Microwave window

Abstract

A window for transmission of radiofrequency, RF, electromagnetic radiation between a first environment and a second environment, is provided. The window comprises: first and second window panels each substantially transparent to the RF electromagnetic radiation, wherein the first window panel is spaced from the second window panel along a first direction such that the window comprises an inter-panel space between the first and second window panels; and the window further comprises one or more gas inlets configured to enable heated gas to flow into the inter-panel space so as to minimise or prevent condensation on the first and / or second window panels.

Description

[0001] MICROWAVE WINDOW

[0002] FIELD OF THE INVENTION

[0003] The present invention is directed to a window and window apparatus for transmission of radiofrequency (RF) electromagnetic radiation, in particular microwave radiation. The window may be used in various applications such as industrial microwave heating, plasma processing or radar applications. The invention has particular utilisation in pyrolysis systems.

[0004] BACKGROUND

[0005] In a conventional pyrolysis process, organic materials such as plastics, biomass, tyres, fabric, wood and the like undergo thermal decomposition in the absence of oxygen. In some cases, microwave radiation is used to provide the required heat. In such cases, one or more microwave generators generate microwave radiation which is transmitted to a pyrolysis reactor via respective waveguides. A window is positioned at the interface between the waveguide and the reactor and allows transmission of the microwaves into the reactor to provide the necessary heating whilst maintaining environmental isolation between the interior of the reactor and the waveguide.

[0006] Typically, such windows are made from low-loss dielectric materials such as quartz, alumina or polytetrafluoroethylene (PTFE) because of their ability to transmit microwave frequencies with minimal reflection or absorption. The window is often designed to match the impedance of the waveguide to prevent signal loss and standing wave formation.

[0007] However, a problem arises due to condensation of vapours (either water or hydrocarbons such as pyrolysis tars and oils) on the surface of the window. Such condensation can cause the window to become blocked, either by condensate, carbon dust present in the reactor, or a combination of the two. Such condensation can also alter the dielectric properties of the window. Thus, the efficiency of microwave transmission through the window is reduced.An additional problem occurs due to the extreme temperatures found in pyrolysis reactors, where temperatures often exceed 500°C. One of the main issues is thermal expansion which can lead to cracking and warping, compromising the seal provided by the window and potentially causing gas and microwave leakage. Furthermore, conventional gaskets or 0-rings often degrade or fail at such high temperatures, meaning that sealing of the window to the waveguide and rector often needs to be performed using more robust but time and cost intensive methods such as brazing or ceramic-metal bonding.

[0008] Accordingly, there is a need to overcome these issues.

[0009] SUMMARY OF INVENTION

[0010] In accordance with a first aspect of the invention there is provided a window for transmission of radiofrequency (RF) electromagnetic radiation between a first environment and a second environment, comprising:

[0011] first and second window panels each substantially transparent to the RF electromagnetic radiation, wherein

[0012] the first window panel is spaced from the second window panel along a first direction such that the window comprises an inter-panel space between the first and second window panels; and

[0013] the window further comprises one or more gas inlets configured to enable heated gas to flow into the inter-panel space so as to minimise or prevent condensation on the first and / or second window panels.

[0014] By providing one or more gas inlets configured to enable heated gas to flow into the inter-panel space, the first and second window panels are heated up and therefore condensation of vapours (e.g. water vapour or hydrocarbon vapours such as pyrolysis tars and oils) on the first and second window panels is advantageously minimised or prevented. In particular, the flow of heated gas minimises or prevents condensation occurring on the surfaces of the first and second window panels facing the respective environment.The one or more gas inlets are configured to enable heated gas to flow into the inter-panel space. Thus, the one or more gas inlets are in fluid communication with the inter-panel space such that the inter-panel space can receive the flow of heated gas.

[0015] As will be understood, to minimise or prevent condensation of vapours on the window panels, the heated gas is configured to heat the first and second window panels to a temperature greater than the temperatures of the first and second environments.

[0016] The first and second window panels are each substantially transparent to the RF electromagnetic radiation. In other words, the material of both the first and second window panels allows transmission (e.g. propagation) of the RF electromagnetic radiation therethrough. Typically, the first and second window panels are formed of the same material. The first and second window panels typically have the same geometry and dimensions.

[0017] The first window panel is spaced from the second window panel along a first direction. The first direction is preferably the direction of propagation of the RF electromagnetic radiation through the window. Preferably, each of the first and second window panels is substantially planar and lies in a plane substantially orthogonal to the first direction.

[0018] Preferably, the window further comprises an intermediate frame structure having a first side and a second side and defining an opening (e.g. extending from the first side to the second side), wherein

[0019] the first window panel is disposed on the first side of the intermediate frame structure and the second window panel is disposed on the second side of the intermediate frame structure, wherein the inter-panel space is bounded by the intermediate frame structure (e.g. an interior surface of the intermediate frame structure) and the first and second window panels.The first and second window panels may be considered to enclose the opening in the intermediate frame structure to thereby bound the inter-panel space. In this way, the first and second window panels are supported at their periphery.

[0020] Typically, the one or more gas inlets are located in the intermediate frame structure. The one or more gas inlets typically provide a gas flow path from the exterior of the intermediate frame structure to the inter-panel space. The one or more gas inlets may be in the form of through holes, or channels, extending through the intermediate frame structure from an exterior of the intermediate frame structure to the inter-panel space.

[0021] Preferably, the one or more gas inlets are arranged such that the heated gas flows into the inter-panel space along a direction substantially perpendicular to the first direction. In other words, the one or more gas inlets are arranged such that the heated gas flows parallel with (or “across”) the first and second window panels. This advantageously helps to avoid “hot spots” and provides an even heating of the first and second window panels.

[0022] Preferably, the one or more gas inlets comprise a plurality of gas inlets, preferably arranged along a first edge of the inter-panel space. By providing a plurality of gas inlets arranged along a first edge of the inter-panel space, this helps to ensure an even (e.g. uniform) heating of the first and second window panels as the heated gas flows from a first edge across the inter-panel space to an opposing edge.

[0023] Preferably, the window further comprises one or more gas outlets configured to allow the heated gas to exit the inter-panel space. Thus, the heated gas flows through the inter-panel space. The one or more gas outlets are in fluid communication with the inter-panel space and provide a gas flow path from the inter-panel space to the exterior of the window. Typically, the one or more gas outlets are located in the intermediate frame structure. In embodiments in which the gas inlet(s) are positioned at an edge of the inter-panel space, preferably the gas outlet(s) are positioned at an opposing edge of the inter-panel space toencourage gas flow across the window panels. In some embodiments, the heated gas exiting the inter-panel space may be recirculated to the one or more gas inlets.

[0024] In preferred embodiments, the window further comprises a first end frame structure defining an opening, and wherein the first window panel is supported between the first side of intermediate frame structure and the first end frame structure. Thus, the first window panel is located between the first side of the intermediate frame structure and the first end frame structure. The first window panel is supported between the intermediate frame structure and the first end frame structure so as to cover the opening in the first end frame structure. Typically, the first end frame structure is configured to interface with the first environment.

[0025] The intermediate frame structure and the first end frame structure typically form part of a window support structure (e.g. of the window) that is configured to support the first and second window panels.

[0026] Preferably, the window further comprises

[0027] a first frame sealing member configured to provide a seal between the intermediate frame structure and the first end frame structure,

[0028] a first panel sealing member configured to provide a seal between the first window panel and the first end frame structure, and

[0029] a second panel sealing member configured to provide a seal between the first window panel and the intermediate frame structure; and wherein

[0030] the window is configured such that a compressive force acting on the first frame sealing member (e.g. as the intermediate frame structure and first end frame structure are compressed along the first direction) is greater than a compressive force acting on the first and second panel sealing members.

