Method for operating a heating device, heating device for carrying out the method, and computer program

Abstract

A method for operating a heating appliance (1) is proposed, comprising a burner (3) to which a combustion mixture of fuel gas and combustion air is supplied, and a first flame sensor (6) and a second flame sensor (13), wherein the first and second flame sensors (6, 13) generate signals (14, 15) with different characteristics with respect to the current power and / or air-fuel ratio (λ) of the heating appliance (1), comprising at least the following steps: a) acquiring a first signal (14) from the first flame sensor (6) and a second signal (15) from the second flame sensor (13), b) determining a mass flow rate (m) of combustion mixture supplied to the burner (3) and the air-fuel ratio (λ) of the combustion mixture taking into account the first and second signals (14, 15), c) adjusting the control of the heating appliance (1) taking into account the mass flow rate (m) and the air-fuel ratio (λ) determined in step b).A method proposed here enables precise control of a heating device (1) using two flame sensors (6, 13).

Description

[0001] The invention relates to a method for operating a heater, a computer program and a heater.

[0002] Gas-fired heaters often have a control of the combustion air ratio, also known as the air ratio lambda (λ), based on a signal from a sensor that is located in a burner or in the vicinity of a flame or the burner of the heater and allows a conclusion to be drawn about the air ratio (λ).

[0003] For example, DE 100 45 270 A1 proposes arranging a temperature sensor in the flame core of a burner and controlling the fuel-air composition based on the measured flame temperature. Due to its size, the temperature sensor used can detect both small and large flames, thus enabling control over a wider modulation range.

[0004] DE 10 2020 126 992 A1 proposes a method for operating a burner with a fuel gas containing more than 95 vol% hydrogen, in which a temperature signal of the flame is included. The temperature signal can thus be configured to check at least one mass flow sensor of the combustion air to be supplied or of the fuel gas. If a mass flow sensor fails, operation of the burner can be continued by increasing the air supply for 1 to 10 seconds and closing it if the flame temperature rises to an excessively low ratio of combustion air to fuel gas. Disadvantageously, this method requires the use of at least two mass flow sensors to achieve precise combustion control. Operating the burner by means of the proposed temporary increase in the air supply and detecting the temperature signal can only enable very imprecise combustion control.

[0005] In addition, the determination of a flame's ionization current is known, which also allows for inferences about the flame's air ratio. However, this method is only robustly applicable to fuels whose combustion releases a sufficient amount of free charge carriers. This is difficult, for example, with hydrogen.

[0006] DE 10 2019 110 976 A1 proposes a method for testing a gas mixture sensor, in which a signal from an ionization sensor of the flame is recorded and assigned to a signal from the gas mixture sensor. To test the gas mixture sensor, the gas mixture to be burned can be changed, and the resulting changes in the signals from the gas mixture sensor and ionization sensor can be recorded and evaluated. This method is also complex and requires the use of a gas mixture sensor. Furthermore, the method is not suitable for use with a hydrogen-containing fuel gas.

[0007] DE 10 2004 055 715 A1 relates to a method for adjusting the air ratio in a combustion system. This method utilizes the fact that the flame temperature T Max is maximum at lambda = 1. The method allows a predefined air mass flow to be set and a corresponding gas mass flow to be determined for the temperature T Max. A target lambda value for hygienic combustion can then be determined and adjusted by increasing the air mass flow. The proposed method is disadvantageous in that it is inaccurate and also requires the combustion system to be operated at lambda = 1, which is associated with an increased risk of flashback.

[0008] DE 100 45 272 A1 describes a combustion device that has a temperature sensor whose length allows the flame height to be determined. A second temperature sensor may be present, located in the main reaction zone. The flame length can be used to determine the current combustion air ratio. Disadvantages include the fact that the combustion device requires special temperature sensors, and the combustion air ratio cannot be determined with sufficient precision.

[0009] JP H05 322159 A describes a combustion system with two burners, each with a flame monitoring device. This document provides no information on improving combustion control.

