GB2599423A

GB2599423A - Method for operating a combustion device, combustion device and heater

Info

Publication number: GB2599423A
Application number: GB2015572.7A
Authority: GB
Inventors: Collins Tom; Dunne Simon; English Sam; Odumosu Timi
Original assignee: Bosch Thermotechnology Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 2020-10-01
Filing date: 2020-10-01
Publication date: 2022-04-06
Anticipated expiration: 2040-10-01
Also published as: EP3978805B1; EP3978805A1; GB2599423B; GB202015572D0

Abstract

A method for operating a combustion device 100 to provide a combustible mixture composed of an air stream ‘A’ and a hydrogen combustion gas stream ‘G’, and to burn the mixture ‘M’ so that heat is generated. The combustible air/fuel mixture is regulated as a function of the heat required, and when low heat power is required the combustible mixture is controlled such that it is a lean mixture, and/or when a high heat power is required the combustible mixture is controlled such that it is a rich mixture. In particular, the air quantity, represented by an air number λ of the air/combustion gas mixture stream is regulated within defined limits in dependence of the range of heating power, and as such λ = λ(Q) and is regulated within the boundaries of: 0.15 / Q + 1 ≤ λ ≤ 0.175 / Q + 1.25, when the relative heating power ‘Q’ is in the range between 0 and 1. The regulating arrangement may include a fan 102, a fuel gas metering unit 104, a mixing unit 106 and regulating apparatus 110.

Description

Method for operating a combustion device, combustion device and heating unit

Prior art

A method for operating a combustion device to provide an air/combustion gas mixture stream composed of an air stream and a combustion gas stream in a predefinable air/combustion gas ratio and to burn the mixture stream is already known from the prior art in which heating power is generated by the combustion and with an air conveying unit conveying an air stream, a combustion gas metering unit metering a combustion gas stream and a mixer unit mixing the mixture stream.

Disclosure of the invention

The invention proceeds from a method for operating a combustion device to provide an air/combustion gas mixture stream composed of an air stream and a combustion gas stream, in particular a hydrogen stream, in at least one predefinable air/combustion gas ratio and to burn the mixture stream, with heating power being generated by the combustion.

The invention is characterised in that the air/combustion gas ratio is varied by means of a regulating apparatus as a function of the heating power, with the air/combustion gas ratio adopting a higher value in the case of lower heating power and/or adopting a lower value in the case of higher heating power.

The invention also relates to a method for operating a combustion device to provide an air/combustion gas mixture stream composed of an air stream and a combustion gas -2 -stream, in particular a hydrogen stream, with at least one predefinable air number A in the mixture stream and to burn the mixture stream, with heating power being generated by the combustion.

The invention is characterised in that the air number A of the air/combustion gas mixture stream is regulated to a value within the air number value interval by means of a regulating apparatus 0.15 / Q + 1 A 0.175 / Q + 1.25 with the interval limits of heating power-dependent air number limit curves A-min (Q) and A-max (Q) being formed A-min = 0.15 / Q + 1 A-max = 0.175 / Q + 1.25 In particular an air conveying unit conveys the air stream, in particular as a function of a power requirement, a combustion gas metering unit meters the combustion gas stream, in particular as a function of the air stream, and a mixer unit mixes the mixture stream.

