Burner

Abstract

A burner for treating an effluent gas stream from a process tool comprises a burner liner comprising a porous sleeve 5 allowing a first gas G1 to flow through to a treatment chamber 6. An array of inl

Description

Field The present invention provides a burner for treating an effluent gas stream from a process tool. The present invention also provides an abatement apparatus, a method, and an additively manufactured porous sleeve. Background Burners are known and are typically used for treating an effluent gas stream from a manufacturing processing tool used in, for example, the semiconductor or flat panel display manufacturing industry. The effluent gas stream must be treated to remove selected compounds therefrom before it can be vented to the atmosphere or disposed of elsewhere. Some known burners use combustion to remove compounds from the effluent gas stream. A fuel gas is conveyed into a treatment chamber and ignited to provide a combustion front. Typically, the fuel gas may be a hydrocarbon fuel. However, there is a desire to move away from the use of hydrocarbon fuels. The effluent gas stream may be conveyed into the treatment chamber for combustion therein. During combustion, the temperature within the treatment chamber may exceed 1000 °C. To increase the performance of the burner for a given fuel load, it is desirable for as much heat as possible to be retained within the treatment chamber during operation. Heat that escapes from the treatment chamber may undesirably transfer to other components of the system. There is a desire for a burner that provides improves heat retention within the combustion chamber during use. The present invention addresses, at least in part, these and other problems with the prior art. Summary In an aspect, the present invention provides a burner for treating an effluent gas stream from a process tool. The burner comprises a burner liner comprising a porous sleeve at least partially defining a treatment chamber. The porous sleeve is configured to allow a first gaseous composition to flow through towards the treatment chamber. The burner further comprises an array of inlets arranged about the porous sleeve and configured to convey a second gaseous composition through the porous sleeve towards the treatment chamber. The porous sleeve comprises a plurality of interconnected substantially concentric layers, each layer comprising an openwork mesh. A plurality of layers immediately adjacent to at least one inlet of the array are arranged to define a substantially unobstructed flow path for the second gaseous composition to flow through towards the treatment chamber. The substantially unobstructed flow path is aligned with the main direction of flow of second gaseous composition exiting the inlet. At least one layer between the substantially unobstructed flow path and the treatment chamber is arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition. The burner may form part of an abatement apparatus. Said abatement apparatus may be, by way of example, an iAtlas as produced by Edwards Limited. The abatement apparatus may be connected to the process tool during use. Preferably, said process tool may be a semiconductor or flat panel display manufacturing process tool. The porous sleeve may be configured to disperse gases passing therethrough, as described in greater detail elsewhere herein. The porous sleeve may be configured to mix the first and second gaseous compositions. The porous sleeve at least partially defines a treatment chamber of the burner. In other words, the porous sleeve provides at least a portion of the surface defining the treatment chamber. Preferably, an innermost layer of the porous sleeve may define at least a portion of the treatment chamber. The treatment chamber may be the portion of the burner in which the abatement of effluent gas stream occurs. Preferably, the treatment chamber may be a combustion chamber. In some cases, the porous sleeve may define substantially the entirety of the treatment chamber. Preferably, an innermost surface of the porous sleeve may at least partially define the treatment chamber. Said innermost surface may be the surface closest to a central axis of the treatment chamber. The treatment chamber may be substantially cylindrical or frustoconical. In such cases, the porous sleeve may provide a portion or the entirety of the curved sidewalls defining the treatment chamber. The treatment chamber may further comprise an inlet configured to convey the effluent gas stream into the treatment chamber. For the avoidance of doubt, said treatment chamber inlet may be distinct and separate from the array of inlets configured to convey the second gaseous composition towards the treatment chamber. The treatment chamber may further comprise an outlet configured to convey the treated gas stream out of the treatment chamber. Preferably the effluent gas stream inlet and the outlet may be arranged at opposite ends of the treatment chamber. Preferably, the effluent gas stream may not pass through the porous sleeve during treatment. For the avoidance of doubt, the first gaseous composition and the second gaseous composition may have different compositions. Preferably, the first or second gaseous composition may comprise a fuel, and the other may comprise an oxidant. In some embodiments, the first or the second gaseous composition alone may not be able to provide a stable combustion front in the treatment chamber. In some embodiments, the first gaseous composition may comprise an oxidant, preferably air. The first gaseous composition may comprise air and hydrogen. Preferably, the hydrogen may be present at less than about 10 %v / v, more preferably less than about 5 %v / v. Preferably, the first gaseous composition may consist essentially of air. In some embodiments, the second gaseous composition may be selected from the list consisting of hydrogen, carbon monoxide, hydrogen and carbon monoxide, or ammonia. Preferably, the second gaseous composition may consist essentially of hydrogen. Preferably, the first gaseous composition and / or the second