[0031] The first frame sealing member provides a seal between the intermediate frame structure and the first end frame structure. In this way, a gas seal is formed to prevent gas leakage into the window from the external environment. The first and second panel sealing members create a gas seal around the first window panel,preventing gas leakage through the window from the first and second environments. In this way, the window provides a gas seal between the first and second environments, and between the first and second environments and the outside of the system.

[0032] In embodiments, the first frame sealing member is located between (e.g. at the interface of) the intermediate frame structure and first end structure. Similarly, in embodiments, the first and second panel sealing members are located between (e.g. at the interface of) the first window panel and the first end frame structure, and between (e.g. at the interface of) the first window panel and the intermediate frame structure, respectively.

[0033] Particularly advantageously, a compressive force acting on the first frame sealing member is greater than a compressive force acting on the first and second panel sealing members. This allows the intermediate frame structure and the first end frame structure to be compressed together to form an effective gas seal, without the compressive force damaging the first window panel engaged by the first and second panel sealing members. Additionally, as the compressive forces on the first and second panel sealing members sealing the window panel are reduced, this enables thermal expansion of the first window panel with reduced chance of damage. Space for thermal expansion of the window panels is particularly advantageous due to the flow of heated gas through the window and in use cases where the window is used in high-temperature environments such as microwave pyrolysis systems.

[0034] Preferably, the first side of the intermediate frame structure comprises a first intermediate interface surface and the first end frame structure comprises an opposing first interface surface, and

[0035] either the intermediate frame structure comprises a first panel ledge recessed from the first intermediate interface surface or the first end frame structure comprise a first panel ledge recessed from the first interface surface, the first panel ledge configured to receive the first window panel.By receiving (e.g. supporting) the first window panel by a recessed first panel ledge, the first window panel is advantageously recessed, or spaced from, the interface between the intermediate frame structure and the first end frame structure when they are connected together. The recessed first panel receiving portion preferably extends (e.g. continuously) around the interior periphery of the respective frame structure.

[0036] By providing a first panel ledge recessed from the respective interface surface (e.g. recessed along the first direction), this allows for the first window panel to be isolated from the compression force acting on the interface surfaces of the intermediate and first end frame structures as they are compressed together. This also provides space for thermal expansion of the first window panel when supported between the intermediate frame structure and the first end frame structure.

[0037] Typically, a recess distance, or depth, of the recessed first panel ledge (e.g. relative to the respective interface surface) is greater than a dimension of the first window panel along the first direction. In other words, the first panel ledge is recessed (or “stepped”) by a distance greater than the thickness of the first window panel. Preferably, the first panel ledge defines a lateral dimension in a plane orthogonal to the first direction greater than that of the first window panel. This provides further space for thermal expansion of the window panel.

[0038] Preferably, the first frame sealing member is laterally spaced from the first panel ledge (e.g. the spaced from along a direction orthogonal to the first direction). Preferably, the first frame sealing member is laterally outward of the first panel ledge. Thus, the first frame sealing member is laterally spaced from the first window panel. In this way, the intermediate frame structure and the first end frame structure can be connected together to form a seal without the first frame sealing member interfacing with the first window panel, thereby avoiding damage. The first panel sealing member and second panel sealing member are both located within the lateral area defined by the first panel ledge so as to form a seal aroundthe first window panel. The first and second panel sealing members may be aligned with each other along the first direction, although this is not essential.

[0039] By providing a recessed first panel ledge as part of either the intermediate frame structure or first end frame structure, the window may be considered to comprise a window support structure comprising a (e.g. recessed) first window panel receiving section between the intermediate frame structure and first end frame structure, and wherein the first window panel is received in the first window panel receiving section. Preferably the first and second panel sealing members are located laterally within the first window panel receiving section, and the first frame sealing member is located laterally spaced from (e.g. laterally outward of) the first panel receiving section.

[0040] Preferably, the first frame sealing member is configured (e.g. by appropriate thickness of the sealing members) such that the first frame sealing member experiences a compressive force before either the first or second panel sealing members as the intermediate frame structure and first end frame structure are compressed (e.g. brought together) along the first direction.

[0041] Typically, the first frame sealing member, first panel sealing member and second panel sealing member are received in respective grooves (e.g. at the respective interfaces). The grooves typically extend around the periphery of the respective frame structures and have depths extending along the first direction. When received in their respective grooves the sealing members typically protrude from the grooves such than when a compression force is applied to connect the intermediate frame structure and first end frame structure, the compression acts on the sealing members. Preferably, the first panel ledge comprises a groove configured to receive a panel sealing member.

[0042] In preferred embodiments, the first frame sealing member is configured to protrude along the first direction from its respective groove such that the first frame sealing member experiences a compressive force before either the first or second panel sealing members as the intermediate frame structure and first end framestructure are compressed (e.g. brought together) along the first direction. In other words, as the frame structures are compressed together, the compressive force initially acts on the frame sealing member rather than the first and second panel sealing members, thereby substantially isolating the compressive force between the frame structures from the first window panel. The first frame sealing member may be configured in this way by providing a larger sealing member than the panel sealing member, and / or by the groove in which the first frame sealing member is received having a smaller depth relative to the interfacing surfaces than the grooves housing the panel sealing member(s). Typically, the frame sealing member is larger (e.g. thicker) than the first and second panel sealing members, and has a correspondingly larger receiving groove.

[0043] Although the use of grooves to receive the sealing members advantageously helps to seat the sealing members in the desired location, this is not essential and in some embodiments it is envisaged that the sealing members may not be received in respective grooves.

[0044] Typically, one of the intermediate frame structure and the first end frame structure comprises the first panel ledge, and the other of the intermediate frame structure and the first end frame structure comprises a recessed sealing portion laterally overlapping with the first panel ledge, preferably wherein the first frame sealing member and one of the first and second panel sealing members are located within the sealing portion. The recessed sealing portion (e.g. recessed along the first direction) overlapping with the first panel ledge advantageously allows additional space along the first direction to allow the sealing members to deform and provide the respective seals, and also provides further room for seating and thermal expansion of the first panel.

[0045] The sealing members are preferably compressive sealing members. Typically, at least one of, preferably each of, the first panel sealing member, second panel sealing member, and the first frame sealing member comprises gland packing. The gland packing may comprise any suitable material such as graphene, PTFE, aramid or Kevlar. However, graphite sealing members are particularly preferredfor their high temperature resistance. Preferably, the sealing members are in the form of graphite gland packing such as graphite cord.

[0046] In preferred embodiments, the window further comprises a second end frame structure defining an opening, and wherein the second window panel is supported between the second side of the intermediate frame structure and the second end frame structure. Thus, the second window panel is located between the second side of the intermediate frame structure and the second end frame structure. The second window panel is typically supported between the intermediate frame structure and the second end frame structure so as to cover the opening in the second end frame structure. Typically, the second end frame structure is configured to interface with the second environment. The second end frame typically forms a constituent part of a window support structure, along with the first end frame structure and the intermediate frame structure.

[0047] The second window panel is preferably supported between the intermediate frame structure and the second end frame structure in a corresponding way to the first window panel as discussed above. Thus, preferably, the window further comprises

[0048] a second frame sealing member configured to provide a seal between the intermediate frame structure and the second end frame structure,

[0049] a third panel sealing member configured to provide a seal between the second window panel and the intermediate frame structure, and

[0050] a fourth panel sealing member configured to provide a seal between the second window panel and the second end frame structure; and wherein

[0051] the window is configured such that a compressive force acting on the second frame sealing member (e.g. as the intermediate frame structure and the second end frame structure are compressed along first direction) is greater than a compressive force acting on the third and fourth panel sealing members.

