Heating device and use of a flame stabilizing device

Abstract

The invention relates to a heating device (10) which is designed to combust a combustion mixture comprising a fuel gas with a hydrogen content of at least 80 percent and combustion air. The combustion mixture is fed to a burner arrangement (1) through a mixture channel (7) by means of a conveying device (6) and can exit through a burner outlet element (4) into a combustion chamber (3) and combust. In the combustion chamber (3), a flame stabilizing device (5) arranged downstream of the burner outlet element (4) as viewed in a flow direction (15) is designed and arranged such that it extends in the immediate vicinity of or within a region of developing flame tips (20) of the flame region (16). The heating device (10) enables operation with particularly good flame stability and with little or no combustion noise.

Description

[0001] The invention relates to a heating device designed for the combustion of a hydrogen-containing fuel gas and a use of a device for flame stabilization.

[0002] Hydrogen combustion in heating devices is becoming more of a focus for the general public, especially for domestic heating devices for heating and / or hot water production.

[0003] The combustion of hydrogen differs significantly from the combustion of fossil fuel gases. Due, among other things, to the high flame speed of hydrogen, flashbacks can occur more frequently, damaging the heater. In addition to heater failure and the associated repair costs, the damage can also result in unburned fuel gas escaping into the environment, posing a significant safety risk. Damage to heaters as a result of flashbacks has frequently been observed in components such as a fan, a gas valve, or other components made of plastic.

[0004] To prevent flashbacks, flame arresters are known from the prior art, for example, which are intended to prevent the flame from spreading into the burner. Such a flame arrester is proposed, for example, in EP 4 160 092 A1. Flame arresters must often withstand multiple flashbacks over their lifetime without compromising functionality, and the flow resistance should not change significantly. These high demands on the effectiveness and service life of flame arresters are disadvantageously difficult to meet, or only with considerable effort. A heater with a flame arrester is also shown in EP 3 974 719 A1.

[0005] US 2019 / 027 7492 A1 describes a combustion system for industrial applications with a flame-holding device that can advantageously reduce pollutant emissions during combustion, particularly emissions of nitrogen oxides and carbon monoxide. This document cannot contribute to solving the problem at hand.

[0006] In addition, the combustion of hydrogen can produce disturbing noises. This could be caused by flame instability in hydrogen flames that occurs in certain operating situations.

[0007] The object of the invention is therefore to at least partially alleviate or solve the problems described with reference to the prior art. In particular, a heater with a burner arrangement is to be provided that effectively prevents the occurrence of flashbacks and is durable. Furthermore, it is desirable that existing heaters can be easily retrofitted with the invention and, in particular, that it requires only minor technical modifications.

[0008] These objects are achieved by the features of the independent patent claims. Further advantageous embodiments of the solution proposed here are specified in the independent patent claims. It is pointed out that the features listed in the dependent patent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. Furthermore, the features specified in the patent claims are further specified and explained in the description, with further preferred embodiments of the invention being presented.

[0009] This is achieved by a heating device configured to burn a combustion mixture of a fuel gas and combustion air, with the fuel gas containing at least 80 percent, in particular at least 90 percent, or even at least 95 percent, of hydrogen. In particular, the heating device can be configured to burn (largely) pure hydrogen as the fuel gas.

[0010] The heater is designed to combust a combustion mixture of this fuel gas and combustion air, which is fed by means of a conveying device through a mixture channel of a burner assembly, exits through a burner outlet element into a combustion chamber, and is combusted there. A flame stabilization device is provided in the combustion chamber, namely downstream of a flame region of the flame forming above the burner outlet element in the combustion chamber. This device is designed and arranged such that developing flame tips of the flame occur in the immediate (adjacent) vicinity of or within the flame stabilization device.

[0011] The heater can be used to supply a building with heat and / or hot water and can be installed either wall-mounted or floor-standing. In particular, the heater can provide a heat output of up to 50 kilowatts.

[0012] The heater can draw in a mass flow of combustion air via an air supply by means of a conveying device, to which a mass flow of combustion gas corresponding to a predetermined combustion air ratio, also known as lambda or air ratio, is added. The resulting combustion mixture can be fed to the burner assembly via a mixture duct, flowing into the burner cavity of the burner assembly and then exiting through the burner outlet element into the combustion chamber, where it is combusted. For this purpose, the heater can comprise an ignition device to ignite the combustion mixture at the burner outlet element. The combustion products can then be fed to a building's exhaust system via an exhaust duct of the heater.

[0013] To control the fuel gas mass flow, the heater can have a gas valve, which can usually include a gas safety valve and a gas control valve. The gas control valve can in particular be a stepper motor valve that can set a defined fuel gas mass flow. Alternatively, the gas control valve can also deliver a fuel gas mass flow according to a transmitted control pressure. The control pressure can be recorded in a Venturi device and can be a measure of the delivered combustion air mass flow. This design is also referred to as a pneumatic gas-air connection. The safety valve is intended to prevent the escape of unburned hydrogen and is released, for example, during a heater start-up process only after the delivery device has started up to a starting power suitable for the start-up process. The aforementioned components can all be parts of the heater itself.