A combustion device should be understood here in particular as a burner or a burner apparatus, by means of which a burnable mixture stream can be provided and burned. The combustion device is in particular used in a heating unit, for example a heating unit for heating at least one room and/or for heating at least one service fluid such as heating water and/or drinking water. The mixture stream is a gas stream comprising an air stream and a combustion gas stream. The air stream is in particular removed from a -3 -surrounding environment of the combustion device or an external environment of a building in which the combustion device is set up. The combustion gas stream is in particular removed from a combustion gas line or a combustion gas tank. The combustion device is in particular designed for the use of the combustion gas, hydrogen. Alternatively or additionally, the combustion device can also be designed for the use of another combustion gas. For its clean and efficient combustion, the mixture stream has a predefinable air/combustion gas ratio or air number A. An air/combustion gas ratio should be understood here as a quantity ratio of air to combustion gas. The air/combustion gas ratio being predefinable should be understood in particular in that the quantity ratio can be set. The mixture stream is ignited in the combustion device and burned by forming a flame. The combustion device comprises a burner opening or burner surface which acts like a flame holder: the flame should burn in a spatially stable manner here. The energy (heat) being released per unit of time during combustion is determined by the size of the burned mixture stream, in particular the size of the burned fuel stream. The energy being released per unit of time characterises the heating power of the combustion device. The heating power can be modulated between a minimum heating power and a maximum heating power in a stepwise or continuous manner. The term heating power can be understood as both absolute heating power (unit: watts) and a relative heating power. The relative heating power is calculated as the actual absolute heating power in relation to the maximum absolute heating power. The relative heating power is a dimensionless variable with values in general between 0 and 1. Since, however, a real combustion device generally cannot be operated at a relative heating power just above 0, the values of the relative heating power are in reality 0 for the switched-off state (no combustion) and in the burning operation between for example 0.05 and 1. An air conveying unit is understood as an apparatus to convey the air stream, in this case it may in particular be an, in particular speed-regulated, air blower or air ventilator or an air valve. The air conveying unit is in particular controlled by an electric signal. The conveying of the air stream can in particular as a function of a power requirement, for example a heating power requirement or a temperature requirement take place to the combustion device and/or heating unit. In particular a variable of the conveyed air volume stream can take place as a function of a variable of a required heating power. A required heating power is in particular understood as a theoretically required heating power which serves to fulfil a need of a user for room heating and/or hot drinking water preparation. In contrast to this, an actual heating power is a measurable variable which correlates with the variable of the mixture stream arriving for combustion. A combustion gas metering unit is understood as an apparatus for metering the combustion gas stream, in this case it may in particular be a combustion gas valve or a combustion gas fitting. The combustion gas metering unit is in particular regulated by an electric and/or a pressure signal. The metering of the combustion gas stream can in particular take place as a function of the air stream. In particular, a variable of the metered combustion gas stream can take place as a function of the variable of the air stream. A mixer unit is understood as an apparatus for combining and mixing air stream and combustion gas stream and for generating the air/combustion gas mixture stream, in this case it may in particular be a Venturi mixer. -5 -

A regulating apparatus is understood as an apparatus to control and/or regulate at least one method step, in particular to vary the air/combustion gas ratio and/or the air number A. Regulating is here understood generally as controlling and/or regulating in the narrower sense. Regulation is here understood generally as control and/or regulation in the narrower sense. With varying, the air/combustion gas ratio and/or the air number A is predefinably changed. By means of the regulating apparatus, a variable integrated regulation can be developed to regulate the air/combustion gas ratio and/or the air number A. A combination means in particular that a target value of a first variable, for example the air stream, is predefined for example on the basis of an electric signal, and that a target value of a subsequent variable, for example the combustion gas stream, is tracked for example on the basis of an electric or a pressure signal in the combination and adapted to the resulting actual value of the first variable. A variable combination means that the target value of the subsequent variable is adapted not only to the actual value of the first variable, but also that this adaptation is varied as a function of a third variable, here the heating power. As a result, the value of the air/combustion gas ratio is regulated such that a heating power-dependent air/combustion gas ratio is set. The air/combustion gas ratio being varied as a function of the heating power should be understood in that the variable of the heating power at least co-determines the value of the air/combustion gas ratio.

The regulating apparatus is in particular designed such that the air/combustion gas ratio and/or the air number A adopts a higher value in the case of lower heating power -6 -and/or adopts a lower value in the case of higher heating power. In this case, the regulating apparatus in particular also interferes with the operation of the air conveying unit, the combustion gas metering unit and/or the mixer unit. In particular, the air/combustion gas ratio is increased with decreasing heating power and decreases with increasing heating power. The variation of the air/combustion gas ratio over the heating power can have a stepwise course or a continuous course. Increasing the air/combustion gas ratio is understood here as reducing the air/combustion gas mixture stream, i.e. reducing the combustion gas content in the mixture stream. Decreasing the air/combustion gas ratio is understood here as increasing the air/combustion gas mixture stream, i.e. enriching the combustion gas content in the mixture stream. The air stream, the combustion gas stream and/or the mixture stream are variable in quantity and can be modulated in a stepwise or continuous manner between a respective minimum value and a respective maximum value.

