METHOD FOR MONITORING THE OPERATION OF A GAS BURNER SYSTEM AND GAS BURNER SYSTEM - Patent application

Abstract

To provide a method for monitoring operation of a gas burner system.SOLUTION: A fuel / air mixture is ignited and a flame 5 is generated by a burner 2 during operation of a gas burner system 1. The temperature of the flame 5 is measured by a flame temperature measurement device 7 cooled actively by impingement of cooling air, and is evaluated by an evaluation device 11. A fuel supply to the burner 2 is interrupted in response to the temperature of the flame 5 dropping below a critical value or having a specific negative gradient. An air-fuel ratio is determined from the temperature of the flame 5. The fuel supply to the burner 2 is interrupted in the event of an anomaly in the air-fuel ratio. The invention further relates to the gas burner system 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[0002] Gas burner systems can be used, for example, in gas condensing boilers and are known in many different embodiments from the prior art. These gas burner systems include a burner, which is capable of combusting a fuel-air mixture during operation. 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] The prior art is known to provide methods for monitoring a burner flame, for example, based on measuring the flame temperature. Such methods at least use a thermocouple with a temperature-sensitive area extending into the flame. When the flame is active, a voltage generated by the flame temperature due to the thermoelectric effect (Seebeck effect) can keep the fuel valve of a gas burner system open against a mechanical spring force. When the fuel valve is open, fuel flows into the burner combustion chamber, maintaining the flame. When the flame is extinguished, the thermocouple cools, the voltage generated by the flame temperature due to the thermoelectric effect decreases, and the fuel valve can no longer be kept open. The spring force then closes the fuel valve.

[0004] This process is relatively simple in design and very robust. However, it has a crucial drawback: when the flame is extinguished, the thermocouple and its protective sheath need time to cool. During this time, the voltage generated by the thermoelectric effect remains high enough to keep the fuel valve open. In practice, it can take as long as 30 seconds for the fuel valve to close. Therefore, according to relevant standards, this method is only permitted for semi-automatic burners, not for domestic use, especially for gas-fired condensing boilers, or for automatic burners used in industrial applications. This is because relevant standards, such as DIN EN 298:2012-11, require the fuel valve to close within one second after the flame has been extinguished.

[0005] Gas burner systems known from the prior art are often operated on 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 this carbon dioxide emission, gas burner systems designed to operate on a mixture of hydrogen and aliphatic fuels, in particular a mixture of hydrogen and natural gas, or on 100% hydrogen (excluding unavoidable impurities) are already known from the prior art. Furthermore, hydrogen has the highest energy density compared to other fuels, such as oil and 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 number. This air-fuel ratio λ is defined as the quotient of the air mass actually available for the combustion process and the minimum air mass theoretically required for complete stoichiometric 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 / 192902 A1. Summary of the Invention

[0007] An object of the present invention is to provide a gas burner system and a method for monitoring the operation of the gas burner system, which can operate the gas burner system reliably and safely.

[0008] A solution to this problem provides a method for monitoring the operation of a gas burner system having the features of claim 1. For gas burner systems, this problem is solved by a gas burner system having the features of claim 6. The subclaims relate to preferred further embodiments of the invention.

[0009] In a method according to the invention for monitoring the operation of a gas burner system, the gas burner system comprises a burner in which a fuel-air mixture is ignited by a burner during operation of the gas burner system to generate a flame, the temperature of the flame is measured by a flame temperature measuring device which is actively cooled by applying cooling air and evaluated by an evaluation device, and in the method according to the invention for monitoring the operation of a gas burner system, the supply of fuel to the burner is interrupted if the temperature of the flame falls below a critical value or if it exhibits a certain negative slope, and the air-fuel ratio is determined from the flame temperature, and if the air-fuel ratio is abnormal, the supply of fuel to the burner is interrupted.

[0010] In a method according to the invention for monitoring the operation of a gas burner system, a flame temperature measuring device, by which the temperature of the flame is measured, is permanently and actively cooled by forced convection with cooling air. This cooling air preferably circulates around the flame temperature measuring device, which preferably includes one or more thermocouples, and particularly in the area between the flame temperature measuring device and its protective sheath. Permanent active cooling of the flame temperature measuring device with cooling air allows the flame temperature measuring device to cool more quickly than in the absence of active cooling after the flame has been extinguished. This advantageously and effectively shortens the reaction time between the extinguishing of the flame and the closing of the fuel valve to interrupt the fuel supply.

[0011] In addition to detecting the presence or absence or onset of a flame, another characteristic can be measured sufficiently quickly based on the principles of active cooling of the flame temperature measuring device presented here: the air number or air-fuel ratio, which is also an important operating parameter of the burner.