gaseous composition may not comprise a hydrocarbon fuel. The array of inlets may be a substantially regular array of inlets. During use, the second gaseous composition may be configured to flow through each of the inlets of the array towards the treatment chamber. The array of inlets may comprise from about 2 inlets to about 1000 inlets. Preferably, the array of inlets may comprise from about 100 to about 900 inlets. For example, the array of inlets may comprise 810 inlets. It will be appreciated that the number of inlets may depend on, for example, the dimensions of the burner, the spacing of the inlets, and the compositions of the first and second gaseous compositions. The array of inlets may have sufficient density such that, when, in use, a combustion front is provided at or immediately adjacent substantially the entirety of the surface of the porous sleeve defining the treatment chamber. The combustion front may have an “egg-box” profile due to different gas flow speeds and / or mixing between the first and second gaseous compositions. The porous sleeve comprises a plurality of interconnected concentric layers. Each layer may comprise a substantially regular openwork mesh. The mesh may consist of one or more repeat units. Preferably each repeat unit of the openwork mesh may be substantially identical. Each repeat unit of the openwork mesh may comprise one or more mesh gap(s). The mesh gap(s) may be the spaces between the material of the openwork mesh. Typically, the volume fraction of mesh gap(s) is(are) relatively large compared to the volume fraction of the repeat unit, preferably a majority of the repeat unit by volume is mesh gap. A plurality of layers immediately adjacent to at least one inlet of the array are arranged to define a substantially unobstructed flow path for the second gaseous composition to flow through towards the treatment chamber. In other words, said plurality of layers may be aligned, or ‘in phase’. This may be defined as the repeat units of adjacent layers being aligned when viewed in a radially inward direction normal to the outer surface of the porous sleeve. The substantially unobstructed flow path for the second gaseous composition to flow through towards the treatment chamber may be defined by a plurality of aligned mesh gaps of adjacent layers. The substantially unobstructed flow path may be linear. The substantially unobstructed flow path may extend in a radial direction. Preferably, the substantially unobstructed flow path may extend in a radially inward direction towards a central axis of the treatment chamber. In some embodiments, the mesh gaps of at least some of the aligned layers may be fully aligned. In other words, there may be a total overlap between the mesh gaps of the layers when viewed in a radially inward direction normal to the outer surface of the porous sleeve. In some embodiments, the mesh gaps of the aligned layers may be partially aligned. This may be defined as there being a linear pathway that extends through a mesh gap of each layer through which the second gas composition may flow substantially unhindered (i.e. the substantially unobstructed flow path). Preferably, said substantially unobstructed flow path may extend in a radially inward direction towards a central axis of the treatment chamber. When the adjacent layers are partially aligned, they may be circumferentially offset, and / or the repeat units of the respective layers may differ. The circumferential offset between adjacent aligned layers may depend on the number and arrangement of the mesh gaps. The circumferential offset between adjacent aligned layers may also depend on the arrangement of inlets in the array. In some embodiments, the circumferential offset between adjacent aligned layers may be less than the circumferential offset between adjacent inlets of the array. For example, the circumferential offset between adjacent aligned layers may be from about zero degrees to about half of the circumferential offset between adjacent inlets of the array. Preferably, the circumferential offset between adjacent aligned layers may be from about a quarter to about a third of the circumferential offset between adjacent inlets of the array. The plurality of aligned layers may be from about 2 layers to about 6 layers, for example 4 layers. The substantially unobstructed flow path is aligned with the main direction of flow of second gaseous composition exiting the inlet. Typically, the plurality of aligned layers may define a plurality of substantially unobstructed flow paths. Preferably, the plurality of aligned layers may define a plurality of substantially unobstructed flow paths, each substantially unobstructed flow path being arranged to correspond with a separate inlet of the array. At least one layer between the substantially unobstructed flow path and the treatment chamber is arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition. Each such layer may be referred to as a baffle layer, or an unaligned layer. The baffle may be a portion of the layer, for example one or more strut or node of the layer, being arranged to obstruct the flow path of the second gaseous composition. The baffle layer(s) may be configured to disperse the second gaseous composition. The baffle layer(s) may increase mixing between the first and second gaseous compositions. In some embodiments, the circumferential offset between each layer (i.e. aligned layer and / or baffle layer) and its nearest neighbouring layer(s) may be uniform throughout the porous sleeve. It will be appreciated that the circumferential offset in such embodiments will depend on the repeat unit of each mesh layer and the size of the porous sleeve. The porous sleeve may provide a substantially regular structure that emulates the random structure of prior art foam and / or fibre layup burner liners. This may enable the control of burner properties in a predictable manner, simplifying optimisation, and remove the need for trial-and-error experimentation associated with known burner liner designs. In burners of the prior art, heat transfer through the porous