Method for operating a heating device, heating device, computer program and use of detected temperatures

Abstract

A method is proposed for operating a heating appliance (1) designed to combust a fuel gas at a burner (3) of the heating appliance (1) with a hydrogen content of at least 80%. The heating appliance (1) comprises a combustion air supply (4) (17) and an exhaust gas outlet, wherein exhaust gas (16) from the exhaust gas outlet can pass into the combustion air supply (4) (17) at a recirculation point (21). The method comprises at least the following steps: a) recording an exhaust gas temperature TA, b) recording a combustion air temperature TL at a measuring point in the recirculation point (21) or, viewed in a flow direction (24) of the heating appliance (1), downstream thereof, c) detecting irregular exhaust gas recirculation based on the exhaust gas temperature TA recorded in step a) and the combustion air temperature TL recorded in step b).In addition, a heating device (1), a computer program product (14) and a use of recorded temperatures are proposed.

Description

[0001] The invention relates to a method for operating a heating device, a heating device, a computer program, and the use of measured temperatures. The heating device is designed to be operated with hydrogen as fuel gas.

[0002] Gas-burning heating appliances for buildings used for heating or hot water supply are well-known in the art. To prevent nitrogen oxides (NOx) from the exhaust gas of such appliances, they can be designed to recirculate exhaust gas from the flue into the combustion air supply. This is called exhaust gas recirculation or exhaust gas recirculation. Exhaust gas recirculation is legally required in many countries. Such a heating appliance with recirculation is presented, for example, in EP 2 442 027A2. Controlling the recirculation of a heating appliance is also known. This is described in EP 2 807 427 A2.

[0003] Furthermore, when using exhaust gas recirculation, it is essential to prevent an excessively high mass flow of exhaust gas from being recirculated into the supplied mass flow of combustion air. Besides reducing the energy efficiency of the heating appliance, this can cause the flame temperature to drop so low that carbon monoxide formation is promoted. Therefore, it is often legally mandated that a heating appliance shuts down when the carbon monoxide concentration in the exhaust gas exceeds a limit of 1000 ppm (parts per million). The carbon monoxide concentration can be detected by a carbon monoxide sensor, thus preventing excessive recirculation by the heating appliance. Controlled recirculation of a heating appliance, as described, for example, in EP 2 807 427 A2, can also prevent excessively high carbon monoxide concentrations. However, the described control of recirculation is complex. DE 10 2020 121 934 B3 also describes a method for controlling a recirculation device.A sensor device is used, specifically designed as a gas chromatograph or a temperature sensor measuring the flame or combustion surface temperature, to determine the fuel composition. This solution is also complex and unsuitable for detecting irregular recirculation.

[0004] DE 10 2021 102 700 A1 describes a method and an arrangement for using at least one property of the air in a combustion air path of a heating appliance for its control and condition analysis. The heating appliance may also have a recirculation device. This method is also not suitable for detecting irregular recirculation.

[0005] In heating appliances designed for hydrogen combustion, carbon monoxide cannot be formed due to the absence of carbon in the fuel. Nevertheless, exhaust gas recirculation is still advisable for hydrogen-powered heating appliances to prevent or reduce the formation of nitrogen oxides. However, excessive recirculation can also have negative effects in hydrogen-powered heating appliances and must be avoided.

[0006] Based on this, the object of the invention is to propose a method for operating a heating device, a heating device, a computer program, and an application that at least partially overcome the disadvantages of the prior art and enable the detection of recirculation in a heating device operated with hydrogen as fuel. In particular, this should enable the safe operation of a hydrogen-powered heating device. Furthermore, the invention should be implementable with no or only minor structural modifications to the heating device.

[0007] 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.

[0008] This involves a method for operating a heating appliance. The heating appliance is designed to combust a fuel gas in a burner containing at least 80% hydrogen, or is operated with this fuel gas. It further includes a combustion air supply and an exhaust gas discharge, whereby exhaust gas from the exhaust gas discharge can pass into the combustion air supply at a recirculation point. The method comprises at least the following steps: a) Recording an exhaust gas temperature TA, b) Recording a combustion air temperature TL at a measuring point in the recirculation point or, viewed in a flow direction of the heating appliance, downstream of it, c) Determining an irregular exhaust gas recirculation based on the exhaust gas temperature TA recorded in step a) and the combustion air temperature TL recorded in step b).

[0009] The procedure can be carried out continuously. In a regular procedure, steps a), b), and c) can be performed at least once in the specified order. In particular, steps a) and b) can be carried out continuously and simultaneously or in parallel.