[0010] EP 3 690 318 A2 discloses a method for controlling the combustion of a heater, in which the air / fuel ratio is determined based on calibration data from the ionization signal. This method may also not be sufficiently accurate and can only be used with fuels that release sufficient charge carriers during combustion.

[0011] However, a determined sensor value can depend on both the air ratio and the mass flow of the combustion mixture consisting of fuel gas and combustion air supplied to the burner. For this reason, the mass flow or volume flow of the combustion mixture is usually determined by a corresponding sensor and included in the control system. In heaters without a corresponding sensor, the power of a conveying device is usually used, for example the speed of a conveying device designed as a fan. However, the power of the conveying device can often only allow a very imprecise conclusion to be drawn about the mass flow of the combustion mixture. For example, an obstruction of the flow path of the combustion mixture or exhaust gas flow can lead to considerable deviations. One cause of this can be an at least partially blocked exhaust system. The resulting inaccurate control of the air ratio can lead to unclean and inefficient combustion.

[0012] Based on this, the object of the invention is to propose a method for operating a heater, a computer program, and a heater that at least partially overcome the described problems of the prior art. In particular, a simple and cost-effective method for operating a heater with control of the combustion air ratio, taking into account a flame temperature signal, is to be provided, enabling consistently precise control. Furthermore, the method should be suitable for at least partially automated implementation. Furthermore, the method should be capable of being reliably used for different fuels.

[0013] These objects are achieved by the features of the independent patent claims. Further advantageous embodiments of the solution proposed here are specified in the independent patent claims. It is pointed out that the features listed in the dependent patent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. Furthermore, the features specified in the patent claims are further specified and explained in the description, with further preferred embodiments of the invention being presented.

[0014] A method for operating a heater contributes to this. The heater has a burner to which a combustion mixture of fuel gas and combustion air is supplied. Furthermore, at least one first flame sensor and one second flame sensor are provided, with both or all flame sensors having or generating signals with (respectively or simultaneously) different characteristics related to the power and / or the air ratio (λ) of the heater. The method comprises at least the following steps: a) detecting a first signal from the first flame sensor and a second signal from the second flame sensor, b) determining a mass flow supplied to the burner ( m ) of the combustion mixture and the air ratio (λ) of the combustion mixture, taking into account the first signal and the second signal, whereby the air ratio (λ) and the mass flow ( m) are determined via multidimensional functions, c) controlling the heater taking into account the mass flow determined in step b) ( m ) and the air ratio (λ) determined in step b).

[0015] During a regular operating procedure, steps a), b), and c) may be performed at least once in the specified order. In particular, steps a) to c) may be repeated multiple times, especially continuously.

[0016] The method is used in particular for the permanently safe operation of a heating device with a sensor-based control of the combustion air mixture, in particular of a heating device in which a direct detection of a mass or volume flow of fuel gas and combustion air to be supplied to a burner of the heating device is not possible.

[0017] The heater can comprise at least one heat generator, in particular a gas condensing boiler, which releases thermal energy through the combustion of a fuel and can transfer it to a heating circuit via at least one heat exchanger, wherein consumers of the heating circuit can be connected to the heater via a heating flow and a heating return. The exhaust gases produced during combustion can be fed to an exhaust system via an exhaust duct of the heater. In the heater, a circulation pump in the heating circuit can be configured to circulate a heat transfer medium (heating water), wherein heat transfer medium heated via a heating flow can be fed to consumers, such as convectors or surface heating systems, and returned to the heat generator or the at least one heat exchanger via a heating return.

[0018] For this purpose, the heater can have a conveying device, in particular a fan, which supplies a combustion mixture of combustion air and fuel gas, for example fossil gas or hydrogen, to a burner of the heater. The heater can have a sensor-based control of the air ratio (λ). For this purpose, the heater can have at least two flame sensors that allow a conclusion to be drawn about a combustion air ratio. In particular, the at least two flame sensors can have different characteristics with regard to the (currently measured) power of the heater and / or the air ratio. In particular, based on a first signal from a first flame sensor and a second signal from a second sensor, these can be determined accordingly on the basis of their different characteristics with regard to power and / or air ratio.