[0014] In particular, the heater can adjust the burner output to meet demand, a process also known as "modulation." When a change in heat demand is detected, for example, taking into account the flow and return temperatures of a heating circuit connected to the heater, a control unit of the heater can adjust the output of the heater's fan and thus the combustion air mass flow to the heat demand. At the same time, a control system adjusts the fuel gas mass flow to the changing combustion air mass flow. To prevent flashbacks in low power ranges, the combustion air ratio is often adjusted, particularly by increasing the proportion of combustion air. The associated increase in flow velocity (with the same heater output) and reduction in flame speed can reduce the risk of flashbacks.Nevertheless, during a modulation process of the heater there is an increased risk of flashback or combustion noise, which can be reduced by the measures proposed here.

[0015] Thus, different flame zones form at different modulation points. In particular, the flame height can vary, and thus the distance of the flame tips of the flame zone from the burner outlet element—or, in other words, the height of the flame zone—can vary. The flame tips refer to parts of the flame zone with the greatest distance from the burner outlet element. For example, the flame tips can refer to a zone with a distance of 50 percent to 100 percent relative to the total distance of the flame zone from the burner outlet element.

[0016] The burner assembly can comprise at least one burner cavity and a burner outlet element through which the combustion mixture can exit into a combustion chamber for combustion. The burner cavity can also have a burner hood, which often contains an inlet for the combustion mixture. In a cylindrical burner, the burner hood often consists of a burner door, which also defines the combustion chamber. In a flat burner or a burner with a flat burner outlet element, the burner hood can separate the burner cavity from the surroundings.

[0017] The burner outlet element can have a cylindrical or, in particular, a flat shape. The burner outlet element comprises a plurality of openings through which the combustion mixture can flow. A burner outlet element is often also referred to as a perforated plate. During normal operation of the heater, the combustion mixture passes through the burner outlet element and then burns above the burner outlet element in the combustion chamber. A flame region forms downstream of the burner outlet element, as seen in the direction of flow. The part of the flame region furthest away from the burner outlet element marks the area in which the flame tips form.

[0018] The design of the burner outlet element requires a pressure drop, which is set during development and is therefore known or can be easily determined.

[0019] The combustion chamber may comprise one or more heat exchangers that can transfer heat generated during combustion to a heat transfer medium circulating in a heating circuit or to domestic water. The heater may, in particular, be a condensing heater, also known as a condensing boiler, in which the exhaust gas is cooled to a temperature that allows the condensation heat of the water vapor contained in the exhaust gas to be utilized. For example, a primary heat exchanger may be arranged at least partially in or on a wall of the combustion chamber, thus enabling the transfer of heat from the exhaust gas stream as well as the thermal radiation from the flame to a heat transfer fluid.

[0020] The heater is designed to burn a fuel gas with a (pure) hydrogen content of at least 80 percent. In particular, the heater can be designed to burn a fuel gas with a content of at least 90 or 95 percent, or even largely pure hydrogen.

[0021] The flame stabilization device can be a three-dimensional structure designed to be permeable to combustion gases. Within the scope of the invention, it was discovered that flame instabilities at the flame tips, also known as flame vibration, can contribute significantly to noise generation during combustion as well as to the flame stability of the entire flame region. This applies particularly to hydrogen combustion. The flame stabilization device proposed here, arranged in the immediate vicinity of or in a region of developing flame tips in the flame region, can advantageously stabilize flame formation during hydrogen combustion and inhibit noise generation.The term "immediate proximity" here specifically means that the flame stabilization device can be arranged downstream of the area of developing flame peaks in a flow direction of the heater. In particular, the flame stabilization device will be arranged and aligned as equidistant as possible from a surface of the burner outlet element. The thickness of the flame stabilization device in the flow direction can be selected such that the desired, above-specified, position of the flame stabilization device relative to occurring flame peaks is maintained throughout the entire modulation range of the heater. The distance between the flame stabilization device and the surface of the burner outlet element should be in a range of 40 millimeters to 60 millimeters.In particular, the distance between the flame stabilization device and the burner outlet element should not be less than 40 millimeters in order to avoid the occurrence of flashbacks.

[0022] The flame stabilization device can locally increase flow resistance in the area of the flame tips or in their immediate vicinity and thus does not have to cover the entire flow cross-section available for flow through the combustion chamber. To this end, the flame stabilization device should be positioned such that all flame tips that occur form in or in the immediate vicinity of the flame stabilization device. Therefore, the flame stabilization device should cover the entire area of developing flames, which can largely correspond to the area of the openings of the burner outlet element. Furthermore, the flame stabilization device can reduce the volume within the combustion chamber or within a heat exchanger that defines the combustion chamber.

