Method for operating a burner device

Abstract

The invention relates to a method for operating a burner device. Air is conveyed into a combustion chamber (1); ignition sparks are generated using an ignition device (2) arranged in the combustion chamber (1), which is flooded with air; a combustible gas is added to the air while the ignition sparks are continuously generated; and in the period of time which starts before the ignition sparks are generated and ends after the combustible gas is added, electric voltage values are measured on the ignition device (2). According to the invention, the voltage values which are measured in the aforementioned period of time and which form a voltage curve are analyzed in order to detect a formation of flames, beginning when the combustible gas-air mixture which contains at least 20 vol.% of hydrogen is combusted.

Description

[0001] The invention relates to a method for operating a burner device according to the preamble of claim 1.

[0002] A method of the type mentioned above is known from document DE 10 2020 107 735 A1. In this method, air is supplied to a combustion chamber. Furthermore, ignition sparks are generated by an ignition device located in the combustion chamber filled with air. In addition, a fuel gas is mixed with the air while the ignition sparks are being generated. Finally, the electrical voltage values ​​applied to the ignition device are measured during the period from before the ignition sparks are generated until after the fuel gas is added. In this solution, however, the voltage measurement is not only performed while the ignition spark is present, but also beforehand, in order to determine, via the voltage change occurring during the measurement, that it has a minimum value, and thus the ignition spark has a minimum quality. Or, to put it another way: This method serves to assess the quality of the ignition spark.

[0003] Documents EP 2 357 410 A2, WO 2015 / 017018 A1 and EP 3 767 175 A1, on which the two-part form of claim 1 is based, show similar relevant methods.

[0004] The invention is based on the objective of improving a method of the type mentioned above. In particular, a method is to be created with which (if necessary, in addition to the aforementioned method) the simplest possible adjustment of the fuel gas-air mixture can be achieved, even when using a fuel gas containing hydrogen.

[0005] This problem is solved by a method of the type mentioned at the outset by the features listed in the characterizing portion of claim 1.

[0006] It is intended that the voltage values ​​measured during the aforementioned period, forming a voltage curve, will be evaluated to detect the formation of a flame that begins with the combustion of the fuel gas-air mixture containing at least 20% hydrogen by volume.

[0007] Thus, the phase of fuel gas mixing during burner start-up is precisely monitored with regard to the resulting electrical voltage. This method serves in particular to determine the quality of the fuel gas and to control the burner based on or derived from this.

[0008] The method according to the invention is characterized in that, for the detection of flame formation, the voltage profile on a capacitor arranged between two electrodes of the ignition device is measured, wherein a comparatively large gradient on the voltage profile of the capacitor is considered as an indication of a comparatively large hydrogen content in the fuel gas and a comparatively small gradient on the voltage profile of the capacitor is considered as an indication of a comparatively small hydrogen content.

[0009] Other advantageous developments of the method according to the invention are set out in the dependent patent claims.

[0010] The method according to the invention, including its advantageous further developments according to the dependent claims, is explained in more detail below with reference to the graphic representation of a preferred embodiment.

[0011] It shows Figure 1 shows a schematic representation of the burner device for carrying out the method according to the invention; Figure 2 shows a voltage profile during flame formation with a small hydrogen content in the fuel gas; and Figure 3 shows a voltage profile during flame formation with a large hydrogen content in the fuel gas.

[0012] In Figure 1A burner device with which the method according to the invention can be carried out is schematically depicted. In this method, air is first supplied to a combustion chamber 1 in a known manner, in particular, as shown, via line 1.1 and burner 1.2. Furthermore, ignition sparks are generated by an ignition device 2, which has two ignition electrodes 2.2 and is arranged in the combustion chamber 1 flooded with air. While the ignition sparks are being generated, a fuel gas is mixed with the air, again via line 1.1 and burner 1.2. During the period from before the generation of the ignition sparks until after the fuel gas has been mixed, electrical voltage values ​​(in the physical unit "volts") applied to the ignition device 2 are also measured. More precisely, the electrical voltage between the aforementioned ignition electrodes 2.2 is measured. For this purpose, the device shown in Figure 1 Schematic representation of voltmeters 2.3.

[0013] Essential to the method according to the invention is that the voltage values ​​measured during the aforementioned period, which form a voltage curve, are evaluated to detect flame formation beginning with the combustion of the fuel gas-air mixture containing at least 20 vol% hydrogen. It is particularly preferred that the fuel gas contains at least 90 vol% hydrogen.

[0014] Equally essential for the method according to the invention is the provision that, for the detection of flame formation, the voltage profile is measured across a capacitor 2.1 arranged between the two electrodes 2.2 of the ignition device 2. Preferably, the voltage profile is recorded analogously, but digitized (in a corresponding electronic unit) for evaluation.

[0015] According to the invention, a change in the voltage curve across capacitor 2.1 during the aforementioned period is interpreted as an indication of flame formation. Depending on the ignition transformer used, this change can optionally be a drop in voltage (as in the Figures 2 and 3 shown) or it could be an increase (not shown separately) in the voltage curve.

