EP4143486B1 - Device and method for combustion control for a fuel gas with a proportion of additive gas - Google Patents

Description

TECHNICAL FIELD

The invention relates to a device and a method for controlling combustion, wherein an additional gas in the fuel gas can be detected and control variables for the combustion can be adjusted accordingly.

TECHNICAL BACKGROUND

One object of the invention is to provide a device and a method for controlling combustion, which makes it possible to detect the type of additional gas, in particular hydrogen, in a fuel gas. In particular, a proportion of the additional gas in the fuel gas should also be able to be determined.

Natural gas is generally used as a fuel gas. Natural gas is a hydrocarbon-containing gas mixture whose chemical composition can vary considerably depending on the location. However, the main component is usually methane, with the proportion varying between 75 and 99 mol%.

In addition to methane, burner test gases can contain an admixture of additional gas, such as nitrogen or propane. However, burner test gases can also consist of 100% methane or even 100% of an additional gas such as propane. Examples are the burner test gases G271 and G21 or G20 and G32.

Motivated by long-term savings in _CO2 emissions, the injection of climate-neutrally produced hydrogen as additional gas into the existing natural gas network with volume shares of up to 40 vol.% is planned.

However, the addition of hydrogen to the base gas creates numerous technical challenges, especially for the operation and combustion control in gas burners. First of all, hydrogen has a lower calorific value per volume than natural gas. This means that in order to achieve a comparable performance, the volume flow of fuel gas must be increased when hydrogen is added. In addition, the reaction kinetics of the Combustion is different from that of pure natural gas, which has a strong influence on the flame speed, length and geometry, as well as the flame temperature, ignition properties and heat radiation.

For example, it was found that with a linear increase in hydrogen concentration, the flame speed increases exponentially. In addition, the maximum laminar flame speed shifts to the fuel-richer area of combustion, i.e. to lower lambda values. Hydrogen reaches the highest maximum flame speed of around 3.5 m/s with a non-preheated combustion mixture. The higher the flame speed, the more likely a transition from deflagration, i.e. the spread of the reaction front by diffusion, to detonation, i.e. the spread of the reaction front due to a pressure wave. In addition, the ignition delay time of hydrogen is 1000 times shorter than that of natural gas, with significantly lower ignition energy and a higher upper ignition limit.

Knowing which additional gas, in particular hydrogen, is present in the fuel gas and in what proportion is therefore essential for the operation and combustion control in gas burners, both from a combustion engineering and safety perspective.

1. a) Feststellen, mit Hilfe der Strom-Spannungskennlinie der protonenleitenden Schicht, ob bei einem Durchströmen der protonenleitenden Schicht mit einem Volumenstrom der H₂/Erdgasmischung eine Wasserstoffverarmung der protonenleitenden Schicht vorliegt, und Messen des Volumenstroms mit einem Sensor zur Messung des Volumenstroms der H₂/Erdgasmischung in die protonenleitende Schicht, welcher mit dem Steuergerät verbunden ist;
2. b) Falls keine Wasserstoffverarmung der protonenleitenden Schicht vorliegt, dann Verändern des Volumenstroms der H₂/Erdgasmischung mittels einer Steuereinrichtung und Wiederholen des vorherigen Schritts;
3. c) Falls eine Wasserstoffverarmung der protonenleitenden Schicht vorliegt, dann Ermitteln der kritischen Stromdichte der protonenleitenden Schicht, bei welcher die Wasserstoffverarmung an der protonenleitenden Schicht mit dem zugehörigen gemessenen Volumenstrom der H₂/Erdgasmischung vorliegt;
4. d) Feststellen, mittels eines Kennfeldes, des H₂-Gehalts der H₂/Erdgasmischung basierend auf der ermittelten kritischen Stromdichte;
5. e) Bestimmen des aktuellen Brennwerts der H₂/Erdgasmischung, basierend auf dem festgestellten H₂-Gehalt der H₂/Erdgasmischung und dem Brennwert der H₂/Erdgasmischung von der Übergabe-Station des Gasnetzes;
6. f) Ausgeben des aktuellen Brennwerts der H_2/Erdgasmischung.