[0012] The flame temperature can be measured very quickly by an actively cooled flame temperature measuring device and is also an indicator of the air number λ or the air-fuel ratio. The actively cooled flame temperature measuring device advantageously makes it possible to detect sufficiently quickly any deviation of the air number or air-fuel ratio from the optimum air number or the optimum air-fuel ratio into a region unfavorable for the combustion process and to shut off the fuel supply. From a safety standpoint, this would be very slow without active cooling of the flame temperature measuring device.

[0013] For cooling purposes, in an advantageous embodiment, a portion of the process air supplied to the combustion chamber of the burner by the ventilation system or drawn into the combustion chamber of the burner by the exhaust gas ventilation system is branched off and used as cooling air for actively cooling the flame temperature measuring device, while the remaining process air serves as combustion air for burning fuel in the combustion chamber.

[0014] The measurement signal of the flame temperature measuring device is preferably read by a fail-safe input module of the evaluation device and evaluated in analog form (i.e., via its signal curve, not digitally via limit values). In this case, a switch-off signal for the fuel valve is generated as soon as the measured temperature drops below a defined temperature limit value, has a certain negative (critical) slope, or an abnormality in the air-fuel ratio is detected. This allows flame extinction based on the flame temperature to be detected both statically (when the flame temperature drops below a certain limit value) and dynamically (when the flame temperature has a certain negative slope indicating flame extinction). Active cooling of the flame temperature measuring device allows a drop in flame temperature to be detected more quickly and reliably than without cooling. Furthermore, in an advantageous embodiment, the presence of a flame can be detected via a certain high temperature, and the onset of a flame can be detected via an increase in 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.

[0015] An increase / decrease in the temperature of the process air or cooling air necessarily results in an increase / decrease in the measured flame temperature. To prevent an increase / decrease in the temperature of the process air or cooling air from being mistakenly interpreted as the onset / extinction of a flame, in an advantageous embodiment, the temperatures of the process air and the cooling air branched off therefrom are also measured by an air temperature measuring device at a position not affected by the flame and evaluated by an evaluation device. Preferably, the air temperature measuring device is disposed inside the air supply line. If the air temperature measuring device also detects an increase / decrease in temperature, this temperature change is preferably not taken into account in the evaluation of the flame temperature, and therefore is evaluated by the evaluation device as a flame being on or off.

[0016] In an advantageous embodiment, a failure of the process air supply is monitored by a pressure measuring device, preferably housed in the air supply line, which measures the pressure of the process air, i.e., 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.

[0017] The flame temperature measuring device is arranged to measure the flame temperature. Since the flame temperature is constant, i.e., independent of burner power (which may vary in modulating burners), at a constant air / fuel ratio or constant air number and when the flame / combustion of the fuel / air mixture is intact, a reduction in burner power will not result in a reduction in the measured temperature and therefore will not lead to fuel valve closure due to inaccurate detection of flame quenching.

[0018] The gas burner system according to the present invention comprises: a burner having 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 contained within the fuel supply line and selectively openable and closable to turn on and off fuel supply to the combustion chamber of the burner; a control device capable of controlling the operation of the gas burner system; an actively cooled flame temperature measurement device configured to measure the temperature of the flame; an evaluation device configured to evaluate the temperature measurement data of the flame temperature measurement device and transmit the evaluation result to the control device, The control device is configured to generate a switch-off signal for the fuel valve if the temperature of the flame falls below a critical value or if the temperature falls at a certain negative gradient, the evaluation device is configured to determine the air-fuel ratio from the temperature of the flame, and the control device is configured to generate a switch-off signal for the fuel valve if there is an abnormality in the air-fuel ratio.

[0019] The gas burner system according to the invention is based on the findings of the method described in detail above, and in particular because flame extinction or air-fuel ratio anomalies are detected very quickly due to active cooling of the flame temperature measuring device, allowing the fuel supply to be stopped very quickly and enabling safe operation of the gas burner system.

[0020] In a preferred embodiment, the gas burner system can include a bypass line, the bypass line containing the flame temperature measuring device, and the bypass line being branched off from the air supply line so that a portion of the process air flowing through the air supply line during operation of the gas burner system is diverted into the bypass line to form cooling air for actively cooling the flame temperature measuring device, and the remaining process air not passing through the bypass line serves as combustion air for the fuel in the combustion chamber of the burner.

[0021] In a particularly preferred embodiment, an air temperature measuring device can be accommodated in the air supply line, which allows the temperature of the process air to be measured at a location that is not affected by the flame temperature.

