Gas heater with flame arrester

Abstract

A gas heater (100) is disclosed, comprising a burner (110) for producing heat from a fuel provided by a fuel supply system (120) and a flame arrester (200) arranged between the fuel supply and the burner. The flame arrester comprises a plurality of plates (210) arranged in a stack, wherein each plate comprises integrally formed shoulders (220) abutting against corresponding shoulders of an adjacent plate within the stack to provide a spacing (d) between the plates. The shoulders and the spacings define inter-plate channels (230) for guiding the fuel to the burner and quenching flames propagating away from the burner. Further, for each inter-plate channel, a width (w) of the inter-plate channel is determined by a lateral separation between adjacent shoulders of a plate and a height (h) of the inter-plate channel is determined by the spacing between adjacent plates of the stack.

Description

Technical Field

[0001] The present invention relates to gas heaters, and more specifically to gas heaters comprising flame arresters for preventing flashback of flames.Background

[0002] Gas heaters are typically used for space heating purposes in various settings, including vehicles. These heaters feature a fuel supply system designed to deliver a fuel to a burner, which converts the energy stored in the fuel to heat through a combustion process.

[0003] To enhance, safety, gas heater may be equipped with a flame arrester, which is a device aimed at preventing flames from flashing back into the fuel supply system. This arrester is typically composed of a series of parallel metallic plates permitting the passage of combustible gas to the burner while effectively quenching flames attempting to propagate back towards the fuel supply.

[0004] Achieving efficient heat dissipation and cooling of the gases below their ignition temperature often necessitates using a relatively large number of plates. Moreover, maintaining uniformity in the spacing between these plates is important for consistent flame quenching and uniform gas flow across the entirety of the arrester. Any deviation in the size of these gaps can result in irregular gas flow, the formation of hot spots, or regions where flames are not adequately quenched.

[0005] Such design requirements present challenges in the fabrication and assembly of the flame arrester. Specifically, aligning a large number of plates in parallel with precise and uniform gap distribution may pose considerable difficulties. Consequently, there exists a need for gas heaters equipped with flame arresters that are simpler and more cost-effective to manufacture and assemble.Summary

[0006] It is an object of the present disclosure to provide a technology that addresses at least some of the above concerns.

[0007] According to an aspect of the present disclosure, there is provided a gas heater comprising a burner for producing heat from a gaseous fuel, a fuel supply system for providing the fuel from a fuel source to the burner, and a flame arrester arranged between the fuel supply and the burner. The flame arrester comprises a plurality of plates arranged in a stack, wherein each plate of said plurality of plates comprises integrally formed shoulders abutting against corresponding shoulders of an adjacent plate within the stack to provide a spacing between each plate of the stack. The shoulders and the spacings define inter-plate channels for guiding the fuel to the burner and quenching flames propagating away from the burner. For each inter-plate channel, a width of the inter-plate channel is determined by a lateral separation between adjacent shoulders of a plate and a height of the inter-plate channel is determined by the spacing between adjacent plates of the stack.

[0008] The integral shoulders make it possible to obtain consistent spacing between the plates without separate spacers or fixtures. By arranging the shoulders to rest against each other throughout the stack, the plates may naturally establish and define the inter-plate channels through their shape. This allows for an improved assembly efficiency and reduces the need for precise spacer placement and attachment. Moreover, by designing the shoulders to abut one another in the stacking direction, the plates can self-align within the stack, thereby reducing the need for dedicated aligning structures or jigs.

[0009] Additionally, integral shoulders can be formed with relatively high precision, for example through press forming, ensuring uniformity across the stack. This precision contributes to more consistent and accurate dimensions of the inter-plate channels compared to using separate components like spacers.

[0010] Furthermore, the shoulders may act as reinforcement structures, enhancing the robustness and structural integrity of individual plates, making handling of the plates easier and improving the robustness of the flame arrester.

