Methods for monitoring the operation of a gas burner system and gas burner system

Abstract

Method for monitoring the operation of a gas burner system (1), wherein a fuel-air mixture is ignited by means of a burner (2) during the operation of the gas burner system (1) and a flame (5) is generated, wherein the temperature of the flame (5) is measured by means of a flame temperature measuring device (7) actively cooled by a supply of cooling air and is evaluated by means of an evaluation device (11), wherein if the temperature of the flame (5) drops below a critical value or with a certain negative gradient, a fuel supply to the burner (2) is interrupted, and wherein a combustion air ratio is determined from the temperature of the flame (5), and in the event of an anomaly in the combustion air ratio, the fuel supply to the burner (2) is interrupted.

Description

[0001] The present invention relates to a method for monitoring the operation of a gas burner system. Furthermore, the present invention relates to a gas burner system.

[0002] Gas burner systems, such as those used in condensing gas boilers, are known in numerous different designs from the prior art. These gas burner systems have a burner by means of which a fuel-air mixture can be combusted during operation. In order to monitor the operation of such gas burner systems, it is necessary to record and evaluate various operating parameters of the burner. This includes, for example, flame monitoring.

[0003] Methods for flame monitoring of a burner based on flame temperature measurement are known from the prior art. Such methods utilize at least one thermocouple whose temperature-sensitive area extends into the flame. An electrical voltage generated by the flame temperature due to the thermoelectric effect (Seebeck effect) during an active flame is sufficient to hold a fuel valve of the gas burner system open against a mechanical spring force. When the fuel valve is open, fuel can flow into the burner's combustion chamber, thus maintaining the flame. When the flame goes out, the thermocouple cools down, causing the electrical voltage generated by the flame temperature due to the thermoelectric effect to decrease and eventually become insufficient to keep the fuel valve open any longer.The fuel valve is then closed by the action of the spring force.

[0004] Such a method is relatively simple to implement and also very robust. However, it has the crucial disadvantage that the thermocouple, along with its protective casing, requires a certain amount of time to cool down after the flame goes out. During this time, the electrical voltage generated by the thermoelectric effect remains high enough to keep the fuel valve in the open position. In practice, this can therefore take up to 30 seconds for the fuel valve to close. For this reason, according to the relevant standards, this method is only permitted for semi-automatic burners, but not for automatic burners used in residential applications, particularly in condensing gas boilers, and in industrial applications.This is because the relevant standards, such as DIN EN 298:2012-11, require a closing time of 1 s for the fuel valves from the time the flame goes out.

[0005] Gas burner systems known from the prior art are frequently operated with aliphatic fuels, such as natural gas. However, these aliphatic fuels have the disadvantage that a significant amount of carbon dioxide (CO2) is produced during the combustion process. To reduce such carbon dioxide emissions, gas burner systems are already known from the prior art that are designed to operate with a mixture of hydrogen and an aliphatic fuel, in particular a hydrogen-natural gas mixture, or even with 100% hydrogen as fuel – apart from unavoidable impurities. Furthermore, hydrogen has the highest energy density compared to other fuels, such as petroleum or natural gas.The use of hydrogen or a hydrogen-natural gas mixture as fuel in a gas burner system affects the burner's operating parameters, such as the air-fuel ratio λ, also known as the air-fuel ratio. This air-fuel ratio λ is defined as the quotient of the actual air mass available for the combustion process and the minimum air mass theoretically required for stoichiometrically complete combustion.

[0006] An example of a gas burner system that can be operated with a fuel content of up to 100% hydrogen is known from WO 2020 / 182 902 A1.

[0007] DE 10 2004 030 299 A1 discloses a method for monitoring the operation of a gas burner system, wherein a fuel-air mixture is ignited and a flame is generated by means of a burner during the operation of the gas burner system, wherein the temperature of the flame is measured by means of a flame temperature measuring device and evaluated by means of an evaluation device, wherein if the gas valve position drops below a critical value or with a certain negative gradient, a fuel supply to the burner is interrupted, and wherein a combustion air ratio is determined from the temperature of the flame.

[0008] DE 199 03 305 A1 describes a method for flame monitoring in which gradient-based flame monitoring is combined with temperature threshold-based flame monitoring. The "flame out" state is detected based on either a gradient or a temperature threshold, thus ensuring the fastest and most reliable "flame out" detection possible.

