Heater

Abstract

A heating device (10) is proposed, designed for the combustion of a combustion mixture of a fuel gas and combustion air, which is supplied to a burner arrangement (1) via a conveying device (14) through a mixture channel (20) and which has a hydrogen content of at least 80 percent. The burner arrangement (1) comprises at least one burner cavity (25), a burner outlet element (4) through which the combustion mixture can exit from the burner cavity (25) into a combustion chamber (22), and a throttling device (5) arranged in the burner cavity (25) which extends over the entire flow cross-section available for the combustion mixture and causes a pressure drop DAD in the range of 25 percent to 40 percent of the pressure drop DAB of the burner outlet element (4).

Description

[0001] The invention relates to a heating device designed to burn a fuel gas containing hydrogen.

[0002] Hydrogen combustion in heating appliances is becoming more of a focus for the general public, especially for domestic heating appliances 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, which can damage 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 and 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 designed to prevent the spread of flames into the burner. One such 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 also not change significantly. These high demands on the effectiveness and service life of flame arresters are difficult to meet, or only with considerable effort.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] This is achieved by a heater configured to burn a combustion mixture of a fuel gas and combustion air, the fuel gas containing at least 80 percent hydrogen. The combustion mixture can be fed to a burner assembly of the heater by means of a conveying device through a mixture channel. The burner assembly has at least the following: a burner cavity, a burner outlet element through which the combustion mixture can escape from the burner cavity into a combustion chamber, and a throttle device arranged in the burner cavity, which extends over the entire flow cross-section available for the combustion mixture flowing through and causes a pressure drop DA D in a range of 25 percent to 40 percent of the pressure drop DA B of the burner outlet element.

[0009] 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.

[0010] 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 incoming 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.In a heater, the delivery device and the mixture channel are often arranged downstream of a mixing point in the flow direction of the heater, where the mass flow of combustion air and the mass flow of fuel gas are brought together. To control the mass flow of fuel gas, the heater can have a gas valve, which can usually comprise 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 mass flow of fuel gas. Alternatively, the gas control valve can also deliver a mass flow of fuel gas in accordance with a transmitted control pressure. The control pressure can be detected in a Venturi device and can be a measure of the delivered mass flow of combustion air. This design is also referred to as a pneumatic gas-air connection.The safety valve is designed to prevent the escape of unburned hydrogen and is only released during the heater start-up process, for example, after the delivery system has been activated to a starting power level suitable for the start-up process. The aforementioned components can all be parts of the heater itself.

[0011] 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 heater fan output and thus the combustion air mass flow to the heat demand. At the same time, a control system adjusts the hydrogen 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, there is an increased risk of flashback during a modulation process of the heater, which can be reduced by the measures proposed here.

[0012] The burner assembly comprises 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.

[0013] 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.

[0014] The design of the burner outlet element determines a pressure drop, which is set during development and is therefore known or easily determined. One idea of ​​the invention is to adjust the pressure drop of the throttle device as a function of the pressure drop of the burner outlet element, thereby significantly reducing the occurrence of flashbacks.

[0015] The combustion chamber may comprise one or more heat exchangers that can transfer the heat generated during combustion to a heat transfer medium circulating in a heating circuit or even to domestic hot water. The heating device may, in particular, be a condensing heating device, 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.

[0016] 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.

[0017] The throttle device is a device or a component arrangement which causes a defined, predetermined pressure drop in the mass flow of the combustion mixture as it flows through it. Within the scope of the invention, it was recognized that the probability of a flashback occurring can be considerably reduced by a predetermined, specifically adjusted pressure drop DA D in the direction of flow through the heater, upstream of the burner outlet element. Advantageously, this makes it possible to dispense with the use of a flame arrester, which is associated with high costs and possible shortcomings in terms of longevity. The throttle device can be a flat structure which has a defined flow resistance. The throttle device can, for example, consist of a grid or a grid structure, a fabric, a perforated sheet, a honeycomb body, a foam body orbe formed with at least one of these components. The throttle device or the at least one protruding component consists in particular of a metallic material.

[0018] According to an (alternative) embodiment, the throttle device can be arranged in a mixture channel of the heating device of the conveying device, namely downstream of the conveying device and upstream of the combustion chamber, as seen in a flow direction of the mixture.

