Burner for a heating device and heating device

Abstract

The invention relates to a burner (3) for a heating appliance (1) for the combustion of a fuel gas, in particular hydrogen. The burner (3) can have a combustion zone (15) with several outlet areas (16) for the fuel gas, each with a plurality of outlet openings (17), wherein: - the cumulative area of ​​the outlet openings (17) of an outlet area (16) is more than 3% and less than 12.5% ​​of the cumulative area of ​​all outlet openings (17) of the combustion zone (15), and - the distance from an outlet opening (17) to the nearest outlet opening (17) of the same outlet area (16) is less than 1 mm.

Description

[0001] The invention relates to a burner for a heating device and a heating device that can be operated with hydrogen and / or a hydrogen-containing fuel gas.

[0002] Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and great efforts are being made to upgrade new or existing heating systems for operation with it. This applies not only to large systems, but also to wall-mounted water heating systems and, in general, to heating systems for heating buildings and / or providing hot water.

[0003] Burners for use in such heaters are widely known. Such a burner is often mounted on a burner door, which is installed in a combustion chamber with a surrounding heat exchanger. The burner can comprise a burner body with at least one perforated area from which a premixed, combustible fuel gas-air mixture (combustion mixture) can emerge. The combustion mixture flows through the burner door into the burner and exits through the perforated area into the combustion chamber, where it burns. The burner can have a cylindrical or (hemispherical) shape, or be flat.

[0004] Holes (outlet openings) are provided in the perforated area, preferably in such a way that the outflow velocity of the fuel gas-air mixture into the combustion chamber is matched to the respective flame velocity (dependent on the fuel gas). Furthermore, it is important that the flame burns at a certain distance from the surface of a burner body to keep its temperature low. This should be aimed for across the entire modulation range (range of different adjustable power) of the heater. The temperature of the burner body must under no circumstances reach the ignition temperature of the fuel gas-air mixture to prevent backfiring within the burner (flame flashback into an interior space of the burner body).

[0005] Hydrogen combustion differs in several respects from previously used fuel gases. In particular, a hydrogen flame is almost invisible to the human eye (but radiates in the ultraviolet spectral range), emits less heat than flames generated with carbon-based fuels, but burns hotter. The present invention is intended to make heating devices particularly suitable for conversion to operation with pure hydrogen or with fuel gas that consists of more than 50%, in particular more than 97%, hydrogen.

[0006] When designing burner bodies for the combustion of hydrogen or fuel gases containing hydrogen, a higher flame speed compared to fossil fuel gases must be taken into account, as this favors the occurrence of flashbacks. To counteract this, the burner can be operated with an increased lambda (combustion air ratio, air number). It is known that the risk of flashback increases with decreasing lambda, i.e., as the combustion air ratio approaches stoichiometric (λ=1). In addition, the flame temperature is higher during hydrogen combustion and the distance of the flame to the burner surface is smaller than during the combustion of fossil fuel gases. Thus, several factors can be identified that justify special efforts to prevent flashbacks during hydrogen combustion.

[0007] However, by bringing the lambda closer to the stoichiometric combustion air ratio, the efficiency of combustion and thus of the heater can be increased. Therefore, when operating a heater, especially with at least a portion of hydrogen, a balance must be struck between safe combustion with the lowest possible risk of flashbacks and efficient combustion.

[0008] For this purpose, WO 2021 / 140 036 A1 proposes a burner with a burner surface comprising surface areas with holes and separation areas that space the surface areas with holes from each other, with a cumulative area of ​​the holes being less than 5.0% of the burner surface. The surface areas with holes define reaction zones that prevent the flame from spreading beyond the separation areas. However, the possibility of safe combustion without flashback would be desirable with an even lower lambda than the proposed burner enables.

[0009] WO 2023 / 078949 A1 also describes a burner designed to combust a hydrogen-containing fuel gas, which can be part of a heating device. It proposes that the burner surface material have a thermal conductivity coefficient of at least 80 W / (mK) and a modulus of elasticity of 150 GPa or less. However, a burner that enables safe combustion without flashback would be desirable, particularly with an even lower lambda than the burner described.

[0010] The object of the present invention is to at least partially solve the problems described with reference to the prior art and in particular to provide a burner and a heater with a low flame flashback limit, which can be operated with low lambda and thus with high combustion efficiency.

[0011] A burner for a heating device is configured to burn a fuel gas. The burner has a combustion zone with several outflow areas for the fuel gas, each with a plurality of outflow openings, wherein the cumulative area of ​​the outlet openings of an outlet area is more than 3% of the cumulative area of ​​all outlet openings of the combustion zone, and the distance from one outlet opening to the nearest outlet opening of the same outlet area does not exceed 1 millimetre [mm].