[0010] The method ensures the safe and energy-efficient operation of the heating appliance by detecting irregular recirculation or recirculation rate within the hydrogen-fueled appliance. Therefore, the method can also be understood as a method for detecting irregular recirculation and / or recirculation rate within the heating appliance. Irregular exhaust gas recirculation can be characterized by a proportion of exhaust gas in the combustion air that is too high or too low (compared to a predefined limit). Specifically, irregular recirculation refers to an excessively high proportion of exhaust gas in the combustion air, which can contribute to unsafe operating conditions of the heating appliance.

[0011] The heating appliance in question is, in particular, a gas-fired heating appliance designed to combust a fuel gas, such as natural gas or, more specifically, hydrogen, with the addition of ambient air, and to generate thermal energy, for example, to heat a heat transfer fluid in a heating circuit or to provide hot water. The heating appliance may, in particular, be a condensing boiler. The heating appliance typically has a conveying device or a fan that can pump a mixture of fuel gas and combustion air through a mixture channel into a combustion chamber containing a burner. The combustion products (exhaust gases) can then be discharged through an exhaust system in the same direction of flow. The exhaust system may consist of an exhaust duct located within the housing of the heating appliance or an exhaust system located outside the appliance.

[0012] The heating appliance may include a control unit that manages and regulates the heating appliance and its combustion process. The control unit may be configured to carry out a procedure proposed here (fully automated).

[0013] The heating appliance may feature exhaust gas recirculation, in which a mass flow of exhaust gas from the appliance's exhaust stream is transferred to a supply mass flow of combustion air or ambient air at a recirculation point. The recirculation point can be located, in particular, within the heating appliance or within its housing. The ratio of exhaust gas to combustion air in the recirculation can be understood as the recirculation rate. Often, the exhaust duct and the combustion air supply run parallel or adjacent to each other, at least in one section, and an opening in the walls of the exhaust duct and combustion air supply, acting as a recirculation point, allows a recirculated exhaust gas stream to flow from the exhaust duct into the combustion air supply. The recirculation point can be a simple opening, but it may also incorporate devices for controlling the recirculation.Advantageously, an irregular recirculation can be detected using the method proposed here, regardless of the design of the recirculation point. It is also possible to locate the recirculation point outside the heating appliance, for example, in an air-exhaust system connected to the heating appliance, where an exhaust pipe runs concentrically to and within a combustion air supply, and a recirculation point can be easily created by means of an opening in the partition between the exhaust pipe and the combustion air supply. The flow cross-section of the recirculation point opening allows the extent of recirculation, or approximately the recirculation rate, to be adjusted.

[0014] The heating appliance includes means for measuring the exhaust gas temperature (TA) and the combustion air temperature (TL). The combustion air temperature (TL) is measured at a measuring point at the recirculation point or, relative to the flow direction through the heating appliance, downstream of it. Therefore, the combustion air temperature (TL) is the temperature of the mixture of intake ambient air and the recirculated exhaust gas. The exhaust gas temperature (TA) can be measured, in particular, in an exhaust duct of the heating appliance, and the combustion air temperature (TL) can be measured in a combustion air supply. Specifically, the exhaust gas temperature (TA) can be measured in the exhaust duct directly downstream of the combustion chamber or as close as possible to the combustion chamber within the exhaust duct.

[0015] The means for sensing the temperature can be, in particular, known temperature sensors, especially resistance-based temperature sensors, which can be arranged in the exhaust gas duct and in the combustion air supply. The means for sensing a temperature TA of the exhaust gas and a temperature TL of the supplied combustion air can be connected to a computer configured to carry out a method proposed herein. The computer can, in particular, be the control unit of the heating appliance.

[0016] The heating appliance is designed to burn hydrogen as fuel, wherein the fuel gas, which is to be combusted with the addition of combustion air, has a hydrogen content of at least 80 percent. In particular, the fuel gas can contain a hydrogen content of at least 90 percent or 95 percent, or be virtually pure hydrogen. During the operation of the process, a hydrogen fuel gas of the aforementioned type is burned.

[0017] According to step a), an exhaust gas temperature TA can be recorded. The exhaust gas temperature TA refers to the temperature of the combustion products or exhaust gases exiting the combustion chamber. The recorded exhaust gas temperature TA can be stored in a memory, for example, in the control unit. The exhaust gas temperature TA can be recorded, in particular, at a measuring point between the combustion chamber and the recirculation point. This measuring point can be located, in particular, at the beginning of the exhaust gas discharge, immediately downstream of the combustion chamber in the direction of flow through the heating appliance.