[0011] The shoulders may be arranged to divide a contour of the plate into depressed areas and elevated areas, each forming a wall of corresponding inter-plate channel. The shoulders may run along a length of the inter-plate channel, aligning with the direction of flow that the channel guides. Consequently, the depressed and elevated areas respectively act as the floor or ceiling of the inter-plate channels. Put another way, the fuel may flow through channels formed by the vertically aligned sections of neighbouring plates - namely, the elevated or depressed areas - separated by the shoulders.

[0012] The shoulders may hence be configured to define alternating depressed and elevated regions, which are interconnected through the shoulders. In some examples, a shoulder may feature both a convex and a concave segment forming a smooth transition between elevated and depressed regions. The elevated region may transition into the convex segment, the convex segment into the concave segment, and the concave segment transition into the depressed region, as seen in a direction orthogonal to the length direction of the inter-plate channel. When the plates are assembled in the stack, the concave segments of one plate may be aligned to rest against the corresponding convex segment of an adjacent plate. The convex and concave segments may also be understood as positive and negative radii of curvature provided by the forming of the elevated and depressed regions. In some examples, the radii of curvature are determined by the press forming tool used.

[0013] Advantageously, the inter-plate channels may be substantially uniform across the entire stack, or at least across a major part of the stack. In different words, a cross-sectional shape and area of the inter-plate channels may be substantially uniform in at least a part of the stack, enhancing the uniformity of fuel flow to the burner. In some examples, at least one of the depressed areas and at least one of the elevated areas may share substantially the same width, contributing to this uniformity. In further examples, at least a subset of the plates may be arranged in a substantially equidistant manner in the stack, further promoting consistent spacing.

[0014] While all plates in the flame arrester may share the same design, featuring substantially identical shoulders, it is recognised that variations may occur. For instance, the stack could include one or more plates with a distinct shape, potentially placed at locations such as the top, bottom, or other parts of the stack. Despite these variations, maintaining a majority of the plates with substantially identical shapes may be preferable to ensure uniform inter-plate channel formation, facilitating consistent gas flow characteristics.

[0015] The shoulders may be configured to provide an elasticity of the stack in the stacking direction. The elasticity allows for the stack to be compressed in the stacking direction and press fitted into a supporting frame. In the stack, the shoulders can abut each other at a specific angle relative to the stacking direction. The angled contact point (or contact line, considering that the shoulders may abut each other along their entire length), may be designed to redistribute compressive forces applied along the stack's vertical axis into lateral forces. As a result, these lateral forces may induce a slight bending in the plates or shoulders, enabling a "springy" characteristic of the stack. This elasticity allows the stack to absorb and dissipate forces and thermal expansion, thereby enhancing its mechanical resilience and contributing to the stability of the assembly. Further, the elasticity, or compressibility, may be employed when fitting the stack into a frame structure. By slightly compressing the stack as it is being inserted into the open space of the frame structure, a tight interference fit may be achieved.

[0016] In some examples, all or a majority of the plates comprises opposing flank portions that run along the inter-plate channels. These flank portion may be formed by folding the edges of the plate back onto themselves. Viewed in the stacking direction, a thickness of such a folded flank portion may be less than a centre-to-centre spacing between adjacent plates of the stack. Consequently, the flank portions may serve as compression stops, establishing a maximum compression limit of the stack. When the stack is compressed to a specific degree, these flank portions come into contact with one another, effectively preventing any further compression of the stack. This may be advantageous from an assembly perspective, as it may reduce the risk of plastic deformation of the plates that could occur due to the inadvertent application of excessive compressive forces.

[0017] The gas heater may be of a catalytic type, in which the burner comprises a catalyst plate for combusting the fuel. The catalytic burner typically combusts the fuel at lower temperatures than burners which rely on an open flame. Further, the catalytic combustion tends to be more efficient and produces fewer emissions of harmful substances. In the present examples, the catalytic reaction may occur when gaseous fuel passes over a catalyst-coated surface, which typically is referred to as a catalytic plate. The catalyst facilitates the oxidation of the gas, releasing heat.

[0018] The flame arrester may be arranged at the catalyst plate, at the side facing the fuel supply, at a predetermined distance sufficient to prevent direct contact between the flame arrester and the catalyst plate. Direct contact may be undesirable, as this can lead to undesirable cooling of the catalyst plate, reducing the temperature below the temperature optimal for catalytic efficiency.