[0019] The throttle device causes a pressure drop DA D of the flowing combustion mixture of at least 25 percent of the pressure drop DAs of the burner outlet element. In particular, the throttle device can generate a pressure drop DA D of at least 30 percent and in particular 33 percent or even 40 percent of the pressure drop DAs of the burner outlet element. A pressure drop refers to the reduction in pressure when a gas (the combustion mixture) flows through the burner outlet element or the throttle device. With a pressure drop DA D set in this way, a significant reduction in the occurrence of flashbacks has been observed. In addition, with a pressure drop DA D set to the above-mentioned range, combustion noise can be reduced to a minimum or even eliminated.

[0020] For this purpose, the pressure drop between the throttle device and the burner outlet element can be determined or measured in a test setup in which ambient air flows through the device at a mass flow rate of 40 liters per minute under ambient conditions. Ambient conditions are typically a normal air pressure of 101.325 kilopascals and a temperature of 20 degrees Celsius.

[0021] In addition, the throttle device can have a shape that improves the mixing of the combustion mixture as it flows through the throttle device. To this end, the throttle device can force the combustion mixture to flow through a flow path inside the throttle device that has constrictions and / or baffles, for example, to form a winding flow path. The resulting homogenization of the combustion mixture can significantly contribute to improving flame stability and thus help prevent flashbacks and the occurrence of combustion noise.

[0022] According to one embodiment, the throttle device can be arranged directly adjacent to the burner outlet element. In particular, the throttle device can be aligned and arranged parallel to the burner outlet element. The distance between the throttle device and the burner outlet element can be minimized, whereby a technically necessary distance can be maintained. A technically necessary distance can be avoided by avoiding contact between the throttle device and the burner outlet element, which could be accompanied by noise generation. Advantageously, with this embodiment, only a small amount of combustion mixture can accumulate in the space between the throttle device and the burner outlet element, whereby the probability of occurrence and the intensity of a flashback as well as the occurrence of combustion noise can be reduced.

[0023] With a flat burner outlet element, the throttle device can advantageously be attached using the same fastening means as the burner outlet element. Optionally, at least one spacer and / or at least one sealing element can be arranged between the burner outlet element and the throttle device to prevent the escape of combustion mixture and the generation of noise due to contact between the burner outlet element and the throttle device.

[0024] According to one embodiment, the distance between the burner outlet element and the throttle device can be less than 50, 15, 10, or 5 millimeters. A particularly effective reduction in burner noise has been observed with a distance between the burner outlet element and the throttle device in a range of 5 millimeters to 15 millimeters. Flashback can also be avoided, especially with a short distance between the burner outlet element and the throttle device.

[0025] According to one embodiment, the throttle device can be constructed in multiple layers. For this purpose, for example, two or three layers of the throttle device can be arranged adjacent to the burner outlet element. The individual layers of the throttle device can be separated by intermediate layers that provide a sealing effect and / or absorb vibrations.

[0026] 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: a burner arrangement of a heating device proposed here, Fig. 3: another burner arrangement, and Fig. 4: parameter curves that can occur during operation of a heating device proposed here.

[0027] 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 22. 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 14, which is designed here as a fan. The fan 14 can have an electric motor as a drive, which can be connected to a speed controller 24, which can regulate a speed of the conveying device 14 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 at a mixing point 19 and can comprise a safety valve and a fuel gas control valve for controlling the mass flow of fuel gas to be added.The resulting combustion mixture of fuel gas and combustion air can flow to the burner assembly 1 via a mixture channel 20, where it can be ignited by an ignition device. Heat generated during combustion can be transferred, for example, to a heat transfer medium of a heating circuit by means of a heat exchanger 21.

[0028] The burner assembly 1 comprises a burner hood 2, a burner cavity 25, an inlet 3 for the combustion mixture from the mixture channel 20, a burner outlet element 4 and a throttle device 5, wherein the inlet 3, the burner plate 4, the burner cavity 25 and the throttle device 5 are arranged at least partially in the burner hood 2. 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 such that combustion mixture can flow from the mixture channel 20 through the inlet 3 into the burner hood 2 and thus the burner cavity 25. After combustion, the combustion products can be discharged to the outside in the flow direction 15 via an exhaust channel 18 arranged in the heater 10 and an exhaust system 17.

[0029] The heater 10 shown here is configured for the combustion of hydrogen. Furthermore, the heater 10 can have a flame monitoring device 26, which can be embodied here, 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 flame monitoring function. The use of a sensor for UV (ultraviolet) radiation emitted by the flame has proven particularly suitable for flame monitoring 26 of a hydrogen combustion flame 16.

[0030] A control and regulation device 23 can be configured to regulate the heater 10. For this purpose, it can be electrically connected, for example, to the speed control 24, the conveyor device 14, the gas valve 12, and the flame monitor 26.