sleeve may be an issue, as this can lead to excessive temperatures in other components of the burner. It is proposed that a factor influencing this may be the location of the combustion front within the treatment chamber. Without wishing to be bound by theory, it is believed that the closer the combustion front is positioned relative to the inner surface of the burner sleeve, the greater the temperature of the exterior of the burner sleeve. Advantageously, the substantially unobstructed flow path(s) of the porous sleeve may allow the second gaseous composition to flow through a portion of the porous sleeve with little obstruction or diversion. Therefore, the second gaseous composition may remain substantially separated from the first gaseous composition whilst within the substantially unobstructed flow path. When the second gaseous composition reaches the baffle layer(s), it may be dispersed by the baffle layer(s) and thereby mix with the first gaseous composition. Accordingly, the position at which the first gaseous composition and second gaseous composition mix can be relatively close to the treatment chamber in comparison to burners of the prior art. This may allow the combustion front to be further from the external surface porous sleeve (i.e. towards the treatment chamber), and reduce the heat transfer to the external surface of the porous sleeve during use. The combustion front may form within the porous sleeve and / or within the treatment chamber. Typically, the plurality of layers immediately adjacent to the inlet array may be arranged to define a substantially unobstructed flow path corresponding with each inlet of the array. Each substantially unobstructed flow path may be aligned with the main direction of flow of second gaseous composition exiting the respective inlet. Advantageously, this may provide a relatively even mixing of the first gaseous composition and the second gaseous composition about the porous sleeve. Typically, the porous sleeve may comprise sufficient layers to be optically opaque when viewed in any direction normal to the surface of the porous sleeve defining the treatment chamber. The minimum number of layers required to achieve optical opacity may be affected by the repeat unit of each layer, and / or by the circumferential offset between adjacent layers. Typically, the porous sleeve may comprise from about 4 layers to about 16 layers, preferably from about 10 layers to about 12 layers. For example, the porous sleeve may comprise 11 layers. Preferably, the wall comprises a greater number of layers than the minimum required to achieve optical opacity, preferably at least twice the number of layers required to achieve optical opacity, more preferably at least three times the number of layers required to achieve optical opacity. Advantageously, three times optical opacity may provide a low back face temperature (e.g. approximately ambient temperature) during use. Typically, a plurality of layers between the substantially unobstructed flow path and the treatment chamber may each arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition. In other words, the porous sleeve may comprise a plurality of baffle layers. Preferably, the porous sleeve may comprise from about 2 to about 6 baffle layers. More preferably, the porous sleeve may comprise 3 or 4 baffle layers. Advantageously, a plurality of baffle layers may increase the mixing of the first gaseous composition with the second gaseous composition within the porous sleeve. Typically, each layer may comprise a plurality of circumferentially spaced right-handed substantially helical struts connected to a plurality of circumferentially spaced lefthanded substantially helical struts and defining therebetween a plurality of mesh gaps. Typically, the mesh may comprise a plurality of struts and nodes arranged to form an openwork mesh of repeat units. Each repeat unit may comprise a plurality of struts and nodes defining one or more mesh gaps. Preferably, adjacent layers of the porous sleeve may be connected. Preferably, at least a portion of the corresponding struts of repeat units in adjacent layers will at least partially but not fully overlap when viewed in a radially inward direction normal to the outermost layer of the wall. Typically, the circumferential offset may be from about 5 % to about 30 % of the strut diameter, about 10 % being an example. Preferably, a layer may comprise at least one right-handed substantially helical strut coupled to at least one left-handed substantially helical strut, preferably a plurality of right-handed substantially helical struts coupled to at least one left-handed substantially helical struts. When a layer comprises two or more right-handed substantially helical struts coupled to two or more left-handed substantially helical struts, preferably the right-handed struts may be substantially parallel, and the lefthanded struts may be substantially parallel. Preferably, at least a portion of the corresponding struts of repeat units in adjacent layers may at least partially but not fully overlap when viewed in a radially inward direction normal to the outermost layer of the wall. The circumferential offset between adjacent layers may be referred to as the inter-layer pitch. Typically, the inter-layer pitch may be from about 5 % to about 30 % of the strut diameter, about 10 % being an example. Preferably, the right-handed struts of each layer may be substantially parallel to right-handed struts of each other layer. Preferably, the left-handed struts of each layer may be substantially parallel to left-handed struts of each other layer. Preferably, the right-handed and left-handed struts of each layer may each have the substantially the same helix pitch. The pitch of a helix may be defined as the height of one complete helix turn, measured parallel to the axis of the helix. The right-handed helical struts and left-handed helical struts of a layer may also be circumferentially offset by an in-layer pitch. Typically, the in-layer pitch may be the same or different to the inter-layer pitch (i.e. the circumferential offset