HEATER

Description

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

[0002] Hydrogen combustion in heating appliances is increasingly coming into focus for the general public, especially for domestic heating appliances for heating and / or hot water preparation.

[0003] The combustion of hydrogen differs significantly from the combustion of fossil fuels. For example, due to the high flame speed of hydrogen, flashbacks are more common and can damage the heating appliance. Besides causing the appliance to fail and incurring repair costs, unburned fuel gas can escape into the environment as a result of the damage, posing a considerable safety risk. Damage to heating appliances caused by flashbacks has frequently been observed in components such as the fan, gas valve, or other parts made of plastic.

[0004] EP 6 987 66 B1 concerns gas burners, particularly for domestic boilers, that offer improved noise reduction and more stable flame formation. The design aims to minimize pressure fluctuations and optimize the efficiency of the gas-air mixture. The gas burner comprises a cylindrical body with inner and outer perforated walls, forming a lower chamber to generate a flame. The gap between the walls is 0.5 mm to 1.2 mm, with the perforations in the inner wall having a larger individual aperture area than those in the outer wall.

[0005] US Patent 5,062,788 A discloses a burner arrangement for the combustion of a combustible mixture of air and liquid, comprising a pairing of inner and outer plates defined by openings in the plates through which the mixture flows. It describes a burner arrangement that provides uniform heat distribution over longer distances and offers high combustion efficiency with minimal excess air. The specific arrangement of the inner and outer plates ensures that the flame does not flow backward through the openings in the plates, thus increasing safety and reducing the risk of flame flashback.

[0006] To prevent flame flashbacks, flame arresters are known from the prior art, for example, which are designed to prevent flame propagation into the burner. Such a flame arrester is proposed, for example, in EP 4 160 092 A1, which discloses the features of the preamble of claim 1. Flame arresters must frequently withstand several flame flashbacks during their service life without any impairment of functionality, and the flow resistance should not change significantly. These high requirements for the effectiveness and service life of flame arresters are difficult or only achievable with considerable effort.

[0007] Furthermore, the combustion of hydrogen can produce disruptive noise. This could be due to flame instability in the hydrogen flames under certain operating conditions.

[0008] It is therefore an object of the invention to at least partially alleviate or solve the problems described with reference to the prior art. In particular, a heating appliance with a burner arrangement is to be provided that effectively prevents the occurrence of flame flashbacks and is durable. Furthermore, it is desirable that existing heating appliances can be easily retrofitted with the invention and, in particular, require only minor technical modifications.

[0009] These problems are solved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the independent claims. It should be noted that the features listed in the dependent claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0010] This is achieved by a heating appliance designed to combust a mixture of 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 heating appliance via a conveying device through a mixture channel. The burner assembly comprises at least the following: The invention comprises a burner cavity, a burner outlet element through which the combustion mixture can exit from the burner cavity into a combustion chamber, and a throttling device arranged in the burner cavity, which extends over the entire flow cross-section available for the flowing combustion mixture. According to the invention, the throttling device 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.

[0011] The heating unit can supply a building with heating and / or hot water and can be wall-mounted or freestanding. In particular, the heating unit can provide a heat output of up to 50 kilowatts.

[0012] The heating appliance can draw in a mass flow of combustion air via an air supply using a conveying device. A mass flow of fuel gas, corresponding to a predetermined combustion air ratio (also known as lambda or air-fuel ratio), is added to this mixture. The resulting combustion mixture can be fed to the burner assembly via a mixture channel, flowing into the burner cavity and then exiting the combustion chamber through the burner outlet element, where it is combusted. The heating appliance may include an ignition device to ignite the combustion mixture at the burner outlet element. The combustion products can then be discharged via an exhaust duct from the heating appliance into the building's exhaust system.In a heating appliance, the delivery system and the mixture channel are often located downstream of a mixing point in one direction of flow, where the mass flow of combustion air and the mass flow of fuel gas are combined. The heating appliance may have a gas valve to control the mass flow of fuel gas, which typically includes a gas safety valve and a gas control valve. The gas control valve can be, in particular, a stepper motor valve capable of setting a defined mass flow of fuel gas. Alternatively, the gas control valve can also deliver a mass flow of fuel gas according to a transmitted control pressure. This control pressure can be measured in a Venturi device and serve as a measure of the delivered mass flow of combustion air. This configuration is also known as a pneumatic gas-air system.The safety valve is designed to prevent the escape of unburned hydrogen and, for example, during the start-up process of the heating unit, is only released after the pumping system has been activated to a starting power level suitable for the start-up process. The aforementioned components can be any part of the heating unit itself.