The regulating apparatus can in particular be designed as an independent component "regulating device". The regulating apparatus can alternatively or additionally (in the sense of a distributed system) also be designed as part of the air conveying unit, the combustion gas metering unit and/or the mixer unit.

The air number A is a special parameter used in combustion technology to characterise the air/combustion gas ratio of an air/combustion gas mixture stream. The air number A is calculated as a quotient of an air quantity L actually present in the mixture stream and an air quantity L-st required for a stoicniometric combustion of the mixture stream: A = L / L-st The relative heating power Q is calculated as a quotient of the actual absolute heating power P and the maximum absolute heating power P-max: Q = P/P-max The above-mentioned formula expressions for the limits of the air number value interval are mathematically defined for relative heating powers Q from the interval: The fact that the removal of the value Q = 0 does not represent a restriction of the validity of the indicated air number value interval for combustion practice is clear from the above comments on the real combustion devices, whereby the values of the relative heating power Q in real combustion operation are between Q-min, for example a value from a range of between 0.05 and 0.1 and Q-max = 1, and adopt the value Q = 0 only for the switched-off state (no mixture formation, no combustion, no appropriate air number definition possible).

Using the invention, a method for operating a combustion device, which is improved in comparison with the known prior art, is provided.

Air/combustion gas mixture streams with an air number A composed of the above-mentioned value interval are particularly advantageous to burn. In particular, air/hydrogen mixture streams with an air number A composed of the above-mentioned value interval are particularly advantageous to burn. The combustion of such an air/combustion gas mixture stream is characterised by safe -8 -ignition, high flame stability (avoidance of rising flames and flame flashback), optimal thermal effectiveness, complete combustion with low contaminant values, low noise development and compatibility with commercially available pneumatic air/gas ratio regulators.

An advantageous embodiment of the invention is characterised in that the regulating apparatus regulates the combustion gas metering unit as a function of the heating power, with the combustion gas metering unit metering a relatively smaller combustion gas stream in the case of lower heating power and metering a relatively larger combustion gas stream in the case of higher heating power.

The regulating of the combustion gas metering unit can in 15 particular take place by means of an electric signal or a pressure signal, which is output from the regulating apparatus to the combustion gas metering unit.

The term, "a relatively smaller (or larger) combustion gas stream" expresses that the decrease (or increase) in the metering of the combustion gas stream does in particular not take place proportionally in the case of lower (or higher) heating power, but rather takes place disproportionately such that the air/combustion gas ratio and the air number A is larger in the case of the lower heating power or smaller in the case of higher heating power.

In particular, the regulating apparatus regulates the combustion gas metering unit as a function of the heating power such that an air number A is set in the mixture stream within the above-mentioned air number value interval. -9 -

In particular, the regulating apparatus can as a distributed system also comprise parts contacting the air stream, for example air throughput measurement units or air pressure probes, which detect a variable of the air stream.

The combustion gas stream is, corresponding to the variable of the air stream and as a function of the heating power, metered such that an air number is set in the mixture stream within the above-mentioned air number value interval.

A further advantageous embodiment of the invention is characterised in that the regulating apparatus regulates the air conveying unit as a function of the heating power, with the air conveying unit conveying a relatively larger air stream in the case of lower heating power and conveying a relatively smaller air stream in the case of higher heating power.

The regulating of the air conveying unit can in particular take place by means of an electric signal or a pressure signal which is output from the regulating apparatus to the 20 air conveying unit.

The term, "a relatively larger (or smaller) air stream" expresses that the decrease (or increase) in the conveying of the air stream does in particular not take place proportionally in the case of lower (or higher) heating power, but rather takes place disproportionately such that the air/combustion gas ratio and the air number A is larger in the case of the lower heating power or smaller in the case of higher heating power.

In particular, the regulating apparatus regulates the air 30 conveying unit as a function of the heating power such that -10 -an air number is set in the mixture stream within the above-mentioned air number value interval.

In particular, the regulating apparatus can as a distributed system also comprise parts contacting the combustion gas stream, for example combustion gas throughput measurement units or combustion gas pressure probes, which detect a variable of the combustion gas stream. The air stream is, corresponding to the variable of the combustion gas stream and as a function of the heating power, metered such that an air number is set in the mixture stream within the above-mentioned air number value interval.