[0009] The object of the present invention is to provide a method for monitoring the operation of a gas burner system and a gas burner system which enable reliable and safe operation of the gas burner system.

[0010] The solution to this problem is provided by a method for monitoring the operation of a gas burner system with the features of claim 1. With regard to the gas burner system, this problem is solved by a gas burner system with the features of claim 6. The dependent claims relate to advantageous embodiments of the invention.

[0011] In an inventive method for monitoring the operation of a gas burner system, wherein a fuel-air mixture is ignited and a flame is generated by means of a burner during the operation of the gas burner system, it is provided that the temperature of the flame is measured by means of a flame temperature measuring device actively cooled by a supply of cooling air and is evaluated by means of an evaluation device, wherein if the temperature of the flame drops below a critical value or with a certain negative gradient, a fuel supply to the burner is interrupted, and wherein a combustion air ratio is determined from the temperature of the flame, and in the event of an anomaly in the combustion air ratio, the fuel supply to the burner is interrupted.

[0012] In the inventive method for monitoring the operation of a gas burner system, the flame temperature measuring device, which detects the flame temperature, is continuously and actively cooled by forced convection with cooling air. This cooling air circulates around the flame temperature measuring device, which preferably comprises one or more thermocouples, and particularly also into the area between the flame temperature measuring device and a protective casing for it. The continuous active cooling of the flame temperature measuring device by means of the cooling air causes the flame temperature measuring device to cool down more quickly after the flame goes out than it would without active cooling. This advantageously and effectively shortens the reaction time between the flame going out and the closing of the fuel valve to interrupt the fuel supply.

[0013] In addition to detecting the presence or absence of the flame, or even its emergence, another property can be measured quickly enough based on the principle of active cooling of the flame temperature measuring device presented here: This is the air-fuel ratio, which is also an important operating parameter of the burner.

[0014] The invention is based on the understanding that the flame temperature, which can be measured very quickly using the actively cooled flame temperature measuring device, is also a measure of the air-fuel ratio λ or the fuel-air ratio. With the actively cooled flame temperature measuring device, it is advantageously possible to quickly detect a deviation of the air-fuel ratio or the fuel-air ratio from the optimal values ​​into ranges unfavorable for the combustion process and to deactivate the fuel supply. From a safety perspective, this would be too slow without the active cooling of the flame temperature measuring device.

[0015] For cooling purposes, in an advantageous embodiment, a portion of the process air, which is supplied to the burner's combustion chamber, for example, by means of a ventilation device or drawn into the burner's combustion chamber by means of an exhaust gas ventilation device, is diverted and used as cooling air for actively cooling the flame temperature measuring device. The remaining portion of the process air forms combustion air for the combustion process of the fuel within the combustion chamber.

[0016] The measurement signal from the flame temperature measuring device is preferably read by a fail-safe input module of the evaluation unit and evaluated, in particular, analogously (i.e., via its signal waveform and not digitally via limit values). A shutdown signal for the fuel valve is generated as soon as a drop in the measured temperature below a defined temperature limit, with a specific negative (critical) gradient, or an anomaly in the combustion air ratio is detected. Flame extinguishment based on the flame temperature can thus be detected both statically (flame temperature falls below a specific limit) and dynamically (flame temperature has a specific negative gradient indicating extinguishment). Active cooling of the flame temperature measuring device allows for faster and more reliable detection of a corresponding drop in flame temperature than without cooling.Furthermore, in an advantageous embodiment, the presence of the flame can be detected via a constant high temperature, and the generation of the flame via a rising temperature. Preferably, the gradient behavior of the flame temperature measured by the flame temperature measuring device is evaluated in this context to detect possible temperature changes. This makes it very easy to determine whether the flame temperature is rising, falling, or remaining constant.

[0017] An increase or decrease in the temperature of the process air or cooling air will inevitably lead to an increase or decrease in the measured flame temperature. To prevent an increase or decrease in the temperature of the process air or cooling air from being erroneously interpreted as a flame starting or going out, an advantageous embodiment additionally measures the temperature of the process air, and thus also of the cooling air diverted from it, using an air temperature measuring device at a location that cannot be influenced by the flame, and evaluates it using the evaluation device. Preferably, the air temperature measuring device is arranged within the air supply line.If an increase / decrease in temperature is also detected by the air temperature measuring device, this temperature change is advantageously not taken into account when evaluating the flame temperature and is therefore not considered by the evaluation device as a flame starting or going out.