The EN 10 2013 224 246 A1 describes, for example, a device for determining the H ₂ content of H ₂ /natural gas mixtures, with an input interface for reading in a calorific value of the H _{2 /} natural gas mixture, which was determined at a transfer station of a gas network; an input interface for the H _{2 /} natural gas mixture, for introducing the H ₂ /natural gas mixture into the device; a proton-conducting layer, which enables the determination of a current-voltage characteristic curve, wherein the proton-conducting layer is fluidically connected to the input interface for the H ₂ /natural gas mixture, and a control device which is connected to the proton-conducting layer and the input interface for the H ₂ /natural gas mixture and is set up to carry out the following steps:

1. a) Determine, using the current-voltage characteristic of the proton-conducting layer, whether a volume flow of the H ₂ /natural gas mixture flows through the proton-conducting layer and measures the volume flow with a sensor for measuring the volume flow of the H ₂ /natural gas mixture into the proton-conducting layer, which is connected to the control unit;
2. b) If there is no hydrogen depletion of the proton-conducting layer, then changing the volume flow of the H ₂ /natural gas mixture by means of a control device and repeating the previous step;
3. c) If there is a hydrogen depletion of the proton-conducting layer, then determining the critical current density of the proton-conducting layer at which the hydrogen depletion at the proton-conducting layer occurs with the associated measured volume flow of the H ₂ /natural gas mixture;
4. (d) determining, by means of a characteristic map, the H ₂ content of the H ₂ /natural gas mixture based on the determined critical current density;
5. (e) determining the current calorific value of the H ₂ /natural gas mixture based on the determined H ₂ content of the H ₂ /natural gas mixture and the calorific value of the H ₂ /natural gas mixture from the gas network transfer station;
6. f) Output of the current calorific value of the H _2/ natural gas mixture.

EP 2 821 705 A1 discloses a gas burner in which the flame temperature and the air ratio are measured by respective sensors

THE SOLUTION OF THE PROBLEM

The above object is solved with the features of independent claim 1 and subordinate claim 11. The dependent claims are directed to particular embodiments of the invention.

A method according to the invention for controlling the combustion of fuel gas by means of a gas burner, wherein the gas burner has a measuring device and a control circuit, and wherein the fuel gas contains natural gas and an additional gas, comprises the step a) of setting a burner load to a first predetermined load value L1 at an actual air ratio λ _Ist .

The term fuel gas describes mixtures of natural gas as the base gas with admixtures of an additional gas of various kinds, such as nitrogen, hydrogen, propane or propene, in variable proportions.

The air ratio or lambda value λ describes an air to fuel gas ratio of an air-fuel gas mixture.

The first predetermined load value L1 is not limited according to the invention. In a preferred embodiment, however, the load value L1 can be in a range of 5 to 10 kW.

The method according to the invention further comprises the step b) of approaching a predetermined target air ratio λ _Soll in a predetermined period of time Δt _L1 .

According to the invention, the target air ratio λ _target is not restricted as long as it is different from the actual air ratio. In a preferred embodiment, λ _actual > λ _target can apply. However, the target air ratio λ _target can particularly preferably be 1. In this case, the actual air ratio λ actual can _be reduced to the range of stoichiometric combustion at λ = 1.

The predetermined time period Δt _L1 is also not restricted according to the invention and can be selected such that the course of the flame temperature T _{F, L1} determined in this time period in step c) contains the information necessary for determining the fuel gas parameter in step d). For example, the predetermined time period Δt _L1 can be between 10s and 60s, preferably between 20s and 40s, particularly preferably 30s.

In general, various variants of the temporal air-fuel gas mixture control (enrichment) in the gas burner are conceivable. Preferably, the predetermined target air ratio λ _{target can be} approached linearly over the time-constant change in the gas flow rate in the gas burner. Alternatively, the predetermined target air ratio λ target _can also be approached parabolically or exponentially over time.

The method according to the invention further comprises the step c) of determining a profile of a flame temperature T _{F, L1} in the time period Δt _L1 .

The term flame temperature as used herein more accurately describes a temperature measurement of the flame from the combustion chamber of the gas burner. However, for simplicity, the term flame temperature will be used below.

The flame temperature can generally be determined in different ways, for example using one or more thermocouples. Preferably, however, the flame temperature can be determined using the thermoelectric effect at the ignition electrode (temperature of the flame at the ignition electrode), as for example in the EP 2 549 187 B1 described.

The above-mentioned thermionic effect (also Richardson effect, Edison effect or Edison-Richardson effect, see for example Neil W. Ashcroft, N. David Mermin: Solid State Physics. Saunders College Publishing, New York 1976, pp. 362-364 ) refers to the fact that electrons can overcome the work function of a heated metal electrode above a material-dependent minimum temperature and can exit the electrode. The current generated in this way allows the temperature of the electrode to be determined. The flame temperature can thus be easily determined using a voltage tapped from the ignition electrode of the burner. Such an ignition electrode is mandatory in the burner chamber of every burner and, once the air-fuel gas mixture has been ignited once, is no longer required for the operation of the gas burner.