[0022] In a preferred embodiment, a pressure measuring device may be housed in the air supply line, which makes it possible to detect whether process air is available.

[0023] In a particularly advantageous embodiment, the gas burner system is configured to operate on a fuel consisting of a mixture of aliphatic fuel and hydrogen, or exclusively on hydrogen, except for natural impurities, although in principle pure aliphatic fuels such as natural gas can also be used.

[0024] The advantages of the method and gas burner system described herein are its simplicity, particularly in terms of the sensor. This is because only one flame temperature measurement device with one or more thermocouples is required, which typically consists of two dissimilar metals welded together, making the flame temperature measurement device very simple and inexpensive to implement. In contrast, optical sensor devices, which are also common in flame monitoring, are based on, for example, ultraviolet light detection, but these sensor devices are substantially more complex. [Brief explanation of the drawings]

[0025] [Figure 1] The basic structure of a gas burner system 1 is shown diagrammatically and in a highly simplified form. DETAILED DESCRIPTION OF THE INVENTION

[0026] Further features and advantages of embodiments of the present invention will be explained in more detail with reference to the attached Figure 1, which shows in a schematic and highly simplified form the basic structure of a gas burner system 1. Based on this illustration, details of a method for monitoring the operating state of the gas burner system 1 will also be explained below.

[0027] The gas burner system 1 includes a burner 2 having a combustion chamber 20, and a fuel supply line 3 and an air supply line 4 connected to the combustion chamber 20 of the burner 2. The fuel supply line 3 accommodates fuel valves 12 that can be selectively opened and closed to release or terminate the fuel supply to the combustion chamber 20 of the burner 2.

[0028] During operation of the gas burner system 1, fuel is supplied to the combustion chamber 20 of the burner 2 via the fuel supply line 3. Process air is supplied via the air supply line 4, part of which forms combustion air for the combustion process and is introduced into the combustion chamber of the burner. As a result, an ignitable fuel-air mixture is obtained in the combustion chamber 20 of the burner during operation of the gas burner system, and is ignited appropriately by an ignition device (not explicitly shown) to generate a flame. Aliphatic fuels, such as natural gas, can be used as fuel. However, it is preferred to use a mixture of hydrogen and an aliphatic fuel, especially natural gas, as fuel. In a particularly advantageous embodiment, the gas burner system 1 is designed so that the burner 2 can be operated using 100% hydrogen as fuel, excluding natural impurities.

[0029] As can be seen in Figure 1, the gas burner system 1 has a bypass line 6 in which a flame temperature measuring device 7 is housed for measuring the temperature of the flame 5. Through the bypass line 6, a proportion of the process air from the air supply line 4 can be directed past the combustion chamber 20 of the burner 2 so that this proportion of air no longer contributes as combustion air to the combustion process of the fuel-air mixture, but can be used as cooling air for active cooling of the flame temperature measuring device 7 by forced convection. The combustion air can be supplied to the combustion chamber 20 of the burner 2 by a fan, for example, or drawn into the combustion chamber 20 of the burner 2 by an exhaust fan.

[0030] Contained within the air supply line 4 is an air temperature measuring device 8 which is configured to measure the temperature of the process air, and a pressure measuring device 9 which measures the air pressure in the air supply line 4. The pressure measuring device 9 is preferably configured for analog pressure measurement and therefore to continuously measure the pressure of the process air in an analog manner rather than detecting a digital switching threshold.

[0031] Furthermore, the gas burner 1 includes a control device 10 configured to control and monitor the operation of the gas burner system 1. In particular, the control device 10 is configured to generate an enable signal or a shut-off signal for a fuel valve 12. Furthermore, a flame temperature measuring device 7, an air temperature measuring device 8, and a pressure measuring device 9 are connected to the gas burner system 1. An evaluation device 11 is provided for receiving and evaluating data measured by these measuring devices. The evaluation device 11 is connected to the control device 10. Although the evaluation device 11 and the control device 10 are shown as two separate devices, in principle it is possible to combine their functions, in particular into the control device 10, thereby increasing the degree of integration.

[0032] The flame temperature measuring device 7 is continuously cooled by forced convection with cooling air. For this purpose, part of the process air supplied from the air supply line 4, part of which bypasses the combustion chamber 20 and enters the bypass line 6, is used as cooling air. This cooling air flows around the flame temperature measuring device 7, which preferably has one or more thermocouples, and in particular between the flame temperature measuring device 7 and the protective jacket. This continuous cooling of the flame temperature measuring device 7 by forced convection allows the flame temperature measuring device 7 to cool more quickly during fire extinguishing than would be possible without this active cooling. This measure advantageously allows the switch-off time between the extinguishing of the flame 5 and the closing of the fuel valve 12 to be significantly reduced.

