COMBUSTION DEVICE FOR A HYDROGEN GAS BOILER

Description

[0001] The present invention is directed to a combustion device for a hydrogen gas boiler. Moreover, the present invention relates to a hydrogen gas boiler comprising such a combustion device and the use of a burner seal for retrofitting a natural gas boiler.

[0002] Combustion appliances, in particular gas boilers, combust gas fuel to heat water for domestic use and / or central heating systems in buildings. Combustion appliances comprise a burner being partially arranged in a combustion chamber. In the combustion chamber, gas fuel is combusted typically to heat water for domestic use and / or for central heating systems in buildings. Usually, a central heating water circuit is heated, as well as a hot water supply. Due to the presence of highly flammable gases in the combustion circuits and systems, conditions for an explosion can occur. Furthermore, the type of combustible gas can even increase this risk. For example, compared to methane or natural gas, hydrogen has higher flammability. Therefore, in case of explosion of a gas boiler using pure hydrogen as fuel gas, the damages could be more severe compared to cases where other fuel gases are used. In addition, the use of hydrogen can lead to further problems. For example, hydrogen is more prone to flashback due to a higher flame speed compared to natural gas.

[0003] The combustion device or parts thereof are typically releasably fastened to a gas boiler housing so that it can be removed from the gas boiler for inspection and / or cleaning purposes or for replacement of the combustion chamber. Typically, screws are used as fastening means. To secure a safe and complete combustion, the combustion chamber has to be sealed against the surrounding environment. To this purpose, burner seals are employed. In this respect, reference is made to EP 4 296 568 A1 and EP 2 083 217 A1. EP 4 296 568 A1 discloses a combustion device for a hydrogen gas boiler configured for the combustion of a fuel gas which comprises at least 20 mol-% of hydrogen. A mounting wall comprising an outer surface and an inner surface, the inner surface facing a combustion chamber of the hydrogen gas boiler. A through hole is formed by the mounting wall for introducing a gas mixture into the combustion chamber via the through hole. A cylindrical burner deck protrudes from the mounting wall into the combustion chamber.

[0004] The gas boiler is operated on demand and not continuously. This means that in particular the fastening means and the burner seal are exposed to high temperature changes. Compared to methane or natural gas, the combustion of hydrogen gas results in higher temperatures inside the combustion chamber. The temperature changes are therefore higher when hydrogen gas is combusted compared to the combustion of methane or natural gas. With increasing operating time the fastening means are loosening and the burner seals suffer from increased wear. The size of hydrogen molecules is smaller than the size of methane or natural gas molecules. Both differences result in the fact that the reliable and long-lasting sealing of a hydrogen gas boiler in which hydrogen gas is combusted is more challenging compared to methane or natural gas.

[0005] It is therefore one object of the present invention to provide a hydrogen gas boiler configured for the combustion of a fuel gas which comprises at least 20 mol-% of hydrogen which provides a sufficient sealing of the combustion chamber over a longer operating time compared to known hydrogen gas boiler .

[0006] The object is solved by the features specified in claims 1 and 14. Advantageous embodiments are the subject of the dependent claims.

[0007] According to an embodiment of the present invention a combustion device for a hydrogen gas boiler configured for the combustion of a fuel gas which comprises at least 20 mol-% of hydrogen, comprises a mounting wall comprising an outer surface and an inner surface, the inner surface facing a combustion chamber of the hydrogen gas boiler, a through hole formed by the mounting wall, a manifold for introducing a gas mixture into the combustion chamber via the through hole and mountable on the mounting wall, and a burner seal for sealing the manifold against the mounting wall, wherein the burner seal is arranged on the outer surface of the mounting wall.

[0008] Within the present invention the outer surface of the mounting wall is to be understood as the surface facing away from the combustion chamber whereas the inner surface is oriented towards the combustion chamber. Moreover, the term "the burner seal being arranged on the outer surface of the mounting wall" should not be understood such that the burner seal has to be in direct contact with the outer surface. Also cases in which other components of the combustion appliance except the mounting wall are arranged between the outer surface and the burner seal may be included.

[0009] The fuel gas that is combustible in the present combustion device can comprise more than 20 mol-% hydrogen, in particular more than 30 mol-%. In particular, fuel gas can comprise more than 50 mol%, in particular more than 90 mol-% hydrogen or be pure hydrogen. Pure hydrogen is defined as comprising at least 98 mol-% hydrogen (hydrogen-fire gas appliance guide PAS4444:2020). Natural gas is a naturally occurring hydrocarbon gas mixture, comprising methane and commonly further comprising varying amounts of among others higher alkanes, carbon dioxide, nitrogen, hydrogen sulfide or helium. The hydrocarbon gas can also comprise or consist of propane. In the application a hydrocarbon combustion appliance is an appliance in which natural gas is combusted.