between layers). Herein a right-hand helix or a left-hand helix may be referred to as an instance. A layer of the wall may comprise one or more instances, typically two or more instances. Preferably from about 6 to about 400 instances, more preferably from about 8 instances to about 120 instances. Reducing the number of instances in a layer will increase the node separation for a given helical pitch and burner liner circumference. The number of instances may typically be higher for burner liners with a relatively high helical pitch (from about 100 to 400 instances) and lower for those with a relatively low helical pitch (from about 6 to about 20 instances). Generally, the higher the number of instances per layer the lower the number of layers required to achieve optical opacity for a given strut diameter and in-layer pitch. The in-layer pitch and inter-layer pitch may be substantially the same. Preferably, the in-layer pitch is from about 5 % to about 30 % of the strut diameter, about 10 % being an example. As discussed, in embodiments, each layer may comprise a plurality of right-handed substantially helical struts coupled to a plurality of spaced left-handed substantially helical struts. Additionally, one or more substantially helical struts of each layer may intersect with and be integrally formed with a substantially helical strut of an adjacent layer. Preferably each substantially helical strut intersects with and is integrally formed with a substantially helical strut of an adjacent layer. In some embodiments, at least one of the plurality of layers immediately adjacent to at least one inlet of the array may comprise one or more partially filled mesh gaps defining an aperture, wherein the aperture defines a portion of the substantially unobstructed flow path. The partially filled mesh gap may comprise a plate portion extending between the struts of the mesh. The aperture may be a hole through said plate portion. Preferably, said layer(s) may comprise partially filled mesh gaps corresponding to each inlet of the array. For the avoidance of doubt, the layer(s) comprising one or more partially filled mesh gaps defining an aperture may be one or more of the aligned layers. Advantageously, the apertures and partially filled mesh gaps may better direct the flow of the second gaseous composition through the substantially unobstructed flow path. Typically, each pair of adjacent layers may be connected by one or more radially extending spacers. The plurality of radially extending spacers may be circumferentially separated. Preferably the spacers may be substantially uniformly spaced about and coupled to the outer surface of an inner of the two layers and the inner surface of the outer of the two layers. The spacers typically separate one layer from an adjacent layer by a radial distance substantially equal to the spacer’s diameter and / or radial thickness. Spacers may advantageously reduce radial / inter-layer conduction of heat, such as when the node-to-node separation is relatively low, and / or increase the thermal path through the burner. The radially extending spacer(s) may be in the form a stave, typically a longitudinally extending stave. Typically, the longitudinally extending stave may be substantially straight, although they may equally be in the form of a helix or part thereof. Typically, each inlet may be embedded in the porous sleeve. In other words, the position at which the second gaseous composition exits the inlet may be embedded within the porous sleeve. The position at which the second gaseous composition exits the inlet may be arranged between the innermost and the outermost surfaces of the porous sleeve. Said innermost and outermost surfaces may refer to their radial position relative to a central axis of the porous sleeve. During use, the second gaseous composition may be separated from the first gaseous composition until it has exited the inlet, at which point the second gaseous composition may be conveyed along the substantially unobstructed flow path. Preferably, each inlet may be embedded to a depth of from about 10% to about 90% of the thickness of the porous sleeve in a substantially radial direction, preferably by from about 20% to about 80%, for example about 33%, about 50% or about 66%. Typically, the porous sleeve may have a substantially uniform thickness in a radial direction. In some embodiments, the porous sleeve may have a thickness of from about 1 mm to about 10 mm, preferably from about 2 mm to about 6 mm. Preferably, the porosity of the porous sleeve may be substantially uniform throughout. Advantageously, this may aid in evenly dispersing the first gaseous composition as it passes through the porous sleeve. In some embodiments, the porous sleeve may be generally tubular. Typically, the porous sleeve may have an axial length of from about 50 mm to about 500 mm, more preferably from about 60 mm to about 200 mm, about 75 mm and about 150 mm being examples. The inside diameter of the porous sleeve may be from about 50 mm to about 250 mm, preferably from about 100 mm to about 200 mm, about 150 mm and about 175 mm being examples. The array of inlets are regularly arranged about the exterior of the porous sleeve. Preferably, the inlets may be a substantially evenly spaced array. Typically, each layer of the porous sleeve may be circumferentially out of phase with its neighbouring layers. The porous sleeve may be metallic. The porous sleeve may be monolithic. In other words, the porous sleeve may be a single piece. The burner may further comprise a perforated wall surrounding the porous sleeve and configured to allow the first gaseous composition to pass therethrough towards the treatment chamber. Preferably, the perforated wall comprises a plurality of apertures (i.e. perforations) configured to enable the first gaseous composition to pass therethrough. The perforated wall may be arranged radially outwardly of the porous sleeve. The perforated wall may be metallic. In embodiments, the apertures of the porous sleeve may be arranged in the spaces between the inlets. The apertures may be arranged