[0033] The measurement signal of the flame temperature measuring device 7 is read by a fail-safe input module of the evaluation device 11 and evaluated by the evaluation device 11 in analog form (i.e., via its progression, and not digitally via a limit value). As soon as the control device 10 detects that the measured flame temperature has dropped below the limit value or that a decrease in the measured flame temperature with a certain (critical) negative slope, indicating that the flame 5 has disappeared, generates a shut-off signal for the fuel valve 12, which closes the fuel valve 12 and interrupts the fuel supply to the combustion chamber 20 of the burner 2. Active cooling of the flame temperature measuring device 7 allows a corresponding temperature decrease to be detected more quickly and reliably than without cooling. Furthermore, evaluating the measurement signal of the flame temperature measuring device 7 allows a reliably detected existing flame 5 by detecting a substantially constant high temperature, and an emerging flame 5 by detecting a rising temperature. Preferably, the gradient behavior of the temperature of the flame 5 measured by the flame temperature measuring device 7 is evaluated in this context to detect possible temperature changes. This makes it very easy to detect whether the temperature of the flame 5 is rising, falling, or remaining constant.

[0034] A rise / fall in the process air temperature inevitably leads to a rise / fall in the flame temperature. To prevent a rise / fall in the process air temperature from being interpreted as the occurrence / extinction of flame 5, the process air temperature is also measured at a position that cannot be affected by flame 5. This is done by an air temperature measuring device 8 disposed in air supply line 4. If an increase / fall in air temperature is detected by air temperature measuring device 8, this temperature change is not taken into account in the evaluation of the flame temperature by evaluation device 11, and therefore is not evaluated as a occurring or extinguishing flame.

[0035] The same applies to the process air pressure measured by the pressure measuring device 9: an increase in pressure leads to a decrease in the flame temperature due to a greater expansion in the flame 5, and a decrease in pressure leads to an increase in the flame temperature due to a smaller expansion in the flame 5. The relevant standards for combustion technology prescribe gas pressure regulators to ensure a constant gas pressure at all times, so there is no need to consider the fuel pressure in this regard.

[0036] Other factors that influence the flame temperature, such as the configuration of the burner 2 and the nitrogen content of the combustion air, can be considered more or less constant and therefore do not have to be compensated for with corresponding process engineering efforts.

[0037] An abnormal air-fuel ratio leading to a drop in flame temperature is considered a disappearing flame 5 and does not require any compensation, which is actually desirable since under this condition the fuel valve 12 must be closed to stop the fuel supply. This behavior further contributes to the operational safety of the gas burner system 1.

[0038] The process air supply and its pressure are monitored by a pressure measuring device 9 in the air supply line 4. If a malfunction of this air supply is detected, the fuel valve 12 is closed. This also contributes to the operational safety of the gas burner system 1. Furthermore, gases involved in the combustion process, such as combustion air, are supplied under higher pressure. Therefore, when they expand during combustion, the flame temperature can decrease due to the Joule-Thomson effect. While this temperature behavior does not necessarily need to be considered, it does indicate that fluctuations in the combustion air pressure, like the combustion air temperature, affect the flame temperature and therefore must be taken into account in the flame evaluation. This is because a possible decrease in pressure, like an increase in the combustion air temperature, can disguise a disappearing flame 5.

[0039] The flame temperature measuring device 7 must be arranged so as to reliably measure the temperature of the flame 5. With a constant air-fuel ratio or constant air number and an intact flame 5 / regular combustion, the flame temperature is constant, i.e. independent of the burner 2 power, which can often fluctuate with a regulated burner 2, so that a reduction in the burner power does not result in a reduction in the measured temperature and therefore does not lead to the closure of the fuel valve 12 due to an inaccurate detection of a disappearing flame 5.

[0040] The advantage of the solution presented here is its simplicity, especially with regard to the sensor: only one flame temperature measuring device 7 with one or more thermocouples is required, which typically consist of two dissimilar metals welded together, and therefore the flame temperature measuring device 7 can be realized very simply and cheaply.

[0041] Flame monitoring of the gas burner system 1 according to the method presented here can be performed, for example, as follows.

[0042] Condition 1: The burner 2 is switched off. The measurement data of the air temperature measuring device 8 and the flame temperature measuring device 7 are not evaluated.

[0043] Condition 2: The burner 2 is activated. First, pre-ventilation is carried out. Due to the supplied air flow, both the air temperature measuring device 8 and the flame temperature measuring device 7 measure the temperature of the process air supplied via the air supply line. To increase the possibility of error detection, it is preferable that both measured temperatures are monitored by an evaluation device 11 with regard to their validity.