A further advantageous embodiment of the invention is characterised in that the regulating apparatus generates a mixture signal as a function of the heating power and outputs it to the combustion gas metering unit and/or the air conveying unit. In this case, the mixture signal is provided, in the case of a lower heating power, to meter a relatively smaller combustion gas stream and/or to convey a relatively larger air stream; and, in the case of higher heating power, to meter a relatively larger combustion gas stream and/or to convey a relatively smaller air stream. The heating power mentioned here can be a detected actual heating power or even a required heating power.

The mixture signal can in particular be an electric signal or a pressure signal. The regulating apparatus generating a mixture signal as a function of the heating power may in particular be understood in that a correlation between heating power and mixture signal in the regulating apparatus, in the form of a mechanism, a value table, a mathematical function and/or an algorithm, can be retrieved which forms the basis for generating the mixture signal.

The mixture signal in particular comprises an individual signal or two partial signals, one for the air conveying unit and/or another for the combustion gas metering unit and acts in particular on the air stream conveyance of the air conveying unit and/or the combustion gas stream metering of the combustion gas metering unit.

In particular, the regulating apparatus regulates the air conveying unit and/or the combustion gas metering unit as a function of the heating power such that an air number is set in the mixture stream within the above-mentioned air number value interval.

A further advantageous embodiment of the invention is characterised in that the regulating apparatus receives and processes a power signal characterising the heating power, with the power signal being based on detection of an actual or required heating power, the mixture stream, the combustion gas stream, the air stream, a blower speed of an air blower conveying the air stream and/or a combustion temperature of the combustion of the air/combustion gas mixture stream, with the regulating apparatus generating the mixture signal based on the power signal.

The power signal can in particular be an electric signal or a pressure signal. To this end, the combustion device comprises at least one measurement apparatus, for example an electric, electronic or pneumatic sensor to detect the heating power, the mixture stream, the combustion gas stream, the air stream, the blower speed of an air blower conveying the air stream and/or the combustion temperature of the combustion of the air/combustion gas mixture stream.

A value of the power signal corresponds to a variable of the heating power. The regulating apparatus receives the power signal and translates it into the mixture signal.

-12 -A further advantageous embodiment of the invention is characterised in that a first detection unit detects the air/combustion gas ratio, in particular the air number A and outputs a corresponding first feedback signal to the regulating apparatus, with the regulating apparatus regulating the air/combustion gas ratio, in particular the air number A as a function of the first feedback signal.

The first detection unit can in particular be a lambda sensor or an ionisation electrode which measure a signal representing the air/combustion gas ratio, in particular the air number A. By means of the first feedback signal, the regulating apparatus can use a closed regulating circuit to regulate the air/combustion gas ratio, in particular the air number A in the above-defined limits.

A further advantageous embodiment of the invention is characterised in that a second detection unit detects a flame stability of the combustion and outputs a corresponding second feedback signal to the regulating apparatus, with the regulating apparatus regulating the air/combustion gas ratio, in particular the air number A as a function of the second feedback signal.

Flame stability is understood here in particular as a spatially-permanent presence of the flame at a desired target distance from the burner opening or burner surface.

In contrast to this, rising of a flame from the burner opening or burner surface means a flame is not burning in a stable manner, an increase of the distance and "blowing away" of the flame from the burner opening or burner surface. This is associated with an undesired extinguishing of the burner and outlet of unburned mixture and represents a dangerous state which must be avoided and/or detected. A flashback of a flame also means a flame is not burning in a -13 -stable manner, a decrease of the distance and sitting of the flame on the burner opening or burner surface, or even a penetration of the flame through the burner opening or burner surface into the interior of the combustion device, for example to the mixer unit. This is associated with undesired overheating of the burner surface or other elements in the interior of the combustion device and represents a dangerous state which must be avoided and/or detected.