in an array that substantially matches the spacing of the array of inlets. The apertures may be substantially evenly distributed on the perforated wall. It will be appreciated that the size and / or distribution of the apertures may depend on the preferred flow distribution of the first gaseous composition. The perforated wall may be substantially surrounded by an outer wall. The perforated wall and the outer wall may be separated by a plenum (i.e. a gap). In use, the first gaseous composition may flow from the plenum, through the perforated wall, and through the porous sleeve towards the treatment chamber. In some embodiments, the ratio of the number of inlets in the array to the number of apertures in the outer wall may be from about 1:2 to about 2:1. Preferably, the number of inlets in the array may be within ±10% of the number of apertures in the perforated wall. In some embodiments, the number of inlets in the array may be equal to the number of apertures in the perforated wall. Typically, the array of inlets may be connected to a manifold configured to divide a flow of the second gaseous composition between the inlets. Preferably, the manifold may be configured to divide said flow of the second gaseous composition substantially evenly between the inlets. The flow may be characterised as a volumetric flow. In embodiments, the entire array of inlets may be connected to a single manifold. Alternatively, a plurality of manifolds may be present and sub-groups of inlets may be connected to each manifold. Advantageously, substantially evenly dividing the flow of the second gaseous composition between the inlets may provide more even mixing with the first gaseous composition upon exiting the inlets, and therefore a more consistent and stable combustion front. Preferably, the manifold comprises a plurality of hollow staves. Each hollow stave is connected to a sub-group of the array of inlets. In embodiments, the hollow staves are substantially evenly spaced about the external surface of the porous sleeve. The hollow staves may be fluidly connected to each other. Each sub-group of the array of inlets may comprise from about 2 to about 50 inlets, preferably from about 10 to about 25 inlets, for example 15 inlets. The inlets of each sub-group may be substantially evenly spaced along the length of the stave. The manifold may comprise from about 2 to about 200 hollow staves, preferably from about 30 to about 100 hollow staves, for example 60 hollow staves. Each of the staves may be connected to a supply of the second gaseous composition. In embodiments, the staves and the perforated wall may be a single, unitary component. In said embodiments, the staves and perforated wall may be a generally tubular structure. Each stave may be connected to the nearest neighbouring staves by a portion of said perforated wall. Preferably, the porous sleeve may be connected to the perforated wall. The porous sleeve may be detachably connected to the perforated wall. Typically, the volumetric flow rate of the first gaseous composition through each of the apertures of the perforated wall may be from about 50 cm3min'1 to about 110 cm3min' 1, preferably from about 70 cm3min'1 to about 90 cm3min'1. For example, the volumetric flow rate of the first gaseous composition through each of the apertures of the perforated wall may be about 80 cm3min'1. Typically, volumetric flow rate of the second gaseous composition through each of the inlets of the array may be from about 10 cm3m in-1 to about 30 cm3m in-1, preferably from about 15 cm3m in-1 to about 25 cm3m in-1. For example, the volumetric flow rate of the second gaseous composition through each of the inlets of the array may be about 20 cm3min'1. Preferably, the burner may be a monolithic component. In other words, the burner may be a single, unitary component. The burner may be manufactured as a monolithic component, preferably by an additive manufacturing technique. For example, the burner may be produced by a powder bed sintering technique. The burner may be metallic. In a further aspect, the present invention provides an abatement apparatus comprising a burner according to any embodiment described herein. The abatement apparatus may comprise one or more further mechanisms configured to treat the effluent gas flow, arranged prior to and / or after the burner. In a further aspect, the present invention provides a method for treating an effluent gas stream from a manufacturing processing tool. The method comprises the step of providing an abatement apparatus according any embodiment described herein. The method further comprises the step of flowing a first gaseous composition through the porous sleeve towards the treatment chamber, and a second gaseous composition through the array of inlets towards the treatment chamber. The method further comprises the step of igniting the mixture of the first and second gaseous compositions to provide a combustion front. The method further comprises the step of flowing an effluent gas stream into the treatment chamber for treatment. In a further aspect, the present invention provides an additively manufactured burner according to any embodiment described herein. The burner being manufactured using a powder bed fusion technique. For the avoidance of doubt, all aspects and embodiments described herein may be combined, mutatis mutandis. Brief Description of Figures Preferred embodiments of the present invention will now be described, with reference to the following figures, in which: Figure 1 shows a cross-sectional view of a portion of a burner; Figure 2 shows a cross-sectional view of a portion of a burner according to an embodiment of the present invention; Figure 3 shows a cross-sectional view of a portion of a layer of a porous sleeve for use in a burner according to an embodiment of the present invention; Figure 4 shows a view of a portion of a porous sleeve for use in a burner according to an embodiment of the present invention; Figure 5 shows a portion of layer of a porous sleeve for use in a burner according to an embodiment of the present invention; Figures 6 