Method for operating a heating device, heating device and computer program product

Abstract

A method is proposed for operating a heating appliance (1) designed for the combustion of a fuel gas containing at least 80 percent hydrogen and comprising a burner (3) arranged in a combustion chamber (8), to which a combustion mixture of the fuel gas and combustion air with a combustion air ratio A predetermined depending on the heat output Q of the heating appliance (1) is supplied, exits through a combustion zone (15) into the combustion chamber (8) and combusts, and the combustion air ratio A to be set is stored as a characteristic curve depending on the heat output Q of the heating appliance (1) in a combustion control of the heating appliance (1), comprising at least the following steps: a) Determining a limit combustion air ratio AG(Q) (17) depending on the heat output Q of the heating appliance (1),b) Comparing the combustion air ratio A according to the stored characteristic curve with the limit combustion air ratio AG(Q) (17) determined in step a), and c) operating the heating appliance (1) with the limit combustion air ratio AG(Q) (17) if, for the current heat output Q, the combustion air ratio A specified according to the characteristic curve is less than the limit combustion air ratio AG(Q) (17), and operating the heating appliance (1) with the combustion air ratio λ specified according to the characteristic curve if, for the current heat output Q, the combustion air ratio A specified according to the characteristic curve is greater than the limit combustion air ratio AG(Q) (17).

Description

[0001] The invention relates to a method for operating a heating device, a heating device, and a computer program product. The heating device can be operated with hydrogen and / or a hydrogen-containing fuel gas, in particular with a fuel gas containing at least 80 percent hydrogen.

[0002] Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and significant efforts are being made to adapt new and existing heating appliances for its operation. This applies not only to large systems but also to wall-mounted units for heating water and, more generally, to heating appliances for building heating and / or hot water supply.

[0003] Burners for use in such heating appliances 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 exit. The combustion mixture flows through the burner door into the burner and exits through the perforated area into the combustion chamber, where it combusts. The burner can be cylindrical, (semi-)spherical, or flat.

[0004] The perforated area contains holes (outlet openings), preferably positioned so that the outflow velocity of the fuel-air mixture into the combustion chamber is matched to the respective flame speed (which depends on the fuel-air mixture). Furthermore, it is important that the flame burns at a certain distance from the surface of the burner body to keep its temperature low. This should be achieved across the entire modulation range (range of adjustable power) of the heating appliance. The temperature of the burner body must never reach the ignition temperature of the fuel-air mixture to prevent reignition within the burner (flame flashback into an interior space of the burner body).

[0005] Hydrogen differs from previously used fuel gases in several ways during combustion. In particular, a hydrogen flame is almost invisible to the human eye (but emits radiation in the ultraviolet spectral range), radiates less heat than flames produced with carbon-based fuels, but burns hotter and has a significantly higher flame speed compared to fossil fuel gases.

[0006] When designing burner bodies for the combustion of hydrogen or hydrogen-containing fuel gases, a higher flame velocity compared to fossil fuel gases must be taken into account, as this promotes the occurrence of flashbacks. To counteract this, the burner can be operated with an increased lambda (air-fuel ratio). A method for operating a burner with a hydrogen-containing fuel gas to prevent flashbacks is described, for example, in WO 2020 / 182 902 A1.

[0007] WO 2020 / 197 391 A1 also describes a method for controlling the combustion of a gas burner, designed to prevent both flame flashbacks and excessively high burner body temperatures that could contribute to flame flashbacks. It proposes determining a target air-fuel ratio based on an input variable, which could be related to the heat demand or the fuel or combustion air flow rate, and incorporating this ratio into the control system. US 2022 / 0 120 440 A1 describes a similar method for operating a burner with a hydrogen-containing fuel gas, where, according to this method, the air-fuel ratio can be adjusted, for example, based on a measured burner temperature.

[0008] In addition to the risk of flame flashback, cracks and / or fractures in the burner surface have been observed in hydrogen-powered burners. The occurrence of these cracks or fractures is independent of flame flashbacks and significantly reduces the service life of a burner fueled by hydrogen. Furthermore, repairs require substantial effort and expense. Moreover, such a crack in the burner surface can increase the burner's flow cross-section, thereby reducing the outflow velocity and increasing the likelihood of flame flashback.