[0018] According to step b), the combustion air temperature TL can be measured at a measuring point either at the recirculation point or, viewed in the direction of flow through the heating appliance, downstream of it. The measuring point for the combustion air temperature TL can, in particular, be located between the recirculation point and the combustion chamber. The measured combustion air temperature TL can also be stored in a memory, for example, in the control unit.

[0019] According to step c), irregular exhaust gas recirculation can be detected using the exhaust gas temperature TA recorded in step a) and the combustion air temperature TL recorded in step b). This detection can involve comparing the exhaust gas temperature TA recorded in step b) with the combustion air temperature TL recorded in step c). The comparison can include determining the ratio or difference between the exhaust gas temperature TA and the combustion air temperature TL. From this, the current exhaust gas recirculation rate can be inferred.

[0020] According to one embodiment, a recirculation parameter characteristic of the recirculation rate can be determined based on the measured exhaust gas temperature TA and the measured combustion air temperature TL and compared with a predefined limit value or a predefined limit range. Irregular recirculation can be detected as a result of this comparison. In this respect, the predefined limit value and / or the predefined limit range can refer to and be compared with the recirculation parameter derived from the measured exhaust gas temperature TA and the measured combustion air temperature TL. Irregular recirculation can generally be detected if the recirculation parameter, which is characteristic of a recirculation rate, lies above a limit value and / or outside a limit range.

[0021] The limit value or limit range can be determined in advance, for example, using a reference heater during tests. For the purpose of automated process execution, the limit value or limit range can be stored in the memory of a computer performing the process, or, in particular, in the memory of a control unit of the heater.

[0022] According to one embodiment, the limit value or limit range can be characteristic of a given proportion of hydrogen in the combustion air. Thus, defining a limit value or limit range can also specify a maximum (or minimum) proportion of hydrogen in the combustion air. Furthermore, defining a limit value or limit range that is characteristic of a given proportion of hydrogen in the combustion air can be carried out on a reference heating appliance within the framework of (laboratory) tests.

[0023] According to one design, if irregular exhaust gas recirculation is detected above the specified limit or outside the limit range, the heating appliance can be switched off. This prevents unsafe operating conditions resulting from potentially excessive recirculation. Furthermore, switching off in the event of excessive recirculation is often a legally mandated approval requirement for heating appliances, which can thus be met.

[0024] According to one embodiment, an additional temperature TU of the supplied combustion air in the flow direction through the heating appliance can be measured upstream of the recirculation point and included in the detection of irregular exhaust gas recirculation in step c). In other words, the temperature TU represents the temperature of the intake ambient air without the influence of the supplied exhaust gas at the recirculation point. Including the temperature TU can improve the accuracy of detecting irregular exhaust gas recirculation.

[0025] According to one implementation, information about irregular recirculation detected in step c) and / or about a heating device switched off due to such irregular recirculation can be displayed on a display unit, made available for retrieval via a network, and / or sent as a message via a network. This allows a user to understand why the heating device was switched off, and also enables a service technician to be informed of the shutdown so that a maintenance appointment can be scheduled and carried out.

[0026] In addition, a heating appliance is proposed for the combustion of a fuel gas with a hydrogen content of at least 80%. The heating appliance comprises an exhaust gas outlet and a combustion air supply with a recirculation point where exhaust gas from the exhaust gas outlet can flow into the combustion air supply. The heating appliance includes a first temperature sensor in the exhaust gas outlet for measuring the exhaust gas temperature TL and a second temperature sensor in the combustion air supply, located at the recirculation point or, viewed in the direction of flow through the heating appliance, downstream of it, for measuring the combustion air temperature TL. The heating appliance also includes a control unit configured to carry out a procedure proposed herein.

[0027] In addition, a control unit for a heating appliance is proposed, designed to execute a procedure proposed here. This control unit may, for example, include a processor. In this context, the processor can, for instance, execute the procedure stored in the control unit's memory. The control unit may be electrically connected to a first temperature sensor in the exhaust gas outlet to measure the exhaust gas temperature TL, and a second temperature sensor in the combustion air supply, located near the recirculation point or, viewed in the direction of flow through the heating appliance, downstream of it, to measure the combustion air temperature TL. It may also be electrically connected to a network (the internet).Furthermore, data recorded or required during the implementation of a procedure proposed here can be stored on a memory of the control and regulating device, for example limit values ​​and / or recorded temperatures.

[0028] Another aspect is the proposal of a computer program comprising commands that cause a computer, for example a control and regulating device of a heating appliance, to execute a procedure proposed here.