shows an example of a component of a burner in accordance with an embodiment of the present invention; Figure 7 shows a cutaway view of a portion of a burner in accordance with an embodiment of the present invention; Figure 8 shows a flow diagram of a method in accordance with an embodiment of the present invention. Detailed Description Figure 1 shows a cross-sectional view of a portion of a burner. The burner comprises inlets (1) conveying a second gaseous composition (G2) towards the treatment chamber (2). In this figure, the second gaseous composition (G2) is illustrated by solid lines exiting the inlets (1). A first gaseous composition (G1) is conveyed towards the treatment chamber (2). The first gaseous composition (G1) is illustrated by dashed lines between the inlets (1). The burner further comprises a porous sleeve comprising a plurality of layers (3). The layers (3) are concentrically arranged. In this example, the circumferential position of each of the layers (3) is substantially random relative to the adjacent layers. In other words, the circumferential position of each layer (3) has no bearing on the circumferential positions of the adjacent layers (3). This arrangement of layers may be referred to as “misaligned” layers. As shown, the misaligned arrangement of the layers (3) results in significant disruption of the flow paths of the first (G1) and second (G2) gaseous compositions, respectively. This results in significant mixing between said first (G1) and second (G2) gaseous compositions throughout the porous sleeve. The mixing of the first (Gi) and second (G2) gaseous compositions in this manner allows the combustion front (4) to form very close to the inner surface of the treatment chamber (2) defined by the porous sleeve. The proximity of the combustion front (4) to the external surface of the porous sleeve may result in more heat being transferred back through the porous sleeve, increasing the back-face temperature of the burner. In turn, this may lead to the thermal energy transferring to other components of the system, which is undesirable. Figure 2 shows a cross-sectional view of a portion of a burner according to an embodiment of the present invention. The burner comprises a burner liner comprising a porous sleeve (5) that at least partially defines the treatment chamber (6). The porous sleeve is configured to allow a first gaseous composition (G1) to flow through towards the treatment chamber (6). The first gaseous composition (G1) is shown by the dashed lines between the inlets (7). The burner further comprises an array of inlets (7) arranged about the porous sleeve. The inlets are configured to convey a second gaseous composition (G2) through the porous sleeve towards the treatment chamber (6). The second gaseous composition (G2) is shown by the solid lines exiting through the inlets (7). The porous sleeve (5) comprises a plurality of substantially concentric layers. Each layer comprises an openwork mesh. A plurality of layers (8) immediately adjacent to at least one inlet (7) of the array are arranged to define a substantially unobstructed flow path for the second gaseous composition (G2) to flow through towards the treatment chamber. The substantially unobstructed flow path is aligned with the main direction of flow of second gaseous composition exiting the inlet. The main direction of flow of second gaseous composition is towards the treatment chamber (6). In this embodiment, the plurality of “aligned” layers (8) defining the substantially unobstructed flow paths at each inlet (7) are the two layers (8) nearest to the inlets (7). The porous sleeve (5) further comprises a layer (9) between the substantially unobstructed flow path and the treatment chamber (6) arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition (G2). In this embodiment, the layer (9) providing the baffle is the innermost layer. As shown, the arrangement of the “aligned” layers (8) and the “baffle” layer (9) results in relatively little mixing between the first (G1) and second (G2) gaseous compositions as the second gaseous composition (G2) passes through the substantially unobstructed flow path. Once the second gaseous composition (G2) reaches the end of the substantially unobstructed flow path and meets the “baffle” layer (9), mixing between the first (G1) and second (G2) gaseous compositions is encouraged as the flow of the second gaseous composition (G2) is diverted. As the first (G1) and second (G2) gaseous compositions mix much closer to the treatment chamber (6), the combustion front (10) is positioned further from the external surface of the porous sleeve (5) in comparison to the arrangement shown in Figure 1. Beneficially, this may reduce the thermal transfer back through the porous sleeve (5). Figure 3 shows a cross-sectional view of a portion of a layer (11) of a porous sleeve for use in a burner according to an embodiment of the present invention. The layer (11) comprises a substantially regular openwork mesh. The mesh comprises a plurality of repeat units (12). In this embodiment, a repeat unit (12) is indicated by the dashed box. The repeat unit (12) comprises a mesh gap (13). The layer (11) comprises a plurality of struts (14) and nodes (15) arranged to form the openwork mesh of repeat units (12). In this embodiment, the mesh gap (13) has a diamond shape. The layer (11) is generally tubular. Figure 4 shows a view of a portion of a porous sleeve for use in a burner according to an embodiment of the present invention. In this example, a pair of layers (16,17) can be seen. The layers (16,17) may each be substantially similar to that shown in Figure 3. The layers (16,17) have substantially the same repeat unit. It can be seen that the first layer (16) is circumferentially offset from the second layer (17) by a distance (d). Accordingly, there are regions of the mesh gaps of the first layer (16) that are blocked by the mesh of the second layer (17), and vice-versa. There are also regions of the respective mesh gaps of the first (16) and second (17) layers that overlap. The layers (16,17) are connected by radially