[0009] The problem described above, namely the occurrence of cracks and fractures in the burner surface, has not yet been solved in the prior art.

[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 propose a method for operating a heating appliance powered by hydrogen as fuel gas, a heating appliance, and a computer program that effectively prevent the formation of cracks and fractures in the burner surface. Furthermore, the invention should not increase the complexity of a heating appliance, or at least not significantly, and should, in particular, also be applicable to heating appliances that have been converted to burn hydrogen.

[0011] These problems are solved by the features of the independent claim. Further advantageous embodiments of the solution proposed here are specified in the dependent claims. It should be noted that the features listed in the 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.

[0012] This involves a method for operating a heating appliance designed to combust a fuel gas containing at least 80 percent hydrogen and comprising a burner with a burner body arranged in a combustion chamber. A combustion mixture of the fuel gas and combustion air with a combustion air ratio predetermined depending on the heat output of the heating appliance is supplied to the burner. The combustion mixture exits through the burner body into the combustion chamber and combusts there. The predetermined or adjustable combustion air ratio is stored as a characteristic curve as a function of the heat output Q of the heating appliance in a combustion control system of the heating appliance, and is specifically retrievable. The method further comprises at least the following steps: a) Determining a limit combustion air ratio lG (Q) as a function of the heat output of the heating appliance, b) Comparison of the specified combustion air ratio l according to the stored characteristic curve with the limit combustion air ratio determined in step a). l G (Q), and c) operating the heating appliance (A) with the limiting combustion air ratio l G (Q) if, for the current heat output of the heating appliance, the combustion air ratio specified according to the characteristic curve is less than the limiting combustion air ratio l G (Q) is, and (B)

[0013] Operating the heating appliance with the combustion air ratio specified according to the characteristic curve, if for the current heat output the combustion air ratio specified according to the characteristic curve is greater than (or equal to) the limit combustion air ratio l G (Q) is.

[0014] Steps a), b), and c) are performed at least once in the specified order during regular operation. Specifically, step a) can be performed only once, while steps b) and c) can be repeated continuously during operation of the heating appliance, particularly during each modulation cycle, i.e., with every change in the operating point or heat output of the heating appliance. This procedure serves to extend the service life of a heating appliance's burner, especially the burner body, and to prevent cracks and fractures of the burner body. The procedure can be fully automated, for example, by a control unit of the heating appliance.

[0015] The heating appliance, burner, and burner body can be configured for the combustion of hydrogen or a fuel gas containing hydrogen. Hydrogen as a fuel is advantageous due to the possibility of sustainable production. The hydrogen content in the fuel gas can be at least 80%, at least 90%, at least 95%, or even 98% to 100%.

[0016] The heating appliance has a conveying device that can draw in a mass flow of combustion air. A mass flow of fuel gas, corresponding to a predetermined combustion air ratio, is added to the combustion air via a gas valve. The resulting combustion mixture is fed to the burner located in the combustion chamber of the heating appliance, exits through a burner body, and combusts. For this purpose, the combustion mixture can be ignited by an ignition device when the heating appliance is started. The heating appliance may include a flame sensor that provides a flame signal, which is used by the combustion control system of the heating appliance. At least one heat exchanger can be used around or on the combustion chamber to transfer the heat generated during combustion to a heat transfer medium, such as heating water.In particular, the heating appliance may be a condensing boiler that cools the combustion reaction products below the dew point of water, thus making the condensation heat of the combustion exhaust gases usable.

[0017] The flame sensor can be a temperature sensor for detecting the flame temperature, a UV sensor (i.e., a sensor for detecting ultraviolet radiation emitted by the flame), or an ionization sensor (ionization electrode) for detecting the flame's ionization current. However, a disadvantage of hydrogen-powered heating appliances is that only a few charge carriers are released, making ionization current measurement as a reliable flame signal unreliable. Therefore, UV sensors or temperature sensors are frequently used for flame monitoring in heating appliances that use hydrogen as fuel gas.