[0023] The flame stabilizing device can comprise or consist of a fiber material, a lattice structure, a (3D) fabric, or a mesh. The flame stabilizing device can thus comprise fibers or elements that are regularly or irregularly spaced to form a three-dimensional structure. This could, for example, be cuboid-shaped. Such a flexible and elastically deformable flame stabilizing device can advantageously be introduced into a combustion chamber particularly easily and can permanently fix itself there due to its inherent elasticity. According to one embodiment, the flame stabilizing device could be folded before being introduced into the combustion chamber. Alternatively, holding elements can be provided in the combustion chamber to fix the flame stabilizing device in a predetermined position.

[0024] Alternatively or additionally, the flame stabilization device can be designed as a largely solid, three-dimensional structure with regular or irregular recesses, thus forming a gas-permeable, porous, or sponge-like structure. A flame stabilization device as a solid, three-dimensional structure can be shaped to fit the burner outlet element or its surface, for example, curved or as the outer surface of a circular cylinder. The flame stabilization device can be fixed in the combustion chamber in any desired manner, whereby any movement of the flame stabilization device due to operation of the heater should be prevented. For example, the flame stabilization device can be wedged, clamped, or fastened in the combustion chamber using fasteners.

[0025] The flame stabilization device and its material meet high requirements for resistance to environmental influences. Within the combustion chamber during hydrogen combustion, this particularly applies to high temperatures, typically in the range of 300 degrees Celsius to 1000 degrees Celsius, high humidity, and acid exposure associated with the resulting condensate. Suitable materials can be, for example, metallic or ceramic materials, a mixture containing at least one of these, or other refractory materials.

[0026] According to one embodiment, the flame stabilization device can extend from a distance of 40 to 60 millimeters from the burner outlet element to a distance of 100 to 200 millimeters from the burner outlet element. The specific size and shape of the flame stabilization device depends on a variety of factors, for example, the shape of the burner and combustion chamber and the burner's power, and can be easily determined by a specialist for a specific heating device in laboratory tests.

[0027] According to a further aspect, the use of a device for flame stabilization and for reducing combustion noise of a heater is proposed, arranged in a combustion chamber downstream of a burner outlet element in a flow direction. The flame stabilization device is designed and arranged such that it is located in the immediate vicinity of or within a region of developing flame tips in a flame region. The heater is designed in particular for the combustion of hydrogen or a mixture containing at least 80 percent hydrogen.

[0028] The details, features, and configurations discussed in connection with the heater may also occur in a use proposed here, and vice versa. In this respect, the features relating to the heater may also be used to characterize the use, and vice versa.

[0029] This therefore provides a heater and a use of a flame stabilization device that at least partially solve the problems described with reference to the prior art. In particular, the heater and its use at least contribute to largely eliminating combustion noise from a hydrogen-powered heater in a particularly simple manner and also increase operational reliability in conjunction with flame stability.

[0030] In addition, the invention is very well suited for retrofitting existing heaters and can often be implemented without any structural changes to the heater.

[0031] 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, and Fig. 2: a combustion chamber of a heating device proposed here.

[0032] Fig. 1 shows, by way of example and schematically, a heater 10. This can comprise a burner arrangement 1 arranged at least partially in a combustion chamber 3. Combustion air can be sucked in from the environment via an air supply 13 in a flow direction 15 by means of a conveying device 6, which is designed here as a fan. The conveying device 6 can have an electric motor as a drive, which can be connected to a speed controller 9, which can regulate a speed of the conveying device 6 by means of a pulse-width modulated (PWM) signal. A gas valve 12 can add fuel gas (here hydrogen) from a fuel gas supply 11 to the sucked-in air mass flow and can comprise a safety valve and a fuel gas control valve for controlling the mass flow of fuel gas to be added. The generated combustion mixture of fuel gas and combustion air can flow via a mixture channel 7 to the burner arrangement 1 and be ignited there by an ignition device.Heat generated during combustion can be transferred by means of a heat exchanger 19, for example, to a heat carrier of a heating circuit.

[0033] The burner assembly 1 comprises a burner hood 2, a burner cavity 23, to which the combustion mixture is supplied from the mixture channel 7 and exits via a burner outlet element 4 into the combustion chamber 3 and burns to form a flame region 16. The burner outlet element 4 of the burner assembly 1 can be as in Fig. 1 shown, have a cylindrical shape, which can be attached with a base surface to a burner door as a burner hood 2 in such a way that combustion mixture can flow from the mixture channel 7 into the burner hood 2 and thus the burner cavity 23. The combustion products can be discharged to the outside after combustion via an exhaust gas channel 18 arranged in the heater 10 and an exhaust gas system 17 in the flow direction 15. In the area of forming flame tips 20 of the flame region 16, a flame stabilization device 5 can be arranged, which is designed and shaped in such a way that largely all flame tips 20 of the flame region 16 (in all occurring operating situations or modulation points) form within or in the immediate vicinity of the flame stabilization device 5.