extending spacers (18). The spacers (18) typically separate one layer from an adjacent layer by a radial distance substantially equal to the spacer’s diameter and / or radial thickness. Spacers (18) may advantageously reduce radial / inter-layer conduction of heat, such as when the node-to-node separation is relatively low, and / or increase the length of the thermal path through the burner liner. The radially extending spacer (18) shown is in the form a longitudinally extending stave. Figure 5 shows a portion of layer of a porous sleeve for use in a burner according to an embodiment of the present invention. The layer (19) is similar to those shown in Figures 3 and 4. This embodiment comprises a plurality of partially filled mesh gaps (20,21). In this case, the partially filled mesh gaps (20,21) comprise a plate portion. For ease of understanding, the plate portions are indicated by the dashed lines. The partially filled mesh gaps (20,21) each define an aperture (22,23). The aperture (22,23) is arranged within the plate portion. In other words, the aperture is a hole within the plate portion. The apertures (22,23) are each configured to define a portion of the substantially unobstructed flow path of the porous sleeve when in use. Each partially filled mesh gap (20,21) of the layer is configured to correspond to a different inlet of the array (not shown). It will be appreciated that whilst in this figure the partially filled mesh gaps (20,21) are present in vertically adjacent mesh gaps, the invention is not limited to this arrangement. The layer may comprise partially filled mesh gaps in any of the mesh gaps of the layer. Figure 6 shows an example of a component (24) of a burner in accordance with an embodiment of the present invention. When in use, the burner liner (not shown) is arranged within the component (24), such that it lines the inner surface of the component (25). The component (24) comprises a plurality of hollow staves (26). Each hollow stave (26) is connected to a plurality of inlets (27). Each hollow stave (26) is connected to a supply of the second gaseous composition. The supply of the second gaseous composition is provided to each of the hollow staves (26) via a port (28). Each stave (26) acts as a manifold to substantially evenly divide the supply of the second gaseous composition between the inlets (27). The hollow staves (26) are arranged in parallel. The hollow staves (26) are arranged about the treatment chamber when in use. Each hollow stave (26) is connected to its nearest neighbouring hollow staves (26) by a perforated wall (29). As shown, the perforated wall (29) comprises a plurality of apertures (30). Each of the apertures (30) is configured to allow the first gaseous composition to pass through the perforated wall (29) during use. On the inside of the component (24), the array of inlets (27) can be seen. Additionally, the apertures (30) are arranged in an array spaced between the array of inlets (27). Each of the inlets (27) protrudes radially inwardly from the internal wall (25). The apertures (30), in contrast, do not protrude radially inwardly. Figure 7 shows a cutaway view of a portion of a burner in accordance with an embodiment of the present invention. The burner comprises a component (24) as described in relation to Figure 6. Arranged within the component (24) is a burner liner comprising a porous sleeve (31). The porous sleeve comprises a plurality of layers (32) immediately adjacent to the inlets (27) of the array that are arranged to provide a substantially unobstructed flow path (33) for the second gaseous composition to flow through towards the treatment chamber (34). In this embodiment, each of the layers (32) defining the substantially unobstructed flow path (33) comprises a plurality of partially filled mesh gaps (35), as described in relation to Figure 5. As can be seen, in this embodiment, the substantially unobstructed flow path (33) is formed by the alignment of the apertures in the partially filled mesh gaps (35) of the layers (32). The substantially unobstructed flow path (33) is aligned with the main direction of flow of the second gaseous composition as it exits the inlet(s) (27). The porous sleeve (31) also comprises a plurality of layers (36) between the substantially unobstructed flow path (33) and the treatment chamber (34) that are arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition. It will be appreciated that other configurations are envisaged, for example a porous sleeve comprising a plurality of layers comprising partially filled mesh gaps, a plurality of aligned layers (without partially filled mesh gaps), and a plurality of baffle layers. Figure 8 shows a flow diagram of a method in accordance with an embodiment of the present invention. The method is for treating an effluent gas stream from a manufacturing processing tool. The method comprises the step of providing an abatement apparatus according any embodiment described herein (37). The method further comprises the step of flowing a first gaseous composition through the porous sleeve towards the treatment 5 chamber, and a second gaseous composition through the array of inlets towards the treatment chamber (38). The method further comprises the step of igniting the mixture of the first and second gaseous compositions to provide a combustion front (39). The method further comprises the step of flowing an effluent gas stream into the treatment chamber for treatment (40). 10 Reference 1. Inlet 2. Treatment chamber 3. Layer 4. Combustion front 5. Porous sleeve 6. Treatment chamber 7. Inlet 8. Layer 9. Layer 10. Combustion front 11. Layer 12. Repeat unit 13. Mesh gap 14. Strut 15. Node 16. Layer 17. Layer 18. Spacer 19. Layer 20. Partially filled mesh gap 21. Partially filled mesh gap 22. Aperture 23. Aperture 24. Component 25. Inner surface 26. Hollow stave 27. Inlet 28. Port 29. Perforated wall 30. Aperture 31. Porous sleeve 32.Layer 33. Substantially unobstructed flow path 34. Treatment chamber 35. Partially filled mesh gap 36. Layer 5 37. Method step 38. Method step 39. Method step 40. Method step