[0018] Various methods for mixture formation are known; in particular, the heating appliance can form a pneumatic or electronic gas-air mixture. In a pneumatic gas-air mixture, a mass flow of fuel gas is added, corresponding to a control pressure in a throttle point (Venturi) of the combustion air supply. An electronic gas-air mixture detects the supplied mass flow of fuel gas directly or indirectly, for example via the rotational speed of the conveying device, and controls the mass flow of fuel gas to be added. For this purpose, the heating appliances have a gas valve that can meter a mass flow of fuel gas.

[0019] The heating appliance can operate at various points within a modulation or output range, thus operating at different power levels. To increase efficiency and service life, modern heating appliances often feature a wide modulation range, for example, from a minimum heat output Q min of 2.5 kilowatts [kW] to a maximum heat output Q max of 21 kW, or a modulation ratio (ratio of maximum to minimum output) of 1:5. A wide modulation range places high demands on the burner due to the highly variable flame characteristics and properties. An operating point or modulation point can also be understood as the heat output Q of the heating appliance.

[0020] The burner can be made from any suitable material. Stainless steel alloys are frequently used due to their good temperature and corrosion resistance, as well as their availability. These can be ferritic or austenitic stainless steel alloys. Austenitic stainless steel alloys, with their higher aluminum content, have proven advantageous compared to ferritic stainless steel alloys.

[0021] It has been observed that cracks or fractures in the burner body, and particularly in the combustion zone, occur at temperatures above a critical temperature that depends on the burner's properties (material, material thickness, combustion zone area, etc.). For example, this critical temperature range for a burner might be between 400°C and 600°C, and for a burner made of a stainless steel alloy, between 450°C and 500°C. One reason for this is the faster atomic diffusion or oxidation of iron atoms compared to chromium atoms, resulting in the formation of Fe₂O₃. Fe₂O₃ is brittle and promotes cracking in the burner body and combustion zone. Conversely, the formation of Cr₂O₃ can strengthen the burner body and combustion zone by forming a protective layer.It should be noted that operating a burner with a burner body temperature exceeding 600 °C carries a high risk of flame flashback and should therefore be avoided. Conversely, at burner temperatures below the limit, the risk of cracking or fracture is very low. The proposed operation of the heating appliance with a combustion air ratio above the limit is intended to ensure that the burner temperature does not exceed the limit during operation.

[0022] The geometric shape of the burner can be any form. In particular, cylindrical or flat burners are known. A burner cavity can be connected to the mixture channel of the heating device, 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 is combusted. A cylindrical burner can be arranged on a burner door and form the burner cavity within it. A flat burner can be connected to a burner hood, and the burner cavity can be bounded by the burner and the burner hood.

[0023] The burner can be monolithic or comprise a burner outlet element that includes the combustion zone and is connected to the burner body. The combustion zone can be understood as a portion of the burner surface and is designed to supply the combustion mixture. For this purpose, the combustion zone has outlet openings (holes). 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. For burners designed for hydrogen combustion, this connection is subject to increased tightness requirements to prevent bypass flows that could cause a flashback.

[0024] The use of a flat burner with hydrogen as a fuel gas presents challenges. Furthermore, the exhaust openings of the combustion zone in a burner designed for hydrogen combustion must have a smaller flow cross-section than those in burners designed for fossil gases in order to achieve a sufficient exhaust velocity below the flame speed of hydrogen. Due to the necessary small exhaust openings, flat burners with a small thickness (i.e., their thickness in the direction of flow through the burner) are advantageous for the burner manufacturing process and, indeed, are only feasible in practice. Finally, the high stresses occurring in a burner outlet element due to high temperatures can also complicate compliance with the increased tightness requirements for a burner designed for hydrogen combustion.Thus, stresses occurring in the burner outlet element can also affect the connection between the burner outlet element and the burner, weakening it and thereby enabling side flows of the combustion mixture.

[0025] The combustion zone can have a largely flat (planar) or a three-dimensional shape. A three-dimensional shape can consist of a raised or recessed area relative to the burner body, or another form such as a bulge.

[0026] The combustion zone and the burner body can have the same material thickness and be within a known range. However, especially if the combustion zone is detachably connected to the burner body, different material thicknesses for the combustion zone and the burner body are also conceivable.