[0010] The manifold serves for introducing the gas mixture into the combustion chamber of the hydrogen gas boiler via the through hole and is mounted on the outer surface of the mounting wall. As noted, in comparison to natural gas, the combustion temperature of hydrogen is significantly higher. In many hydrogen gas boilers the combustion chamber is provided on the inner surface and the burner seal is arranged on the inner surface of the mounting wall. In contrast to that, by the arrangement of the burner seal on the outer surface in the mounted state, the mounting wall acts as an insulation such that the temperature the burner seal is exposed to in operation of the hydrogen gas boiler is significantly reduced. Moreover, the temperature of the environment of the burner seal arranged on the outer surface is lower compared to an arrangement on the inner surface. The burner seal is therefore heated to a lower degree compared to an arrangement on the inner surface. The thermal stress acting on the burner seal is therefore reduced which leads to a sufficient sealing of the combustion chamber over a longer operating time. Due to the arrangement of the burner seal on the outer surface in the mounted state, a reliable sealing of the manifold against the mounting wall can be provided in case the fuel gas comprises more than 20 mol-% hydrogen.

[0011] According to the invention, the burner comprises a burner deck, the burner deck being insertable into the through hole and configured to protrude into the combustion chamber. The burner seal can seal the burner, in particular the burner deck, against the mounting wall. For obtaining an equal distribution of the gas mixture inside the burner chamber and to reduce the risk of flashbacks, the burner deck has a perforation area. The burner can also be mounted on the outer surface of the mounting wall such that both the manifold and the burner can be mounted within the same mounting step, thereby reducing the installation work.

[0012] Alternatively, the burner can be mounted to the manifold. The manifold and the burner can as a whole be mounted to the mounting wall of the combustion device. This simplifies the assembling process.

[0013] In a further embodiment the burner comprises an installation section protruding radially outwards from the burner deck, the installation section is facing or contacting the outer surface when the burner is fastened to the mounting wall or to the manifold. The installation section can be arranged at one end of the burner deck. The installation section is typically provided by a flange. The burner is thus easier to access compared to an installation on the inner surface. It is therefore not necessary to disassemble the entire mounting wall or parts thereof for cleaning and / or inspection purposes or for the replacement of the burner.

[0014] In a further embodiment the installation section is either contacting the burner seal and the outer surface or the burner seal and the manifold when the burner is fastened to the mounting wall. In this embodiment the manifold is used to fasten the burner seal on the outer surface of the mounting wall. No further fastening elements are needed for the fastening of the burner seal. In an embodiment in which the burner seal surrounds the installation section, the burner seal can seal against the manifold and outer surface. In that case the burner seal contacts the manifold and the outer surface.

[0015] In a further embodiment the manifold has a recess for receiving the burner seal. That means, the burner seal and the manifold cannot rotate relative to each other. The fixing means support the correct positioning of the burner seal, thereby avoiding a misalignment of the burner seal which may compromise its sealing function.

[0016] In another embodiment the burner seal has at least one radially extending portion that radially protrude the manifold when the combustion chamber is fastened to the mounting wall. For this purpose, the manifold and / or the mounting wall may be provided with cut-outs through which the radially extending portions may run. The radially extending portions are visible from the outside of the combustion appliance. It may happen that the service technician forgets to mount the burner seal in case of inspection and / or cleaning and / or replacement of the burner. In this embodiment it is easy to check the presence of the burner seal in the assembled state. The risk that the combustion appliance is operated without the burner seal is thereby decreased and the operational safety is increased.

[0017] The manifold can comprise a hole which can be used to receive a sensor, in particular a UV sensor.

[0018] In a further embodiment the burner seal is made of chloroprene rubber (CR), polyethylene terephthalate (PET), poly-chlorotrifluoroethylene (PCTFE), fluorine rubber (FKM), polytetrafluoroethylene (PTFE), acrylonitrile rubber (NBR), polyamide (PA) or styrene-butadiene rubber (SBR). As mentioned, the size of the hydrogen molecules is smaller than the size of methane or natural gas molecules which aggravates the sealing of the combustion chamber when hydrogen is used. These materials have been proven to be suitable for sealing the combustion chamber when hydrogen is used.