[0013] The heating appliance can adjust its burner output to the demand, a process also known as "modulation." Upon detecting a change in heat demand, for example, by considering the flow and return temperatures of a heating circuit connected to the appliance, a control unit can adjust the fan output and thus the combustion air flow rate to the heat demand. Simultaneously, a control system adjusts the hydrogen flow rate to the changing combustion air flow rate. To prevent flame flashbacks at low output levels, the combustion air ratio is often adjusted, particularly by increasing the proportion of combustion air. The resulting increase in flow velocity (at the same appliance output) and reduction in flame speed can mitigate the risk of flame flashbacks.Nevertheless, during a modulation process of the heating device there is an increased risk of flame flashback, which can be reduced by the measures proposed here.

[0014] The burner assembly comprises at least a burner cavity and a burner outlet element through which the combustion mixture can exit into a combustion chamber for combustion. The burner cavity may also have a burner hood, which often contains an inlet for the combustion mixture. In a cylindrical burner, the burner hood is frequently a burner door that simultaneously delimits 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 surrounding environment.

[0015] The burner outlet element can have a cylindrical or, in particular, a flat shape. It comprises a multitude 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 heating appliance, the combustion mixture passes through the burner outlet element and then burns in the combustion chamber above it.

[0016] The design of the burner outlet element results in a pressure drop, which is set during development and is therefore known or easily determined. One aspect of the invention is to adjust the pressure drop of the throttling device as a function of the pressure drop of the burner outlet element, thereby significantly reducing the occurrence of flame flashbacks.

[0017] The combustion chamber can include one or more heat exchangers that transfer the heat generated during combustion to a heat transfer medium circulating in a heating circuit or to domestic hot water. The heating appliance can be, in particular, 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.

[0018] The heating appliance is designed to burn a fuel gas containing at least 80 percent (pure) hydrogen. In particular, the heating appliance can be configured to burn a fuel gas containing at least 90 or 95 percent hydrogen, or even virtually pure hydrogen.

[0019] The throttling device is a device or component arrangement that 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 discovered that by a predetermined, specifically set pressure drop DA D in the flow direction of the heating device, upstream of the burner outlet element, the probability of a flame flashback can be significantly reduced. Advantageously, this eliminates the need for a flame arrestor, which is associated with high costs and potential shortcomings regarding durability. The throttling device can be a planar structure exhibiting a defined flow resistance. For example, the throttling device can consist of a grid or grid structure, a fabric, a perforated sheet, a honeycomb structure, or a foam body.It must be designed with at least one of these components. The throttling device or the at least one protruding component consists in particular of a metallic material.

[0020] According to an (alternative) embodiment, the throttling device can be arranged in a mixture channel of the heating device of the conveying device, namely, viewed in a flow direction of the mixture, downstream of the conveying device and upstream of the combustion chamber.

[0021] The throttling device causes a pressure drop (DA D) of the combustion mixture flowing through it of at least 25 percent of the pressure drop (DA B) of the burner outlet element. In particular, the throttling device can generate a pressure drop (DA D) of at least 30 percent, and especially 33 percent or even 40 percent, of the pressure drop (DA B) 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 throttling device. With such a pressure drop (DA D) set, a significant reduction in the occurrence of flame flashbacks has been observed. Furthermore, with a pressure drop (DA D) set to the aforementioned range, combustion noise can be reduced to a minimum or eliminated entirely.