The inventors have discovered that the course of the flame temperature T _F as a function of time at a given load value has characteristic features, the evaluation of which allows a conclusion to be drawn as to the type of additional gas and the proportion in which it is present in the fuel gas.

For this purpose, the method according to the invention comprises the step d) of determining a fuel gas parameter from the profile of the flame temperature T _{F, L1} and deriving a control variable for controlling the combustion in the gas burner as a function of the fuel gas parameter.

The term fuel gas parameter is to be interpreted broadly here and refers to the type and proportion of the additional gas in the fuel gas. In a preferred embodiment, the fuel gas parameter can therefore correspond to a volume proportion of the additional gas in the fuel gas.

As already described in detail, different additional gases can be mixed with the fuel gas. In a further preferred embodiment, however, the additional gas can be hydrogen. In this way, the inventive A planned injection of hydrogen into the natural gas network can be flexibly addressed.

The fuel gas parameter can therefore, for example, indicate which additional gas is present in the fuel gas and what the proportion of additional gas is. Depending on the specific fuel gas parameter, a corresponding control variable can then be derived for controlling the combustion in the gas burner.

Calibration coefficients can be stored in the form of a characteristic curve to determine the proportion of additional gas. Depending on the proportion determined, the control variable for combustion can then be derived independently by a control circuit in the gas burner and the combustion can be adjusted.

In a preferred embodiment, the method according to the invention can further comprise, between steps c) and d), the step i) of returning to the air ratio λ _Ist and setting the burner load to a second predetermined load value L2 > L1, as well as the step ii) of restarting the predetermined target air ratio λ _Soll in a predetermined period of time Δt _L2 , and the step iii) of determining the course of the flame temperature T _{F, L2} in the period Δt _L2 , wherein in step d) the combustion gas parameter can then be determined from the courses of the flame temperature T _{F, L1} and T _{F, L2} .

In this way, the fuel gas parameter in step d) can advantageously be determined even more precisely and the combustion control can be derived even more precisely.

The load value L2 is also not restricted according to the invention as long as the flame kinetics differ significantly from the load value L1. According to a preferred embodiment, however, the load value L2 can be in a range of 10 to 20 kW.

In a further preferred embodiment, the fuel gas parameter can be determined by comparing the respective determined flame temperature curve T _F with a corresponding reference curve of the flame temperature T _{F, Ref.} for natural gas as fuel gas. For this purpose, for example, the flame temperature curve at a predetermined load value for natural gas as fuel gas can be stored in the control circuit of the gas burner. From a comparison of a currently determined flame temperature curve at the same load value, it can then be determined, which additional gas is present in the currently available fuel gas and what the proportion is.

In a further preferred embodiment, the fuel gas parameter can be determined based on a minimum flame temperature T _{F, min.} and/or based on one or more flame temperature differences ΔT _F determined from the respective course of the flame temperature T _F. For example, the type and proportion of an additional gas can be determined based on the measurement of a minimum and/or maximum starting from an initial state. For hydrogen, for example, the height of the difference to a characteristically occurring maximum in the flame temperature course is specific. The extent of the height difference also shows the proportion of hydrogen.

In a further preferred embodiment, the gas burner can additionally have an ignition electrode, means for generating an ignition voltage and a switch arrangement for connecting the ignition electrode to and for disconnecting the ignition electrode from the means for generating the ignition voltage, and the course of the flame temperature T _F can be determined in each case using the ignition electrode. As already mentioned above, the course of the flame temperature can advantageously be determined in particular using the thermionic effect at the ignition electrode.

A gas burner according to the invention comprises a control circuit and a measuring device which are configured to carry out a method which comprises the step a) of setting a burner load to a first predetermined load value L1 at an actual air ratio λ _Ist ; the step b) of approaching a predetermined target air ratio λ _Soll in a predetermined period of time Δt _L1 ; the step c) of determining a profile of a flame temperature T _{F, L1} in the period Δt _L1 ; and the step d) of determining a combustion gas parameter from the profile of the flame temperature T _{F, L1} and deriving a control variable for controlling the combustion in the gas burner depending on the combustion gas parameter.

In a preferred embodiment, the control circuit and the measuring device can additionally be configured to carry out a method which, between steps c) and d), additionally _comprises the step i) of returning to the air ratio λ and setting the burner load to a second predetermined Load value L2 >L1; the step ii) of restarting the predetermined target air ratio λ _target in a predetermined period of time Δt _L2; ; and the step iii) of determining the course of the flame temperature T _F , _L2 in the period Δt _L2 , wherein in step d) the combustion gas parameter can be determined from the courses of the flame temperature T _{F, L1} and T _{F, L2} .

