 wherein one or both of the roof and the gas outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

38. The module defined in claim 35 wherein the gas outlet is connected to and supported by the outer shell of the roof and not connected in a fixed way to the thermal insulation andthe inner skin of the roof and, as a consequence, the gas outlet can move relative to these components (i.e., the thermal insulation and the inner skin) and there is a gap between the gas outlet and these components that allows relative movement to accommodate thermal expansion.

39. The module defined in claim 38 wherein one or both of the inner skin of the roof and the gas outlet is configured so that the gap defines or comprises a choking structure that restricts microwave leakage through the gap, while allowing the gap to continue to accommodate thermal expansion in use of the microwave energy zone to heat material passing through the zone.

Images