[0022] For this purpose, the pressure drop between the throttling device and the burner outlet element can be determined or measured in a test setup where ambient air flows through at a mass flow rate of 40 liters per minute under ambient conditions. Ambient conditions are defined as a standard atmospheric pressure of 101.325 kilopascals and a temperature of 20 degrees Celsius.

[0023] Furthermore, the throttle device can have a shape that improves the mixing of the combustion mixture as it flows through it. To achieve this, the throttle device can force the combustion mixture to flow through a flow path inside the throttle device, which features constrictions and / or baffles, for example, to create a convoluted flow path. The resulting homogenization of the combustion mixture can significantly improve flame stability and thus help to prevent flame flashbacks and combustion noise.

[0024] According to one embodiment, the throttling device can be arranged directly adjacent to the burner outlet element. In particular, the throttling device can be aligned and arranged parallel to the burner outlet element. The distance between the throttling device and the burner outlet element can be minimized while maintaining a technically necessary distance. This technically necessary distance can be achieved by preventing contact between the throttling device and the burner outlet element, which could result in noise. Advantageously, in this embodiment, only a small amount of combustion mixture can accumulate in the space between the throttling device and the burner outlet element, thereby reducing the probability and intensity of flame flashback as well as the occurrence of combustion noise.

[0025] With a flat burner outlet element, the throttle device can advantageously be attached using the same fastening means as the burner outlet element. If necessary, 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 noise generation due to contact between the burner outlet element and the throttle device.

[0026] According to one embodiment, the distance between the burner outlet element and the throttling device can be less than 50, 15, 10, or 5 millimeters. A particularly effective reduction in burner noise was observed with a distance between the burner outlet element and the throttling device in the range of 5 to 15 millimeters. Flame flashback can also be prevented, especially with a small distance between the burner outlet element and the throttling device.

[0027] According to one embodiment, the throttling device can be constructed in multiple layers. For example, two or three layers of the throttling device can be arranged adjacent to the burner outlet element. The individual layers of the throttling device can be separated by intermediate layers that provide a sealing effect and / or absorb vibrations.

[0028] The invention and its technical context 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 shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations described in the figures and combine them with other components and findings from the present description. It should be emphasized that the figures, and especially the depicted dimensions, 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 the operation of a heating device proposed here.

[0029] Fig. 1 Figure 10 shows an exemplary and schematic representation of a heating device 10. This device can include a burner assembly 1, which is at least partially located in a combustion chamber 22. Combustion air can be drawn 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 blower. The blower 14 can have an electric motor as its drive, which can be connected to a speed control 24 that can regulate the 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 drawn-in air mass flow at a mixing point 19 and includes a safety valve and a fuel gas control valve for controlling the mass flow of fuel gas to be added.The combustion mixture of fuel gas and combustion air produced can flow via a mixture channel 20 to the burner assembly 1 and be ignited there by an ignition device. Heat generated during combustion can be transferred, for example, to a heat transfer medium in a heating circuit via a heat exchanger 21.

[0030] 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 at least partially arranged in the burner hood 2. The burner outlet element 4 of the burner assembly 1 can be configured as shown in Fig. 1 The burner hood 2 is shown to have a cylindrical shape and can be attached to a burner door with a base surface such that the combustion mixture from the mixture channel 20 can flow through the inlet 3 into the burner hood 2 and thus into the burner cavity 25. After combustion, the combustion products can be discharged to the outside via an exhaust gas channel 18 arranged in the heating unit 10 and an exhaust system 17 in the flow direction 15.

[0031] The heating device 10 shown here is designed for the combustion of hydrogen. The heating device 10 can also include a flame monitoring device 26, which, for example, can be configured as an electrode for measuring ionization current. Alternatively or additionally, another sensor, such as a thermal, optical, acoustic, or chemical sensor, can be provided to perform the flame monitoring function. In particular, the use of a sensor for UV (ultraviolet) radiation emitted by the flame has proven suitable for flame monitoring 26 of a flame 16 during hydrogen combustion.

