Method for operating a heating device which can be operated with hydrogen, heating device and computer program

Abstract

A method for operating a hydrogen-powered heating appliance (1), wherein a mixture of a hydrogen-containing fuel gas and air is combusted in a combustion chamber (17) and a glow plug (12) is associated with the combustion chamber (17), the method comprising the following steps: a) detecting a combustible mixture in the combustion chamber (17), b) activating the glow plug (12) by applying a predetermined electrical voltage, c) monitoring at least one electrical voltage or electrical resistance of the glow plug (12) and detecting abrupt changes, d) determining a flame temperature using the glow plug (12). A heating appliance and a computer program are also specified.

Description

[0001] The invention relates to a method for operating a hydrogen-powered heating device, a heating device and a computer program for operating a heating device.

[0002] The invention relates in particular to a method and an arrangement for observing combustion processes in a combustion chamber, especially for detecting the presence or extinguishing of flames and for preventing flame flashback into a burner operated with a mixture of fuel gas and air (premix burner). Furthermore, a computer program is provided which initiates the execution of such a method by the heating device.

[0003] To monitor a combustion process and / or to determine the operating status of fully and / or partially premixed burners, e.g., in heating appliances, flame monitoring using ionization current or ionization potential can be employed. For this purpose, an ionization electrode is positioned in the combustion chamber near the burner, preferably in a flame zone. When a flame is present, a measurable (electrical) ionization signal is generated, which serves as an indicator of flame presence.

[0004] Another option is monitoring flame temperatures or burner / burner surface temperatures. Thermocouples can be used for this purpose, positioned on and / or near the burner. When a flame is present, a usable temperature signal is generated, which can be used as an indicator of flame presence. However, the use of thermocouples can lead to undefined conditions regarding gas flow through the burner surface. Attaching thermocouples directly to the burner surface or routing cables inside the burner generally affects the flow distribution of the fuel gas-air mixture within the burner or as it passes through the burner surface.This can lead to localized overheating of the burner surface and potentially to temperature-induced spontaneous combustion of the fuel gas-air mixture inside the burner. Similarly, thermocouples in direct contact with a flame have insufficient durability. Due to the inertia of thermocouples, rapid evaluation and correlation with the burner's operating status are not straightforward.

[0005] Rapid detection of whether a flame has been ignited or extinguished (the function of a so-called flame detector) is of particular importance for the safety of operating a heating appliance with a burner. Such flame monitoring using a glow plug is described in WO 03 / 052320 A1.

[0006] DE 198 22 140 C1 also describes a glow plug in a vehicle heater, the resistance value of which is evaluated during glow pauses to detect a flame in a combustion chamber.

[0007] DE 100 45 270 A1 describes a sensor for determining a flame core temperature, which is used for regulating or controlling a gas burner.

[0008] Hydrogen combustion differs from that of commonly used fuel gases in several respects; in particular, a hydrogen flame is almost invisible to the human eye, emits less heat than flames produced with carbon-based fuels, and / or requires different measuring systems than those used in heating appliances for hydrocarbon fuels. Therefore, the present invention relates to burners for hydrogen as a fuel gas.

[0009] Currently, gas heating appliances use a wide variety of components to monitor or analyze the combustion process. For example, a single appliance might contain an ignition electrode, a UV sensor for flame detection, and a lambda probe for regulating the gas-air mixture. This multitude of components leads to increased costs, labor, and / or a greater need for installation space.

[0010] The invention is based on the objective of at least partially solving the problems described with reference to the prior art. In particular, several functions of flame formation, monitoring and / or control are to be combined in a single component, preferably achieving a space-saving, robust and reliable design of a hydrogen-operated heating device.

[0011] This problem is solved by the features of the independent claims. Advantageous embodiments are specified in the respective dependent claims. The description, particularly in conjunction with the figure, illustrates the invention and provides a preferred embodiment.

[0012] This involves a method for operating a hydrogen-powered heating appliance, wherein a mixture of hydrogen-containing fuel gas and air is burned in a combustion chamber, and a glow plug is associated with the combustion chamber. The method comprises at least the following steps: a) Detecting a combustible mixture in the combustion chamber, b) Activating the glow plug by applying a predetermined electrical voltage, c) Monitoring at least one electrical voltage and / or electrical resistance of the glow plug and detecting a sudden change in the electrical voltage and / or electrical resistance of the glow plug, wherein the sudden change exceeds a predetermined threshold and the sudden change is accompanied by the ignition of a flame in the combustion chamber, d) Determining a flame temperature using the glow plug.