The second detection unit can in particular be a temperature sensor or an optical sensor. They measure a signal representing the flame stability, for example an "excessively cold" (rising tendency) or "excessively hot" (flashback tendency) burner surface or an excessively large or excessively small flame distance from the burner surface. The temperature sensor can for example be arranged close to the burner surface. By means of the second feedback signal, the regulating apparatus can use a regulating circuit to regulate the air/combustion gas ratio, in particular the air number A, in the above-mentioned limits, whereby a safe operation of the combustion device with stable flame formation is ensured.

When the regulating apparatus for example determines on the basis of a signal of the second detection unit that the flame is not burning in a stable manner, it can regulate the air/combustion gas ratio, in particular the air number A, within the above-defined limits such that a desired flame stability is set once again.

A further advantageous embodiment of the invention is 30 characterised in that a third detection unit detects a combustion noise of the combustion and outputs a corresponding third feedback signal to the regulating -14 -apparatus, with the regulating apparatus regulating the air/combustion gas ratio, in particular the air number A as a function of the second feedback signal.

The third detection unit can in particular be an acoustic 5 sensor or a vibration sensor. They measure a signal representing the combustion noise, for example an "excessively loud" or strongly vibrating combustion (in relation to a predefinable limit value). By means of the third feedback signal, the regulating apparatus can use a regulating circuit to regulate the air/combustion gas ratio, in particular the air number A, in the above-defined limits, whereby a quiet operation of the combustion device is ensured.

A further advantageous embodiment of the invention is characterised in that the regulating apparatus outputs an error message when a predefinable flame stability or a predefinable noise limit value or a predefinable vibration limit value is not reached within the air number value interval.

Since a deviation of the flame stability and/or the noise limit value and/or vibration limit value may represent a dangerous state which must be avoided, it may be reasonable to supplement the error message with a shut-down of the combustion device.

The invention also relates to a combustion device, in particular a hydrogen combustion device, for a heating unit to heat at least one room and/or to heat at least one service fluid, with the combustion device being designed to carry out a method according to any one of the above-described methods.

-15 -Such a combustion device ensures an operation which is characterised by high flame stability, high effectiveness, low contaminant values and low noise development.

The invention further relates to a heating unit with a 5 combustion device according to the invention.

Drawings Further configurations and advantages are found in the following description of the drawings. In the drawing, exemplary embodiments of the invention are represented. The drawing, the description and the claims include numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them to form appropriate further combinations.

Figure 1 shows a first exemplary embodiment of a combustion device, Figure 2 shows a second exemplary embodiment of a combustion device, Figure 3 shows a third exemplary embodiment of a 20 combustion device, Figure 4 shows a limit curve course of the air number values A in a selected value interval as a function of the relative heating power Q. The Figures 1, 2 and 3 described below (particularities are highlighted in each case) each show a combustion device 100 for providing an air/combustion gas mixture stream M composed of an air stream A and a combustion gas stream G, in particular a hydrogen stream G, in at least one -16 -predefinable air/combustion gas ratio and for burning the mixture stream M, with heating power being generated by the combustion. The combustion device 100 comprises an air conveying unit 102, a combustion gas metering unit 104, a mixer unit 106, a burner surface 108 or a burner opening 108, a regulating apparatus 110 and lines for air, combustion gas, mixture or signal-carrying connection of the aforementioned components.

The air conveying unit 102 serves to suction an air stream A, in particular from a surrounding environment 1 of the combustion device 100 and to convey the air stream A to the mixer unit 106. For example, the air conveying unit 102 is a speed-regulatable air blower 102. The air conveying unit 102 is regulated by the regulating apparatus 110, for example based on a signal Si of a required heating power, by means of specifying a target conveying value 520, in particular a target blower speed 520. A power signal 521, in particular an actual conveying value such as for example an actual blower speed is detected at the air conveying unit 102 according to Figure 3 which describes a variable of the heating power (here in particular the actually conveyed air stream A).

The combustion gas metering unit 104 serves to meter a combustion gas stream G, with the combustion gas stream G being guided into the mixer unit 106. For example, the combustion gas metering unit 104 is a pneumatically regulatable combustion gas valve 104 (in particular Figure 1) or electronically regulatable combustion gas valve 104 (in particular Figures 2 and 3). A mixture signal 53 specifies an actuating value to the combustion gas metering unit 104, on the basis of which the combustion gas stream G is metered.