[0032] A control and regulating unit 23 can be configured to control the heating device 10. For this purpose, it can be electrically connected, for example, to the speed control 24, the conveying device 14, the gas valve 12, and the flame monitoring device 26.

[0033] Fig. 2 Figure 1 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. The inlet 3 is partially, the burner outlet element 4 is fully, and the throttle device 5 is fully. The burner outlet element 4 of the burner arrangement 1 has a flat / planar shape. The combustion mixture is introduced into the burner arrangement 1 in the flow direction via the inlet 3, in particular by means of the conveying device 14. There, the combustion mixture then encounters the (flat / planar) throttle device 5, through which it flows towards the subsequently arranged burner outlet element 4. The combustion mixture also flows through the burner outlet element 4 before it is finally combusted on the opposite side in a flame area 16.This represents a normal or desired combustion situation.

[0034] Fig. 3 Figure 1 shows another illustration of a burner arrangement 1 of the heating appliance 10, in which the structure and arrangement of the throttling device 5 can be seen. Also shown in Fig. 3 The burner arrangement 1 shown comprises a flat burner outlet element 4, which, together with the throttle device 5, is arranged in or on the burner hood 2. The throttle device 5 and the burner outlet element 4 are arranged parallel and directly adjacent to each other. In this example, the throttle device comprises a first layer 6 and a second layer 7, which are also positioned parallel and directly adjacent to each other. 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, respectively, can be arranged in a manner that allows for the creation of a seal between the first layer 6 and the second layer 7.The throttling device 5 and the burner outlet element 4, as well as the sealing elements 8, are fastened with the same fastening means 9, which in this example are designed as screws. Therefore, the invention is also very well suited for retrofitting existing burner assemblies 1.

[0035] Fig. 4 Figure 27 shows an example of the relationship between the pressure drop DAB of the burner outlet element 4 and the pressure drop DAD of the throttle device 5, given in Pascals [Pa], for a combustion mixture flow rate of 40 liters per minute [l / min]. It was found that in a range where the pressure drop DAD of the throttle device 5 is at least one-third of the pressure drop DAB of the burner outlet element 4, no noise generation occurs. Fig. 4represented by an arrow. When the pressure drop DA D of the throttling device 5 was less than one third of the pressure drop DA B of the burner outlet element 4, an increasing noise development 28, also represented by an arrow, could be observed. Reference symbol list

[0036] 1 Burner assembly 2 Burner hood 3 Combustion mixture inlet 4 Burner outlet element 5 Throttle device 6 First position throttle device 7 Second position throttle device 8 Sealing element 9 Fastening means 10 Heater 11 Fuel gas supply 12 Gas valve 13 Air supply 14 Conveyor device 15 Flow direction 16 Flame area 17 Exhaust system 18 Exhaust duct 19 Mixing point 20 Mixture channel 21 Heat exchanger 22 Combustion chamber 23 Control and monitoring unit 24 Speed ​​control 25 Burner cavity 26 Flame monitoring 27 Progression 28 Increasing noise level 29 No noise level DA B Pressure drop burner outlet element DA D Pressure drop throttle device

Claims

1. Heating appliance (10) designed to combust a combustion mixture consisting of a fuel gas with a hydrogen content of at least 80 per cent and combustion air, which is fed by means of a conveyor device (14) through a mixture channel (20) of a burner arrangement (1), and the burner assembly (1) of the heating appliance (10) comprises at least the following: - a burner cavity (25), - a burner outlet element (4) through which 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, characterised in that the throttle device (5) causes a pressure drop DAD in a range of 25 per cent to 40 per cent of the pressure drop DAB of the burner outlet element (4).

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

3. Heating appliance (10) according to claim 1, wherein the throttling device (5) is arranged immediately adjacent to the burner outlet element (4).

4. Heating appliance 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 plate, a honeycomb structure.

5. Heating appliance (10) according to one of the preceding claims, wherein the throttle device (5) is constructed in multiple layers.

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