Method and device for reliably operating and controlling a combustion process in a heating apparatus for the combustion of hydrogen

Description

[0001] The invention relates to a method and an arrangement for the safe operation and control of a combustion process in a heating appliance which can be operated with pure hydrogen or a fuel gas with more than 90% hydrogen content, preferably more than 97%.

[0002] Hydrogen, either as a fuel gas or as an additive to other fuel gases, is becoming increasingly important, and significant efforts are being made to adapt new and existing heating appliances for its operation. This includes not only large-scale systems but also wall-mounted water heaters and, more generally, heating appliances for building heating and / or hot water supply. Hydrogen combustion differs from that of previously used fuel gases in several ways; in particular, a hydrogen flame is almost invisible to the human eye, and different measuring systems are required than those used in heating appliances based on hydrocarbon fuels. Currently, heating appliances generally use simple and robust sensors for ionization, temperature, light or heat radiation, pressure, flow rate, and similar parameters to regulate the appliances and ensure their safe operation.However, some measurements cannot be reliably performed with conventional sensors when using hydrogen as a fuel gas. One important function is detecting the presence of a stable flame (a so-called flame detector), another is adjusting the ratio of combustion air to fuel gas (lambda value) to ensure stable and environmentally friendly combustion.

[0003] In state-of-the-art heating appliances, ionization measuring devices are frequently used, both for detecting the presence of flames and for controlling the combustion process. For example, DE 39 37 290 A1 discloses the ability to measure the electrical conductivity of a flame area in a combustion chamber and to adjust the mixture ratio of combustion air to fuel gas so that the electrical conductivity remains within a specific target range or at a specific target value. A corresponding control device for a burner with an ionization electrode is known, for example, from EP 1 154 202 A2. Similar to the Langmuir probe used in plasma physics, measuring conductivity with an ionization electrode also constitutes a Langmuir probe. This measuring method is invasive, meaning that the combustion process is affected by the insertion of an electrode.However, combustion processes using hydrogen as a fuel gas exhibit much lower ionization in their flames, so that often (at least at low power output and / or high lambda during the operation of a heating appliance) no ionization signal suitable for monitoring or control can be measured. Therefore, alternative measurement methods are used, in particular those based on measuring ultraviolet radiation from the combustion process or those based on temperature measurements.

[0004] The use of optical sensors with optical filters for a specific application in heating appliances operated with hydrogen-containing fuel gas is already known, for example, from EP 3 663 648 A1. Optical measuring systems in heating appliances are also known from EP 2 223 016 B1, although these two documents mainly deal with observing flame radiation, i.e., radiation emissions in the combustion chamber. Another example is provided in EP 3 825 623 A1, which discloses an emergency operating control of a heating appliance by means of a secondary combustion control after detecting an implausibility or fault in a primary combustion control. However, the proposed method is not suitable for hydrogen-operated heating appliances.

[0005] EP 3 663 646 A1 also discloses such an observation of flame radiation, wherein a first and a second ionization signal of a flame are detected and a common ionization signal is derived from them, and furthermore, a first and a second flame sensor are provided that detect radiation emitted by the flame and a common flame signal is derived from their signal. EP 3 663 646 A1 discloses the features of the preamble of the first claim.

[0006] Due to the high temperatures and strong emissions in the vicinity of flames, established measurement methods and the evaluation of such measurements are quite complex, as errors should be avoided as much as possible in safety-critical functions. Generally, the more complex a measurement system is, the greater its susceptibility to errors. Therefore, for safety functions such as flame detectors, it is desirable, or even mandatory, that errors in the measurement systems are detected quickly and appropriate safety measures are initiated. If the extinguishing of flames or the failure to ignite an incoming flammable mixture of hydrogen and air in a combustion chamber is not detected, dangerous accumulations or the release of flammable or even explosive mixtures can occur, which must be avoided at all costs.Situations where a flame detector falsely indicates the presence of flames that are not actually there are particularly critical. This should be detected as quickly as possible so that appropriate measures can be taken.

[0007] It is therefore an object of the invention to provide a method and an arrangement that at least partially solve the aforementioned problems and, in particular, enable the reliable monitoring and control of a combustion process in a heating appliance for hydrogen combustion, ensuring that errors in flame monitoring, especially the false detection of non-existent flames, can be detected quickly and appropriate measures can be taken. Reliable emergency operation, even in the event of a measurement system failure, should also be possible. The creation of a corresponding computer program is also an object of the invention.