[0031] Fig. 2 shows in detail and schematically a burner arrangement 1, which has a burner hood 2, an inlet 3 for the combustion mixture from the mixture channel 20, a burner outlet element 4 and a throttle device 5, wherein the inlet 3 is partially arranged, the burner outlet element 4 (completely) and the throttle device 5 (completely) are arranged in the burner hood 2. The burner outlet element 4 of the burner arrangement 1 has a flat / plane shape. Via the inlet 3, in particular by means of the conveying device 14, the combustion mixture is introduced into the burner arrangement 1 in the flow direction. There, the combustion mixture then encounters the (flat / plane) throttle device 5, through which it flows to the downstream burner outlet element 4. The combustion mixture also flows through the burner outlet element 4 before it is finally burned on the opposite side in a flame region 16.This represents a normal or desired combustion situation.

[0032] Fig. 3 shows a further illustration of a burner assembly 1 of the heater 10, in which the structure and arrangement of the throttle device 5 can be seen. Fig. 3 The burner arrangement 1 shown comprises a flat burner outlet element 4, which is arranged together with the throttle device 5 in or on the burner hood 2. The throttle device 5 and the burner outlet element 4 are arranged parallel and directly adjacent to one another. In the example, the throttle device comprises a first layer 6 and a second layer 7, which are also positioned parallel and directly adjacent to one another. To ensure the tightness of the burner arrangement 1 and to prevent vibrations and noise, a sealing element 8 is arranged between the burner hood 2 and the first layer 6 of the throttle device 5, between the first layer 6 and the second layer 7 of the throttle device 5, and between the second layer 7 and the burner outlet element 4. The sealing element 8 can also ensure a minimum distance between the adjacent components. Advantageously, the first layer 6 and the second layer 7 orThe throttle device 5 and the burner outlet element 4, as well as the sealing elements 8, are attached with the same fastening means 9, which in the example are designed as screws. In this respect, the invention is also very well suited for retrofitting to existing burner assemblies 1.

[0033] Fig. 4 shows, by way of example, a curve 27 of the ratio of the pressure drop DAs of the burner outlet element 4 and the pressure drop DA D of the throttle device 5, specified in Pascal [Pa] at a flow rate of combustion mixture of 40 liters per minute [l / min]. It was found that in a range in which the pressure drop DA D of the throttle device 5 is at least one-third of the pressure drop DAs of the burner outlet element 4, no noise development 29 occurs, in which Fig. 4represented by an arrow. At a pressure drop DA D of the throttle device 5 of less than one-third of the pressure drop DAs of the burner outlet element 4, an increasing noise development 28, also represented by an arrow, was observed. List of reference symbols

[0034] 1Burner arrangement 2Burner hood 3Combustion mixture inlet 4Burner outlet element 5Throttle device 6First layer of throttle device 7Second layer of throttle device 8Sealing element 9Fasteners 10Heater 11Fuel gas supply 12Gas valve 13Air supply 14Feed device 15Flow direction 16Flame area 17Exhaust system 18Exhaust duct 19Mixing point 20Mixture duct 21Heat exchanger 22Combustion chamber 23Regulating and control unit 24Speed ​​control 25Burner cavity 26Flame monitoring 27Progression 28Increasing noise 29No noise DA B Pressure drop burner outlet element DA D Pressure drop throttle device

Claims

1. Heating device (10) designed for the combustion of a combustion mixture of a fuel gas with a hydrogen content of at least 80 percent and combustion air, which is supplied to a burner arrangement (1) through a mixture channel (20) by means of a conveying device (14), and the burner arrangement (1) of the heating device (10) comprises at least the following: - a burner cavity (25), - a burner outlet element (4) through which the combustion mixture can exit from the burner cavity (25) into a combustion chamber (22), - a throttle device (5) arranged in the burner cavity (25), which extends over the entire flow cross-section available for the combustion mixture flowing through and has a pressure drop DA D in a range of 25 percent to 40 percent of the pressure drop DA B of the burner outlet element (4).

2. Heating device (10) according to one of the preceding claims, wherein the burner outlet element (4) is flat.

3. Heating device (10) according to one of the preceding claims, wherein the throttle device (5) is arranged immediately adjacent to the burner outlet element (4).

4. Heating device according to one of the preceding claims, wherein the throttle device (5) comprises at least one element from the following group: a grid, a fabric, a foam, a perforated sheet, a honeycomb body.

5. Heating device (10) according to one of the preceding claims, wherein the throttle device (5) has a multi-layer construction.

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

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