[0019] In another embodiment the mounting wall forms a burner door, the outer surface being located on the burner door. The burner door, sometimes also referred to as front plate, is removable or is rotatably suspended in the remaining mounting wall or the hydrogen gas boiler housing and / or is used to close the combustion chamber. The access to components of the hydrogen gas boiler that are located inside a hydrogen gas boiler housing like heat exchangers is gained in a fairly easy way.

[0020] A further embodiment is characterized in that an insulation blanket is arranged on the inner surface. The insulation blanket reduces the amount of heat that can dissipate through the mounting wall. This heat can be used to heat water for domestic use and / or for central heating systems, thereby increasing the efficiency of the combustion appliance. Moreover, the temperatures the burner seal is exposed to can be further lowered thereby reducing the thermal stress acting thereon.

[0021] According to one aspect of the invention, a hydrogen gas boiler is provided that comprises a combustion device according to the present invention and a combustion appliance housing, the hydrogen gas boiler housing enclosing a combustion chamber in which the combustion device is at least partially arranged. The combustion device is fixable to the hydrogen gas boiler housing. The hydrogen gas boiler housing has an interface that is configured to be connected to the combustion device. In particular the burner door may be mechanically connected to the remaining hydrogen gas boiler housing. The connection can be a form-fitting or force fitting connection. In particular, the connection can be releasable. That means the connection can be released without destroying the combustion device and / or the housing.

[0022] According to an aspect of the invention an inventive combustion device can be used for retrofitting a natural gas combustion appliance to a hydrogen gas boiler configured to combust fuel gas comprising at least 20 mol% hydrogen, in particular at least 30 mol % hydrogen.

[0023] Thus, it is also possible to convert a combustion appliance such as a hydrocarbon gas boiler into a hydrogen gas boiler in a very easy and safe way while reducing human error by way of the concept of prevention through design. The combustion device according to the invention is in addition simple and inexpensive. In other words, the conversion can be realized in a very short time and only requires replacing a minimum number of components. In particular, it is not necessary to connect or disconnect a plurality of cables and / or to attach or detach a plurality of sensors which can lead to defects such as errors in part setup, missing parts, wrong parts, adjustment errors, mis-operation, or not following procedures due to human errors connected to these defects, in particular forgetfulness, inexperience and misidentification and above all inadvertent error which is strongly connected to most of these defects. Thus, the combustion device according to the invention reduces a number of human error sources such as inadvertent error, misunderstanding, forgetfulness, misidentification, and inexperience by reducing the number of parts to be disconnected, replaced and connected to a minimum. In fact, the present combustion device is ready to be mounted in a hydrogen gas boiler, by simply fixing the frame structure to a suitable housing of the hydrogen gas boiler. In addition, the modular nature of the combustion device allows the possibility to provide a combination of different components suitable for a hydrogen gas hydrogen gas boiler depending on and optimized to the configuration and working principle of the respective (natural gas) combustion appliance to be converted. Thus, the combustion device according to the invention has overall lower skill-requirements for the conversion which leads to increased safety and reduced conversion time.

[0024] In another embodiment, the hydrogen gas boiler comprises a volume reducer that is arranged inside an inner space of the burner and in particular inside the burner deck. The volume reducer reduces the amount of potentially explosive gas and air mixture inside the burner, thereby reducing possible damages during the explosion. Also, the volume reducer placed inside the burner deck enhances the stability of flames on the burner deck and determines an even temperature distribution over the burner deck. In particular, the volume reducer improves the homogeneity of the flow speed of the mixture, thereby reducing the risk of flashback. Thus, hydrogen can be used as a fuel gas without having a high explosive risk. The volume reducer can have a cylindrical shape and / or be at least partially formed from solid material.