[0027] The combustion zone can comprise several exhaust gas outlets, in which the exhaust ports are arranged. The exhaust ports can have any shape, in particular circular, rectangular, square, or elongated shapes. It is also possible to combine different shapes within a single exhaust gas outlet.

[0028] The arrangement of the exhaust openings within an exhaust region is also arbitrary. The geometric shape of the exhaust region, defined as the outer contour of all exhaust openings within the exhaust region, can be, for example, rectangular, square, approximately circular, oval, or even rhombus- or polygonal. The orientation of non-rotationally symmetrical intake areas relative to the orientation of the combustion zone can also be varied. Generally, the arrangement of the exhaust openings within an exhaust region should be at least approximately uniformly distributed.

[0029] The characteristic curve for the combustion air ratio to be set can be stored in a memory, for example, in the control unit used for combustion regulation. The characteristic curve can be a known curve for combustion control of a hydrogen-powered heating appliance. The characteristic curve thus specifies a combustion air ratio to be set as a function of the heating appliance's heat output Q. The invention makes it possible to avoid modulation ranges during heating appliance operation in which critical temperatures could occur when applying the characteristic curve, and to achieve this by means of modulation points according to the limiting combustion air ratio. l to replace G (Q), which prevents these critical modulation ranges.

[0030] According to step a) of the procedure, a limiting combustion air ratio is determined. lG (Q), which depends on the heat output of the heating appliance, is set. A deviation below the limiting combustion air ratio l The combustion air ratio (G(Q)) of the heating appliance during operation can cause the burner temperature to rise above the limit temperature (for example, 450 °C or even 475 °C), thus increasing the risk of cracking. Therefore, operating the heating appliance with a combustion air ratio above the limit combustion air ratio can be problematic. l G (Q) thus effectively prevents a weakening of the burner material and therefore the formation of cracks or fractures. The limiting combustion air ratio l G (Q) depends on the heating appliance and, in particular, its modulation range, the shape and material of the burner, and the hydrogen content of the fuel gas. The limiting combustion air ratio lG (Q) can be determined in advance through laboratory tests on a reference heating device. Therefore, step a) can only be performed once or as needed. For automated execution, the limiting combustion air ratio can be used. l G (Q) must be stored in a memory, for example in a process-executing control and monitoring unit, and be retrievable.

[0031] According to step b), the combustion air ratio can be adjusted according to the stored characteristic curve with the limit combustion air ratio determined in step a). l G (Q) is compared. The comparison is made in relation to a current or target heat output Q of the heating device. Step b) can be carried out continuously or permanently, or triggered by a modulation process, i.e., a change / adjustment of the heat output Q of the heating device.

[0032] According to step c), the heating appliance can be operated with the limiting combustion air ratio. l G (Q) occurs when, for the current heat output, the combustion air ratio specified according to the characteristic curve is less than the limiting combustion air ratio. l G (Q) is. Otherwise, or as an alternative, the heating appliance can be operated with the combustion air ratio specified according to the characteristic curve if, for the current heat output, the combustion air ratio specified according to the characteristic curve is greater than (or equal to) the limiting combustion air ratio. l G (Q) is. Step c) thus ensures that the heating appliance always operates with a combustion air ratio greater than the specified limit combustion air ratio. lG (Q) is operated, thus ensuring that burner temperatures exceeding the limit temperature are excluded. Step c) can be performed continuously or permanently, or triggered by a modulation process, i.e., a change / adjustment of the heating unit's heat output Q.

[0033] According to one embodiment, the limit combustion air ratio determined in step a) can l G(Q) can be a piecewise linear function as a function of the heat output Q. The limiting air-fuel ratio can be used for this purpose. l G (Q) through several points P x (Q, l G (Q)) can be specified. In particular, the limiting combustion air ratio can be l G (Q) has fewer than five linear sections, or in particular three or fewer linear sections.