[0012] The burner can be used for various heating devices, i.e., devices for heating and / or hot water supply. For example, a wall-mounted heater for heating and hot water supply is mentioned. Combustion air or a gas with an oxygen content can be supplied to the heater for combustion. The burner can be used independently of the exhaust system, particularly in single- and multiple-configuration exhaust systems. The burner can be used as a standalone burner or as part of an arrangement with a burner function.

[0013] The heater can be a partially or fully premixed heater. For this purpose, a conveying device of the heater can draw in a mass flow of combustion air via a combustion air supply and convey it towards a combustion chamber in which the burner is arranged. The conveying device can in particular be a fan. A mass flow of fuel gas can be added to the drawn-in mass flow of combustion air according to a predetermined combustion air ratio (lambda), and the resulting combustion mixture can be fed to the burner via a mixture channel. Various methods for mixture formation are known; in particular, the heater can form a pneumatic or electronic gas-air connection. In a pneumatic gas-air connection, a mass flow of fuel gas corresponding to a control pressure in a throttle point (venturi) of the combustion air supply is added.An electronic gas-air control system measures the supplied fuel gas mass flow directly or indirectly, for example, via the speed of the conveyor system, and controls the fuel gas mass flow to be added. For this purpose, the heaters are equipped with a gas valve that can meter the fuel gas mass flow.

[0014] The heater can operate at different operating points within a modulation or power range, allowing it to be operated at different power levels. To increase efficiency and service life, modern heaters often feature a wide modulation range, for example, from 2.5 kilowatts [kW] to 21 kW or a modulation rate (ratio of maximum to minimum power) of 1 to 5. A wide modulation range places high demands on the burner due to the widely varying flame configurations and properties.

[0015] The heater and burner can be configured to burn hydrogen or a fuel gas containing a hydrogen content. Hydrogen as a fuel is advantageous due to the possibility of sustainable production. The hydrogen content in the fuel gas can, in particular, be at least 50 percent [%], at least 75%, or, in particular, at least 90%.

[0016] The burner can be made of any suitable material. Stainless steel is often used due to its good temperature and corrosion resistance and its easy availability.

[0017] The geometric shape of the burner can be any shape. Cylindrical or flat burners are particularly well known. A burner cavity can be connected to the mixture channel of the heater, and incoming fuel gas can be directed from the burner cavity into the combustion chamber via outlet openings arranged in a combustion zone, where it burns.

[0018] The combustion zone can be understood as a portion of the burner surface designed to supply the combustion mixture for combustion. For this purpose, the combustion zone has outlet openings (holes). The area of ​​the combustion zone can be considered the area defined by the outlet openings, i.e., the smallest contiguous area in which all outlet openings are located. The combustion zone can form a monolithic unit with the burner body or be detachably connected to it, for example, by means of a screw connection.

[0019] The combustion zone can have a shape that is at least largely flat (plane) or even three-dimensional. A three-dimensional shape can consist of a raised or recessed portion relative to the burner body or another shape, such as a bulge.

[0020] The combustion zone and the burner body can have the same material thickness and be within a known range. Different material thicknesses for the combustion zone and the burner body are also conceivable, especially if the combustion zone is detachably connected to the burner body.

[0021] The combustion zone comprises several outflow areas for the fuel gas, in which the outflow openings are arranged. It is proposed that the cumulative area of ​​the outflow openings in an outflow area be more than 3 percent [%] and less than 12.5 percent of the cumulative area of ​​all outflow openings in the combustion zone. It was determined that the proposed area ratio can achieve improved cooling and heat dissipation from the burner.

[0022] According to one embodiment, the minimum distance between two outflow areas can be at least 3 millimeters [mm] and not more than 100 millimeters.

[0023] In addition, the distance between one outlet opening and the next in the same outlet area is less than 1 millimeter [mm]. However, this distance should ensure the mechanical stability of the outlet openings.

[0024] The outlet openings can have any shape, including circular, rectangular, square, or elongated holes. It is also possible to combine different shapes within one outlet area.

[0025] The arrangement of the outlet openings within an outlet area is also arbitrary. A geometric shape of the outlet area, as the outer contour of all outlet openings in the outlet area, can be, for example, rectangular, square, approximately circular, oval, or even the shape of a rhombus or polygon. The orientation of non-rotationally symmetrical receiving areas relative to the orientation of the combustion zone can also be varied. Generally, the arrangement of the outlet openings within an outlet area should be at least approximately evenly distributed.