[0025] In a further embodiment, the hydrogen gas boiler is a modulating hydrogen gas boiler, meaning that the heating output can be adapted to a heating demand. In other words, a modulating hydrogen gas boiler is able to modulate its power in real-time in order to provide the exact level of heat needed. A modulating hydrogen gas boiler is more energy-efficient than a non-modulating boiler in terms of fuel gas usage. The modulating hydrogen gas boiler therefore doesn't continuously work at 100% of its power. When the modulating hydrogen gas boiler operates, the modulating hydrogen gas boiler only uses a percentage of its power and only how much the modulating hydrogen gas boiler needs to maintain a set temperature. The amount the modulating hydrogen gas boiler uses depends on the ambient temperature, the external temperature, the number of people currently in the household, and other similar parameters. The modulating hydrogen gas boiler does not start, switch off or remain at full power unnecessarily. By avoiding unnecessary start-ups, which typically result in a fuel spike, energy efficiency can be improved compared to non-modulating hydrogen gas boilers. Modulating hydrogen gas boilers can operate with more or fewer modulation stages. The greater the number of modulation stages, the greater the energy efficiency. Suitable numbers of modulation stages comprise more than 1 modulation stage, in particular more than 1 modulation stage up to 10 modulation stages, in particular at least 3 modulation stages, in particular at least 4 modulation stages, in particular at least 5 modulation stages, in particular at least 10 modulation stages. Modulating hydrogen gas boiler include various parts which are configured to modulate in a predetermined number of stages, including for example modulating burners, modulating exchangers, modulating thermostats, modulating coils, modulating electronic cards, modulating controllers or control units, and modulating pumps.

[0026] In a further embodiment the hydrogen gas boiler is a heat and / or hot water appliance. In a further embodiment the hydrogen gas boiler is configured to be integrated in a building management system. In an embodiment the hydrogen gas boiler is a heating appliance wherein the output temperature is ≥ 85 °C, in particular 90 to 100 °C. In these embodiments, the combustion appliance is adapted for the needs of domestic use and / or of central heating systems in buildings.

[0027] In a further embodiment the hydrogen gas boiler has a output power of 4 kW to 2 MW, in particular 4 kW to 100 kW, 4 kW to 80 kW, 4 kW to 60 kW, 4 kW to 50 kW, 4 kW to 40 kW; in particular 6 kW to 100 kW, 6 kW to 80 kW, 6 kW to 60 kW, 6 kW to 50 kW, 6 kW to 40 kW; in particular 12 kW to 100 kW, 12 kW to 80 kW, 12 kW to 60 kW, 12 kW to 50 kW, 12 kW to 40 kW; in particular 20 kW to 40 kW; in particular 30 kW to 2 MW, in particular 30 kW to 150 kW, in particular 30 kW to 320 kW, in particular 40 kW to 150 kW, in particular 40 kW to 320 kW, in particular 45 kW to 150 kW, in particular 45 kW to 320 kW.

[0028] Another aspect of the invention is directed to the use of a hydrogen gas boiler inventive combustion device in a hydrogen gas boiler. This has the advantage that the thermal stress acting on the burner seal is reduced which leads to a sufficient sealing of the combustion chamber over a longer operating time.

[0029] A particular use is directed to the use of such a combustion device for retrofitting a natural gas combustion appliance to a hydrogen gas boiler configured to combust fuel gas comprising at least 20 mol% hydrogen, in particular at least 30 mol % hydrogen. In this way, it is possible to modify an already installed combustion appliance that is used for the combustion of natural gas such that hydrogen gas can be combusted without big effort.

[0030] The present invention is described in detail with reference to the drawings attached wherein Figure 1shows an embodiment of a part of a combustion appliance of the present invention by means of a principle sectional view, Figure 2is a perspective view of a combustion device of the combustion appliance of the present invention, and Figure 3shows the combustion device of Figure 2 by means of a front view.

[0031] Figure 1 shows an embodiment of a hydrogen gas boiler 11 of the present invention by means of a principle sectional view. In Figure 1 the hydrogen gas boiler 11 is shown in the mounted state. The hydrogen gas boiler 11 according to the first embodiment is a hydrogen gas boiler that is configured for the combustion of a fuel gas that comprises at least 20 mol-% of hydrogen. It should be noted that also fuel gas with more than 30 mol% of hydrogen or pure hydrogen may be combusted by the hydrogen gas boiler 11 according to the present invention.

[0032] The hydrogen gas boiler 11 comprises a combustion chamber 14 and a combustion device 10 having a burner 12 which at least partly is arranged in the combustion chamber 14. The burner 12 has a burner deck 13 which is partly arranged inside the combustion chamber 14 and has a tube-like shape that defines a longitudinal axis AL. A flange-like installation section 16 is arranged on one end of the burner deck 13 wherein the installation section 16 is protruding radially outwards with respect to the longitudinal axis AL. Moreover, the burner deck 13 has a perforated section. Further, the combustion device 10 comprises a volume reducer 33 arranged inside the burner deck 13, a ring-shaped burner seal 28 and a bent manifold 30.