[0016] According to the invention, it is further provided that a comparatively large gradient in the voltage curve of capacitor 2.1 is interpreted as indicating a comparatively large hydrogen content in the fuel gas, and a comparatively small gradient in the voltage curve of capacitor 2.1 as indicating a comparatively small hydrogen content. As can be seen, this shows Figure 2 including the small and Figure 3 the large gradient.

[0017] Again with reference to the two figures, it is further preferred that there be a comparatively large difference (see Figure 2 ) between the voltage value at capacitor 2.1 before and after flame formation as an indication of a comparatively small difference (see Figure 3 ) between the voltage value at capacitor 2.1 before and after flame formation is considered an indication of a comparatively large hydrogen content in the fuel gas.

[0018] To put it another way: Using the detection method according to the invention, it is ultimately even possible to determine how much hydrogen is contained in the fuel gas, because this proportion influences - as shown - on the one hand the steepness and on the other hand the final level of the curve.

[0019] Regarding the aforementioned adjustment of the fuel gas-air mixture, it is furthermore preferably provided, as is known per se, that the volume flow of supplied fuel gas is continuously increased from zero during the specified period. However, it is also particularly preferred according to the invention that the volume flow of supplied fuel gas is kept constant from the moment a flame is detected, i.e., the ratio of fuel gas to air is ideally fixed precisely at the ratio at which the flame was produced (optimal combustion).

[0020] In other words, the method according to the invention is characterized in particular as follows: The burner is started by supplying a constant volume flow of air to the combustion system. The ignition is then switched on, causing high-voltage discharges to form between the ignition electrodes 2.1. Within a few milliseconds, the resulting plasma of ionized air reaches its maximum breakdown voltage. The ignition spark induces a voltage on the capacitor 2.1, which serves as a measurement signal and is digitized in the (not shown) burner control unit. When the ignition is switched on, the capacitor 2.1 exhibits typical capacitor charging behavior. To suppress electromagnetic effects, the digitized signal is filtered by software.Provided that a "safe" ignition has been established (see again document DE 10 2020 107 735 A1), the gas safety valve opens and the gas control valve is operated according to the characteristic curve (gas ramp). After the fuel gas-air mixture reaches the combustion chamber or the electrodes, thermochemical, predominantly exothermic reactions begin immediately, leading to self-sustaining flame propagation. The exothermicity of the flame itself leads to a change in the conductivity at the ignition electrodes 2.1, which reduces the breakdown voltage. This causes the capacitor to discharge, even though the ignition is switched on. The digitized signal also changes according to the selected filter settings. Using threshold-based (level-based) or gradient-based evaluation of the signal, various processes of the start-up sequence, such as flame detection or stopping the gas ramp, can be controlled, as described in more detail above.Conclusions about the composition of the fuel gas-air mixture can be drawn, for example, by evaluating the ignition time and the gradient of the signal. Reference symbol list

[0021] 1 Combustion chamber 1.1 Cable 1.2 Burner 2 Ignition device 2.1 Capacitor 2.2 Ignition electrode 2.3 Voltmeter

Claims

1. A method for operating a burner device, in which air is conveyed into a combustion chamber (1), in which ignition sparks are generated using an ignition device (2) that is arranged in the combustion chamber (1), which is flooded with the air, in which during continuous generation of the ignition sparks, a fuel gas is admixed with the air, and in which in the time period from before generation of the ignition sparks until after the admixture of the fuel gas, electric voltage values applied at the ignition device (2) are measured, wherein the voltage values which are measured in the said time period and which form a voltage curve are evaluated to detect flame formation which begins with combustion of the fuel gas / air mixture containing at least 20 vol% hydrogen, characterized in that to detect the flame formation, the voltage curve is measured at a capacitor (2.1) arranged between two electrodes of the ignition device (2), wherein a comparatively large gradient at the voltage curve of the capacitor (2.1) is assessed as a sign for a comparatively large hydrogen proportion in the fuel gas and a comparatively small gradient at the voltage curve of the capacitor (2.1) is assessed as a sign for a comparatively small hydrogen proportion in the fuel gas.

2. The method according to claim 1, characterized in that a change of the voltage curve at the capacitor (2.1) in the said time period is assessed as a sign for the flame formation.

3. The method according to claim 1 or 2, characterized in that a comparatively large difference between the voltage value at the capacitor (2.1) before and after the flame formation is assessed as a sign for a comparatively small hydrogen proportion in the fuel gas and a comparatively small difference between the voltage value at the capacitor (2.1) before and after the flame formation is assessed as a sign for a comparatively large hydrogen proportion in the fuel gas.

4. The method according to any one of claims 1 to 3, characterized in that a volumetric flow of supplied fuel gas is increased continuously in the said time period, starting from zero.

5. The method according to claim 4, characterized in that from the determination of flame formation, the volumetric flow of supplied fuel gas is kept constant.

6. The method according to any one of claims 1 to 5, characterized in that the fuel gas contains at least 90 vol% hydrogen.

7. The method according to any one of claims 1 to 6, characterized in that although the voltage curve is detected in an analogue manner, it is digitized for evaluation.

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