[0019] The term "different characteristics with regard to power and / or air ratio" refers here to the fact that a first relationship between the first sensor signal and the air ratio and / or the power differs (significantly) from a second relationship between the second sensor signal and the air ratio and / or the power of the heater to such an extent that an intersection can be identified as clearly as possible. In particular, the relationships themselves or their gradients can differ significantly from one another. The different characteristics can be recognized, for example, if the same burner situation leads to (significantly) different measurement results or signals. During operation, the two flame sensors detect the same amount of air at the same time or at the same time.a different signal is generated during the same period, whereby statements about the actual air ratio and / or performance of the burner can be derived from this different characteristic, in particular by comparing both signals and / or a joint evaluation.

[0020] The mass flow ( m ) of the combustion mixture can be a measure of the heater's performance. It is also possible to use a volume flow of the combustion mixture as a measure of the heater's performance, which can be converted into a mass flow given knowledge of the density of the combustion mixture.

[0021] The first flame sensor or the second flame sensor can in particular be an ionization electrode, a temperature sensor, a lambda probe or an optical sensor, in particular a UV sensor.

[0022] An ionization electrode is a device for measuring the ionization current of a flame in the heater's burner. By applying a voltage to an ionization electrode, an ionization current flowing, for example, through a burner body can be measured, which allows conclusions to be drawn about the power and / or air ratio. The ionization electrode can advantageously be a hot-surface igniter, which is also configured to serve as the burner's ignition device. A hot-surface igniter can thus enable the detection of a flame temperature and an ionization current of the flame, as well as serve as an ignition device.

[0023] In this context, it should be noted that the first and second flame sensors can be implemented by a single sensor (flame sensor system) configured to provide a first and second signal with different characteristics related to the heater's power and / or air ratio (λ). An example of this could be a hot surface igniter as described above.

[0024] The temperature sensor can, in particular, be arranged such that a flame temperature of the heater can be detected. For this purpose, the temperature sensor can be arranged in the combustion chamber of the heater, in particular in an area of ​​the combustion chamber where a flame develops during regular use.

[0025] The temperature sensor can be located near the flame core, near the flame base, or near the flame tip when the burner is in operation. Alternatively, a spaced-apart arrangement from the flame is also possible. The flame temperature sensor could be attached or located on the burner itself or on a burner door; advantageously, such a design can be easily integrated into existing assembly processes. The temperatures to be measured by the flame temperature sensor can, for example, range between 100 °C (degrees Celsius) and 1,500 °C.

[0026] The temperature sensor can be any temperature sensor that can, in particular, deliver or provide an electrical signal as a measure of its temperature. The signal can, for example, consist of a measurable electrical resistance, for example a measuring resistor such as a platinum or silicon measuring resistor, a thermistor (NTC) or a thermistor (PTC) as a flame temperature sensor. The flame temperature sensor can also be a semiconductor temperature sensor that can provide a directly processable electrical signal representative of the temperature. Alternatively, temperature sensors comprising a quartz crystal, a thermocouple, pyroelectric materials, and / or a fiber optic temperature sensor can also be provided as the flame temperature sensor.In particular, the flame temperature sensor can also be a hot surface igniter, i.e., a resistance heater that can be heated to a temperature above the ignition temperature of the fuel-combustion air mixture. This advantageously reduces the complexity of the proposed heater, since the ignition device, temperature sensor, and a device for heating the temperature sensor can be implemented in a single component. For example, the temperature sensor can be a silicon nitride or silicon carbide hot surface igniter.

[0027] A lambda sensor can be a conventional lambda sensor configured to determine the oxygen content in the exhaust gas flow of the heater. Based on this information, a conclusion can be drawn about the combustion air ratio of the combustion mixture. By incorporating a second flame sensor, which allows a conclusion to be drawn about the mass flow of the combustion mixture, a method proposed here can also be used to determine the mass flow and / or the air ratio using a lambda sensor.