[0033] The hydrogen gas boiler 11 further comprises a hydrogen gas boiler housing 31 delimiting the combustion chamber 14 that is closed by means of a burner door 20 (see Figure 2). The burner door 20 forms a mounting wall 18 that is provided with a through hole 22 and has an outer surface 24 and an inner surface 26. The outer surface 24 is facing to the exterior while the inner surface 26 is facing to the interior of the hydrogen gas boiler 11 and in particular to the combustion chamber 14 of the burner 12. The mounting wall 18 may also be formed directly by the hydrogen gas boiler housing 31.

[0034] A gas mixture comprising the fuel gas is guided into the manifold 30 in a flow direction that is approximately perpendicular to the longitudinal axis AL. The respective guiding means are not further shown. The flow direction of the gas mixture is changed inside the manifold 30 such that the gas mixture penetrates the through hole 22 approximately parallel to the longitudinal axis AL. The volume reducer 33 is in the shown air-tight so that the gas mixture cannot enter the volume reducer 33. It thus flows into the annular space formed between the volume reducer 33 and the burner deck 13 until it reaches the perforation area of the burner deck 13. After having passed the perforation area of the burner deck, the gas mixture is ignited inside the combustion chamber 14. The heat thereby generated is transferred to heat exchangers (not shown) arranged inside the hydrogen gas boiler housing 31.

[0035] The burner seal 28 comprising a burner seal recess 29 for receiving a part of the installation section 16. Specifically, the installation section 16 is inserted from radial direction referring to the longitudinal axis AL into the burner seal recess 29. The burner seal recess 29 is extends from a bottom side of the burner seal 28 in radial direction towards an upper side of the burner seal 28 but does not reach the upper side of the burner seal 28. In a direction along the longitudinal axis AL the burner seal recess 29 is arranged between a front and back side of the burner seal 28. Thus, a part of the burner seal 28 extends along the longitudinal axis AL when the installation section 16 is arranged in the burner seal recess 29 and is in contact with the manifold 30. Another part of the burner seal 28 extends in the opposite direction when the installation section 16 is arranged in the burner seal recess 29 and is in contact with the mounting wall 18. Additionally, a part of the installation section 16 is in contact with the mounting wall 18.

[0036] The manifold 30 comprises a recess 32 for receiving a part of the burner seal 28. Said recess is shaped such that delimits the position of the burner seal 28 in radial direction and along the longitudinal axis AL. As is explained more in detail in figure 2 The manifold 30 is fastened to the outer surface 24 of the mounting wall 18 by fastening means 44, in this embodiment by threaded rods 41. The burner 12 is fastened to the manifold 30 by fastening means 34. In the mounted state, a radial outer part of installation section 16 is arranged inside the burner seal recess 29 and thus along the longitudinal axis AL in contact with the burner seal 28. A radial inner part of the installation section 16 is in contact with the outer surface 24 and the burner seal 28 along the longitudinal axis AL. Thus, the burner seal 28 seals the combustion chamber 14 against the mounting wall 18. By tightening the screws, the manifold 30 is pressed against the burner seal 28 which exerts a certain pressure on the burner seal 28 ad installation section 16. As a result, a friction force between the outer surface 24 and the installation section 16 and the burner seal 28 is generated by which the combustion device10 is fastened to the mounting wall 18.

[0037] The hydrogen gas boiler 11 is further provided with an insulation blanket 36 that is arranged on the inner surface 26.. The insulation blanket 36 can be pre-assembled on the burner deck 13. By this arrangement, the transport of heat through the mounting wall 18 is reduced. The thermal stress acting on the burner seal 28 and the fastening means 34 is reduced, thereby increasing their lifetime.

[0038] Figure 2 shows the combustion device 10 according to the present invention by a perspective exploded view. The burner seal 28 is attached on the installation section 16 of the burner 12. Further, the burner seal 28 is provided with a radially extending portion 38 that is approximately ear- or omega-shaped. However, the shape of the radially extending portion 38 may be freely chosen. The recess 32 of the manifold 30 comprise a non shown cut-out through which the radially extending portion 38 can run in the mounted state. Due to the omega-shape, an undercut is formed such that the radially extending portion 38 is positioned relative to the manifold 30 when introduced into the cut-out 40.

[0039] The manifold 30 is directly connected with the mounting wall 18 by means of several fastening means. Each of the fastening means comprises a threaded rod 41 that is mounted on the outer surface 24 of the mounting wall 18. The manifold 30 is equipped with mounting holes 42 through which the threaded rods 41 penetrate in the mounted state. The manifold 30 is fastened to the mounting wall 18 by nuts 44 that are screwed on the threaded rods 41.