[0019] The term `flame arrester' commonly describes a device designed to inhibit flame propagation within the gas heater. Alternative terms, such as `flame trap', `flame stop', and `flashback arrestor' may also be used to denote similar functionalities.

[0020] By the shoulders being 'integral' or `integrally formed' is typically meant that the shoulders are formed as a unified part of the plate rather than being a separate piece that is attached or added later. The shoulders may hence be formed from the same piece of material as the plate itself, preferably through a process such as stamping or press forming.

[0021] The fuel may in some examples comprise a gas such as natural gas, propane, biogas, or hydrogen. However, the fuel may as well be formed of an aerosolised liquid, such as gasoline, diesel, or ethanol.

[0022] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.Brief Description of the Drawings

[0023] Various aspects and examples of the present disclosure will be readily understood from the embodiments discussed in the following detailed description and the accompanying drawings, in which: Figure 1 is a cross-sectional view of a gas heater, comprising a catalytic burner and a flame arrester according to an example. Figure 2 shows a perspective view of a stack of plates of a flame arrester according to an example. Figure 3 is a cross section of a portion of the stack in figure 2. Figures 4a-c are cross sections of plates of flame arresters according to some examples. Figures 5a-c are perspective views of flame arresters according to some examples of the present disclosure. Detailed Description

[0024] Figure 1 is a schematic cross-sectional view of a gas heater 100 in accordance with an embodiment of the present disclosure. The gas heater 100 may, for example, be configured for space heating purposes in various settings, including vehicles. The gas heater 100 comprises a fuel supply system 120 designed to deliver gaseous fuel to a burner 110, which converts the energy stored in the fuel to heat through a combustion process. The heat produced during the combustion process within the burner 110 may be harnessed by a heat exchanger assembly 130 arranged downstream of the burner 110.

[0025] A flame arrester 200 may be arranged between the fuel supply 120 and the burner 110 for guiding the fuel to the burner 110 and quenching flames propagating away from the burner 110. The flame arrester 200 comprises a plurality of plates 210, or lamellae, arranged in a stack permitting the passage of gas through inter-plate channels while effectively quenching flames attempting to propagate back towards the fuel supply 120. Exemplary flame arrester designs are discussed below with reference to figures 2-5c.

[0026] The burner 110 may be of a catalytic type, comprising a catalyst plate 112 for combusting the fuel. As illustrated in the present figure, the flame arrester 200 may be arranged at the catalyst plate 112, at the side facing the fuel supply. The flame arrester 200 may be arranged at a predetermined distance from the catalyst plate 112, sufficient to prevent direct contact between the flame arrester 200 and the catalyst plate 112. The spacing between the flame arrester 200 and the catalyst plate 112 is provided to avoid undesired cooling of the catalyst plate 112, as lower temperatures might negatively impact the combustion process and lead to inefficient combustion of the fuel.

[0027] The fuel supply system 120 typically includes a fuel tank or a connection to such a tank. The fuel supply system 120 may deliver a mixture of fuel and air (or oxygen) to the burner 110, where the fuel is combusted to release heat. The fuel may in some examples comprise a gas such as natural gas, propane, biogas, or hydrogen. However, the fuel may as well be formed of an aerosolised liquid, such as gasoline, diesel, or ethanol.

[0028] During operation, the fuel may be mixed with air by the fuel supply system 120 and guided in a gaseous flow to the burner 110 through the inter-plate channels of the flame arrester 200. In the example shown in figure 1, the fuel / air mixture is passed over surfaces of the catalytic plate 112 covered by a catalyst, such as platinum, palladium, or rhodium, which lowers the activation energy required for combustion and allows the fuel to oxidise and release heat without the use of an open flame. The heated gaseous flow, comprising the combustion by-products, may then be guided to the heat exchanger arrangement 130 for transferring the heat to a secondary medium, such as air, water, or another fluid, for further transport to the space that is to be heated.