[0018] In an advantageous embodiment, a failure of the process air supply is monitored by means of a pressure measuring device, which is preferably located within the air supply line. This pressure measuring device detects the pressure of the process air and thus also the cooling air. If a failure of the process air supply is detected, the fuel valve is closed, thus interrupting the fuel supply to the combustion chamber.

[0019] The flame temperature measuring device is arranged to measure the flame temperature. Since the flame temperature is constant with a constant fuel-air ratio or constant air-fuel ratio and an intact flame / combustion of the fuel-air mixture, i.e., independent of the burner output (which can vary in a modulating burner), a reduction in burner output will not lead to a reduction in the measured temperature and therefore will not cause the fuel valve to close due to an incorrect detection of a flame going out.

[0020] A gas burner system according to the invention comprises - a burner with a combustion chamber, - a fuel supply line and an air supply line connected to the combustion chamber of the burner, - at least one fuel valve located within the fuel supply line that can be selectively opened and closed to release and stop the fuel supply to the combustion chamber of the burner, - a control device by means of which the operation of the gas burner system can be controlled, - an actively cooled flame temperature measuring device designed to measure the temperature of the flame, - an evaluation unit designed to evaluate temperature measurement data from the flame temperature measuring device and to transmit the results of the evaluation to the control unit, wherein the control device is configured to generate a shutdown signal for the fuel valve when the temperature of the flame drops below a critical value or when the temperature drops with a certain negative gradient, and wherein the evaluation device is configured to determine a combustion air ratio from the temperature of the flame and wherein the control device is configured to generate a shutdown signal for the fuel valve in the event of an anomaly in the combustion air ratio.

[0021] The gas burner system according to the invention, which is based on the findings of the method already described in detail above, enables safe operation of the gas burner system, since in particular a flame extinguishing or an anomaly in the combustion air ratio can be detected very quickly due to the active cooling of the flame temperature measuring device, so that a very rapid shutdown of the fuel supply can take place.

[0022] In a preferred embodiment, the gas burner system may have a bypass line within which the flame temperature measuring device is housed. This bypass line is arranged to branch off from the air supply line, so that during operation of the gas burner system, a portion of the process air flowing through the air supply line is diverted into the bypass line, providing cooling air for the flame temperature measuring device. The remaining portion of the process air, which does not flow through the bypass line, forms the combustion air for the fuel within the burner's combustion chamber.

[0023] In a particularly preferred embodiment, an air temperature measuring device can be housed within the air supply line. Using this air temperature measuring device, the temperature of the process air can be measured at a location that is not influenced by the flame temperature.

[0024] In an advantageous embodiment, a pressure measuring device can be housed within the air supply line. This pressure measuring device can then be used to detect whether the process air is available.

[0025] In a particularly advantageous embodiment, it is proposed that the gas burner system be configured for operation with a fuel consisting of a mixture of an aliphatic fuel and hydrogen, or, apart from natural impurities, exclusively of hydrogen. However, a purely aliphatic fuel, such as natural gas, can also be used.

[0026] One advantage of the method described here, as well as the gas burner system, lies particularly in its simplicity at the sensor level. Only one flame temperature measuring device with one or more thermocouples is required, typically consisting of just two different metals welded together. This allows for a very simple and cost-effective implementation of the flame temperature measuring device. In contrast, the optical sensor devices also commonly used for flame monitoring, which are based, for example, on UV light detection, are considerably more complex.

[0027] Further features and advantages of exemplary embodiments of the present invention are described with reference to the enclosed Fig. Figure 1 explains in more detail the basic structure of a gas burner system 1 in a highly simplified schematic form. Based on this representation, details of a method for monitoring the operation of the gas burner system 1 will be explained in more detail below.

[0028] The gas burner system 1 comprises a burner 2 with a combustion chamber 20, a fuel supply line 3, and an air supply line 4, which are connected to the combustion chamber 20 of the burner 2. A fuel valve 12 is located within the fuel supply line 3, which can be selectively opened and closed to allow or stop the fuel supply to the combustion chamber 20 of the burner 2.