[0052] In embodiments, the second frame sealing member is located between (e.g. at the interface of) the intermediate frame structure and second end structure. Similarly, in embodiments, the third and fourth panel sealing members are locatedbetween (e.g. at the interface of) the second window panel and the intermediate frame structure, and between (e.g. at the interface of) the second window panel and the second end frame structure, respectively.

[0053] Preferably, the second side of the intermediate frame structure comprises a second intermediate interface surface and the second end frame structure comprises an opposing first interface surface, and

[0054] either the intermediate frame structure comprises a second panel ledge recessed from the second intermediate interface surface or the second end frame structure comprises a second panel ledge recessed from the first interface surface, the second panel ledge configured to receive the second window panel.

[0055] Preferably, the second frame sealing member is laterally spaced from the second panel ledge (and thus laterally spaced from the second window panel).

[0056] Thus, the window may be considered to comprise a window support structure comprising a (e.g. recessed) second window panel receiving section between the intermediate frame structure and second end frame structure, and wherein the second window panel is received in the second window panel receiving section. Preferably the third and fourth panel sealing members are located laterally within the second window panel receiving section, and the second frame sealing member is located laterally spaced from (e.g. laterally outward of) the second panel receiving section.

[0057] Preferably, the second frame sealing member is configured (e.g. by appropriate thickness of the sealing members) such that the second frame sealing member experiences a compressive force before either the third or fourth panel sealing members as the intermediate frame structure and second end frame structure are compressed (e.g. brought together) along the first direction.

[0058] Preferably, the second frame sealing member, third panel sealing member and fourth panel sealing member are received in respective grooves. However, similarly to as discussed above, this is not essential.Preferably, the second frame sealing member is configured to protrude along the first direction from its respective groove such that the second frame sealing member experiences a compressive force before either the third or fourth panel sealing members as the intermediate frame structure and second end frame structure are compressed along the first direction.

[0059] Typically, one of the intermediate frame structure and the second end frame structure comprises the second panel ledge, and the other of the intermediate frame structure and the second end frame structure comprises a recessed sealing portion laterally overlapping with the second panel ledge, preferably wherein the second frame sealing member and one of the third and fourth panel sealing members are located within the sealing portion.

[0060] In a similar manner to as discussed above, the second frame sealing member third panel sealing member, and fourth panel sealing member comprise gland packing, preferably graphite gland packing.

[0061] Preferably, the first end frame structure comprises a first end flange portion surrounding the respective opening, the intermediate frame structure comprises an intermediate flange portion surrounding the respective opening, and the second end frame structure comprises a second end flange portion surrounding the respective opening, wherein

[0062] each of the first end flange portion, intermediate flange portion and second end flange portion comprises a first set of connecting features for connecting the first end frame structure, second end frame structure and intermediate frame structure together. In preferred embodiments, the first set of connecting features may comprise a set of bolt holes (e.g. extending along the first direction) whereby the first end, second end and intermediate frame structures may be bolted together and compressed to form the seals via the aligned bolt holes. However, alternative means of connecting the structure together may be used. For example, the connecting features may comprise threaded holes whereby screws are used to connect and compress the frame structures together.Typically, the interface surfaces of the first end frame structure, intermediate frame structure and second end frame structure described above are located on the respective flange portions.

[0063] In embodiments, each of the first end flange portion, intermediate flange portion and second end flange portion comprises a second set of connecting features for connecting the window to the first and second environments. The second sets of connecting features may comprise respective sets of bolt holes (e.g. aligned along the first direction), wherein the sets of bolt holes in each of the first end flange portion, intermediate flange portion and second end flange portion align with each other. However, alternative connecting features may be used such as threaded screw holes. Preferably, the second sets of connecting features are positioned laterally outward from the first and second window panels and laterally outward from the first sets of connecting features.

[0064] Advantageously, the second set of connecting features is separate from (independent of) the first set of connecting features. This means that the window may be sealed by connecting the first end, second end and intermediate frame structures via the first set of connecting features independently of connecting the window to the first and second environments. In this way, fragile materials may be used for the first and second window panels (e.g. alumina or quartz) without needing to compromise on the torque required to connect the window to the first and second environments (e.g. which may include a pyrolysis reactor).

[0065] In some embodiments, the window may further comprise a third window panel spaced from the first window panel along the first direction and defining a second inter-panel space between the first window panel and the third window panel, and wherein the window is configured to provide a vacuum in the second inter-panel space. In such embodiments, the use of a vacuum advantageously provides insulation towards the first window panel such that there are less heat losses caused by the heating effect on the first window panel due to the heated gas.The assembly of intermediate frame structure, first end frame structure, second end frame structure, and the first and second window panels, may be described as a “cassette”. The various components thereof are typically removably connectable. For example, the window may be dismantled for maintenance of replacement of the window panels. In this way, the window may be considered a (e.g. modular) “window assembly”.

[0066] Preferably, the various components of the window are coaxial with and aligned with each other along the first direction. Typically, the window has a substantially rectangular cross-sectional geometry. This is particularly useful for applications in which the window is coupled to a waveguide. However, it will be appreciated that other cross-sectional geometries may be used.

[0067] In accordance with a second aspect of the invention, there is provided a window for transmission of radiofrequency, RF, electromagnetic radiation between a first environment and a second environment, comprising:

[0068] a first window panel substantially transparent to the RF electromagnetic radiation;

[0069] a first frame structure (e.g. defining an opening); and

[0070] a second frame structure (e.g. defining an opening), and wherein the first window panel is supported between the first frame structure and the second frame structure; and wherein the window further comprises

[0071] a first frame sealing member configured to provide a seal between the first frame structure and the second frame structure,

[0072] a first panel sealing member configured to provide a seal between the first window panel and the first frame structure, and

[0073] a second panel sealing member configured to provide a seal between the first window panel and the second frame structure; and wherein

[0074] the window is configured such that a compressive force acting on the first frame sealing member is greater than a compressive force acting on the first and second panel sealing members.Thus, the window of the second aspect of the invention provides the corresponding advantages described above in relation to the first aspect of the invention regarding the frame structures being able to be connected and compressed together to form a secure gas seal around the first window panel without the compression force damaging the first window panel. Additionally, this arrangement allows for thermal expansion of the first window panel which is particularly advantageous when the window is used in high-temperature use cases, for example when one of the first and second environments is a (microwave) pyrolysis reactor.

[0075] In embodiments, the first frame sealing member is located between (e.g. at the interface of) the first frame structure and the second frame structure. Similarly, in embodiments, the first and second panel sealing members are located between (e.g. at the interface of) the first window panel and the first frame structure, and between (e.g. at the interface of) the first window panel and the second frame structure, respectively.

[0076] Preferably, the first frame structure comprises a first interface surface and the second frame structure comprises an opposing second interface surface, and either the first frame structure comprises a first panel ledge recessed from the first interface surface or the second frame structure comprise a first panel ledge recessed from the second interface surface, the first panel ledge configured to receive the first window panel. Preferably, the first frame sealing member is laterally spaced from the first panel ledge (and therefore laterally spaced from the first window panel).

[0077] As discussed in relation to the first aspect of the invention, the use of a recessed first panel ledge advantageously provides space for thermal expansion of the first window panel when supported between the first and second frame structures, and helps to isolate the compression between the first and second frame structures from the first window panel. By providing a recessed first panel ledge as part of either the first or second frame structure, the window may be considered to comprise a window support structure (comprising the first and second framestructures) comprising a (e.g. recessed) first window panel receiving section between the first frame structure and second structure, and wherein the first window panel is received in the first window panel receiving section.

[0078] The window of the second aspect of the invention may comprise further advantageous features as described above in relation to the first aspect of the invention.

[0079] Preferably, the first frame sealing member is configured (e.g. by appropriate thickness of the sealing members) such that the first frame sealing member experiences a compressive force before either the first or second panel sealing members as the first and second frame structures are compressed (e.g. brought together) along the first direction.