[0013] The sequence of steps described here can be followed at least once during the (proper) operation of the heating appliance. However, it is possible that the steps partially overlap (temporally) or are executed in parallel. Successive execution is possible, whereby another step is triggered (immediately or with a delay) only upon completion of a previous step or a defined partial result or event. The time periods required for the steps can differ, with the preferred approach being that steps a) to c) are executed during the combustion start-up process, and step d) then enables the maintenance of a predetermined combustion state for a longer period, in particular until the combustion is to be completed or terminated.

[0014] The heating appliance is a gas-fired boiler designed to burn hydrogen, a fuel gas, with the addition of ambient air to generate heat energy, for example, to heat a heat transfer fluid in a heating circuit or to provide hot water. In particular, the heating appliance may be a condensing boiler. The appliance has a combustion chamber and a conveying device (e.g., a fan) that can supply a mixture of fuel gas and combustion air to the combustion chamber. The combustion products can then be discharged through an exhaust system.

[0015] A single glow plug is located on or in the combustion chamber. The glow plug's function is to ignite the fuel-gas mixture without an ignition source such as a spark. For this to work, it must reach the ignition temperature of the fuel-gas mixture. This temperature is generally high enough that gases ignite spontaneously when they come into contact with the glow plug's surface along with air. The ignition point depends on the specific fuel and usually also on the pressure.

[0016] When glow plugs are used, for example, in a gas heater, they must develop a surface temperature of at least approximately 600 °C for the gas-air mixture to ignite spontaneously. In practice, the values ​​are usually higher to ensure reliable ignition. Glow plugs, or "hot surface igniters" (HSI), feature a ceramic contact surface for contact with the gas-air mixture, which is embedded in an insulating ceramic (such as steatite (magnesium silicate), cordierite (magnesium aluminum silicate), or high-percentage aluminum oxide (90–96%)). They can be connected to an electrical power source via cables and develop high surface temperatures when current flows. Like a thermistor, they can exhibit decreasing resistance as temperatures rise. In this case, a glow plug with PTC (positive temperature coefficient) behavior is preferred, where the electrical resistance increases with temperature.The ignition elements of the glow plugs are specifically designed so that (when new) they reach surface temperatures of up to 1,500°C after only a short time, for example within 2.0 to 15.0 seconds.

[0017] According to step a), a combustible mixture is first detected in the combustion chamber. While this can be determined by sensors, it is preferred that it be done computationally, particularly using the control unit. For example, the gas-air mixture composition arriving in the combustion chamber can be determined based on (queried or specifically set) valve positions and / or the (queried or specifically set) delivery rate of a blower. If the expected conditions are met or have been verified, step a) can be considered successfully completed.

[0018] According to step b), the glow plug is activated by applying a predetermined electrical voltage. For this purpose, the control unit can apply a current or voltage to the glow plug, for example, using a DC voltage source, a transformer, etc. This heats the ceramic of the glow plug, specifically at a predetermined temperature change rate and / or a target temperature. The glow plug's behavior can be monitored. It is possible for the applied electrical voltage to result in a controlled, continuous, or pulsed temperature increase.

[0019] According to step c), the electrical voltage and / or electrical resistance of the glow plug is monitored. The focus is particularly on the temporal evolution of these parameters. Minor changes or changes occurring at low speeds are irrelevant, especially up to a certain threshold. However, a sudden change in electrical voltage and / or electrical resistance that (significantly) exceeds the predefined thresholds is of interest. Such a sudden change is accompanied by a significant temperature increase in the combustion chamber and therefore by the ignition of a flame. From this point on, it can be assumed, for example, that the flame is burning in the combustion chamber and that step c) has been successfully completed.

[0020] According to step d), after the presence of a flame in the combustion chamber is detected, the flame temperature is determined using the glow plug. Here, too, the electrical voltage and / or resistance of the glow plug can be monitored, with the focus in this phase being on a relatively smooth or controlled continuous adjustment of the parameters. Monitoring can be based, for example, on a tolerance range for the parameters, which can also be derived from a characteristic curve for the combustion process. A deviation from the tolerance range can then trigger countermeasures in the mixture composition and / or an error signal.

[0021] As part of step a), a release signal can be communicated to initiate step b). The release signal can be a command or a flag in the control unit's software. It is possible that this release signal must be present before step b) is executed.