-17 -The mixer unit 106 serves to combine air stream A and combustion gas stream G and mix them to form a mixture stream M. For example, the mixer unit 106 is a Venturi nozzle 106. A power signal S21, in particular an actual air stream signal such as for example an air pressure is detected at the mixer unit 106 according to Figure 1 which describes a variable of the heating power (here in particular the actually conveyed air stream A). The combustion gas metering unit 104 according to Figure 1 is 10 regulated based on the power signal 521.

The mixture stream M escapes into a combustion chamber 2 at the burner surface 108 (not represented here), is ignited and burned forming flames F. The combustion device 100 also comprises a regulating apparatus 110 configured to vary the air/combustion gas ratio as a function of the heating power, with the air/combustion gas ratio adopting a higher value in the case of lower heating power and/or adopting a lower value in the case of higher heating power. The regulating apparatus 110 is in particular configured to regulate an air number A which describes the air/combustion gas ratio of the mixture stream M, to a value from a selected air number value interval, with the air number value interval being defined by a lower air number limit curve A-min and an upper air number limit curve A-max as follows: A-min = 0.15 / Q + 1 A-max = 0.175 / Q + 1.25 The values of the lower air number limit curve A-min and the upper air number limit curve A-max depend on the value -18 -of the heating power. In this case, Q denotes the value of the relative heating power of the combustion device 100.

In particular, an actually adjusted air number value A is at best substantially in the middle between the lower and the upper air number limit. Therefore, the air number limit curves A-min and A-max represent the admissible deviations of the air number A from an ideal value.

The regulating apparatus 110 according to Figure 1 regulates the combustion gas stream G based on a power signal 321, in particular an air pressure signal which is detected at the mixer unit 106 and describes the variable of the heating power (here in particular the air stream A flowing through the mixer unit). The power signal 321 acts on the regulating apparatus 110. The regulating apparatus 110 then causes the metering of an adapted combustion gas stream G by means of a mixture signal 33 such that the air number A in the mixture stream M adopts values from the selected value interval.

The combustion gas metering unit 104 and at least parts of the regulating apparatus 110 according to Figure 1 can in particular be formed by a pneumatic air/combustion gas ratio regulator 112. A pneumatic air/combustion gas ratio regulator 112 can in particular be understood as a fitting, which is combined to form a structural unit and is composed of regulating apparatus 110 and combustion gas metering unit 104. The air/combustion gas ratio regulator 112 receives a power signal 321 describing an air stream A, for example an air pressure signal, translates it into a mixture signal 33, for example an actuating signal for a combustion gas pressure, opens the gas valve in particular to set a combustion gas pressure in correlation with the air pressure and meters a combustion gas stream G -19 -corresponding to the air stream A. The aforementioned correlation is defined by settings carried out on the air/combustion gas ratio regulator 112 (for example an offset setting for the ratio, in particular difference from combustion gas pressure and air pressure).

The regulating apparatus 110 according to Figure 2 controls both the air stream A and the combustion gas stream G by means of two mixture signals 53 based on a required heating power Si. This regulation takes place so that the air number A in the mixture stream M adopts values from the selected value interval. The basis of the mixture signals S3 can be a value table, a parameterised functional equation or another calculation algorithm which is stored in the regulating apparatus 110 and establishes a correlation with the required heating power 51.

The regulating apparatus 110 according to Figure 3 regulates the air stream A based on the required heating power Si. The combustion gas stream G is metered based on a power signal 521 detected at the air conveying unit 102, in particular an actual conveying value, such as for example an actual blower speed, which describes a variable of the actually conveyed air stream A, by means of a mixture signal 53. This regulation takes place such that the air number A in the mixture stream M adopts values from the selected value interval. The basis of the mixture signal 33 can be a value table, a parameterised functional equation or another calculation algorithm which is stored in the regulating apparatus 110 and establishes a correlation with the power signal S21.

The combustion device 100 according to Figure 3 shows an optional first detection unit 114 to detect the actual air/combustion gas ratio, in particular the actual air -20 -number A and to output a corresponding first feedback signal 54 to the regulating apparatus 110, with the regulating apparatus 110 regulating the air/combustion gas ratio, in particular the air number A, as a function of the first feedback signal 54 such that the actual air number A in the mixture stream M adopts values from the selected value interval. The first detection unit 114 can comprise a lambda probe or an ionisation electrode. The regulation of the air/combustion gas ratio takes place in particular by regulating the combustion gas metering unit 104. The first feedback signal 54 influences the mixture signal 53 output by the regulating apparatus 110.