[0034] According to one embodiment, the function of the boundary combustion air ratio can be lG (Q) has two sections, namely a first section and a second section. The first section can be bounded by a first point and a second point, and the second section can be bounded by the second point and a third point. The first and second sections thus border each other directly at the second point. The first point can be defined by a boundary air-fuel ratio. λ G Q = A − B × Qmin Q max This is given at the (pre-known or set) minimum heat output Qmin of the heating device. The parameter A can be set within a range of 1.9. <A<2,2 liegen und der Parameter B in einem Bereich 1,3<B<1,7 liegen. Der zweite Punkt kann bei einer Wärmeleistung Q in einem Bereich von 40 % bis 80 % der (vorbekannten bzw. eingerichteten) maximalen Wärmeleistung Q max des Heizgeräts liegen. Der dritte Punkt kann bei der (vorbekannten bzw. eingerichteten) maximalen Wärmeleistung Q max des Heizgeräts. Weiter kann dann vorgesehen sein, dass im zweiten Abschnitt das Grenzverbrennungsluftverhältnis l G (Q) is constant and in a range of 1< l G <1.2.

[0035] According to one embodiment, the method can be preceded by a step 0), which involves converting the heating appliance from combustion of a fuel gas containing no or less than 20 percent hydrogen to combustion of a fuel gas containing at least 80 percent hydrogen. This step 0) can, for example, include replacing at least one component adapted for hydrogen operation, such as the gas valve, a gas nozzle, a seal, etc. Step 0) can, for example, include updating or replacing the heating appliance software, in particular the combustion air-fuel ratio characteristic curves underlying the combustion control. Therefore, the method can also contribute to the conversion and commissioning of a heating appliance for operation with a fuel gas containing at least 80% hydrogen.

[0036] According to one embodiment, the burner can have a flame arrestor. This can be arranged between the burner surface and the mixture channel and can be made of a known material. A flame arrestor can significantly reduce the risk of a flashback, as it prevents the flame from passing into the mixture channel.

[0037] In addition, a heating appliance is proposed, configured or converted for the combustion of a fuel gas containing at least 80% hydrogen. The heating appliance comprises a conveying device for supplying a mass flow of combustion air, a gas valve for metering the fuel gas to be added, a combustion chamber and a burner arranged in the combustion chamber, as well as a control unit configured to adjust the combustion air-fuel ratio of the heating appliance. The heating appliance may include a control unit configured to carry out a procedure proposed herein. The control unit may include a processor capable of executing instructions from a computer program that effect the execution of a procedure presented herein.The control and regulating device may also have a memory on which a computer program product, which executes a procedure proposed here, and on which procedure-related parameters, such as a characteristic curve or a limit combustion air ratio, are stored. l G (Q), are deposited or are.

[0038] In addition, a computer program product is proposed that causes a heating device proposed here to execute a procedure proposed here.

[0039] The details, features, and advantageous configurations discussed in connection with the process may also occur in the heating device and computer program presented here, and vice versa. In this respect, full reference is made to the explanations provided therein for a more detailed characterization of the features.

[0040] It should be noted as a precaution that the numerical terms used here ("first", "second", etc.) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific configuration described. Where a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory.

[0041] This document proposes a method for operating a heating device, a heating device itself, and a computer program that at least partially solve the problems described with reference to the state of the art. In particular, the method, the heating device, and the computer program enable robust operation of the heating device and, in particular, significantly increase the service life of the burner or burner body.

[0042] Furthermore, the invention can be implemented particularly easily, for example in the form of a software update as part of a conversion of a heating appliance from the use of fossil / natural fuel gases to the use of hydrogen-containing fuel gases with a hydrogen content of at least 80%.

[0043] 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 sequence of a procedure proposed here, Fig. 2: a heating device proposed here, and Fig. 3: parameter curves that can occur when carrying out a procedure proposed here.

[0044] Fig. 1Figure 1 shows, by way of example and schematically, the sequence of a procedure proposed here. The execution of steps a), b), and c), as depicted in blocks 110, 120, and 130, can be carried out at least once in the specified order during a regular procedure. In particular, step a) can be carried out only once. Steps b) and c) can be carried out continuously, repeatedly, or triggered by a modulation process, i.e., a change in the operating point or heat output of the heating device 1. The procedure serves to extend the service life of the burner 3 of the heating device 1 and thus to ensure robust operation of the heating device 1.