[0040] The burner 12 is attached to the manifold 30 by further fastening means. Each of the further fastening means comprises a further screw 34 that protrudes through a hole 39 arranged in the installation section 16 of the burner 12. The further screw 34 is inserted into a non shown hole of the manifold 30.

[0041] Figure 3 shows a part of the hydrogen gas boiler 11 from along a direction indicated by the arrow D in Figure 2. From fig. 3 it is evident that that the radially extending portion 38 radially protrudes from the manifold 30.Reference list

[0042] 10combustion device 11combustion appliance 12burner 13burner deck 14combustion chamber 16installation section 18mounting wall 20burner door 22through hole 24outer surface 26inner surface 28burner seal 29burner seal recess 30manifold 31hydrogen gas boiler housing 32recess 33volume reducer 34further screws 36insulation blanket 38radially extending portions 39hole 41threaded rod 42mounting hole ALlongitudinal axis Darrow

Claims

1. Combustion device (10) for a hydrogen gas boiler (11) configured for the combustion of a fuel gas which comprises at least 20 mol-% of hydrogen, comprising - a mounting wall (18) comprising an outer surface (24) and an inner surface (26), the inner surface (26) facing a combustion chamber (14) of the hydrogen gas boiler (11), - a through hole (22) formed by the mounting wall (18), - a manifold (30) for introducing a gas mixture into the combustion chamber (14) via the through hole (22) and mountable on the mounting wall (18), and - a burner seal (28) for sealing the manifold (30) against the mounting wall (18), wherein the burner seal (28) is arranged on the outer surface (24) of the mounting wall (18), wherein the combustion device (10) comprises a burner (12) which comprises a burner deck (13), the burner deck (13) being insertable into the through hole (22) and configured to protrude into the combustion chamber (14), in particular the burner seal (28) sealing the burner deck (13) against the mounting wall (18).

2. Combustion device (10) according to claim 1, wherein the burner (12) comprises an installation section (16) protruding radially outwards, the installation section (16) is facing or contacting the outer surface (24) when the burner (12) is fastened to the mounting wall (18) or to the manifold (30).

3. Combustion device (10) according to claim 2, wherein a. the installation section (16) is either contacting the burner seal (28) and the outer surface (24) or the burner seal (28) and the manifold (30) when the burner (12) is fastened to the mounting wall (18) and / or b. the burner seal (28) is in contact with the manifold (30) and the outer surface (24).

4. Combustion device (10) according to one of the preceding claims, wherein the manifold (30) has a recess (32) for receiving the burner seal (28).

5. Combustion device (10) according to one of the preceding claims, wherein the burner seal (28) has at least one radially extending portion (38) that radially protrude the manifold (30) when the manifold (30) is fastened to the mounting wall (18).

6. Combustion device (10) according to one of the preceding claims, wherein the burner seal (28) is made of chloroprene rubber (CR), polyethylene terephthalate (PET), poly-chlorotrifluoroethylene (PCTFE), fluorine rubber (FKM), polytetrafluoroethylene (PTFE), acrylonitrile rubber (NBR), polyamide (PA) or styrene-butadiene rubber (SBR).

7. Combustion device (10) according to one of the preceding claims, wherein the mounting wall (18) forms a burner door (20), the outer surface (24) being located on the burner door (20).

8. Combustion device (10) according to one of the preceding claims, wherein an insulation blanket (36) is arranged on the inner surface (26).

9. Hydrogen gas boiler (11) comprising a combustion device (10) according to one of the preceding claims and a hydrogen gas boiler housing (31), the hydrogen gas boiler housing (31) enclosing a combustion chamber (14) in which the burner (12) is at least partially arranged.

10. Hydrogen gas boiler (11) according to claim 9, wherein the hydrogen gas boiler (11) comprises a volume reducer (33) that is arranged inside the burner (12).

11. Hydrogen gas boiler (11) according to one of the claims 9 or 10, the hydrogen gas boiler (11) being a modulating hydrogen gas boiler (11) adaptable to heat demands.

12. Hydrogen gas boiler (11) according to one of the claims 9 to 11, wherein the hydrogen gas boiler (11) is a heat and / or hot water appliance.

13. Hydrogen gas boiler (11) according to one of the claims 9 to 12, wherein the hydrogen gas boiler (11) is configured to be integrated in a building management system.

14. Use of a combustion device (10) according to one of the claims 1 to 8 for retrofitting a natural gas boiler to a hydrogen gas boiler (11) configured to combust fuel gas comprising at least 20 mol% hydrogen, in particular at least 30 mol % hydrogen.