In a further preferred embodiment, the gas burner can additionally comprise an ignition electrode, means for generating an ignition voltage and a switch arrangement for connecting the ignition electrode to and for disconnecting the ignition electrode from the means for generating the ignition voltage.

The method according to the invention and the gas burner according to the invention have numerous advantages. For example, while calibration by means of ionization when starting up to lambda 1 is sufficient to differentiate whether a burner test gas such as G21 or G271 is present, the method described above can be used to determine whether there is an additional gas in the fuel gas, what type it is and how high the proportion is. Hydrogen proportions cannot be determined with the calibration by means of ionization described above due to other causalities of the target values.

With the method according to the invention and the gas burner according to the invention, the nominal air ratios and thus also the device performance for hydrogen-containing fuel gases can be achieved, as well as low NO _x values. This can avoid the risk of thermoacoustics and overheating of the gas burner.

In addition, no upstream system with corresponding data exchange is necessary, since the detection of the additional gas and its proportion takes place in the gas burner. A simple sensor system can be used for this; lambda sensors are not necessary.

SHORT DESCRIPTION OF THE CHARACTERS

• Figures 1 to 5 show schematically embodiments of the method for controlling the combustion of fuel gas by means of a gas burner, as well as embodiments of the gas burner.
  In particular, Figure 1 a flow chart to illustrate an embodiment of a method for controlling the combustion of fuel gas by means of a gas burner, wherein the gas burner has a measuring device and a control circuit, and wherein the fuel gas contains natural gas and an additional gas.
• Figure 2 shows a flow chart of a further embodiment of a method for controlling the combustion of fuel gas by means of a gas burner, wherein the gas burner has a measuring device and a control circuit, and wherein the fuel gas contains natural gas and an additional gas.
• Figure 3 shows two flame temperature curves at a first predetermined load value L1 for methane as fuel gas and for a mixture of methane and hydrogen as fuel gas.
• Figure 4 shows the two flame temperature curves at the first predetermined load value L1 from Figure 3 and additionally the flame temperature curves at a second predetermined load value L2 also for methane as fuel gas and for a mixture of methane and hydrogen as fuel gas.
• Figure 5 shows a block diagram of a gas burner according to an embodiment.

DETAILED DESCRIPTION OF THE FIGURES AND PREFERRED EXAMPLES OF IMPLEMENTATION

In the following, examples or embodiments of the present invention are described in detail with reference to the accompanying figures. Identical or similar elements in the figures may be designated by the same reference numerals, but sometimes also by different reference numerals.

It should be emphasized that the present invention is in no way limited or restricted to the embodiments described below and their design features, but further comprises modifications of the embodiments, in particular those which are included within the scope of the claims by modifying the features of the examples described or by combining individual or several features of the examples described.

Figure 1 shows a flow chart to illustrate an embodiment of a method for controlling the combustion of fuel gas by means of a gas burner, wherein the gas burner has a measuring device and a control circuit, and wherein the fuel gas contains natural gas and an additional gas.

In step S101, a burner load is set to a first predetermined load value L1 at an actual air ratio λ _Ist . The load value is not restricted according to the invention. In a preferred embodiment, the load value L1 can be in a range from 5 to 10 kW. The load value L1 can advantageously be stored in the control circuit of the gas burner and automatically approached in step S101 when the method is carried out.

The actual air ratio λ _Actual is also not limited according to the invention and can, for example, result from a current mixture control during the normal operation of the gas burner. In this way, the method can be carried out during ongoing gas burner operation and the mixture control can be flexibly and optimally adapted to varying combustion gases, for example by adding an additional gas, in particular hydrogen.

As from Figure 1 As can be seen, in a next step S102 a predetermined target air ratio λ _{Soll is} approached in a predetermined period of time Δt _L1 . The target air ratio λ _Soll is also not restricted according to the invention, but it is different from the actual air ratio λ _Ist . In a preferred embodiment, λ _Ist > λ _Soll can apply. This advantageously takes into account the fact that in normal operation of a gas burner with natural gas as the fuel gas, the mixture control is in the lean range, so that the air ratio λ _Soll can be achieved by enriching the mixture. Particularly preferably, stoichiometric combustion can be started at λ _Soll = 1. In general, various variants of the temporal mixture control (enrichment) in the gas burner are conceivable. Preferably, the predetermined target air ratio λ _Soll can be approached linearly over the time constant change in the gas flow rate in the gas burner. Alternatively, the predetermined target air ratio λ _Soll can also be approached parabolically or exponentially over time.