[0029] Another aspect proposes using a measured exhaust gas temperature TA and a measured combustion air temperature TL, recorded at a measuring point at the recirculation point or, viewed in the flow direction of a heating appliance, downstream of it, to detect irregular exhaust gas recirculation of the heating appliance. Detecting irregular exhaust gas recirculation can, in particular, include determining or estimating a recirculation parameter that is characteristic of a recirculation rate.

[0030] The details, features, and advantageous configurations discussed in connection with the process may also occur in the computer program, heating device, and / or its use 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.

[0031] 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.

[0032] This document describes a method for operating a heating device, a heating device itself, a computer program, and a method for using recorded temperatures, which 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 each contribute to detecting irregular recirculation in a hydrogen-powered heating device. This can increase operational reliability and reduce pollutant emissions, especially nitrogen oxide (NOx) emissions, from a hydrogen-powered heating device.

[0033] Furthermore, the invention advantageously does not increase the complexity of a heating device proposed here compared to heating devices according to the prior art, or only to an insignificant extent.

[0034] 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 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 method proposed here, Fig. 2: a heating device proposed here, and Fig. 3: a further representation of a heating device proposed here.

[0035] Fig. 1 Figure 1 shows an exemplary and schematic representation of the sequence of steps in a proposed procedure. This procedure serves to ensure the safe operation of a heating device 1, in particular to detect irregular recirculation within the device. The sequence of steps a), b), and c), represented by blocks 110, 120, and 130, can occur during normal operation. Specifically, the proposed procedure, and thus blocks 110, 120, and 130, can be carried out continuously while the heating device 1 is in operation. Blocks 110 and 120, and thus steps a) and b), can also be executed in parallel or simultaneously.

[0036] Fig. 2 shows an exemplary and schematic representation of a heating appliance 1 proposed here. Ambient air 15 can be drawn in via a combustion air supply 4 by a conveying device 2. A recirculated exhaust gas stream 16 from an exhaust gas duct 10 of the heating appliance 1 can be fed into the ambient air 15 at a recirculation point 21. Adding the recirculated exhaust gas stream 16 can significantly minimize the emission of nitrogen oxides from the heating appliance 1. A mass flow of hydrogen, corresponding to a predetermined combustion air ratio, can be added as fuel gas from a fuel gas supply 8 to a mass flow of combustion air 17, formed from ambient air 15 and the supplied recirculated exhaust gas stream 16, via a gas valve 5. The resulting combustion mixture can be fed via a mixture channel 12 to a burner 3 of the heating appliance 1, located in a combustion chamber 22, and combusted there.A heat exchanger 13 can be arranged in the combustion chamber 22, which can transfer the heat generated during combustion to a heating circuit 23 with a flow 6 and a return 9. The heating appliance 1 can also have a flame monitoring device 20, which here is designed as a UV sensor, i.e., a sensor for detecting the intensity of ultraviolet radiation. Combustion products or exhaust gases 25 generated during combustion can be fed to an exhaust system 11 via the exhaust duct 10. The exhaust system 11 and the exhaust duct 10 can be understood as the exhaust system of the heating appliance 1. The conveying device 2 can be a blower.

[0037] The recirculation point 21 forms a connection between the exhaust gas discharge, here the exhaust gas duct 10, and the combustion air supply 4 17, through which a recirculated exhaust gas flow 16 can pass from the exhaust gas duct 10 into the combustion air supply 4 17. A first temperature sensor 18, which can detect an exhaust gas temperature TA, can be arranged in the exhaust gas duct 10. In the combustion air supply 4 17, viewed in a flow direction 24 of the heating appliance 1, a second temperature sensor 19, which detects a combustion air temperature TL, can be arranged downstream of the recirculation point 21.

[0038] A control unit 7 of the heating appliance 1 can be electrically connected to the gas valve 5, the conveying device 2, the flame monitoring device 20, the first temperature sensor 18 and the second temperature sensor 19, wherein the control unit 7 can be configured to execute a method proposed herein as a computer program product 14. The control unit 7 can be connected to a network 26, in particular the Internet, and transmit data to and from the network 26 via this connection.

[0039] Fig. 3Figure 1 shows an exemplary and schematic representation of a proposed heating appliance 1, in which the combustion air supply 4 17 and the exhaust gas duct 10 are arranged concentrically and parallel, at least in one section. The combustion air supply 4 17 is located on the outside and the exhaust gas duct 10 on the inside, thus enabling the transfer of residual heat from the exhaust gas 25 to the combustion air 17 or the supplied ambient air 15. At the recirculation point 21, the exhaust gas duct 10 can have at least one opening through which the recirculated exhaust gas flow 16 can pass from the exhaust gas duct 10 into the combustion air supply 4 17.