[0028] An optical sensor can be configured to detect electromagnetic radiation emitted by a flame of the heater. The radiation to be detected can be visible light (to humans), infrared radiation (IR), and / or ultraviolet radiation (UV).

[0029] According to one embodiment, signals from the first and second flame sensors can be detected in step a), wherein the first and second flame sensors are different flame sensors. Advantageously, flame sensors can be selected that, either by themselves or due to the sensor, exhibit significant or distinct differences in the characteristics with regard to the power and / or air ratio of a heater.

[0030] According to one embodiment, signals from the first and second flame sensors can be detected in step a), with the first and second flame sensors being arranged at different positions relative to the burner of the heater or to a flame occurring at the burner. In particular, the first and second flame sensors can have a (significantly) different distance from the burner or the flame.

[0031] According to the invention, in step b) the air ratio (λ) and the mass flow ( m) is determined using multidimensional (mathematical) functions. Advantageously, a first and a second flame sensor can also be provided, which, either by themselves or due to the sensor, exhibit significant or specific differences in the characteristics with regard to the power and / or air ratio of a heater.

[0032] As already stated at the beginning, a change in a signal from such a flame sensor can usually be attributed to a change in the air ratio and / or a change in the heater's power output, combined with a change in the mass or volume flow of the combustion mixture. For example, a signal change indicating an increase in flame temperature can be attributed to an increase in power or a change in the air ratio. Thus, all possible combinations of air ratio and mass flow of the combustion mixture for various incoming sensor signals can be understood as a three-dimensional function, and two three-dimensional functions can be formed that represent the (first or second) signal of the (first or second) flame sensor as a function of mass flow and air ratio.For a given sensor value (e.g., a flame sensor voltage of 1.43 V), a two-dimensional function can now be created that represents the mass flow as a function of the air ratio, or the air ratio as a function of the mass flow. Based on the first and second signals, two two-dimensional functions can thus be determined, the intersection of which can indicate an operating point.

[0033] According to a further embodiment, a three-dimensional function can be determined for each of the first and second signals, wherein a first function can represent the mass flow as a function of the first and second signals, and a second function can represent the air ratio as a function of the first and second signals. This enables a direct determination of the mass flow and air ratio.

[0034] A three-dimensional function described above representing all possible combinations of air ratio and mass flow of the combustion mixture (or power of the heater) for various incoming sensor signals can be determined, for example, by means of a reference heater with appropriately arranged first and second flame sensors, wherein the air ratio and power of the reference heater are known and thus a relationship between the sensor signal (from the first and second flame sensors) and an air ratio and a power of the heater can be determined, for example, based on characteristic map recordings of the heater.

[0035] According to one embodiment, further operating parameters of the heater can be included in the implementation of step b). Including additional operating parameters of the heater can enable a more precise determination of the air ratio and the heater's power.

[0036] According to one embodiment, the further operating parameters can be an ambient temperature, a temperature in the combustion air supply, a power of a conveying device of the heater and / or a temperature in a flow and / or a return of the heater.

[0037] According to a further aspect, a heating device is also proposed, comprising a control and regulation device as proposed here. The heating device can be a gas heating device, in particular a gas-operated gas heating device. The gas heating device can have a burner and a conveying device with which a combustion mixture of

[0038] Combustion gas and combustion air can be supplied to a burner. The heater can, in particular, have a control system for the composition of the combustion mixture (air ratio, combustion air ratio) taking into account a first and second signal from a first and second flame sensor.

[0039] According to a further aspect, a computer program is also proposed, comprising instructions which cause the heating device according to the invention to carry out the steps of the method according to the invention.

[0040] A machine-readable storage medium on which the computer program is stored is also proposed. This machine-readable storage medium is usually a computer-readable data storage medium.