[0034] The heater 10 shown here is configured for the combustion of hydrogen. Furthermore, the heater 10 can have a (device for) flame monitoring 14, which can be configured, for example, as an electrode for measuring ionization current. Alternatively or additionally, another sensor, e.g., a thermal, optical, acoustic, or chemical sensor, can be provided to fulfill the function of flame monitoring 14. The use of a sensor for UV (ultraviolet) radiation emitted by the flame has proven particularly suitable for flame monitoring 14 of a flame region 16 of hydrogen combustion.

[0035] A control and regulation device 8 can be configured to regulate the heater 10. For this purpose, it can be electrically connected, for example, to the speed control 9, the conveyor device 6, the gas valve 12, and the flame monitor 14.

[0036] Fig. 2shows in detail and schematically a burner arrangement 1 equipped with a largely flat burner outlet element 4. Combustion mixture can enter the burner hood 2 and thus the burner cavity 23 in the flow direction 15, and after penetrating the burner outlet element 4, form a flame region 16 with flame tips 20. The combustion chamber 2 can be delimited by the heat exchanger 19, to which heat transfer medium is supplied from a return line 21 of a heating circuit and, after heating, is discharged into a flow line 22 of the heating circuit. The combustion products can be evacuated from the combustion chamber 3 via a combustion product discharge line 24 in the flow direction 15 and fed to the exhaust gas duct 18.

[0037] The flame stabilization device 5 can also be designed to be largely flat or planar, or even curved, in the case of a flat burner outlet element 4, in order to be positioned in the immediate vicinity of or within the area of developing flame peaks 20. The flame stabilization device 5 can have a thickness 25 that is adapted to the modulation range of the heater 10 such that the flame peaks 20 of all modulation points occur in the immediate vicinity of or within the flame stabilization device 5. List of reference symbols

[0038] 1Burner arrangement 2Burner hood 3Combustion chamber 4Burner outlet element 5Flame stabilization device 6Feeding device 7Mixture channel 8Regulating and control unit 9Speed control 10Heater 11Fuel gas supply 12Gas valve 13Air supply 14Flame monitoring 15Flow direction 16Flame area 17Exhaust system 18Exhaust channel 19Heat exchanger 20Flame tip area 21Return 22Flow 23Burner cavity 24Expulsion of combustion products 25Thick flame stabilization device

Claims

1. Heating device (10) designed to burn a combustion mixture of a fuel gas with a hydrogen content of at least 80 percent and combustion air, which mixture is fed to a burner arrangement (1) by means of a conveying device (6) through a mixture channel (7), exits through a burner outlet element (4) into a combustion chamber (3) and is burned, wherein a flame stabilizing device (5) is provided in the combustion chamber (3) and is arranged downstream of the burner outlet element (4) as seen in a flow direction (15), which device is designed and arranged in such a way that it extends in the immediate vicinity of or within a region of forming flame tips (20) of a flame region (16).

2. Heating device (10) according to one of the preceding claims, wherein the flame stabilizing device (5) is aligned parallel to the burner outlet element (4) and perpendicular to a flow direction (15).

3. Heating device (10) according to one of the preceding claims, wherein the device for flame stabilization has a thickness (25) in the flow direction (15) which is selected such that the region of forming flame tips (20) for the entire modulation range of the heating device (10) is formed largely within or in the immediate vicinity of the device for flame stabilization (5).

4. Heating device (10) according to one of the preceding claims, wherein the device for flame stabilization (5) is designed and arranged such that the entire area of forming flame tips (20) of the flame region (16) in the entire modulation range of the heating device (10) is formed within or in the immediate vicinity of the device for flame stabilization (5).

5. Heating device (10) according to one of the preceding claims, wherein the flame stabilizing device (5) comprises at least one element from the following group: a grid, a fabric, a porous body, a honeycomb body.

6. Heating device (10) according to one of the preceding claims, wherein the device for flame stabilization (5) is introduced in one or more layers in the combustion chamber (3) of the heating device (10) and is permanently fixed there due to its own elasticity.

7. Heating device (10) according to one of the preceding claims, wherein the heating device (10) forms a pneumatic gas-air combination.

8. Use of a device for flame stabilization (5) arranged in the combustion chamber (3) downstream of a burner outlet element (4) as seen in a flow direction (15), which device is designed and arranged such that it is located in the immediate vicinity of or within a region of forming flame tips (20) of a flame region (16), for flame stabilization and / or for reducing combustion noise.

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