[0022] After detecting a sudden change, a flame detection signal can be communicated. This flame detection signal can be a command or a flag in the control unit's software. It is possible that this flame detection signal must be present before step d) is executed. This flame detection signal may also activate further safety or operating routines, so that from this point onward, the heating appliance operates in a so-called regular combustion mode. If such a sudden change is not detected within a predefined ignition interval, a flame failure signal can be communicated.

[0023] After detecting a sudden change, the monitoring of further sudden changes can be temporarily deactivated. In particular, it is possible that a new set of test parameters or specifications (for voltage and / or resistance) can then be defined, possibly automatically, and taken into account for monitoring. If a sudden change is then detected, a flame failure signal can be communicated.

[0024] As part of step d), the electrical resistance of the glow plug can be observed. This resistance is temperature-dependent and therefore correlates with the flame of the burner in the vicinity, or the temperature in the combustion chamber. It is possible to provide the control unit with curves or limit values ​​that allow for an evaluation of the temperature based on the measured electrical resistance of the glow plug.

[0025] Based on a measured electrical resistance, the air-fuel ratio of the mixture can be determined. It is possible to infer the current combustion temperature from the measured electrical resistance, which then allows for a (calculated or empirical) determination of the current air-fuel ratio (lambda) of the mixture. For example, an increased resistance indicates a higher temperature and thus a richer mixture with a larger proportion of fuel gas relative to air. Similarly, a reduced resistance indicates a lower temperature and thus a leaner mixture with a smaller proportion of fuel gas relative to air.

[0026] Starting with a determined air-fuel ratio, the actual air-fuel ratio of the mixture can be adjusted. Based on the results of the air-fuel ratio determination, the fuel gas supply and / or the air supply can then be adjusted, i.e., increased or decreased, until the desired air-fuel ratio of the mixture is achieved.

[0027] Following a further aspect, a heating device according to claim 8 is proposed.

[0028] The heating appliance has a control unit designed to perform flame ignition, flame monitoring, and mixture adjustment (only) using the glow plug. In particular, decisions regarding flame ignition, desired flame characteristics, and / or desired mixture adjustment can be made (essentially) only or at least using signals or data generated by the glow plug or its operating behavior.

[0029] The heating device preferably does not additionally include at least one of the following components: ignition electrode, UV sensor, ionization electrode, lambda probe. In the prior art, these components fulfilled individual functions of operating or monitoring the heating device and may be unnecessary with the glow plug application proposed here.

[0030] Following a further aspect, a computer program is proposed, comprising instructions that cause the heating device to execute the process steps of the method according to the invention. The computer program can be stored on a storage medium, which can be separate or integrated into the control unit. The control unit can include a processor that can execute the instructions of the computer program in conjunction with the components of the heating device.

[0031] The explanations of the method can also serve to characterize the heating device or the computer program – and vice versa. The heating device is configured to carry out the method according to the invention.

[0032] To solve the aforementioned tasks, a glow plug, specifically a high-temperature ignition (HSI), is used for several functions. The HSI is employed for reliable ignition, flame detection, and gas-air mixture control. Ignition is achieved by actively applying a voltage to the HSI, whose temperature also increases with rising voltage. The flame is detected by the abrupt change in resistance or current at the HSI, because the temperature in the burner rises due to the ignition of the gas-air mixture. Gas-air mixture control is ensured by the resistance at the applied temperature. This utilizes the dependence of the flame temperature (or proximity of the flame) on the air-fuel ratio.

[0033] The invention achieves the integration of multiple functions into a single component, thereby reducing costs, installation space and / or complexity, as well as increasing reliability.

[0034] The invention will now be explained in more detail with reference to the figure. The figure relates to a preferred configuration of a heating device, with the individual components being presented by way of example. This disclosure is intended to illustrate the invention but not to limit it.

[0035] It represents: Figure 1 : a heating appliance, set up to carry out the procedure proposed here.