[0029] Figure 2 is a perspective view of flame arrester 200, which may be designed for integration into a gas heater 100 similar to the one depicted in figure 1. This flame arrester 200 features a stack of plates or sheets 210 that are arranged substantially parallel to each other and with spacings forming inter-plate channels 230 facilitating the passage of a gaseous flow through the arrester 200. Specifically, figure 2 illustrates a configuration of 30 substantially identical and parallel plates 210 stacked atop one another. It is important to note that this configuration servers as an example; the actual number of plates 210 in the flame arrester 200 can vary, with possibilities including fewer or greater than 30 plates. In some examples, the flame arrester 200 may comprise several hundreds of plates 210, such as 300 or more. Additionally, the flame arrester 200 may include other plates with different configurations not depicted here. Therefore, references to `plates', `set of plates', or `plurality of plates' should be understood to not exclude additional plates.

[0030] The plates 210 may be formed of a metal sheet, with a thickness often less than 1 mm, and in some cases even less than 0.5 mm. In the particular example shown in figure 2, the plates 210 may be formed of a metal sheet having an average thickness of about 0.3 mm. The plates 210 may be formed through a press forming, or stamping process, in which a press tool applies force to the sheet material against a die. This pressure causes the sheet to deform and assume the shape of the die cavity. Consequently, this process provides the plates 210 with a specific contour in which shoulders 220 divide each plate 210 into depressed areas 242 and elevated areas 244. These shoulders 220 may extend along the inter-plate channels 230, aligning with the direction of flow guided by the channels 230. The depressed areas 242 and the elevated areas 242 may hence act as the floor or ceiling of the inter-plate channels 230. As hot gases from the burner 110 passes through the channels, the surfaces of the inter-plate channels 230 (i.e., the depressed and elevated areas 242, 244) may dissipate heat from the gases to reduce the temperature below the ignition temperature and prevent flames from propagating through the flame arrester 200.

[0031] Furthermore, the shoulders 220 and the alternation between depressed and elevated areas 242, 244 may aid in the alignment of the plates 210 within the stack. In the example depicted in figure 2, this configuration helps the depressed areas 242 of one plate 210 to be fitted in the corresponding depressed areas 242 of the plate 210 directly beneath it in the stack.

[0032] Each plate 210 in the depicted stack further comprises opposing flank portions 250, or edge portions, that run along the inter-plate channels 230. These flank portions 250 may be formed by folding the edges of the plate 210 back onto themselves, as shown in further detail in figure 3.

[0033] Figure 3 is an enlarged side view of the flank portions 250 of a subset of the plates 210 shown in figure 2. In this particular example, the spacing, or centre-to-centre spacing d between the plates 210 in the stack is determined by the shoulders 220. When stacked, the shoulders 220 of one plate 210 directly abut the corresponding shoulders of the adjacent plates 210, creating contact lines 262 extending along the shoulders 220. The shoulders 220 may be designed so that the spacing between the plates 210 exceeds the thickness of the flank portions 250, i.e., the combined thickness of the edges of a plate 210 when folded back onto themselves. This design choice allows for adjacent flank portions 250 to be separated by a gap 264, introducing a degree of compressibility of the stack. During compression of the stack, this gap 264 may be reduced until the flank portions 250 abut against each other. The flank portions 250 may hence serve as compression stops, establishing the maximum level of compression of the stack.

[0034] The shoulders 210 typically abut each other along the contact lines 262 at a specific angle in relation to the stack's vertical axis (i.e., the stacking direction). This allows compressive forces applied along the vertical axis to be redistributed into lateral components, orthogonal to the vertical axis. As a result, these lateral forces may induce a slight bending in the plates or shoulders, enabling a certain elasticity of the stack that can accommodate compressible forces and thermal expansion of the plates.

[0035] The geometry of the inter-plate channels 230 may be defined by their width w and height h, as well as their length (not shown). The width w is determined by the lateral separation between adjacent shoulders 230 of a plate, i.e., as seen in a direction orthogonal to the length direction of the inter-plate channels 230, whereas the height h is determined by the spacing d between adjacent plates 210 of the stack and the thickness of the plates 210. In different words, the width w of a channel may be determined by the width of the depressed and elevated areas 242, 244, respectively. The channel width w may in some examples be 10 mm or more, such as 20 mm or more, such as 40 mm or more. The height h of the channels may be less than 1 mm, such as 0.6 mm or less. In this particular example, the height h of the channels may be about 0.4 mm.