[0029] During operation of the gas burner system 1, fuel is fed into the combustion chamber 20 of the burner 2 via the fuel supply line 3. Process air is supplied via the air supply line 4, a portion of which forms combustion air for the combustion process and is introduced into the combustion chamber 20 of the burner 2. This results in an ignitable fuel-air mixture being obtained within the combustion chamber 20 of the burner 2 during operation of the gas burner system 1. This mixture is ignited by an ignition device (not explicitly shown here) to produce a flame 5. An aliphatic fuel, such as natural gas, can be used as the fuel. However, it is preferred to use a mixture of hydrogen and an aliphatic fuel, particularly natural gas, as the fuel.In a particularly advantageous embodiment, the gas burner system 1 is designed such that the burner 2 can be operated with 100% hydrogen as fuel - apart from natural impurities.

[0030] As in Fig.As can be seen in Figure 1, the gas burner system 1 has a bypass line 6, within which a flame temperature measuring device 7 is housed, designed to measure the flame temperature of the flame 5. Through the bypass line 6, a certain proportion of the process air from the air supply line 4 can be diverted past the combustion chamber 20 of the burner 2, so that this air no longer contributes to the combustion process of the fuel-air mixture as combustion air, but can be used as cooling air for actively cooling the flame temperature measuring device 7 by forced convection. The combustion air can, for example, be supplied to the combustion chamber 20 of the burner 2 by a fan or drawn into the combustion chamber 20 of the burner 2 by an exhaust fan.

[0031] Within the air supply line 4 are housed an air temperature measuring device 8, which is configured to measure the temperature of the process air, and a pressure measuring device 9, which is configured to measure the air pressure within the air supply line 4. The pressure measuring device 9 is preferably designed to be configured for analog pressure measurement and thus does not detect a digital switching threshold, but continuously measures the pressure of the process air in an analog manner.

[0032] Furthermore, the gas burner system 1 includes a control unit 10, which is configured to control and monitor the operation of the gas burner system 1. In particular, the control unit 10 is configured to generate an enable signal or a shut-off signal for the fuel valve 12. In addition, an evaluation unit 11 is provided, which is connected to the flame temperature measuring device 7, the air temperature measuring device 8, and the pressure measuring device 9 in order to receive and evaluate the data measured by these measuring devices. The evaluation unit 11 is, in turn, connected to the control unit 10.Although the evaluation unit 11 and the control unit 10 are shown here as two separate units in the drawing, it is fundamentally possible to integrate their functions into a single unit, in particular into the control unit 10, and thus increase the degree of integration.

[0033] In this design, the flame temperature measuring device 7 is continuously cooled by forced convection with the cooling air. For this purpose, a portion of the process air already supplied via the air supply line 4, which partially bypasses the combustion chamber 20 and enters the bypass line 6, is used as cooling air. This cooling air circulates around the flame temperature measuring device 7, which preferably has one or more thermocouples, and in particular between this flame temperature measuring device 7 and a protective casing. This continuous cooling of the flame temperature measuring device 7 by forced convection causes it to cool down more quickly when the flame 5 goes out than it would without this active cooling. This measure advantageously makes it possible to significantly shorten the shutdown time between the extinguishing of the flame 5 and the closing of the fuel valve 12.

[0034] The measurement signal from the flame temperature measuring device 7 is read by a fail-safe input module of the evaluation unit 11 and evaluated analogously (i.e., via its curve and not digitally via limit values) by the evaluation unit 11. As soon as a drop in the measured flame temperature below a critical limit value or a drop in the measured flame temperature with a specific (critical) negative gradient, indicating that the flame 5 has extinguished, is detected, the control unit 10 generates a shutdown signal for the fuel valve 12. This causes the fuel valve 12 to close, thus interrupting the fuel supply to the combustion chamber 20 of the burner 2. Due to the active cooling of the flame temperature measuring device 7, a corresponding drop in temperature can be detected more quickly and reliably than without cooling.Furthermore, by evaluating the measurement signals from the flame temperature measuring device 7, the presence of a flame 5 can be reliably detected by recording a substantially constant high temperature, and a developing flame 5 can be reliably detected by recording a rising temperature. Preferably, the gradient behavior of the flame 5 temperature measured by the flame temperature measuring device 7 is evaluated in order to detect any temperature changes. This makes it very easy to determine whether the flame 5 temperature is rising, falling, or remaining constant.