[0026] According to one embodiment, the cumulative area of ​​all outflow openings of an outflow area can be less than 90 square millimeters [mm 2< ], preferably less than 30 mm 2<.

[0027] According to one embodiment, the respective individual area of ​​all outflow openings can be less than 2.5 mm 2< , in particular less than 0.5 mm 2<.

[0028] According to one embodiment, the combustion zone can have at least 8 outflow areas.

[0029] According to one embodiment, each outflow area can have at least 4 outflow openings.

[0030] According to one embodiment, the burner can have a flame arrester. This can be arranged between the burner surface and the mixture channel and can be made of a known material. A flame arrester can further minimize the risk of flashback.

[0031] According to a further aspect, a heating device is also proposed, comprising a burner as presented here. The heating device can be configured, in particular, for the combustion of hydrogen or a hydrogen-containing fuel gas.

[0032] Thus, a burner for a heater and a heater are proposed here that at least partially solve the problems described with reference to the prior art. In particular, the burner and the heater enable robust operation of the heater while simultaneously increasing operational efficiency. In particular, a burner with a reduced flame flashback limit can be proposed, enabling safe operation with a lower lambda compared to known burners.

[0033] It was found that the formation of larger outflow areas with an increased number of outflow openings can significantly reduce the temperature of the combustion zone and the combustion body, and consequently lower the flashback limit.

[0034] Another advantage is that the burner can easily be retrofitted to existing heating devices.

[0035] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures, and in particular the proportions shown, are only schematic. They show: Fig. 1: a heating device proposed here, Fig. 2: an outflow area of ​​a burner proposed here, Fig. 3: a design of a combustion zone, Fig. 4: an alternative design of a combustion zone, Fig. 5: courses of flame flashback limits of burners with different combustion zones, and Fig. 6 a)-c): arrangements of outflow openings within an outflow area.

[0036] Fig. 1shows, by way of example and schematically, a heating device 1 proposed here. This can draw in combustion air through a conveying device 2 via a combustion air supply 4 and add a fuel gas from a gas supply 13, for example hydrogen, to the sucked-in mass flow of combustion air via a gas valve 5. The combustion mixture of fuel gas and combustion air can now be fed via a mixture channel 11 to a burner 3 arranged in a combustion chamber 8. The burner 3 can be fastened to a burner door 6 and connected to the mixture channel 11 such that combustion mixture can flow into a burner cavity surrounded by a burner body 14. The combustion mixture can then exit via a combustion zone 15 of the burner 3 and be burned.

[0037] The combustion products can be fed from the combustion chamber 8 to an exhaust line (exhaust system) 10 via an exhaust pipe 9. A flame monitor 12, for example a UV sensor, can also be arranged on the burner door 6. The UV sensor can be arranged outside the combustion chamber 8, protected from the high temperatures of the burner 3. The heater 1 can also have a control and regulating device 7. The heater 1 can be configured, in particular, to burn hydrogen as a fuel. For this purpose, the burner 3 can have a burner body 14 suitable for burning hydrogen, with a combustion zone 15.

[0038] Fig. 2also shows, by way of example and schematically, an outflow region 16 of the combustion zone 15. This can comprise 46 outflow openings 17, which can have a circular shape and form a geometric shape 20. The outflow openings 17 can have a diameter 18 and be arranged at a distance 19 from the nearest outflow opening 17 of less than 1 mm.

[0039] Fig. 3 also shows, by way of example and schematically, a combustion zone 15 with 28 outflow areas 16 according to the Fig. 2 The outflow areas 16 can be arranged symmetrically with respect to a first axis 26 and a second axis 27 of the combustion zone 15. The combustion zone 15 can comprise a flange 28 for attachment to a burner body 14 with holes 21 for a screw connection to the burner body 14. For example, the diameter 18 can be 0.8 mm and the distance 19 can be 0.4 mm.

[0040] Fig. 4shows, by way of example and schematically, an alternative embodiment of a combustion zone 15. This also comprises 28 outflow regions 16 arranged symmetrically with respect to a first axis 26 and a second axis 27 of the combustion zone 15. The outflow openings 17 of the receiving regions 16 are arranged here in an approximately circular geometric shape 20.