[0036] Figure 4 shows a plate 210 in which the width w 1 of the depressed areas 242 and the width w 2 of the elevated areas 244 are substantially the same, resulting in the flame arrester 200 having substantially uniform inter-plate channels 230 over the full width. Other configurations are however possible, as shown in figures 4b and c. Figures 4b and c show examples where the channels 230 formed by the elevated areas 244 are wider than the channels 230 formed by the depressed areas 422. This may be achieved by arranging the shoulders 220 defining the depressed areas at a closer distance w 1 than the distance w 2 between the shoulders 220 defining the elevated areas 244. Figure 4c also shows an example of a plate 210 without any folded flank portions 250.

[0037] Advantageously, the inter-late channels 230 have a width-to height ratio that is relatively large, ensuring the gaseous flow encounters an extensive surface area. This extensive exposure helps cooling the gas to temperatures below its ignition point. In specific examples, this ratio exceeds 10, and may reach values of 50 or more.

[0038] As best shown in figures 4a-c, the shoulders 220 may comprise a convex segment 222 and a concave segment 224 extending along the inter-plate channels 230. These segments 222, 224 may also be understood as positive and negative radii of curvature of the surface of the plate, forming the respective shoulders 220. Typically, these radii of curvature may be formed by the by the press forming tool used to define the alternate lowered and raised areas 242, 244 of the plates 210. Moving from left to right in the figures, the elevated area 244 transitions into the convex segment 222 (as seen from above; from below, it may be considered concave), which in turn transitions into the concave segment 224. The concave segment 224 then transitions into the depressed area 242. When stacked, the concave segment 224 of one of the plates is aligned with, and rests against, the convex segment 222 of an adjacent one of the plates 210 to form the contact lines 262 illustrated in figure 3.

[0039] Figures 5a-c show various examples of the stack arranged in a support structure facilitating mounting of the flame arrester 200 into a gas heater 100, such as the one shown in figure 1. The support structure, which also may be referred to as a frame assembly or housing, typically comprises a pair of top / bottom panels or plates 272, between which the stack is fitted. The stack may be press fitted between the top / bottom panels 272, which in turn may be connected by side elements, or lateral supports / walls 274, which may extend along the stack to complete an enclosed frame structure. Two examples of such lateral supports 274 are indicated in figures 5a and c.

[0040] Figure 5a shows rod-shaped lateral support elements 274 slotted into recesses formed into the flank portions 250 of the flame arrester plates 210. The recesses may be designed to snugly accommodate the full width of the lateral supports 274, ensuring they do not extend beyond the stack's sides. Moreover, by slotting the lateral supports 274 into the flame arrester plates 210, the lateral support 274 may facilitate alignment of the plates 210 within the stack and improve the structural integrity of the stack.

[0041] Further, as shown in figure 5a, the top and bottom panels 272 may be equipped with corresponding recesses to seat the lateral supports 274. The lateral supports 274 may be attached to the top and bottom panels 272 by means of press fitting or welding. In further examples, the end portions of the lateral supports 274 may be deformed after insertion into the respective top and bottom panels 272 to form a joint with the same. This design facilitates the integration of the entire assembly within an external frame structure 274, as depicted in figure 5b.

[0042] An alternative design in shown in figure 5c, in which the lateral supports 274 are formed as brackets connecting the top and bottom panels 272. Instead of the rod-shaped design depicted in figure 5a, the lateral supports 274 in figure 5c are formed of sheet-like structures that can be arranged to span the distance between the top and bottom panels 272. The end portions of these lateral supports 274 may engage in an interlocking mechanism 275 with the corresponding end portions of the top and bottom panels 272, exemplified by a tongue and groove joint or a hook engaging a groove, as indicated in figure 5c. To facilitate attachment, the stack may be slightly compressed in the stacking direction, enabling the lateral supports 274 to securely snap into the receiving structure of the top and bottom panels 272 for the interlocking mechanism 275.