[0080] Typically, the first frame sealing member, first panel sealing member and second panel sealing member are received in respective grooves. Advantageously, the first frame sealing member may be configured to protrude from its respective groove such that the first frame sealing member experiences a compressive force before either the first or second panel sealing members as the first frame structure and second frame structure are compressed together.

[0081] In some embodiments, it is envisaged that the sealing members may not be received in respective grooves.

[0082] Typically, one of the first frame structure and the second frame structure comprises the first panel ledge, and the other of the first frame structure and the second frame structure comprises a recessed sealing portion laterally overlapping with the first panel ledge, preferably wherein the first frame sealing member and one of the first and second panel sealing members is located within the sealing portion.

[0083] As with the first aspect of the invention, preferably, at least one of, preferably each of, the first frame sealing member, first panel sealing member, and the secondpanel sealing member comprises gland packing, preferably graphite gland packing.

[0084] The window of the second aspect of the invention may comprise a single window panel (i.e. “single glazed”). However, in some embodiments, the window may further comprise a second window panel substantially transparent to the RF electromagnetic radiation, wherein

[0085] the first window panel is spaced from the second window panel along a first direction, and further wherein

[0086] the window further comprises a third frame structure defining an opening, and wherein the second window panel is supported between the first frame structure and the third frame structure such that the second window panel is disposed on an opposing side of the first frame structure from the first window panel.

[0087] In embodiments where the window of the second aspect comprises first and second window panels, the window may include any of the features described above in relation to the first aspect of the invention.

[0088] As described herein, the first and second aspects of the invention provide a window for transmission of RF electromagnetic radiation between a first environment and a second environment. The first environment may be one of: a waveguide, a microwave applicator, a microwave launcher, a pyrolysis rector; and the second environment may be one of: a waveguide, a microwave applicator, a microwave launcher, a pyrolysis rector. In preferred embodiments, the first environment is a waveguide and the second environment is a pyrolysis reactor. In other words, the window provides an interface between the waveguide and the pyrolysis reactor. The window may, for example, be described as a pyrolysis reactor window.

[0089] Preferably, the first window panel comprises alumina. Similarly, preferably the second window panel comprises alumina. However, the window panels may be formed of or comprise other materials such as mica or quartz.In preferred embodiments, the RF radiation is microwave radiation. The window is preferably configured for use in a microwave pyrolysis system. Typical frequencies of microwave radiation used for microwave pyrolysis include 896MHz and 915MHz dependent on the country of operation.

[0090] In accordance with a third aspect of the invention, there is provided a window apparatus comprising:

[0091] a window according to any of the examples of the first aspect of the invention discussed above; and

[0092] a gas supply apparatus configured to provide a flow of heated gas to the inter-panel space through the one or more gas inlets.

[0093] Preferably, the heated gas comprises Nitrogen. However, other (typically inert) gases may be used, such as Argon, Neon or Carbon Dioxide. The heated gas may typically have a temperature in the range of 400°C to 700°C.

[0094] The gas supply apparatus is configured to provide a flow of heated gas to the inter-panel space through the one or more gas inlets of the window. Thus, the gas supply apparatus is in flow communication with (e.g. connected to) the one or more gas inlets, for example by gas supply lines. By providing a flow of heated gas to the inter-panel space condensation of the first and second window panels is minimised or prevented, and therefore the third aspect of the invention provides the same advantages discussed above.

[0095] In accordance with a fourth aspect of the invention, there is provided a (e.g. microwave) pyrolysis reactor comprising a window or window apparatus according to any of the aspects of the invention discussed above. The pyrolysis reactor is configured to provide pyrolysis of materials, typically organic materials such as plastics, biomass, tyres, fabric, wood and the like. Herein, the term “pyrolysis” has its usual meaning in the art, and refers to a process where material undergoes thermal decomposition in the absence of oxygen. A pyrolysis reactor comprising a window or window apparatus as described herein is preferably configured toprovide heat to the materials undergoing pyrolysis by microware irradiation, and thus the window is configured to transmit microwave radiation.

[0096] In accordance with a fifth aspect of the invention there is provided a pyrolysis system comprising:

[0097] a pyrolysis reactor according to the fourth aspect of the invention;

[0098] a microwave generator; and

[0099] a waveguide configured to guide microwaves generated in the microwave generator to the window of the pyrolysis reactor (e.g. whereby to allow transmission of microwave electromagnetic radiation from the microwave generator to the pyrolysis reactor).

[0100] In accordance with a further aspect of the invention we provide a method of transmitting RF electromagnetic radiation through a window, comprising:

[0101] providing a window or window apparatus according any of the examples of the first or third aspects described above; and

[0102] flowing a heated gas through the inter-panel space so as to minimise or prevent condensation on the first and / or second window panels.

[0103] BRIEF DESCRIPTION OF DRAWINGS

[0104] Example embodiments of the present invention will now be described with reference to the appended drawings, in which:- Figure 1 is a schematic diagram illustrating a portion of a pyrolysis system comprising a window according to an embodiment of the invention;

[0105] Figure 2 is an exploded diagram of a window according to an embodiment of the invention;

[0106] Figure 3A is a plan view of an intermediate frame structure according to an embodiment of the invention;

[0107] Figure 3B is a cross-sectional view through the intermediate frame structure of Figure 3A;

[0108] Figure 3C is a further cross-sectional view through the intermediate frame structure of Figure 3A;Figure 3D is a further cross-sectional view through the intermediate frame structure of Figure 3A;

[0109] Figure 4A is a plan view of a first end (“top”) frame structure according to an embodiment of the invention;

[0110] Figure 4B is a cross-sectional view through the first end frame structure of Figure 4A;

[0111] Figure 4C is a further cross-sectional view through the first end frame structure of Figure 4B;

[0112] Figure 5A is a plan view of a second end (“bottom”) frame structure according to an embodiment of the invention;

[0113] Figure 5B is a cross-sectional view through the second end frame structure of Figure 5A;

[0114] Figure 5C is a further cross-sectional view through the second end frame structure of Figure 5A;

[0115] Figure 6 is a cross-sectional view through a portion of the window according to an embodiment of the invention;

[0116] Figure 7 is a cross-sectional view through a portion of a window according to a further embodiment of the invention; and

[0117] Figure 8 is an exploded diagram of a window according to a further aspect of the invention.

[0118] DETAILED DESCRIPTION

[0119] The following description focusses on microwave-based pyrolysis systems. However, it will be appreciated that the window of the present invention may be utilised in other applications such as other industrial microwave heating processes, plasma processing, radar applications and the like.

[0120] Figure 1 is a schematic diagram showing a portion of a pyrolysis system 1 incorporating a window 100 according to an embodiment of the invention. The system 1 comprises a pyrolysis reactor 10 configured to perform pyrolysis of any suitable organic material, as is known in the art, and may typically operate at temperatures in the range of 400-1000°C. In a preferred implementation, the pyrolytic reactor 10 is configured to pyrolyse waste plastics material for plasticchemical recycling, but in alternative implementations may provide pyrolysis of other waste materials such as biomass, tyres, fabric and the like. The waste material is fed into the reactor 10 from feed 12.

[0121] The chemical reactions occurring in the reactor produce pyrolysis gas that exits the reactor through reactor exit port 11. In the case of plastic waste pyrolysis, the pyrolytic gas will typically comprise a mixture of hydrocarbon gases such as linear and branched alkanes and alkenes ranging from C1 to C40, aromatic compounds ranging from benzene to compounds comprising several benzenic rings and some oxygenated or nitrogenated compounds depending on the nature of the feedstock. The pyrolysis gas is then processed in one or more downstream processing units, schematically shown at 40, to recover useful products such as pyrolysis oil. The further downstream processing units may include a cyclone to separate particulate matter from the pyrolysis gas flow, and a condensation system to recover liquid pyrolysis oil from the pyrolysis gas.