[0008] These tasks are solved by a method and an arrangement, as well as a computer program product according to the independent claims. Advantageous further developments and embodiments are specified in the respective dependent claims. Embodiments and advantages are also described below, particularly in connection with the figures.

[0009] A method for the safe operation and control of a combustion process in the combustion chamber of a heating appliance contributes to solving this problem. Hydrogen, or a fuel gas containing more than 90%, particularly more than 97%, hydrogen, is combusted with air. A primary sensor system not based on ionization measurement is used to detect the presence of flames and, if necessary, to control the air-to-fuel gas ratio. Secondarily (as needed and / or additionally), an ionization measurement is performed in a flame zone within the combustion chamber. The ionization signal from this secondary sensor enables or triggers fault detection and / or emergency operation in the event of a malfunction of a primary sensor and / or its associated primary sensor electronics.

[0010] As mentioned above, ionization measuring devices are proven systems that are only unsuitable when using hydrogen as fuel and at low power output and / or high lambda values ​​of a heating device due to insufficient charge carriers in the resulting small flames. At higher power outputs and sufficiently low lambda values, however, they measure reliably. If a primary sensor falsely signals the presence of flames, even though they have extinguished or failed to ignite, a typical heating device control electronics system attempts to increase the power output because the expected temperature increase does not occur. However, such a power increase (modulation) of the combustion process can also occur for other reasons and be a completely error-free process. According to the invention, an (additional) ionization measurement can be performed to differentiate between these two types of power increase. Above a certain orAt the specified minimum power output, sufficient charge carriers are present in the flame zone for reliable ionization measurement. As is typical in known combustion processes, an ionization current can then be measured, and a reliably interpretable ionization signal can be derived from it using established methods. If such a signal does not occur above a certain minimum power output, this indicates the absence of a flame (and thus a fault or misinterpretation of the measurement results from the primary sensor, which failed to detect this). This allows for a quick and reliable shutdown of the heating device and the triggering of an error message.

[0011] According to the invention, ionization measurement during operation below a minimum heating appliance power level may not always provide a usable ionization signal for control purposes. In a preferred embodiment, this signal is therefore disregarded or discarded, but used at higher power levels. In the event of a failure or misinterpretation of the primary sensor, this signal is used to determine whether flames are still present and, if necessary, to perform emergency control in a power range above the minimum power level. Preferably, the ionization measuring device is always operational, but is only used above a certain minimum power level to check the primary sensor. If the primary sensor is defective, the ionization measuring device can still be used for flame monitoring and control, although possibly only at power levels above the minimum power level (emergency operation).

[0012] According to the invention, if the flames go out, but are falsely detected by the primary sensor, and a typical control system incorrectly attempts to increase the heating device's power output without a usable ionization signal being detectable above a minimum power level, the absence of this signal allows the system to conclude that the flames have gone out and initiate safety measures. This embodiment is particularly important for complying with safety regulations and preventing the heating device from restarting with a defective primary sensor.

[0013] Preferably, the primary sensor technology is based on the measurement of ultraviolet radiation in or around the combustion chamber, which is a reliable measurement method in all power ranges.

[0014] Alternatively, the primary sensor system is based on measuring temperatures in or around the combustion chamber, which allows the presence of flames to be detected at any power output and enables control of the combustion process. Depending on the design, one or more temperature sensors are used for this purpose.

[0015] Preferably, after a false flame signal is detected by the primary sensor, this signal is no longer considered during a restart of the heating appliance in emergency mode. Instead, the heating appliance is operated, if necessary, only in a power range where the secondary ionization measurement can be used for flame detection and control, with the ionization measurement replacing the primary sensor. This allows for a limited but safe emergency operation until the primary sensor can be serviced.

[0016] An arrangement for the safe operation and control of a combustion process in the combustion chamber of a heating appliance for the combustion of hydrogen or a fuel gas containing more than 90% hydrogen with air also contributes to solving the problem. This arrangement includes a primary sensor system not based on ionization measurement for detecting the presence of flames and for controlling the air-to-fuel gas ratio. A secondary ionization measuring device is also provided for measuring ionization in a flame zone within the combustion chamber. The ionization signal from this secondary sensor enables fault detection and / or emergency operation in the event of a malfunction of the primary sensor and / or its associated primary sensor electronics. The arrangement is configured to carry out the procedure.