[0041] A control and regulating device for a heater is also proposed, configured to carry out a method proposed here. For this purpose, the control and regulating device can, for example, have and / or be equipped with a processor. In this context, the processor can, for example, execute the method stored in a memory (of the control and regulating device). Advantageously, operating data and, for example, corresponding functions that indicate possible combinations of air ratio and power of the heater for a first and second signal from the first and second flame sensor can also be stored in the memory of the control and regulating device for carrying out a method proposed here.

[0042] A control device for a heater with at least two flame sensors is configured to carry out a method of the type presented here. A heater can be designed with such a control device.

[0043] In particular, a heating device is proposed, comprising a burner, at least two flame sensors, and means adapted to carry out the steps of the method proposed here. Furthermore, a computer program comprising instructions that cause this heating device to carry out the steps of the method may be provided.

[0044] The details, features, and advantageous embodiments discussed in connection with the method may also occur in the computer program, the control unit, the heater, and the use presented here, and vice versa. In this respect, reference is made in full to the explanations therein for a more detailed characterization of the features.

[0045] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily specify any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or part of the majority of these components, but this is not mandatory.

[0046] Thus, a method for operating a heater, a computer program, and a heater are provided here, which at least partially solve the problems described with reference to the prior art. In particular, the method for operating a heater, the computer program, and the heater at least contribute to enabling reliable and long-term stable control of a heater, in particular of the combustion air ratio, based on a detected flame temperature. Furthermore, a method proposed here can be implemented entirely by computer and thus requires no structural modifications to a heater.

[0047] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and, in particular, the proportions shown are only schematic. They show: Fig. 1: a sequence of a method presented here, Fig. 2: a heating device proposed here, Fig. 3: an arrangement of the first and second flame sensor and Fig. 4: parameter curves that can occur when carrying out a method proposed here.

[0048] Fig. 1shows, by way of example and schematically, a sequence of a method proposed here. The method serves to operate a heating device 1, in particular to control an air ratio λ of the combustion mixture. The sequence of steps a), b), and c) represented by blocks 110, 120, and 130 can occur during a regular operating sequence, whereby these can, in particular, be repeated regularly or permanently.

[0049] Fig. 2shows, by way of example and schematically, a heating device 1 proposed here, set up for the combustion of a fuel gas such as natural gas or hydrogen. This comprises a burner 3 arranged in a combustion chamber 8. Combustion air is sucked in by a fan 2 via a combustion air supply 4, and fuel gas is added to the sucked-in mass flow of combustion air via a gas valve 5, and the combustion mixture of fuel gas and combustion air is fed to the burner 3 via a mixture channel 12. A heat exchanger 11 arranged in the exhaust gas path of the burner 3 can transfer heat generated during combustion in the combustion chamber 8 to a heat transfer medium circulating in a heating circuit (not shown here). Combustion products produced during combustion can be fed to an exhaust system 10 via an exhaust pipe 9.A first flame sensor 6 and a second flame sensor 13 are arranged in the combustion chamber 8 such that a first signal from the first flame sensor 6 and a second signal from a flame of the burner 3 are detected. The first flame sensor 6 and the second flame sensor 13 are different flame sensors; for example, the first flame sensor 6 can be a temperature sensor and the second flame sensor 13 can be an ionization electrode. The ionization electrode and the temperature sensor have significantly different characteristics with regard to an air ratio λ and mass flow. m of the mass flow supplied to the burner 3 combustion mixture.

[0050] A control and regulation device 7 is configured to regulate the heater 1. For this purpose, it is electrically connected to at least the first flame sensor 6, the second flame sensor 13, the fan 2, and the gas valve 5. Based on the first signal and second signal from the first and second flame sensors 6, 13, the control and regulation device 7 can adjust the flame at the burner 3 to an air ratio λ and a mass flow m close and regulate them. The mass flow m can be a measure of the (current) performance of heater 1.