[0122] The operating temperature of the reactor 10 is initiated using microwave radiation. The pyrolysis system 1 comprises a microwave generator 20 configured to generate microwave radiation. The microwave radiation is guided from the microwave generator 20 to the reactor 10 via waveguide 30. A window 100 is provide at the interface between the waveguide 30 and the pyrolysis reactor 10 and allows transmission of the microwave radiation from the waveguide 30 to the reactor 10 whilst providing a seal between the two environments. The window 10 is typically connected to the wall of the reactor 10 so as to close an aperture in the reactor wall.

[0123] In the pyrolysis system 1 schematically shown in Figure 1, a single microwave generator 20 is illustrated. However, it will be appreciated that in alternative systems, more than one microwave generator may be used, typically having a respective waveguide and window within the reactor. Alternative positions of the microwave window(s) are also envisaged. For example, rather than the “top down” configuration shown in Figure 1 where the microwave window 100 is positioned in the top of the reactor, in some alternative embodiments microwaveradiation may be introduced into the reactor though one or more windows arranged around the sides of the reactor.

[0124] As will be appreciated, condensation of vapours produced in the reactor 10 on the window 100 will adversely affect the transmission efficiency of the microwave radiation into the reactor, and therefore negatively impact the heating of the feedstock and the pyrolytic reactions. The window 100 of the present invention is configured to minimise or prevent condensation from forming on the window, as will now be explained in further detail.

[0125] Figure 2 is an exploded diagram showing the main components of a window 100 according to an embodiment of the present invention. The window 100 comprises a first window panel 101 having a first surface 101a and an opposing second surface 101b, and a second window panel 103 having a first surface 103a and an opposing second surface 103b. In the present embodiment the first and second window panels are made of alumina which is substantially transparent to the microwave radiation. However, other materials may be used for the first and second window panels, such as quartz or mica. The first and second window panels typically have the same geometry and dimensions as each other.

[0126] The first and second window panels are supported by a window support structure shown generally at 180 and comprising a first end frame structure 110 (also referred to herein as a “top” frame structure), an intermediate frame structure 120, and a second end frame structure 130 (also referred to herein as a “bottom” frame structure). The window support structure 180 is configured to support (or “hold”) the first and second window panels 101, 103 such that they are spaced apart along the direction of microwave propagation through the window. Here, the direction of propagation of the microwave radiation is indicated by D. Referring back to the “top down” configuration of the microwave radiation application to the pyrolysis reactor in Figure 1 , the first surface 101 a of the first window panel 101 faces the waveguide 30, and the second surface 103b of the second window panel 103 faces the interior of the reactor 10. It is desirable to prevent condensation from forming on the second surface 103b of the second window panel 103 in particular.When assembled, the components of the window are substantially co-axial with each other.

[0127] As discussed above, the first and second window panels 101, 103 are spaced apart along the direction D. The first window panel 101 is positioned on a first side of the intermediate frame structure 120 (the side facing the waveguide 30), and is received by recessed first panel ledge 124 of the intermediate frame structure 120 as will be described in further detail herein. The second window panel 103 is positioned on the second opposing side of the intermediate frame structure 120 (the side facing the reactor) and is received by recessed second panel ledge 134 of the second end frame structure. The first and second window panels 101, 103 cover and enclose the opening 120a defined by the intermediate frame stricture 120 and therefore form an inter-panel space bounded by the first and second window panels, and the interior surface of the intermediate frame structure.

[0128] The intermediate frame structure 120 comprises a plurality of gas inlets 150 configured to allow heated gas to flow into the inter-panel space between the first and second window panels. As more clearly shown in Figure 3B, the gas inlets 150 are in the form of channels extending through the intermediate frame structure 120 from a first end 150a at the exterior of the intermediate frame structure to a second end 150b at the interior of the intermediate frame structure and therefore into the inter-panel space. The gas is provided by a gas supply device (not shown) coupled to the first end 150a of the gas inlets, for example by suitable gas supply lines.

[0129] The gas inlets 150 are arranged such that the gas flow into the inter-panel space is along a direction substantially parallel with the plane in which the first and second window panels lie (i.e. substantially perpendicular to the direction of microwave propagation D). Hence, the gas flows “across” the first and second panels, providing uniform heating of the panels.

[0130] The plurality of gas inlets 150 are arranged along a first edge of the intermediate frame structure so as to provide a flow of heated gas across the panels 101 , 103.The intermediate frame structure 120 additionally comprises a plurality of gas outlets 160 positioned on the opposing edge of the intermediate frame structure, configured to allow the heated gas to escape from the inter-panel space, thereby enabling a flow of heated gas through the inter-panel space and across the window panels 101, 103. The gas outlets 160 typically have the same structure as the gas inlets and are typically each connected to a gas line where the gas may be evacuated from the system. In some embodiments it is envisaged that the gas exiting the inter-panel space may be re-circulated to the gas inlets 150. The arrangement of the gas inlets and outlets may be varied dependent on the geometry and dimensions of the window 100 to provide uniform heating of the window panels.

[0131] In the presently described embodiment, the heated gas is Nitrogen, although other suitable (typically inert) gases may be used such as Argon, Neon or Carbon Dioxide. Inert gases are preferred in case of a window breakage or seal failure. As will be appreciated, in order to minimise or prevent condensation occurring on the second window panel 103, the heated gas will need to have a temperature sufficient to heat the second window panel 103 to a temperature greater than that in the reactor 10. Thus, although the temperature of the gas will vary dependent on the particular process and the feedstock for microwave pyrolysis applications, the heated gas is typically supplied to the inter-panel space at a temperature in the range of 400°C to 700°C.

[0132] Referring back to Figure 2, each of the top frame structure 110, intermediate frame structure 120 and bottom frame structure 130 comprises a flange portion surrounding the respective opening. The flange portion of the top frame structure is shown generally at 112, the flange portion of the intermediate frame structure is shown generally at 122, and the flange portion of the bottom frame structure is shown generally at 132.

[0133] The top flange portion 112 comprises a first set of bolt holes 119 arranged around the periphery of the top frame structure. The intermediate flange portion 122 comprises a corresponding first set of bolt holes 129, and similarly the bottom flange portion 132 comprises a corresponding first set of bolt holes 139. Theframe structures are configured such that when the window is assembled, the first sets of bolt holes 119, 129, 139 align with each other (along the direction D) and consequently the top, bottom and intermediate frame structures can be connected together using bolts or other suitable fixings, supporting the first and second window panels therebetween. As will be explained further herein, the window 100 comprises features that enable the frame structures 110, 120, 130 to be connected and compressed together in this way with suitable torque to generate a good gas seal but without damaging the first and second window panels. The combination of the top, bottom and intermediate frame structures, together with the first and second window panels, may be referred to as a “cassette”.

[0134] Each of the top frame structure, intermediate frame structure, and bottom frame structure comprises a second set of bolt holes (shown at 118, 128 and 138 respectively). The second sets of bolt holes are positioned laterally outward of the first sets of bolt holes. When assembled, the second set of bolt holes on each of the frame structures aligns with each other along direction D and the window may be connected to the waveguide and the reactor using bolts or other suitable fixing means provided through bolt holes 118, 128, 138. The first and second sets of bolt holes are independent of each other: the first sets of bolt holes are used to seal the window itself, whereas the second sets of bolt holes are used to seal the window to the waveguide 30 on one side and the reactor 10 on the other side. This means that the desired torque may be used to seal the window to the reactor and to the waveguide without damaging the window panels of the window.

[0135] As depicted in Figure 2, typically the top, bottom and intermediate frame structures have substantially the same lateral geometry and dimensions whereby the first and second sets of bolt holes on each flange portion align with each other when the cassette is assembled.