[0040] In block 110, the exhaust gas temperature TA of the exhaust gas 25 can be measured using the first temperature sensor 18, as per step a). This measurement can be carried out by the control unit 7.

[0041] In block 120, according to step b), the combustion air temperature TL of the combustion air 17 can be measured using the second temperature sensor 19. For this purpose, the second temperature sensor is positioned downstream of the recirculation point 21 in the direction of flow 24, so that the combustion air temperature TL is the temperature of the supplied ambient air 15 containing the recirculated exhaust gas flow 16. Step b) can also be carried out by the control unit 7.

[0042] In block 130, irregular exhaust gas recirculation can be detected according to step c) based on the exhaust gas temperature TA recorded in block 110 (step a)) and block 120 (step b)) and the combustion air temperature TL recorded in step b). For this purpose, the exhaust gas temperature TA recorded in step a) can be compared with the combustion air temperature TL recorded in step b) to derive a recirculation parameter. This recirculation parameter is characteristic of the current recirculation rate, i.e., the proportion of exhaust gas 25 in the combustion air 17. The recirculation parameter determined in this way can be compared with a limit value or a limit range, and irregular recirculation can be identified based on this comparison. Reference symbol list

[0043] 1 Heating unit 2 Conveyor 3 Burner 4 Combustion air supply 5 Gas valve 6 Flow 7 Control and monitoring unit 8 Fuel gas supply 9 Return 10 Exhaust duct 11 Exhaust system 12 Mixing channel 13 Heat exchanger 14 Computer program product 15 Ambient air 16 Recirculated exhaust gas flow 17 Combustion air 18 First temperature sensor 19 Second temperature sensor 20 Flame monitoring 21 Recirculation point 22 Combustion chamber 23 Heating circuit 24 Flow direction 25 Exhaust gases 26 Network

Claims

1. A method for operating a heating appliance (1) configured for the combustion of a fuel gas at a burner (3) of the heating appliance (1) with a hydrogen content of at least 80%, and comprising a supply (4) combustion air (17) and an exhaust gas discharge, wherein exhaust gas (16) from the exhaust gas discharge can pass into the supply (4) combustion air (17) at a recirculation point (21), comprising at least the following steps: a) Determining an exhaust gas temperature T A , b) Determining a combustion air temperature T L at a measuring point in the recirculation point (21) or, viewed in a flow direction (24) of the heating appliance (1), downstream of it, c) Determining an irregular exhaust gas recirculation based on the exhaust gas temperature T recorded in step a). A and the combustion air temperature T recorded in and step b). L .

2. The method of claim 1, wherein in step c) a comparison is made based on the exhaust gas temperature T recorded in step a). A and the combustion air temperature T recorded in and step b). L The determined recirculation parameter, which is characteristic of a recirculation rate, is compared with a predetermined limit value and / or a predetermined limit range.

3. Method according to claim 2, wherein the limit value and / or the limit range is characteristic for a predetermined proportion of hydrogen in the combustion air (17) supplied to the burner (3).

4. Method according to one of the preceding claims, wherein the heating device (1) is switched off when irregular exhaust gas recirculation is detected.

5. Method according to one of the preceding claims, wherein in step d) information about the detection of irregular exhaust gas recirculation and / or about a switched-off heating device (1) is displayed by means of a display unit, made available for retrieval via a network (26) and / or sent as a message via a network (26).

6. Heating appliance, designed for the combustion of a fuel gas with a hydrogen content of at least 80% and comprising an exhaust gas outlet and a supply (4) combustion air (17) with a recirculation point (21) in which exhaust gas (25) from the exhaust gas outlet can pass into the supply (4) combustion air (17), and a first temperature sensor (18) in the exhaust gas outlet and a second temperature sensor (19) in the supply (4) combustion air (17) in the region of the recirculation point (21) or, viewed in a flow direction (24) of the heating appliance (1), downstream thereof, and comprising a control and regulating device (7) and means adapted to perform a method according to one of the preceding claims.

7. Computer program product (14) comprising commands that cause a heating device (1) according to claim 6 to execute a method according to any one of claims 1 to 5.

8. Use of a measured exhaust gas temperature T A and a measured combustion air temperature T L , detected at a measuring point in a recirculation point (21) or, seen in a flow direction (24) of a heating appliance (1), downstream of it, to detect an irregular exhaust gas recirculation of the heating appliance (1).

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