[0017] For this purpose, an evaluation electronics unit is provided (which can also be integrated into a control electronics unit) which is designed to check whether an ionization signal occurs when the heating device's power output is increased above a minimum level as desired by a control system, so that if this signal is absent, it can be concluded that the flames have extinguished despite a false detection of flames by the primary sensors and thus that there is a fault in the primary sensors.

[0018] In particular, the evaluation electronics are designed to switch off the heating device, trigger an error message and / or perform a switchover after detecting a fault in the primary sensor system, so that the heating device can only be operated (for a defined period) in a power range suitable for ionization measurements, and the ionization measuring device is used to detect the presence of flames and to control the combustion process.

[0019] Another aspect concerns a computer program product comprising commands that cause the described arrangement to execute the described procedure. The evaluation of the data measured by the sensors and its further use in the heating device require a program and data for the control and regulation of the heating device, both of which must be updated occasionally.

[0020] The explanations of the procedure can be used to further characterize the arrangement, and vice versa.

[0021] A schematic embodiment of the invention, to which it is not limited, and the functioning of the method will now be explained in more detail with reference to the drawing. It illustrates: Fig. 1: a heating device with primary and secondary sensors.

[0022] Fig. 1The figure schematically shows parts of a heating appliance, in particular a combustion chamber 1 with a burner 14 arranged therein. During operation, air is supplied to the burner 14 via an air supply 3 with a blower 5, to which fuel gas, here essentially hydrogen, is added via a fuel gas supply 4 by means of a fuel gas valve 6. The resulting mixture burns in a flame chamber 9, forming flames 2, essentially to water (vapor).

[0023] For a safe combustion process, it is crucial to be able to quickly detect the presence or extinguishing of flames. This function of a flame detector primarily serves to enable the rapid closure of the fuel gas valve if the flames fail to ignite or extinguish. This minimizes the accumulation or release of unburned mixture. Ionization measuring devices have long been successfully used as flame detectors in many conventional heating appliances for carbon-based fuels. However, flames during hydrogen combustion contain very few charge carriers, meaning that reliable ionization measurements cannot be performed with small flames (low heating appliance output).

[0024] For this reason, other primary sensors 7 are used as flame detectors, in particular UV sensors (for measuring ultraviolet radiation from the flame area 9) or temperature sensors (for measuring the heat development of the combustion process). A primary sensor 7 may also be used to control the combustion process, in particular to adjust the air-to-fuel ratio (lambda). Both functions are so important that a failure of the primary sensor 7 or its associated primary sensor electronics 11 must be detected as quickly as possible, and in particular, a restart of the heating appliance in the event of a defective primary sensor 7, 11 must be prevented.

[0025] A particularly critical situation arises when the primary sensors 7, 11 falsely detect flames 2, even though they are not present. The present invention can be especially useful in this case. If the flames 2 have extinguished during a combustion process, while the primary sensors still falsely detect flames 2, no further heat is generated, but the fuel gas valve 6 is not (yet) closed. Typical control electronics 13 will, however, detect that not enough heat is being generated and will consequently increase the power output. Such an increase in power output (modulation) of the combustion process can also occur for other reasons and be a completely error-free process. Here, an ionization measurement can be used to distinguish between these two types of power increase. Above a certain minimum power output, there are sufficient charge carriers in the flame zone 9 for a reliable ionization measurement.As is common in known combustion processes, an ionization current can then be measured, and a reliably interpretable ionization signal can be derived from it using known methods. For this purpose, an ionization electrode 8 is arranged in the flame zone 9. Its signal is processed by ionization measurement electronics 12 and evaluated by evaluation electronics 10. If the ionization measurement 8, 12 detects a signal during an increase in power, this indicates a fault-free (intended) increase in power (modulation). However, if there is no signal, only a fault can be present, and the fuel gas valve 6 must be closed immediately to prevent the escape of unburned air-fuel gas mixture. This typically results in an error message or even a lockout of the device until maintenance by qualified personnel.These functions are performed by the evaluation electronics 10, which can also be integrated into a control electronics 13.

[0026] However, with heating appliances, it is often desirable that an emergency operation can continue even in the event of a malfunction, provided that this operation can be carried out safely. This possibility is additionally offered here by the ionization measurement 8, 12, if operation is limited to power levels at which the ionization measurement 8, 12 functions, i.e., to power levels above the minimum power level required for ionization measurements. If the evaluation electronics 10 detect that the primary sensor 7, 11 is malfunctioning (precisely because no ionization signal occurs when the power level is increased), it switches off the primary sensor 7, 11 and uses the ionization measurement 8, 12 for future flame monitoring and control until the appliance has been serviced.For this purpose, the control electronics 13 must ensure that only power ranges are permitted in which the ionization measurement 8, 12 functions, which does mean a restriction of operation, but no loss of safety and availability.