[0136] The various features of the top, bottom and intermediate frame structures will now be described in further detail.

[0137] Figure 3A is a plan view of the intermediate frame structure 120, showing the top side thereof (i.e. the side facing the waveguide in the presently describedconfiguration). The intermediate frame structure 120 defines (e.g. surrounds) an opening 120a extending from the first (“top”) side to the second (“bottom”) side of the frame structure. In the rectangular geometry configuration illustrated in Figure 3A, the intermediate frame structure may be considered to be comprised of a first pair of opposing edges 121a, 121b, and a second pair of opposing edges 121c, 121 d. As shown in Figure 2, the gas inlets 150 are disposed in edge 121a, and the gas outlets 160 are disposed in opposing edge 121b.

[0138] The intermediate frame structure comprises a flange portion 122 surrounding the opening 120a and comprising first 129 and second 128 sets of bolt holes as discussed above.

[0139] Figure 3B is a cross-sectional view through a portion of the intermediate frame structure 120 showing a gas inlet 150 as previously discussed. The references to “top” and “bottom” refer to the configuration of the window 100 shown in Figure 1. The top surface forms a first intermediate interface surface 125 configured to interface with a corresponding interface surface of the top frame structure 110. As seen in Figure 3B, the recessed first panel ledge 124 defines a surface that is recessed from (“stepped from”) the first intermediate interface surface 125 such that the recessed first panel ledge receives the first window panel.

[0140] The first panel ledge 124 extends around the interior periphery of the intermediate frame structure and is recessed from the first intermediate interface surface 125 by a distance H. Thus, the first panel ledge may be described as having a depth H. In the present embodiment, the depth H of the first panel ledge is greater than the thickness of the first window panel 101. Similarly, the lateral dimensions defined by panel ledge 124 (indicated by Rxand Ryin Figure 3A) are greater than the corresponding lateral dimensions of the first window panel 101. In this way, the panel ledge 124 allows for thermal expansion of the first window panel in use without fouling on the intermediate frame structure 120 which may lead to warping or cracking. Although in the presently described embodiment the depth H is greater than the thickness of the first window panel 101 , this is not essential.The first panel ledge 124 comprises a seal groove 124a extending around the periphery of the intermediate frame structure and configured to receive a panel sealing member as will be described herein.

[0141] The bottom surface of the intermediate frame structure 120 forms a second intermediate interface surface 126 configured to interface with a corresponding interface surface of the bottom frame structure. As seen in Figure 3B, on the opposing side to the panel ledge 124, the intermediate frame structure 120 comprises a sealing portion 127 recessed from the second intermediate interface surface 126 and extending around the periphery of the frame structure. The recessed sealing portion 127 comprises a panel seal groove 127a and a frame seal groove 127b positioned laterally outward from the panel seal groove 127a and laterally outward from the first panel ledge 124. When the first window panel 101 is supported on ledge 124, the edge of the window panel 101 panel lies laterally between the panel seal grooves 127a and 124a, and the frame seal groove 127b, as indicated by line P-P. In some embodiments, the window may not include a recessed sealing portion (e.g. dependent on the thickness of the window panels).

[0142] Sealing members are positioned in grooves 127a, 127b and 124a to provide sealing of the window as will be explained herein.

[0143] Figure 3C is a cross-sectional view through the intermediate frame structure 120 along Y-Y, showing a bolt hole 128 of the second set of bolt holes extending through the frame structure from top to bottom. The bolt hole is positioned laterally outward of both the first panel ledge 124 and the sealing portion 127 such that connection of the window to the reactor and waveguide is independent of the connection between the frame structures of the window itself.

[0144] Figure 3D is a cross-sectional view through the intermediate frame structure 120 along section line AA-AA, showing a bolt hole 129 of the first set of bolt holes extending through the frame structure.Figure 4A illustrates a plan view of the top frame structure 110, showing the bottom side thereof (i.e. the side facing away from the waveguide 30). The top frame structure defines (e.g. surrounds) an opening 110a extending from the first (“top”) side to the second (“bottom”) side of the frame structure and has substantially the same lateral geometry and dimensions as the intermediate frame structure 120. The top frame structure comprises a flange portion 112 surrounding the opening 110a and comprising first 119 and second 118 sets of bolt holes as discussed above. The top frame structure 110 comprises a recessed sealing portion 117 extending around the underside periphery of the top frame structure 110.

[0145] Figure 4B is a cross-sectional view of the top frame structure 110 along section line AE-AE, showing the sealing portion 117 and bolt hole 119 of the first set of bolt holes in more detail. As seen in Figure 4B, the top frame structure 110 comprises a nut receiving portion 119a whereby a bolt extending through the first bolt holes of the bottom, intermediate and top frame structures may be torqued to connect and compress the bottom, intermediate and top frame structures. However, alternative means of connecting and torquing the frame structures are envisaged. For example, in alternative embodiments, threaded holes may be used, with screws used to connect the frame structures.

[0146] The bottom side of the top frame structure 110 comprises a first top interface surface 115, with the sealing portion 117 recessed from the first top interface surface 115. The sealing portion 117 comprises panel seal groove 117a and frame seal groove 117b located laterally outward of the panel seal groove 117a.

[0147] When the intermediate frame structure 120 and the top frame structure 110 are connected (using bolts extending through bolt holes 119, 129, 139), first and second panel sealing members (not shown) are positioned within the panel seal grooves 117a and 124a respectively, and a first frame sealing member (not shown) is positioned within the frame seal groove 117b. The sealing members protrude from their respective grooves. Thus, when the intermediate frame structure 120 and the top frame structure are connected to bring the first intermediate interface surface 125 and the first top interface surface 115 together, the first and second panel sealing members located in grooves 117a and 124a engage the first windowpanel 101 and provide a seal around the panel that is received on ledge 124. Additionally, the frame sealing member located in frame seal groove 117b provides a seal between the intermediate and top frame structures.

[0148] The configuration of the grooves and sealing members is such that as compression is applied to the intermediate and top frame structures, the compressive force experienced by the frame sealing member is greater than the compressive force experienced by the first and second panel sealing members. This is achieved as the groove 117a housing the first panel sealing member is recessed further from surface 115 than groove 117b housing the first frame sealing member. In this way, the first frame sealing member in groove 117b engages the first intermediate interface surface 125 first as the frame structures are compressed together. The recessed nature of the sealing portion 127 provides room for compression of the sealing members to form the gas seal as well as providing additional thermal expansion room for the first window panel 101.

[0149] The frame seal groove 117b is positioned laterally spaced from the first panel ledge 124 as clearly seen in Figure 6. This configuration means that compression applied to the window when connecting the intermediate and top frame structures together is substantially isolated from the first window panel.

[0150] Although the use of grooves is preferred to aid seating and lateral positioning of the sealing members, it is envisaged that in some embodiments grooves may not be used and the sealing members instead placed appropriately on the interfacing surfaces before compression and sealing of the window. In such cases, sealing members of different thickness may be used to ensure that the compressive force experienced by the frame sealing member is greater than the compressive force experienced by the first and second panel sealing members.

[0151] The sealing members are preferably gland packings. The sealing members typically comprise graphite cord or rope, or a similar material. A suitable sealing member is the product K3222 from Klinger Limited, UK.Once the intermediate frame structure 120 and the top frame structure 110 are connected and compressed to create a gas seal, the first window panel 110 is supported between the two frame structures.

[0152] Figure 4C is a cross-sectional view through the top frame structure 110 along line AD-AD, showing bolt hole 118. As can be seen from Figure 4C, the second sets of bolt holes are laterally spaced from the sealing portion 117. In this way, the torque applied when connecting the sealed window to the first and second environments is independent of the seal generated by constructing the cassette. The top frame structure 110 comprises a second top interface surface 116 which is configured to interface with the waveguide 30 (or other environment in alternative embodiments).