[0045] Fig. 2Figure 1 shows an exemplary and schematic representation of a proposed heating appliance 1. This appliance can draw in combustion air via a combustion air supply 4 through a conveying device 2 and add a fuel gas from a gas supply 13, for example hydrogen, to the drawn-in mass flow of combustion air via a gas valve 5. The combustion mixture of fuel gas and combustion air can then be fed via a mixture channel 11 to a burner 3 arranged in a combustion chamber 8. The burner 3 can be attached to a burner door 6 and connected to the mixture channel 11 in such a way that the combustion mixture can flow into a burner cavity surrounded by a burner body 14. Subsequently, the combustion mixture can exit via a combustion zone 15 of the burner 3 and be combusted.

[0046] The combustion products can be fed from the combustion chamber 8 to an exhaust pipe (exhaust system) 10 via an exhaust pipe 9. A flame monitoring device 12, for example a UV sensor, can also be arranged on the burner door 6. The UV sensor can be located outside the combustion chamber 8, protected from the high temperatures of the burner 3. The heating unit 1 can also have a control unit 7. The heating unit 1 can be specifically designed for the combustion of hydrogen as fuel. For this purpose, the burner 3 can have a burner body 14 suitable for hydrogen combustion with a combustion zone 15.

[0047] The control and regulating device is configured to execute a procedure proposed here, i.e., blocks 110, 120 and 130, and may include a memory on which a computer program product 16 proposed here is stored.

[0048] Fig. 3This diagram shows exemplary parameter curves that can occur when carrying out a procedure proposed here. It depicts a diagram showing the combustion air-fuel ratio curve, expressed in kilowatts. l This is shown as a function of the heat output Q of the heating appliance. In addition, the corresponding temperatures of burner 3 and combustion zone 15 for the respective operating points are shown. The heating appliance 1 has a minimum heat output Q min 23 of 5 kW and a maximum heat output Q max 23 of 35 kW, and thus a modulation ratio of 1:7. Furthermore, in Fig. 3 The characteristic curve 25 of the combustion control of the heating device 1 is shown, which can be stored on a memory of the control and regulating unit 7.

[0049] In block 110, a limiting combustion air ratio can be determined according to step a). l G (Q) 17 is determined. The limiting combustion air ratio lG(Q) 17 can be piecewise linear and comprise a first section 18 and a second section 19. The first section 18 can be defined by a first point 20 and a second point 21. The first point 20 can be determined at the minimum heat output Q min 23 by the relationship λ G Q = A − B × Q Q max can be determined. With A=2.05 and B=1.5, the following results: Q = Qmin = 5.25kW a marginal combustion air ratio l G (Q min )=1.825. A second point 21 can be used for a heat output of 70% of Q max = 24.5 kW with l G (0.7 x Q max )=1 is given. The first point 20 and the second point 21 thus define the first section 18 of the limiting combustion air ratio. l G (Q) 17 fixed. The second area 19 can be determined by a constant l G = 1 is specified and extends from the second point 21 to the third point 22 at the maximum heat output Q max 35 kW.

[0050] In block 120, according to step b), the characteristic curve 25 of the combustion control can be used with the limiting combustion air ratio. l G (Q) 17 can be compared.

[0051] In block 130, according to step c), the operation of the heating appliance with the limiting combustion air ratio can be determined as a result of the comparison from step b). l G (Q) as the combustion air ratio to be set by the combustion control, if for the current heat output the combustion air ratio specified according to the characteristic curve is smaller than the limit combustion air ratio l G (Q) is. If, for the current heat output, the combustion air ratio specified according to the characteristic curve is greater than the limiting combustion air ratio l G (Q) is, the heating appliance is operated with a combustion air ratio according to characteristic curve 25, if for the current Heat outputthe combustion air ratio specified according to characteristic curve 25 is greater than the limiting combustion air ratio l G (Q) is. As in Fig. 3 To be recognized, the heating appliance 1 in the present example operates in a range of approximately 5.25 kW < Q < 17 kW with the limiting combustion air ratio. l G (Q) operated.