[0027] The present invention enables the safe operation of hydrogen-powered heating devices and simultaneously reduces the risks of faulty primary sensors 7, 11 with high availability through an emergency operation with ionization measurement 8, 12. Reference symbol list

[0028] 1 Combustion chamber (of a heating appliance) 2 Flames 3 Air supply 4 Fuel gas supply 5 Blower 6 Fuel gas valve 7 Primary sensor (UV sensor, temperature sensor) 8 Ionization electrode 9 Flame area 10 Evaluation electronics 11 Primary sensor electronics 12 Ionization measurement electronics 13 Control electronics 14 Burner

Claims

1. A method for the safe operation and control of a combustion process in a combustion chamber (1) of a heating appliance, wherein hydrogen or a fuel gas containing more than 90% hydrogen is combusted with air, wherein, furthermore, at least for the detection of the presence of flames (2), a primary sensor system (7, 11) is used, and wherein, secondarily, an ionisation measurement (8, 12) is carried out in a flame region (9) within the combustion chamber (1), characterised in that the ionisation signal of the ionisation measurement (8, 12) detects a fault and / or initiates an emergency control mode in the event of a malfunction of a primary sensor (7) and / or associated primary sensor electronics (11), wherein the method comprises at least one of the following steps a., b. or c., in which: a. Above a minimum output, the ionisation measurement (8, 12) is carried out in order to distinguish between two types of output increase; b. the ionisation measurement (8, 12) does not always provide a signal usable for control during operation below a minimum output of the heating appliance, so that this signal is discarded, but at higher output measures an ionisation signal with which, in the event of a failure of the primary sensor system (7, 11), it is determined whether flames (2) are still present, and with which, if necessary, an emergency control mode is also carried out in a power range above the minimum power; c. if the flames (2) go out but are incorrectly detected by the primary sensors (7, 11) and consequently the output of the heating appliance is increased by a control electronics unit (13), and no usable ionisation signal is detected above a minimum output, the extinction of the flames (2) is inferred from the absence of this ionisation signal and a safety measure is initiated.

2. Method according to claim 1, wherein the primary sensor system (7, 11) detects ultraviolet radiation in or at the combustion chamber (1).

3. A method according to claim 1, wherein the primary sensor system (7, 11) detects temperatures in or at the combustion chamber (1).

4. A method according to one of the preceding claims, wherein the primary sensor system (7, 11) not based on ionisation measurement is also used to control the air-to-fuel gas ratio.

5. A method according to one of the preceding claims, wherein, following the detection of a false flame signal by the primary sensor system (7, 11), it is no longer taken into account during a restart of the heating appliance in emergency mode, but the heating appliance is operated, if necessary, only within a power range in which the secondary ionisation measurement (8, 12) can be used to detect flames (2) and for control via , wherein the ionisation measurement (8, 12) replaces the primary sensor system (7, 11).

6. Arrangement for the safe operation and control of a combustion process in a combustion chamber (1) of a heating appliance for the combustion of hydrogen or a fuel gas containing more than 90% hydrogen with air, wherein primary sensor technology (7, 11) is provided and configured, and wherein a secondary ionisation measuring device (8, 12) is provided for measuring ionisation in a flame region (9) within the combustion chamber (1), the ionisation signal of which, in the event of a fault in a primary sensor (7) and / or associated primary sensor electronics (11), an evaluation electronics unit (10) is provided which is configured to check, in the event of a power increase of the heating appliance beyond a minimum power level sought by a control electronics unit (13), whether an ionisation signal is present, so that, in the absence of this signal, it can be concluded that the flames (2) have gone out despite a false detection of flames (2) by the primary sensor system (7, 11) and thus that there is a fault in the primary sensor system (7, 11), and the arrangement is configured to carry out a method according to one of the preceding claims.

7. An arrangement according to claim 6, wherein the evaluation electronics (10) are configured, upon detection of a fault in the primary sensor system (7, 11), to switch off the heating appliance, trigger a fault message and / or perform a switchover, such that the heating appliance can only be operated within a power range suitable for ionisation measurements, and the ionisation measuring device (8, 12) is used to detect the presence of flames (2) and to control the combustion process.

8. A computer program product comprising instructions that cause the system according to any one of claims 6 to 7 to perform the method according to any one of claims 1 to 5.

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