[0153] Figure 5A is a plan view of the bottom frame structure 130 showing the top side thereof (i.e. the side facing away from the reactor 10). The bottom frame structure has substantially the same lateral geometry and dimensions as the intermediate and top frame structures. The bottom frame structure defines (e.g. surrounds) an opening 130a extending from the first (“top”) side to the second (“bottom”) side of the frame structure. The bottom frame structure 130 comprises a flange portion 132 surrounding the opening 130a and comprising first 139 and second 138 sets of bolt holes as discussed above. The bottom frame structure 130 comprises a recessed second panel ledge 134 extending around the interior periphery of the bottom frame structure 130 and which is configured to receive and support the second window panel. The flange portion 132 is laterally outward of the second panel ledge 134.

[0154] Figure 5B illustrates a cross-sectional view through the bottom frame structure along section line AB-AB. The bottom frame structure 130 comprises a first bottom interface surface 135 and an opposing second bottom interface surface 136. As shown in Figure 5B, the bottom frame structure includes a recessed second panel ledge 134 having a depth H. The panel ledge 134 is configured to receive, and support, the second window panel 103, and generate a gas seal via panel sealing member located in groove 134a. Similarly to the first panel ledge 124 of the intermediate frame structure described above, the depth H of the panelledge 134 is greater than the thickness of the second window panel (although this is not essential), and the lateral dimensions defined by the panel ledge 134 are greater than the lateral area of the second window panel 103 so as to allow space for thermal expansion.

[0155] The second panel ledge 134 comprises panel seal groove 134a. A fourth panel sealing member (e.g. graphite cord) is provided in groove 134a so ensure a good seal between the second window panel 103 and the bottom frame structure. Referring back to Figure 3D, when the bottom frame structure and intermediate frame structure are connected together and compressed, a third panel sealing members located in panel seal groove 127a and the fourth panel sealing member provide a seal around the second window panel 103. Additionally, second frame sealing member located in frame seal groove 127b provides a seal between the interfacing surfaces of the bottom and intermediate frame structures.

[0156] The second bottom interface surface 136 is configured to interface with the reactor 10 (or other environment in alternative embodiments), with the window connected to the reactor using bolts engaged through bolt holes 138.

[0157] Figure 5C is a cross-sectional view through the bottom frame structure along section line AC-AC, showing bolt hole 139 of the first set of bolt holes used to connect the bottom frame structure to the intermediate and top frame structures. The first bolt hole 139 is laterally spaced from the recessed second panel ledge 134. When the bottom frame structure 130 is connected to the intermediate frame structure 120, the first bottom interface surface 135 engages with second intermediate interface surface 126 of the intermediate frame structure. In the same manner as described above with regard to the intermediate frame structure and the top frame structure, as the bottom frame structure and intermediate frame structure are compressed along direction D, the compressive force experienced by the second frame sealing member located in groove 127b is greater than the compressive force experience by the third and fourth panel sealing members. Additionally, as frame seal groove 127b is laterally positioned outward of the second panel ledge, the compressive force on the frame sealing member is isolated from the window.Figure 6 is a cross-sectional view through a portion of the window 100 when assembled. The direction of propagation of the microwave radiation, D, is shown for reference. As can be seen from the cross-sectional view of Figure 6, when the first and second window panels 101, 103 are received by respective panel ledges 124, 134, the window panels are spaced apart along direction D, forming interpanel space shown generally at 200. The inter-panel space is bounded by second surface 101b of the first window panel, first surface 103a of the second window panel, and the interior surface 120’ of intermediate frame structure 120. The heated gas is introduced into the inter-panel space via gas inlet 150.

[0158] Also shown in the cross-sectional view of Figure 6 are the first frame sealing member 1170b, and the first and second panel sealing members 1170a and 1240a providing seals as described above. The sealing members are not shown in grooves 127b, 127a and 134a.

[0159] As schematically illustrated in Figure 6, the first panel ledge 124 may be considered to at least partly provide a first panel receiving section 80 of the window support structure within which the first window panel 101 is received. Similarly, the second panel ledge 134 may be considered to at least partly provide a second panel receiving section 90 of the window support structure within which the second window panel 103 is received. It will be appreciated that the location of the panel ledges and the grooves may be varied across the various frame structures of the window. For example, it is envisaged that at the interface between the intermediate frame structure 120 and top frame structure 110, the first window panel 101 may be received by a panel ledge located in the top frame structure 110.

[0160] In a further embodiment, the window may comprise a further (third) window panel, substantially co-axial with the first and second window panels, and defining a second inter-panel space. Figure 7 is a cross-sectional view through a portion of window 200 according to such an embodiment. As shown in Figure 7, a third window panel 105 is positioned on the waveguide side of the first window panel 101 such that the first window panel 101 is located between the second and third window panels. The third window panel 105 is supported between top framestructure 110 and a further frame structure 140. The sealing between the top frame structure 110, the further frame structure 140, and the third window panel is substantially as discussed above.

[0161] Thus, a second inter-panel space 400 is created between the first and third window panels and bounded by the interior surface of the top frame structure 110. Instead of providing a flow of heated gas to the second inter-panel space 400, a vacuum is applied to the second inter-panel space 400, for example using a suitable vacuum pump in fluid communication with opening 450 to the second inter-panel space 400. The use of a second inter-panel space comprising a vacuum in this way provides insulation towards the top of the window (with the bottom of the window 200 facing the reactor as in Figure 1 ), such that there is less heat losses caused by the heating effect on the first window panel due to the heated gas.

[0162] Figure 8 is a schematic exploded view showing the main components of a window 300 according to a further aspect of the invention. In this example, the window 300 comprises a single window panel 301 supported between first frame structure 320 and second frame structure 310. The first frame structure 320 and second frame structure 310 form a window support structure 380. In this way, the window 300 is “single glazed” and does not comprise an inter-panel space configured to receive heated gas. However, window 300 comprises the advantageous features described above in relation to windows 100, 200 that allow the frame structures to be connected together and compressed to form an effective gas seal without damaging the window panel 301. The window 300 also enables thermal expansion of the window panel, which is particularly advantageous when the window is used in high temperature environments such as a pyrolysis reactor.

[0163] The first frame structure 320 and second frame structure 310 are connected together in substantially the same manner as the intermediate and top frame structures described with reference to window 100. In particular, window panel 301 is received on window panel ledge 324 located on first frame structure 320, and sealing members in the form of graphite gland packings are used to generatea gas seal between the frame structures 320, 310 and between the window panel 320 and the frame structures.

[0164] The first frame structure 320 comprises a flange portion 322 having first 329 and second 328 sets of bolt holes, and similarly second frame structure 310 comprises flange portion 312 having corresponding first 319 and second 329 sets of bolt holes. The first sets of bolt holes are used to assemble and compress the window to form the gas seals, and the second sets of bolt holes are used to connect the window to the first and second environments between which the window provides an RF electromagnetic radiation (e.g. microwave radiation) interface.

[0165] In the above description, the various frame structures and window panels have a substantially rectangular cross-sectional geometry. In this way the window is particularly suited to interfacing with a rectangular waveguide. However, in general, other cross-sectional geometries may be used.

Claims

CLAIMS1. A window for transmission of radiofrequency, RF, electromagnetic radiation between a first environment and a second environment, comprising: first and second window panels each substantially transparent to the RF electromagnetic radiation, whereinthe first window panel is spaced from the second window panel along a first direction such that the window comprises an inter-panel space between the first and second window panels; andthe window further comprises one or more gas inlets configured to enable heated gas to flow into the inter-panel space so as to minimise or prevent condensation on the first and / or second window panels.