[0043] In the above examples, the stack of flame arrester plates 220 may be press fitted into the support structure 272, 274, 276. This technique commonly relies on the precision manufacturing of both elements, i.e., the stack and the support structure, to ensure a snug fit, where the dimensions of the stack are slightly larger than the receiving space within the frame to create a tight interference fit upon insertion. However, due to the compressibility in the stacking direction enabled by the shoulders 210, resulting in the stack being 'springy', the flame arrester 200 can more easily accommodate minor variations in manufacturing tolerances, ensuring a snug fit within the frame structure even when there are slight discrepancies in dimensions. Further, a stack with inherent compressibility can better accommodate thermal expansions and contractions, maintaining a consistent fit and performance across a range of operating temperatures.

[0044] The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, the flame arrester 200 may comprise two of more distinct sets of plates, wherein each set may have a uniform design among its plates. However, the design may vary from one set to another, allowing for tailored functionality and performance across different sections of the arrester.

[0045] It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A gas heater(100), comprising: a burner (110) for producing heat from a gaseous fuel; a fuel supply system (120) for providing the fuel from a fuel source to the burner; and a flame arrester (200) arranged between the fuel supply and the burner, wherein: the flame arrester comprises a plurality of plates (210) arranged in a stack; each plate of said plurality of plates comprises integrally formed shoulders (220) abutting against corresponding shoulders of an adj acent plate within the stack to provide a spacing (d) between each plate of the stack; the shoulders and the spacings define inter-plate channels (230) for guiding the fuel to the burner and quenching flames propagating away from the burner; and for each inter-plate channel, a width (w) of the inter-plate channel is determined by a lateral separation between adjacent shoulders of a plate and a height (h) of the inter-plate channel is determined by the spacing between adjacent plates of the stack.

2. The gas heater according to claim 1, wherein, for each of the plurality of plates, the shoulders divide a contour of the plate into depressed areas (242) and elevated areas (244), each of the depressed and elevated areas forming a wall of a respective inter-plate channel.

3. The gas heater according to claim 2, wherein each shoulder comprises a convex segment (222) and a concave segment (224) extending along the inter-plate channels, wherein the elevated area transitions into the convex segment, the convex segment transitions into the concave segment, and the concave segment transitions into the depressed area, as seen in a direction orthogonal to the inter-plate channels.

4. The gas heater according to claim 3, wherein the plurality of plates are stacked on top of each other, wherein the concave segment of one of the plates is aligned with, and rests against, the convex segment of an adjacent one of the plates.

5. The gas heater according to any of claims 2-4, wherein at least one of the depressed areas and at least one of the elevated areas have substantially the same width.

6. The gas heater according to any of the preceding claims, wherein at least a subset of the plurality of plates are arranged in a substantially equidistant manner in the stack.

7. The gas heater according to any of the preceding claims, wherein a cross-sectional shape and area of the inter-plate channels are substantially uniform across at least a portion of the stack.

8. The gas heater according to any of the preceding claims, wherein each of the plurality of plates is a press formed plate.

9. The gas heater according to any of the preceding claims, wherein the shoulders are configured to provide an elasticity of the stack in the stacking direction.

10. The gas heater according to any of the preceding claims, wherein each plate of said plurality of plates comprises opposing flank portions (250) extending along the inter-plate channels, and wherein each flank portion is formed by an edge of the plate being folded onto the plate.

11. The gas heater according to claim 10, wherein a thickness of the flank portion, as seen in the stacking direction, is less than a centre-to-centre spacing between adjacent plates of the stack.

12. The gas heater according to any of the preceding claims, wherein the flame arrester comprises a supporting structure (272, 274, 276), and wherein the stack is press fitted into the supporting structure.

13. The gas heater according to any of the preceding claims, wherein the burner is a catalytic burner comprising catalyst plate for combusting the fuel.

14. The gas heater according to claim 13, wherein the flame arrester is arranged at the catalyst plate, at a predetermined distance sufficient to prevent direct contact between the flame arrester and the catalyst plate.

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