The length of the period Δt _L1 is also not limited according to the invention, insofar as the course of a flame temperature T _F , _L1 determined in this period in step S103, which is used to determine the fuel gas parameter in step S104 necessary information. For example, the predetermined period Δt _L1 can be between 10s and 60s, preferably between 20s and 40s, particularly preferably 30s.

As already mentioned, in step S103 the profile of the flame temperature T _F , _L1 in the time period Δt _L1 is determined. The flame temperature T _{F, L1} can be measured in different ways, for example using one or more thermocouples. Preferably, however, the flame temperature T _F , _L1 can be determined using an ignition electrode by utilizing the thermoelectric effect. For this purpose, according to a preferred embodiment, the gas burner can additionally have an ignition electrode, means for generating an ignition voltage and a switch arrangement for connecting the ignition electrode to and for disconnecting the ignition electrode from the means for generating the ignition voltage. To determine the flame temperature profile T _{F, L1} in the time period Δt _L1 , the flame temperature T _F , L1 can be measured continuously, but individual measured values can also be recorded at a certain time interval within the time period Δt _L1 , as long as a sufficiently accurate flame temperature profile T _{F, L1} can be recorded. For this purpose, for example, the number of measured values recorded can be increased in the areas in which characteristic features in the flame temperature curve T _F , _L1 are to be expected, for example minima and/or maxima, whereas in uncharacteristic areas, for example with a constant flame temperature curve T _F , _L1 , fewer measured values can be recorded.

As in Figure 1 As shown, in step S104 a fuel gas parameter is then determined from the course of the flame temperature T _F , _L1 and a control variable for controlling the combustion in the gas burner is derived depending on the fuel gas parameter. The determination of the fuel gas parameter and the derivation of the control variable are described below with reference to the Figures 3 to 5 described in more detail.

Figure 2 shows a flow chart of a further embodiment of a method for controlling the combustion of fuel gas by means of a gas burner, wherein the gas burner has a measuring device and a control circuit, and wherein the fuel gas contains natural gas and an additional gas.

In the Figure 2 The process steps S201 to S204 shown can be adapted to the Figure 1 shown process steps S101 to S103, whereby step S204 Step S104 can be replaced. As in Figure 2 As shown, in step S201 the air ratio λ _Ist can be reduced and the burner load can be set to a second predetermined load value L2 > L1. The air ratio λ _Ist can be the value in Figure 1 shown original air ratio λ _actual . In this way, when the predetermined target air ratio λ _{target is} approached again in a predetermined period of time Δt _L2 in step S202, the same air ratio range can be run at a different load value L2.

According to the invention, the load value L2 is not restricted as long as the flame kinetics differ significantly from the load value L1. According to a preferred embodiment, however, the load value L2 can be in a range of 10 to 20 kW.

Step S203 in Figure 2 can then provide for the determination of the course of the flame temperature T _F , _L2 in the period Δt _L2 . Analogous to Figure 1 Here too, the measurement of the flame temperature T _{F, L2} and the length of the time period Δt _L2 are not restricted according to the invention. However, here too, the flame temperature is advantageously measured using the ignition electrode and the length of the time period Δt _L2 advantageously corresponds to the length of the time period Δt _L1 .

In step S204, as in Figure 2 As shown, the combustion gas parameter can then be determined from the flame temperature curves T _{F, L1} and T _{F, L2} and a control variable for controlling the combustion in the gas burner can be derived.

In the following, the determination of the fuel gas parameter from the course of the flame temperature T _{F, L1} or T _{F, L2} with reference to the Figures 3 and 4 explained in more detail. The inventors have found it advantageous that the course of the flame temperature T _F for natural gas as a fuel gas has specific characteristics at the respective predetermined first and second load values L1 and L2 in comparison to mixtures of natural gas and an additional gas. Based on the evaluation of these specific characteristics, the type of additional gas and its proportion in the fuel gas can then be determined as a fuel gas parameter.

First, Figure 3 Flame temperature curves T _F , _L1 at a first predetermined load value L1 for pure methane (G20) as fuel gas 1 and for 70% methane and 30% hydrogen as fuel gas 2. Since the main component of natural gas is methane, pure methane is used as a substitute for natural gas in the present example. In this way, a uniform reference point can be advantageously created, independent of variations caused by sites.