Claims

1. A burner for treating an effluent gas stream from a process tool, the burner comprising:a burner liner comprising a porous sleeve at least partially defining a treatment chamber, wherein the porous sleeve is configured to allow a first gaseous composition to flow through towards the treatment chamber;an array of inlets arranged about the porous sleeve and configured to convey a second gaseous composition through the porous sleeve towards the treatment chamber;wherein the porous sleeve comprises a plurality of interconnected substantially concentric layers, each layer comprising an openwork mesh,wherein a plurality of layers immediately adjacent to at least one inlet of the array are arranged to define a substantially unobstructed flow path for the second gaseous composition to flow through towards the treatment chamber, wherein the substantially unobstructed flow path is aligned with the main direction of flow of second gaseous composition exiting the inlet, andwherein at least one layer between the substantially unobstructed flow path and the treatment chamber is arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition.

2. The burner according to claim 1, wherein the plurality of layers immediately adjacent to the inlet array are arranged to define a substantially unobstructed flow path corresponding with each inlet of the array, wherein each substantially unobstructed flow path is aligned with the main direction of flow of second gaseous composition exiting the respective inlet.

3. The burner according to claim 1 or 2, wherein the porous sleeve comprises sufficient layers to be optically opaque when viewed in any direction normal to the surface of the porous sleeve defining the treatment chamber.

4. The burner according to any preceding claim, wherein a plurality of layers between the substantially unobstructed flow path and the treatment chamberare each arranged to provide a baffle at least partially obstructing the flow path of the second gaseous composition.

5. The burner according to any preceding claim, wherein each layer comprises a plurality of circumferentially spaced right-handed substantially helical struts connected to a plurality of circumferentially spaced left-handed substantially helical struts and defining therebetween a plurality of mesh gaps.

6. The burner according to claim 5, wherein at least one of the plurality of layers immediately adjacent to at least one inlet of the array comprises one or more partially filled mesh gaps defining an aperture, wherein the aperture defines a portion of the substantially unobstructed flow path.

7. The burner according to any preceding claim, wherein each pair of adjacent layers are connected by one or more radially extending spacers, preferably wherein each spacer is a longitudinally extending stave.

8. The burner according to any preceding claim, wherein each inlet is embedded in the porous sleeve, preferably wherein each inlet is embedded to a depth of from about 10% to about 90% of the thickness of the porous sleeve in a substantially radial direction, preferably by from about 20% to about 80%, for example about 33%, about 50% or about 66%.

9. The burner according to any preceding claim, wherein the array of inlets are regularly arranged about the exterior of the porous sleeve, preferably wherein the inlets are in a substantially evenly spaced array.

10. The burner according to any preceding claim, wherein each layer of the porous sleeve is circumferentially out of phase with its neighbouring layers.

11. The burner according to any preceding claim, wherein the porous sleeve comprises from about 4 to about 16 layers, preferably from about 10 to about 12 layers.

12. The burner according to any preceding claim, further comprising a perforated wall surrounding the porous sleeve and configured to allow the first gaseouscomposition to pass therethrough towards the treatment chamber, preferably wherein the perforated wall comprises a plurality of apertures configured to enable the first gaseous composition to pass therethrough.

13. An abatement apparatus comprising a burner according to any preceding claim.

14. A method for treating an effluent gas stream from a manufacturing processing tool, comprising the steps of:a. providing an abatement apparatus according to claim 13;b. flowing a first gaseous composition through the porous sleeve towards the treatment chamber, and a second gaseous composition through the array of inlets towards the treatment chamber;c. igniting the mixture of the first and second gaseous compositions to provide a combustion front; andd. flowing an effluent gas stream into the treatment chamber for treatment.

15. An additively manufactured burner according to any one of claims 1 to 12 manufactured using a powder bed fusion technique.s

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