[0044] State 3:The burner 2 is ignited and the fuel-air mixture is ignited so as to produce a flame 5. The rise in flame temperature measured by the flame temperature measuring device 7 is evaluated as a developing flame 5. A certain flame temperature must be reached within a specified safety time for ignition. If this is not the case, the burner 2 is switched off by closing the fuel valve 12 and interrupting the fuel supply to the burner 2.

[0045] State 4: The burner 2 is ignited, but the flame 5 must still stabilize. The flame temperature measured by the flame temperature measuring device 7 may still fluctuate slightly at the high point. However, after a certain time, the flame temperature must stabilize at the high point. If this is not the case, the burner 2 is switched off by closing the fuel valve 12 and interrupting the fuel supply.

[0046] Status 5: Burner 2 is running, and flame 5 is stable. A drop in flame temperature, measured by flame temperature measuring device 7, is evaluated as flame out 5. Burner 2 can be switched off by closing fuel valve 12 and interrupting the fuel supply. A drop in flame temperature can also be caused by an increase or decrease in air count. The flame temperature monitoring described here cannot distinguish this effect from flame out 5. However, this is not critical, and is even desirable, since an increase or decrease in air count can cause a dangerous situation during operation of burner 2. If an abnormal air count is detected, fuel valve 12 is closed, cutting off the fuel supply and shutting down the burner.

Claims

1. A method for monitoring the operation of a gas burner system (1), comprising: During operation of the gas burner system (1), a fuel-air mixture is ignited by the burner (2), A flame (5) is generated, The temperature in the vicinity of the flame (5) is measured by a flame temperature measuring device (7) that is actively cooled by applying cooling air, and evaluated by an evaluation device (11); The temperature of the cooling air is measured by an air temperature measuring device (8) at a position not affected by the temperature in the vicinity of the flame (5) and evaluated by an evaluation device (11); When the temperature in the vicinity of the flame (5) falls below a critical value or reaches a certain negative slope, the supply of fuel to the burner (2) is interrupted; and a method in which the air-fuel ratio is determined from the temperature in the vicinity of the flame (5), and in which the supply of fuel to the burner (2) is interrupted if the air-fuel ratio is abnormal.

2. 2. The method according to claim 1, characterized in that a part of the process air led to the burner (2) is branched off to provide cooling air for the flame temperature measuring device (7).

3. 2. The method according to claim 1, characterized in that the gradient behavior of the temperature in the vicinity of the flame (5) is evaluated.

4. 4. The method according to claim 1, wherein the pressure of the cooling air is measured by a pressure measuring device (9) and evaluated by an evaluation device (11).

5. A gas burner system (1), comprising: a burner (2) having a combustion chamber (20); a fuel supply line (3) and an air supply line (4) connected to the combustion chamber (20) of the burner (2); at least one fuel valve (12) housed in the fuel supply line (3) and selectively openable and closable to activate and terminate the fuel supply to the combustion chamber (20) of the burner (2); a control device (10) capable of controlling the operation of the gas burner system (1); a flame temperature measuring device (7) configured to measure the temperature in the vicinity of the flame (5); an air temperature measuring device (8) housed in the air supply line (4); an evaluation device (11) configured to evaluate temperature measurement data from the flame temperature measurement device (7) and transmit the evaluation result to the control device (10); The control device (10) is configured to generate a switch-off signal for the fuel valve (12) when the temperature in the vicinity of the flame (5) falls below a critical value or when the temperature drops at a specific negative gradient, the evaluation device (11) is configured to determine the air-fuel ratio from the temperature in the vicinity of the flame (5), and the control device (10) is configured to generate a switch-off signal for the fuel valve (12) when there is an abnormality in the air-fuel ratio.

6. 6. The gas burner system (1) according to claim 5, further comprising a bypass line (6) in which a flame temperature measuring device (7) is accommodated, the bypass line (6) being arranged branched off from the air supply line (4) so ​​that a portion of the process air flowing through the air supply line (4) during operation of the gas burner system (1) is diverted into the bypass line (6) and forms cooling air for actively cooling the flame temperature measuring device (7).

7. 6. A gas burner system (1) according to claim 5, characterized in that the pressure measuring device (8) is accommodated in the air supply line (4).

8. 8. The gas burner system (1) according to any one of claims 5 to 7, characterized in that the gas burner system (1) is configured to operate on a fuel consisting of a mixture of aliphatic fuel and hydrogen, or on a fuel consisting exclusively of hydrogen except for natural impurities.

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