In the example in Figure 3 the load value L1 is set to 10kW. The actual air ratio λ _Ist was in the lean range and the respective air-fuel gas mixture was enriched from λ _Ist > 1 to the target air ratio λ _Soll = 1 in the period Δt _L1 = 30s using linear mixture control. The flame temperature curve T _F , _L1 was also determined during this period. Standardized values for the flame temperature T _F , _L1 determined using an ignition electrode are plotted on the y-axis. At this point it is pointed out that the values in the Figures 3 and 4 The flame temperature values plotted are given in an artificial unit [I] which is inversely related to the actual temperature. The values Figure 3 and 4 The values shown are digitized measured values that an AD converter in the gas burner's automatic firing system can determine from a corresponding input channel. The time t in [s] is plotted on the x-axis.

As from Figure 3 As can be seen, the respective curves for pure methane as fuel gas 1 and for 70% methane and 30% hydrogen as fuel gas 2 show different characteristic features as a function of time t. Both curves 1, 2 show a different degree of pronounced minimum 1a, 2a (indicated by arrow 3). The minimum 2a for 70% methane and 30% hydrogen as fuel gas also occurs earlier than the minimum 1a for pure methane as fuel gas.

Figure 4 shows the flame temperature curves at the first predetermined load value L1 = 10kW from Figure 3 and additionally the flame temperature curves at a second predetermined load value L2 = 20 kW also for pure methane as fuel gas and for the mixture of 70% methane and 30% hydrogen as fuel gas.

Before determining the flame temperature curves T _{F, L2} at the load value L2 = 20kW, the air ratio was reduced to the original actual air ratio λ _Actual (as can be seen from the step-like jumps in curves 1 and 2). In the Figure 4 In the flame temperature curves shown, the gas burner runs at a constant load with the same air ratio, for example λ = 1.34, in the areas in which the flame temperature signals are constant. Basically, the different load values (load levels) are accompanied by different base levels of the flame temperature. At the load value L2 = 20kW, the corresponding air-fuel gas mixture was enriched from λ _actual < 1 to the target air ratio λ _target = 1 by means of linear mixture control in the period Δt _L2 = 60s. The flame temperature curve T _F , _L2 was also determined during this period.

As from Figure 4 As can be seen, the respective curves for pure methane as fuel gas 1 and for 70% methane and 30% hydrogen as fuel gas 2 also show different characteristic features as a function of time t at the load value L2 = 20kW. Both curves 1, 2 again show a different degree of pronounced minimum 1b, 2b (indicated by arrow 4), with curve 2 for 70% methane and 30% hydrogen as fuel gas additionally showing a maximum 2c following the minimum 2b. Even at the load value L2 = 20kW, the minimum 2b for 70% methane and 30% hydrogen as fuel gas is ahead of the minimum 1b for pure methane as fuel gas.

According to a preferred embodiment, the fuel gas parameter can be determined by comparing the respective determined flame temperature curve T _F with a corresponding reference curve of the flame temperature T _{F, Ref.} for natural gas as fuel gas.

Referring to the Figures 3 and 4 For example, the flame temperature curve T _F for pure methane can serve as a reference curve at the load values L1 = 10kW and L2 = 20kW. From the comparison with the flame temperature curve T _F determined for 70% methane and 30% hydrogen as fuel gas at the same load values L1 and L2, the fuel gas parameter can then be determined based on the different characteristic features, as described above.

According to a further preferred embodiment, the fuel gas parameter can be determined in each case based on a minimum flame temperature T _{F, min.} and/or based on one or more flame temperature differences ΔT _F determined from the respective course of the flame temperature T _F.

As referring to the Figures 3 and 4 As described, for example, a mixture of 70% methane and 30% hydrogen shows a temporally advanced minimum in the course of the flame temperature T _{F, L1} compared to pure methane at the first predetermined load value L1. The difference in relation to the initial value (indicated by arrow 3 in the Figures 3 and 4 ) is also lower for the mixture of 70% methane and 30% hydrogen. At the load value L2 = 20kW, the mixture of 70% methane and 30% hydrogen also shows a temporally preceding minimum in the course of the flame temperature T _F , _L2 , compared to pure methane, as well as a maximum following the minimum. Also at the load value L2, the difference of the minimum in relation to the initial value (indicated by the arrow 4 in Figure 4 ) is lower for the mixture of 70% methane and 30% hydrogen. From the height difference of the maximum in relation to the initial value (indicated by arrow 5 in Figure 4 ) the proportion of hydrogen in the fuel gas can also be determined, since this is specific for hydrogen.