[0052] By carrying out step c) (Block 130) it can be ensured that the burner 3 of the heating device 1 is not heated to a temperature greater than the limit temperature of 450 °C, thereby effectively preventing the occurrence of cracks or fractures of the burner 3, particularly in the area of ​​the combustion zone 15. Reference symbol list

[0053] 1 Heating unit 2 Conveyor 3 Burner 4 Combustion air supply 5 Gas valve 6 Burner door 7 Control and monitoring unit 8 Combustion chamber 9 Exhaust pipe 10 Exhaust system 11 Mixture channel 12 Flame monitoring 13 Gas supply 14 Burner body 15 Combustion zone 16 Computer program product 17 Limit combustion air ratio l G (Q) 18 first section 19 second section 20 first point 21 second point 22 third point 23 minimum heat output Q min 24 maximum heat output Q max 25 characteristic curve 110 block 120 block 130 block

Claims

1. Method for operating a heating appliance (1) designed for the combustion of a fuel gas containing at least 80 percent hydrogen, and comprising a burner (3) arranged in a combustion chamber (8), to which a combustion mixture of the fuel gas and combustion air with a combustion air ratio predetermined depending on the heat output Q of the heating appliance (1) is supplied. l is supplied, which exits through a combustion zone (15) of the burner (3) into the combustion chamber (8) and burns, whereby the specified combustion air ratio l as a characteristic curve depending on the heat output Q of the heating device (1) is stored in a combustion control of the heating device (1), and the procedure further comprises at least the following steps: a) Determining a limit combustion air ratio l G (Q) (17) depending on the heat output Q of the heating appliance (1), b) comparing the given combustion air ratio laccording to the stored characteristic curve with the limit combustion air ratio determined in step a). l G (Q) (17), and c) operating the heating appliance (1) with the limiting combustion air ratio l G (Q) (17) if the specified combustion air ratio is used for the current heat output Q l smaller than the limiting combustion air ratio l G (Q) (17) is, and operating the heating appliance (1) with the specified combustion air ratio l , if the specified combustion air ratio is used for the current heat output Q l greater than the limiting combustion air ratio l G (Q) (17) is.

2. Method according to claim 1, wherein the limit combustion air ratio determined in step a) l G (Q) (17) is a piecewise linear function as a function of the heat power Q.

3. Method according to claim 2, wherein the function of the limiting combustion air ratio l G (Q) (17) comprises a first section (18) bounded by a first point (20) and a second point (21), and a second section (19) bounded by a second point (21) and a third point (22), wherein at the first point (20) at the minimum heat output Q min of the heating appliance (1) the limit combustion air ratio l G (Q) 17 = A − B × Qmin Q max is, where the parameter A is in a range of 1.9 <A<2,2 liegt und der Parameter B in einem Bereich 1,3<B<1,7 liegt, wobei weiter der zweite Punkt (21) bei einer ersten Wärmeleistung Q in einem Bereich von 50 % bis 90 % der maximalen Wärmeleistung Q max (24) of the heating device (1) is located , and the third point (22) is at the maximum heat output Q max (24) lies, and also the limiting combustion air ratio l G(Q) (17) is constant at the second point (21) and at the third point (22) and in a range of 1< l G <1.2 4. Method according to one of the preceding claims, wherein in step a) the limiting combustion air ratio l G (Q) (17) is set such that the temperature of the burner (3) does not exceed a specified limit temperature.

5. The method according to claim 4, wherein the limiting temperature is in a range of 400 °C to 600 °C.

6. Method according to one of the preceding claims, wherein the heating device (1) is converted in a step 0) from operation with a fossil fuel gas to operation with hydrogen as fuel gas.

7. Heating appliance (1) designed for the combustion of a fuel gas with a hydrogen content of at least 80% and comprising a conveying device (2), a gas valve (5), a combustion chamber (8), a burner (3) arranged in the combustion chamber (8) and a control and regulating device (7) designed to regulate a combustion air ratio l to adjust the heating device (1), and further comprising means adapted such that the heating device (1) performs a method according to claim 1.

8. Heating appliance (1) according to claim 7, wherein the heating appliance (1) is configured to provide heat via a heating circuit and to heat drinking water or domestic hot water.

9. Computer program product (16) comprising commands that cause a heating device (1) according to claim 7 to execute a method according to claim 1.

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