[0051] In block 110, according to step a), a first signal 14 of the first flame sensor 6 and the second signal 15 of the second flame sensor 13 can be detected. Step a) can be performed in particular by the control unit 7, wherein the detected signals 14, 15 can be stored in a memory of the control unit 7.

[0052] Fig. 3shows, by way of example and schematically, a burner 3 of the heating device 1 with a cylindrical burner body 18, on which a first flame sensor 6 and a second flame sensor 13 are arranged. In this alternative example, the first flame sensor 6 and the second flame sensor 13 can be the same sensors (types). The first flame sensor 6 can have a distance 16 from the burner body 18 and the second flame sensor 13 can have a distance 17 from the burner body 18, wherein the distance 16 of the first flame sensor 6 is significantly smaller than the distance 17 of the second flame sensor 13. This different distance of the flame sensors 16, 17 results in a different characteristic with regard to the air ratio λ and the mass flow. m of the mass flow of combustion mixture supplied to burner 3.

[0053] In block 120, according to step b), a mass flow of combustion mixture supplied to the burner and the air ratio (λ) of the combustion mixture can be determined or calculated taking into account the first and second signals 14, 15.

[0054] Fig. 4 shows an example and schematic diagram that shows a function of possible combinations of air ratio λ and mass flow m for a detected first signal 14 of the first flame sensor 6 and a function of possible combinations of air ratio λ and mass flow m for a detected second signal 15 of the second flame sensor 13. An operating point 19 can be defined as the intersection point of the functions, i.e. the combination of air ratio λ and mass flow m which is possible according to the first and second signals 14,15.

[0055] In block 130, according to step c), the heater 1 can determine the air ratio λ and mass flow mbe included in the control of the heater 1 by the control and regulation unit 7. List of reference symbols

[0056] 1 Heater 2 Fan 3 Burner 4 Combustion air supply 5 Gas valve 6 First flame sensor 7 Control unit 8 Combustion chamber 9 Exhaust pipe 10 Exhaust system 11 Heat exchanger 12 Mixture channel 13 Second flame sensor 14 First signal 15 Second signal 16 Distance to first flame sensor 17 Distance to second flame sensor 18 Burner body 19 Operating point

Claims

1. Method for operating a heating device (1), comprising a burner (3), to which a combustion mixture of combustion gas and combustion air is supplied, and a first flame sensor (6) and a second flame sensor (13), wherein the first flame sensor (6) and second flame sensor (13) generate signals with different characteristics with respect to a current power and / or air ratio (λ) of the heating device (1), comprising at least the following steps: a) detecting a first signal (14) of the first flame sensor (6) and a second signal (15) of the second flame sensor (13), b) determining a mass flow (ṁ) of the combustion mixture supplied to the burner (3) and the air ratio (λ) of the combustion mixture, taking into account the first signal (14) and the second signal (15), wherein the air ratio (λ) and the mass flow (ṁ) are determined using multidimensional functions, c) controlling the heating device (1) taking into account the mass flow (ṁ) determined in step b) and the air ratio (λ) determined in step b).

2. Method according to claim 1, wherein the first flame sensor (6) and the second flame sensor (13) are selected from the following group: ionization electrode, temperature sensor, lambda probe, optical sensor, hot surface igniter.

3. Method according to claim 2, wherein the first flame sensor (6) and the second flame sensor (13) are different elements of the group.

4. Method according to any one of the preceding claims, wherein the first flame sensor (6) and the second flame sensor (13) are arranged at different positions relative to the burner (3) of the heating device (1).

5. Method according to any one of the preceding claims, wherein in step b) the air ratio (λ) and / or the mass flow (ṁ) is determined by way of an artificial intelligence, which has been trained in preliminary tests with a known mass flow (ṁ) and known air ratio (λ).

6. Heating device (1) with a burner (3), at least two flame sensors (6, 13) and a regulating and control device adapted to carry out the steps of the method according to claim 1.

7. Computer program, comprising commands which cause the heating device (1) of claim 6 to carry out the steps of the method according to claim 1.

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