[0041] Fig. 5 shows, as an example, four curves 22, 23, 24, 25 of a flame back limit of different burners 3 with combustion zones 15. The flame back limit is the minimum possible heat output without the occurrence of a flame back as a function of the lambda. The following table shows the properties of the corresponding combustion zones 15 of the burners 3 assigned to the curves 22, 23, 24, 25: Course 22 23 24 25 combustion zone flat flat arched arched Total area of ​​all outlet openings 400 mm 2 400 mm 2 520 mm 2< 520 mm 2< Diameter of outlet opening 0.6 mm 0.6 mm 0.6 mm 0.6 mm Geometric shape outflow area rhombus square hexagon square Outlet openings per outlet area 12 49 various 7 / 19 / 37 64 Number of outflow areas 118 29 100 29 Area of ​​one outflow area / total area of ​​all outflow openings 0,8% 3,4% 1% 3,4% Flashback limit at lambda = 1.3 5.4 kW 3.5 kW 10 kW 6.2 kW

[0042] Thus, the combustion zones 15 for the curves 22 and 23 have the same total area of ​​all outlet openings 17. By arranging the outlet openings 17 according to the present invention, the burner 3 according to curve 23 can have a significantly lower flashback limit of 3.5 kW at lambda = 1.3 compared to the burner 3 according to curve 22, which has a flashback limit of 5.4 kW at the same lambda = 1.3. Thus, a heater 1 equipped with the burner 3 and a combustion zone 15 according to curve 23 can enable more efficient combustion by lowering the lambda.

[0043] Analogously, the combustion zones 15 according to curves 24 and 25 have the same sum of the areas of all outflow openings 17. The combustion zones 15 according to curves 24 and 25 are curved outwards, for example with a largely circular (hemispherical) curvature with a diameter in the region of the extension of the combustion zone 15 in the direction of the second axis 27. The burner 3 according to curve 24 has outflow regions 16 with a geometric shape 20 of a hexagon with 7, 19, or 37 outflow openings 17. The burner 3 according to curve 25 can, due to an arrangement of the outflow openings 17 according to the present invention, reduce the flameback limit to 6.2 kW compared to 10 kW of the burner 3 according to curve 24.

[0044] The invention thus enables a lowering of the flameback limit of a combustion zone 15 of a burner 3 during the combustion of hydrogen, and thus enables a burner 3 according to the present invention to be operated at a lower lambda. This can increase combustion efficiency and reduce hydrogen consumption. List of reference symbols

[0045] 1 Heater 2 Conveyor system 3 Burner 4 Combustion air supply 5 Gas valve 6 Burner door 7 Control unit 8 Combustion chamber 9 Exhaust pipe 10 Exhaust system 11 Mixture duct 12 Flame monitoring 13 Gas supply 14 Burner body 15 Combustion zone 16 Outflow area 17 Outflow opening 18 Diameter 19 Distance 20 Geometric shape 21 Hole screw connection 22 First run 23 Second run 24 Third run 25 Fourth run 26 First axis 27 Second axis 28 Flange

Claims

1. Burner (3) for a heating device (1), designed to burn a fuel gas, comprising a combustion zone (15) with a plurality of outflow areas (16) for the fuel gas, each with a plurality of outflow openings (17), wherein - the cumulative area of the outflow openings (17) of an outflow area (16) is more than 3% and less than 12.5% of the cumulative area of all outflow openings (17) of the combustion zone (15), and - the distance from one outflow opening (17) to the nearest outflow opening (17) of the same outflow area (16) is less than 1 mm.

2. Burner (3) according to claim 1, wherein the combustion zone (15) corresponds to the smallest contiguous area in which all the outflow openings (17) are arranged.

3. Burner (3) according to one of the preceding claims, wherein the minimum distance between two outflow areas (16) is at least 3 mm.

4. Burner (3) according to one of the preceding claims, wherein the cumulative area of all outflow openings (17) of an outflow area (16) is less than 30 mm 2 is.

5. Burner (3) according to one of the preceding claims, wherein the area of an outflow opening (17) is less than 0.5 mm 2 is.

6. Burner (3) according to one of the preceding claims, wherein the combustion zone (15) has at least 8 outflow areas (16).

7. Burner (3) according to one of the preceding claims, wherein each outflow region (16) has at least 4 outflow openings (17).

8. Burner (3) according to one of the preceding claims, wherein the outflow openings (17) have a circular, rectangular, square shape or the shape of an elongated hole 9. Burner (3) according to one of the preceding claims, wherein the combustion zone (15) has a flat or three-dimensional shape.

10. Burner (3) according to one of the preceding claims, wherein the combustion zone (15) is detachably connected to the burner body (14).

11. Burner (3) according to one of the preceding claims, wherein the burner (3) has a flame arrester.

12. Heating device (1) comprising a burner (3) according to one of the preceding claims.

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