[0035] An increase or decrease in the process air temperature will inevitably lead to an increase or decrease in the flame temperature. To prevent an increase or decrease in the process air temperature from being incorrectly interpreted as the ignition or extinguishing of a flame 5, the temperature of this process air is additionally measured at a point that cannot be influenced by the flame 5. This is done using the air temperature measuring device 8, which is located within the air supply line 4. If the air temperature measuring device 8 detects an increase or decrease in the air temperature, this temperature change is not taken into account when evaluating the flame temperature using the evaluation unit 11 and is therefore not interpreted as the ignition or extinguishing of a flame 5.

[0036] The same applies to the process air pressure, which is measured by means of the pressure measuring device 9, whereby an increase in pressure leads to a reduction in the flame temperature due to greater expansion in the flame 5, and a decrease in pressure leads to an increase in the flame temperature due to less expansion in the flame 5. The fuel pressure does not need to be taken into account in this context, since the relevant combustion technology standards always prescribe a gas pressure regulator to ensure a constant gas pressure.

[0037] Other factors that influence the flame temperature, such as the design of burner 2 and the nitrogen content of the combustion air, can be considered more or less constant and therefore do not need to be compensated for with corresponding process engineering effort.

[0038] A deterioration (anomaly) in the fuel-air ratio, leading to a reduction in flame temperature, does not need to be compensated for in any way, as this is interpreted as a flame extinguishing 5, which is even desirable under these conditions since the fuel supply must also be shut off in this case by closing the fuel valve 12. This behavior further contributes to the operational reliability of the gas burner system 1.

[0039] A failure of the process air supply, as well as the process air pressure, is monitored by the pressure measuring device 9 within the air supply line 4. If a failure of this air supply is detected, the fuel valve 12 is closed. This also contributes to the operational reliability of the gas burner system 1. If a gas involved in the combustion process, such as the combustion air, expands during combustion because it is supplied at a higher pressure, this can also lead to a reduction in flame temperature due to the Joule-Thomson effect. This temperature behavior does not necessarily have to be taken into account, but it does show that pressure fluctuations of the combustion air—similar to the temperature of the combustion air—have an influence on the flame temperature and must therefore be considered in flame evaluation.Because a possible reduction in pressure, as well as an increase in the temperature of the combustion air, could mask a flame going out 5.

[0040] The flame temperature measuring device 7 must be positioned so that it can reliably measure the temperature of the flame 5. Since the flame temperature is constant with a constant fuel-air ratio or constant air-fuel ratio and an intact flame 5 / regular combustion, i.e., independent of the burner 2 output, which can vary considerably in the case of a modulating burner 2, a reduction in burner output will not lead to a reduction in the measured temperature and therefore will not cause the fuel valve 12 to close due to an incorrect detection of a flame 5 going out.

[0041] The advantage of the solution described here lies particularly in its simplicity at the sensor level. Only one flame temperature measuring device 7 with one or more thermocouples is required, which typically consist of just two different metals welded together, so that the flame temperature measuring device 7 can be implemented very simply and cost-effectively.

[0042] The flame monitoring of the gas burner system 1 according to the method presented here can be carried out, for example, as follows:

[0043] State 1: Burner 2 is switched off. The measurement data from the air temperature measuring device 8 and the flame temperature measuring device 7 are not evaluated.

[0044] State 2: Burner 2 is activated. Initially, pre-ventilation takes place. Due to the supplied airflow, both the air temperature measuring device 8 and the flame temperature measuring device 7 assume the temperature of the process air supplied via the air supply line. To increase the fault detection capabilities, both measured temperatures are preferably monitored for plausibility by the evaluation unit 11.

[0045] State 3: Burner 2 is ignited and the fuel-air mixture is ignited, producing flame 5. An increase in flame temperature, measured by the flame temperature measuring device 7, is registered as the formation of flame 5. A specific flame temperature must be reached within a defined safety time for ignition. If not, burner 2 is shut off by interrupting the fuel supply to burner 2 through the closing of the fuel valve 12.