Other additional gases also have such characteristic features. For example, nitrogen as an additional gas, in contrast to hydrogen, also shows a maximum at the load value L1 that follows the minimum. Propane as an additional gas, on the other hand, does not show any maximum in the course of the flame temperature. However, here too the two minima are shifted to shorter times compared to pure methane, with the difference to the initial value being larger in each case than with methane.

Figure 5 shows a block diagram of a gas burner according to an embodiment. The gas burner 100 has a combustion chamber 101 in which a combustion process can take place by supplying an air-combustion gas mixture. An ignition electrode 102 projects into the combustion chamber 101. Optionally, an ionization electrode can also be provided in the gas burner 100, which also projects into the combustion chamber. An ionization electrode is generally used for flame monitoring.

The ignition electrode 102 is connected to a device for generating an ignition voltage 104 in such a way that the ignition electrode 102 can be separated from the device for generating the ignition voltage 104. This can be done by a switch arrangement 103 connected between the ignition electrode 102 and the device for generating the ignition voltage 104. The switch arrangement 103 can in particular be set up in such a way that after the ignition electrode 102 is separated from the device for generating the ignition voltage 104, the ignition electrode 102 is connected as a passive electrode.

The gas burner 100 also has a measuring device 105. The measuring device 105 can be used to determine the temperature of the flame at the electrode by utilizing the aforementioned thermoelectric effect and thus measure the flame temperature curve at a correspondingly set load value. For this purpose, the switch arrangement 103 is connected to the measuring device 105 and can receive signals from the measuring device 105. The measuring device 105 can also have a time measuring device, via which the predetermined time periods can be set.

The measuring device 105 is also connected to a control circuit 106. The combustion in the gas burner 100 can be controlled via the control circuit 106 using a burner control 109. The burner control 109 has a valve control 110 for changing the proportion of fuel gas in the air-fuel gas mixture, as well as a fan control 111 for varying the proportion of air.

The control circuit 106 has in particular a device for determining a fuel gas parameter 107. The device for determining the fuel gas parameter 107 is connected to the measuring device 105 and receives the measured values determined in the respective time periods for determining the flame temperature, which were determined by means of the ignition electrode 102 in the combustion chamber 101. In the device for determining the fuel gas parameter 107, the flame temperature curves are evaluated and, as described above, the fuel gas parameter is determined based on the respective characteristic features. The fuel gas parameter represents a type of additional gas determined and its proportion in the fuel gas, for example hydrogen, proportion 30%.

The device for determining the combustion gas parameter 107 is connected to a device for deriving a control variable 108 for controlling the combustion in the gas burner 100. The control variable can be, for example, an air ratio λ that is changed taking the combustion gas parameter into account and/or a changed volume flow. By adding hydrogen, for example, the maximum of the laminar flame speed shifts to smaller lambda values, and a higher volume flow is also required for a performance comparable to pure natural gas.

The controlled variable is then transmitted by the device for deriving the controlled variable 108 to the burner control 109, which can then regulate the combustion in the gas burner 100 accordingly or adapt it to the changed fuel gas via the valve control 110 and/or the fan control 111.

REFERENCE SIGNS

1

Flame temperature curve T _{F, L1} T _{F, L2} for pure methane

2

Flame temperature curve T _{F, L1} T _{F, L2} for 70% methane and 30% hydrogen

1a

Minimum in the flame temperature curve T _{F, L1} for pure methane

2a

Minimum in the flame temperature curve T _{F, L1} for 70% methane and 30% hydrogen

1b

Minimum in the flame temperature curve T _{F, L2} for pure methane

2 B

Minimum in the flame temperature curve T _{F, L2} for 70% methane and 30% hydrogen

2c

Maximum in the flame temperature curve T _{F, L1} for 70% methane and 30% hydrogen

3

Difference of the minimum to the initial value in the flame temperature curve T _{F, L1} for 70% methane and 30% hydrogen

4

Difference of the minimum to the initial value in the flame temperature curve T _{F, L2} for 70% methane and 30% hydrogen

5

Difference of the maximum to the initial value in the flame temperature curve T _{F, L2} for 70% methane and 30% hydrogen

100

Gas burner

101

Combustion chamber

102

Ignition electrode

103

Switch arrangement

104

Device for generating an ignition voltage

105

Measuring device

106

Control circuit

107

Device for determining a fuel gas parameter

108

Device for deriving a controlled variable

109

Burner control

110

Valve control

111

Fan control

Claims (13)