[0036] Fig. 1Figure 1 schematically shows a heating device 1 that can be operated with hydrogen or a hydrogen-containing fuel gas. Air (usually outside air / ambient air) is drawn in by a blower 3 via an air supply 2 and conveyed through a supply line 13 at an inlet side into a combustion chamber 9 of a burner body 7. Fuel gas is mixed with the airflow generated by the blower 3 in a mixer 6 (e.g., a Venturi nozzle) via a fuel gas supply 4 and a fuel gas valve 5. The burner body 7 has a (closed) end face 11 opposite the inlet side, which essentially determines the shape of the burner body 7. The burner body 7 can be designed (circumferentially) with a perforated plate that has a plurality of openings 14 through which the fuel gas-air mixture exits and is combusted in the vicinity of which the mixture is burned externally. Flames 18 (flame area 8) are therefore generated in a combustion chamber 17, which is surrounded by a housing 15.The combustion gases produced are discharged through an exhaust system 16.

[0037] A glow plug 12 is provided, which is arranged in the combustion chamber 17 in the vicinity of the flames 18 and, if necessary, fixed to the housing 15. The glow plug 12 is connected to a control unit 10 so that signals and / or data from the glow plug 12 can be received and, if necessary, evaluated there. The glow plug 12 can also be connected to a DC voltage source, which can supply electrical current under the control of the control unit 10. This enables controlled operation and monitoring of the operating parameters of the glow plug 12.

[0038] The control and regulating unit 10 can also regulate and / or monitor the operation of the fuel gas valve 5 and / or the blower 3.

[0039] The heating device 1 is configured to perform the following functions or process steps: a) detecting a combustible mixture in the combustion chamber 17 by means of an evaluation of current operating parameters of the fuel gas valve 5 and the blower 3 by the control unit 10, b) activating the glow plug 12 by applying a predetermined electrical voltage, whereby the glow plug 12 is heated, c) monitoring at least one electrical voltage or electrical resistance of the glow plug 12 and detecting a sudden change in the electrical voltage and / or electrical resistance of the glow plug 12, wherein the sudden change exceeds a predetermined threshold value, and the sudden change is accompanied by the ignition of a flame 18 in the combustion chamber 17, and d) determining a flame temperature using the glow plug 12 based on a resistance measurement at the glow plug 12. Reference symbol list

[0040] 1 Heating unit 2 Air supply 3 Blower 4 Fuel gas supply 5 Fuel gas valve 6 Mixer 7 Burner body 8 Flame area 9 Combustion chamber 10 Control and regulating unit 11 Front panel 12 Glow plug 13 Supply line 14 Openings 15 Housing 16 Exhaust system 17 Combustion chamber 18 Flame

Claims

1. Method for operating a heating appliance (1) that can be operated with hydrogen, wherein a mixture of a combustible gas containing hydrogen and air is combusted in a combustion chamber (17) and an incandescent igniter (12) is assigned to the combustion chamber (17), wherein the method comprises the following steps: a) detecting a combustible mixture in the combustion chamber (17), b) activating the glow igniter (12) by applying a predetermined electrical voltage, c) monitoring at least one electrical voltage or one electrical resistance of the glow igniter (12) and detecting a sudden change in the electrical voltage and / or electrical resistance of the glow igniter (12), wherein the sudden change exceeds a predetermined threshold value and the sudden change is accompanied by the ignition of a flame (18) in the combustion chamber (17), and d) determining a flame temperature by means of the glow igniter (12).

2. . Method according to claim 1, characterised in that, as part of step a), an enable signal is communicated to initiate step b).

3. . Method according to claim 1 or 2, characterised in that a flame detection signal is communicated after detecting an abrupt change.

4. . Method according to one of claims 1 to 3, characterised in that, after detecting an abrupt change, the monitoring of further abrupt changes is temporarily deactivated.

5. . Method according to one of the preceding claims, characterised in that, as part of step d), the electrical resistance of the glow igniter (12) is observed.

6. . Method according to claim 5, characterised in that an air ratio of the mixture is determined based on a determined electrical resistance.

7. . Method according to claim 6, characterised in that an actual air ratio of the mixture is set based on a determined air ratio.

8. . Heating appliance (1) comprising a combustion chamber (17) associated with an incandescent igniter (12) and to which a mixture of a combustible gas containing hydrogen and air can be supplied, as well as a regulation and control unit (10) which is designed to perform flame ignition, flame monitoring and mixture adjustment with the glow igniter (12), and a method according to one of claims 1 to 7.

9. . Heating appliance (1) according to claim 8, characterised in that it does not additionally have at least one of the following components: ignition electrode, UV sensor, ionisation electrode, lambda probe.

10. . Computer program comprising commands that cause the heating appliance (1) of claim 8 to perform the method steps according to claim 1.

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