2. The window of claim 1 , further comprising an intermediate frame structure having a first side and a second side and defining an opening, whereinthe first window panel is disposed on the first side of the intermediate frame structure and the second window panel is disposed on the second side of the intermediate frame structure, wherein the inter-panel space is bounded by the intermediate frame structure and the first and second window panels.

3. The window of claim 2, wherein the one or more gas inlets are located in the intermediate frame structure.

4. The window of any of the preceding claims, wherein the one or more gas inlets are arranged such that the heated gas flows into the inter-panel space along a direction substantially perpendicular to the first direction.

5. The window of any of the preceding claims, wherein the one or more gas inlets comprise a plurality of gas inlets, preferably arranged along an edge of the inter-panel space.

6. The window of any of the preceding claims, further comprising one or more gas outlets configured to allow the heated gas to exit the inter-panel space.

7. The window of claim 6 when dependent on claim 2, wherein the one or more gas outlets are located in the intermediate frame structure.

8. The window of any of claims 2 to 7 when dependent on claim 2, further comprising a first end frame structure defining an opening, and wherein the first window panel is supported between the first side of intermediate frame structure and the first end frame structure.

9. The window of claim 8, wherein the window further comprisesa first frame sealing member configured to provide a seal between the intermediate frame structure and the first end frame structure,a first panel sealing member configured to provide a seal between the first window panel and the first end frame structure, anda second panel sealing member configured to provide a seal between the first window panel and the intermediate frame structure; and whereinthe window is configured such that a compressive force acting on the first frame sealing member is greater than a compressive force acting on the first and second panel sealing members.

10. The window of claim 8 or claim 9, wherein the first side of the intermediate frame structure comprises a first intermediate interface surface and the first end frame structure comprises an opposing first interface surface, andeither the intermediate frame structure comprises a first panel ledge recessed from the first intermediate interface surface or the first end frame structure comprise a first panel ledge recessed from the first interface surface, the first panel ledge configured to receive the first window panel.

11. The window of claim 10 when dependent on claim 9, wherein the first frame sealing member is laterally spaced from the first panel ledge.

12. The window of any of claims 9 to 11, wherein the first frame sealing member, first panel sealing member and second panel sealing member are received in respective grooves.

13. The window of claim 12, wherein the first frame sealing member is configured to protrude along the first direction from its respective groove such that the first frame sealing member experiences a compressive force before either the first or second panel sealing members as the intermediate frame structure and first end frame structure are compressed along the first direction.

14. The window of any of claims 10 to 13, wherein one of the intermediate frame structure and the first end frame structure comprises the first panel ledge, and the other of the intermediate frame structure and the first end frame structure comprises a recessed sealing portion laterally overlapping with the first panel ledge, preferably wherein the first frame sealing member and one of the first and second panel sealing members are located within the sealing portion.

15. The window of any of claims 9 to 14, wherein at least one of, preferably each of, the first frame sealing member, the first panel sealing member and the second panel sealing member comprises gland packing, preferably graphite gland packing.

16. The window of any of claims 8 to 15, further comprising a second end frame structure defining an opening, and wherein the second window panel is supported between the second side of the intermediate frame structure and the second end frame structure.

17. The window of claim 16, wherein the window further comprisesa second frame sealing member configured to provide a seal between the intermediate frame structure and the second end frame structure,a third panel sealing member configured to provide a seal between the second window panel and the intermediate frame structure, anda fourth panel sealing member configured to provide a seal between the second window panel and the second end frame structure; and whereinthe window is configured such that a compressive force acting on the second frame sealing member is greater than a compressive force acting on the third and fourth panel sealing members.

18. The window of claim 16 or claim 17 wherein the first end frame structure comprises a first end flange portion surrounding the respective opening, the intermediate frame structure comprises an intermediate flange portion surrounding the respective opening, and the second end frame structure comprises a second end flange portion surrounding the respective opening, whereineach of the first end flange portion, intermediate flange portion and second end flange portion comprises a first set of connecting features for connecting the first end frame structure, second end frame structure and intermediate frame structure together.

19. The window of claim 18, wherein each of the first end flange portion, intermediate flange portion and second end flange portion comprises a second set of connecting features for connecting the window to the first and second environments.

20. The window of any of the preceding claims, further comprising a third window panel spaced from the first window panel along the first direction and defining a second inter-panel space between the second window panel and the third window panel, and whereinthe window is configured to provide a vacuum in the second inter-panel space.

21. A window for transmission of radiofrequency, RF, electromagnetic radiation between a first environment and a second environment, comprising: a first window panel substantially transparent to the RF electromagnetic radiation;a first frame structure defining an opening; anda second frame structure defining an opening, and wherein the first window panel is supported between the first frame structure and the second frame structure; and wherein the window further comprisesa first frame sealing member configured to provide a seal between the first frame structure and the second frame structure,a first panel sealing member configured to provide a seal between the first window panel and the first frame structure, anda second panel sealing member configured to provide a seal between the first window panel and the second frame structure; and whereinthe window is configured such that a compressive force acting on the first frame sealing member is greater than a compressive force acting on the first and second panel sealing members.

22. The window of claim 21 , wherein the first frame structure comprises a first interface surface and the second frame structure comprises an opposing second interface surface, andeither the first frame structure comprises a first panel ledge recessed from the first interface surface or the second frame structure comprise a first panel ledge recessed from the second interface surface, the first panel ledge being configured to receive the first window panel.

23. The window of claim 22, wherein the first frame sealing member is laterally spaced from the first panel ledge.

24. The window of any of claims 21 to 23, wherein the first frame sealing member, first panel sealing member and second panel sealing member are received in respective grooves.

25. The window of claim 24, wherein the first frame sealing member is configured to protrude from its respective groove such that the first frame sealing member experiences a compressive force before either the first or second panelsealing members as the first frame structure and second frame structure are compressed together.

26. The window of any of claims 22 to 25, wherein one of the first frame structure and the second frame structure comprises the first panel ledge, and the other of the first frame structure and the second frame structure comprises a recessed sealing portion laterally overlapping with the first panel ledge, preferably wherein the first frame sealing member and one of the first and second panel sealing members is located within the sealing portion.

27. The window of any of claims 21 to 26, wherein the window further comprises a second window panel substantially transparent to the RF electromagnetic radiation, whereinthe first window panel is spaced from the second window panel along a first direction, and further whereinthe window further comprises a third frame structure defining an opening, and wherein the second window panel is supported between the first frame structure and the third frame structure such that the second window panel is disposed on an opposing side of the first frame structure from the first window panel.

28. A window apparatus comprising:a window according to any of claims 1 to 20; anda gas supply apparatus configured to provide a flow of heated gas to the inter-panel space through the one or more gas inlets.

29. The window of any of claims 1 to 20, or the window apparatus of claim 28, wherein the heated gas comprises nitrogen.

30. The window or window apparatus of any of the preceding claims, wherein the first window panel comprises quartz, and the second window panel comprises quartz.

31. The window or window apparatus of any of the preceding claims, wherein the RF electromagnetic radiation is microwave radiation.

32. The window or window apparatus of any of the preceding claims, wherein the first environment is one of: a waveguide, a microwave applicator, a microwave launcher, a pyrolysis rector; and the second environment is one of: a waveguide, a microwave applicator, a microwave launcher, a pyrolysis rector.

33. A pyrolysis reactor comprising a window or window apparatus according to any of the preceding claims.

34. A pyrolysis system comprising:a pyrolysis reactor according to claim 33;a microwave generator; anda waveguide configured to guide microwaves generated in the microwave generator to the window of the pyrolysis reactor.

35. A method of transmitting radiofrequency electromagnetic radiation through a window, comprising:providing a window according to any of claim 1 to 20 or a window apparatus according to claim 28; andflowing a heated gas through the inter-panel space so as to minimise or prevent condensation on the first and / or second window panels.

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