1. Method for controlling the combustion of fuel gas by means of a gas burner (100), wherein the gas burner (100) has a measuring device (105) for measuring the flame temperature and a control circuit (106), wherein the fuel gas contains natural gas and an additional gas, and wherein the method comprises:

   a) setting (S101) a burner load to a first predetermined load value L1 at an actual air ratio λ_actual;

   b) starting (S102) a predetermined setpoint air ratio λ_setpoint in a predetermined time period Δt_L1;

   c) determining (S103) a profile of a flame temperature T_{F, L1} (1, 2) in the time period Δt_L1; and

   d) determining (S104) a fuel gas parameter from the profile of the flame temperature T_{F, L1} (1, 2) and deriving (S104) a controlled variable for controlling the combustion in the gas burner (100) as a function of the fuel gas parameter.
2. Method according to Claim 1, wherein the method additionally comprises the steps between steps c) and d):

   i) returning (S201) to the air ratio λ_actual and setting the burner load to a second predetermined load value L2 > L1;

   ii) restarting (S202) the predetermined setpoint air ratio λ_setpoint in a predetermined time period Δt_L2;

   iii) determining (S203) the profile of the flame temperature T_F, _L2 (1, 2) in the time period Δt_L2,

   wherein in step d) the fuel gas parameter is determined (S204) from the profiles of the flame temperature T_{F, L1} and T_{F, L2} (1, 2).
3. Method according to claim 1 or 2, wherein the fuel gas parameter is determined by a comparison of the respective determined flame temperature profile (1, 2) with a corresponding reference profile (1) of the flame temperature T_{F, Ref.} for natural gas as fuel gas.
4. Method according to one of claims 1 to 3, wherein the fuel gas parameter is determined in each case on the basis of a minimum flame temperature T_F, _min (1a, 2a, 1b, 2b) and/or on the basis of one or more flame temperature differences ΔT_F (3, 4, 5) determined from the respective profile of the flame temperature T_F.
5. Method according to one of claims 1 to 4, wherein the load value L1 lies in a range from 5 to 10 kW.
6. Method according to claim 2 or one of claims 3 to 5 when dependent on claim 2, wherein the load value L2 lies in a range from 10 to 20 kW.
7. Method according to one of claims 1 to 6, wherein the gas burner (100) additionally has an ignition electrode (102), means for generating an ignition voltage (104) and a switch arrangement (103) for connecting the ignition electrode (102) to and for separating the ignition electrode (102) from the means for generating the ignition voltage (104), and the profile of the flame temperature T_F (1, 2) is determined in each case on the basis of the ignition electrode (102).
8. Method according to one of claims 1 to 7, wherein λ_actual > λ_setpoint.
9. Method according to one of claims 1 to 8, wherein the fuel gas parameter corresponds to a volume fraction of the additional gas in the fuel gas.
10. Method according to one of claims 1 to 9, wherein the additional gas is hydrogen.
11. Gas burner (100) having a measuring device (105) for measuring the flame temperature and having a control circuit (106), which are configured to carry out a method which comprises the following steps:

    a) setting (S101) a burner load to a first predetermined load value L1 at an actual air ratio λ_actual;

    b) starting (S102) a predetermined setpoint air ratio λ_setpoint in a predetermined time period Δt_L1;

    c) determining (S103) a profile of a flame temperature T_{F, L1} (1, 2) in the time period Δt_L1; and

    d) determining (S104) a fuel gas parameter from the profile of the flame temperature T_{F, L1} (1, 2) and deriving (S104) a controlled variable for controlling the combustion in the gas burner (100) as a function of the fuel gas parameter.
12. Gas burner (100) according to Claim 11, wherein the measuring device (105) and the control circuit (106) are additionally configured to carry out a method which additionally comprises the following steps between steps c) and d):

    i) returning (S201) to the air ratio λ_actual and setting the burner load to a second predetermined load value L2 > L1;

    ii) restarting (S202) the predetermined setpoint air ratio λ_setpoint in a predetermined time period Δt_L2;

    iii) determining (S203) the profile of the flame temperature T_F, _L2 (1, 2) in the time period Δt_L2,

    wherein in step d) the fuel gas parameter is determined from the profiles of the flame temperature T_F, _L1 and T_F, _L2 (1, 2).
13. Gas burner (100) according to Claim 11 or 12, wherein the gas burner (100) additionally has an ignition electrode (102), means for generating an ignition voltage (104) and a switch arrangement (103) for connecting the ignition electrode (102) to and for separating the ignition electrode (102) from the means for generating the ignition voltage (104).

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