[0046] State 4: Burner 2 is ignited, but the flame 5 still needs to stabilize. The flame temperature, measured by the flame temperature measuring device 7, may still vary slightly at a high level. After a certain time, however, the flame temperature must be stable at a high level. If not, burner 2 is switched off by interrupting the fuel supply through the closing of the fuel valve 12.

[0047] State 5: Burner 2 is in operation, and the flame 5 is stable. A decrease in the flame temperature, measured by the flame temperature measuring device 7, is interpreted as flame 5 going out. Burner 2 is shut down by interrupting the fuel supply through closing the fuel valve 12. A decrease in flame temperature can also be caused by an increasing or decreasing air ratio. While the flame temperature monitoring described here cannot distinguish this effect from flame 5 going out, this is not critical and is even desirable, as an increasing or decreasing air ratio can also lead to potentially dangerous situations during burner 2 operation. If an air ratio anomaly is detected, burner 2 is shut down by interrupting the fuel supply through closing the fuel valve 12.

Claims

[1] Method for monitoring the operation of a gas burner system (1), wherein a fuel-air mixture is ignited by means of a burner (2) during the operation of the gas burner system (1) and a flame (5) is generated, wherein the temperature of the flame (5) is measured by means of a flame temperature measuring device (7) actively cooled by an application of cooling air and is evaluated by means of an evaluation device (11), wherein if the temperature of the flame (5) falls below a critical value or with a certain negative gradient, a fuel supply to the burner (2) is interrupted, and wherein a combustion air ratio is determined from the temperature of the flame (5), and if there is an anomaly in the combustion air ratio, the fuel supply to the burner (2) is interrupted. [2] Method according to claim 1, characterized by, that a portion of the process air supplied to the burner (2) is diverted to provide cooling air for the flame temperature measuring device (7). [3] Method according to one of claims 1 or 2, characterized by , that a gradient behavior of the temperature of the flame (5) is evaluated. [4] Method according to any one of claims 1 to 3, characterized by , that the temperature of the cooling air is measured by means of an air temperature measuring device (8) at a position outside a temperature influence area of ​​the flame (5) and is evaluated by means of the evaluation device (11). [5] Method according to any one of claims 1 to 4, characterized by , that the pressure of the cooling air is recorded by means of a pressure measuring device (9) and evaluated by means of the evaluation device (11). [6] Gas burner system (1), comprising - a burner (2) with a combustion chamber (20), - a fuel supply line (3) and an air supply line (4) which are connected to the combustion chamber (20) of the burner (2), - at least one fuel valve (12) located within the fuel supply line (3) which can be selectively opened and closed to release and stop the fuel supply to the combustion chamber (20) of the burner (2), - a control device (10) by means of which the operation of the gas burner system (1) can be controlled, - an actively cooled flame temperature measuring device (7) designed to measure the temperature of the flame (5), - an evaluation device (11) which is designed to evaluate temperature measurement data from the flame temperature measuring device (7) and to transmit the results of the evaluation to the control device (10), wherein the control device (10) is configured to generate a shutdown signal for the fuel valve (12) when the temperature of the flame (5) falls below a critical value or when the temperature falls with a certain negative gradient, and wherein the evaluation device (11) is configured to determine a combustion air ratio from the temperature of the flame (5) and wherein the control device (10) is configured to generate a shutdown signal for the fuel valve (12) in the event of an anomaly in the combustion air ratio. [7] Gas burner system (1) according to claim 6, characterized by, that the gas burner system (1) has a bypass line (6) within which the flame temperature measuring device (7) is housed and which is arranged to branch off from the air supply line (4) so ​​that during operation of the gas burner system (1) a portion of the process air flowing through the air supply line (4) is diverted into the bypass line and forms cooling air for active cooling of the flame temperature measuring device (7). [8] Gas burner system (1) according to one of claims 6 or 7, characterized by , that an air temperature measuring device (8) is housed within the air supply line (4). [9] Gas burner system (1) according to any one of claims 6 to 8, characterized by , that a pressure measuring device (9) is housed within the air supply line (4). [10] Gas burner system (1) according to any one of claims 6 to 9, characterized by, that the gas burner system (1) is designed for operation with a fuel consisting of a mixture of an aliphatic fuel and hydrogen or consisting exclusively of hydrogen except for natural impurities.

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