Furthermore, the combustion device 100 according to Figure 3 shows an optional second detection unit 116 to detect a flame stability of the combustion and to output a corresponding second feedback signal 56 to the regulating apparatus 110, with the regulating apparatus 110 regulating the air/combustion gas ratio, in particular the air number A, as a function of the second feedback signal S6 such that the air number A in the mixture stream M adopts values from the selected value interval. The second detection unit 116 can comprise a temperature sensor in or on the plane of the burner surface 108. Using this temperature sensor, a distance D of the flame F from the burner surface 108, which characterises the flame stability, can be detected and compared with a target distance. The regulation of the air/combustion gas ratio takes place in particular by regulating the combustion gas metering unit 104. Using the air/combustion gas ratio or the air number A, the target distance can also be reset. The second feedback signal 56 influences the mixture signal 53 output by the regulating apparatus 110.

-21 -The first detection unit 114 and the second detection unit 116, which are shown on the combustion device 100 according to Figure 3, can also be used with the combustion devices 100 according to Figure 1 or Figure 2.

Figure 4 shows the limit curve courses A-min and A-max of the selected lower and upper air number limits as a function of the relative heating power Q. An overall modulation range of the relative heating power Q of the combustion device 100 between a minimum value Q-min > 0 and a maximum value Q-max = 1 can be classified, in an advantageous consideration, into three operational sections.

The courses of the limit curves A-min and A-max of the selected lower and upper air number limits are designed as a function of the relative heating power Q based on these three considered operational sections which each have restrictions in the direction of higher and/or lower air number values and determine an admissible minimum and/or maximum value for the air number in the case of a determined relative heating power.

In a first operational section, between a minimum relative heating power Q-min (for example in the range Q-min -0.05... 0.1) and approximately Q -0.15, the air number value interval ensures that a low flame speed and low ignition energy are maintained in the mixture stream M. In this first operational section, the ignitability of the air/combustion gas mixture stream M and the safe ignition of the flame F are of central importance. The air number value A should be so high that a flame speed of the mixture stream M is so low that overpressures, as a result of sudden ignition of the mixture stream M, are safely -22 -controllable and sufficiently quiet. The low flame speed helps to avoid a flashback of the flame. The air number value A should otherwise, however, also be low such that the ignition energy of the mixture stream M is so low that a quick and reliable ignition of a flame is possible. Low ignition energy means that the mixture stream easily ignites and ensures a reliable, undelayed and safely controllable ignition.

In a second operational section, approximately between the 10 relative heating powers Q = 0.15 and Q = 0.4, the air number value interval ensures the avoidance of flame flashback.

In order to avoid flame flashback, the air number value A should be so high that interplay of outlet speed of the mixture stream M at the burner surface 108 and flame speed in the mixture stream M excludes a flame flashback. In order to ensure this, the outlet speed must be higher than the flame speed. Stoichiometric mixture streams (air number A = 1) have the highest flame speed. By raising the air number, the flame speed is reduced. Otherwise, by raising the air number, the outlet speed of the mixture stream is also increased because the mixture volume stream is increased. Thus, a flame flashback can also be avoided in the case of relatively low heating powers.

In a third operational section, approximately between the relative heating power Q = 0.4 and a maximum relative heating power Q-max = 1 (nominal heating power of the combustion device 100), the air number value interval ensures an optimal thermal effectiveness, complete combustion, avoidance of rising flames and compatibility with pneumatic air/combustion gas ratio regulators 112.

-23 -In this third operational section, a thermal effectiveness of the combustion, a complete combustion of the mixture stream M and the compatibility of the air number value interval with the possibilities of pneumatic air/combustion gas ratio regulators 112 are crucial. The pneumatic air/gas ratio regulation is based on flow restrictions and a nominally specified regulated gas pressure from the gas valve. As a result, a shape of the air number limit curves, which can deliver the regulated air/combustion gas system, is physically restricted. Compatibility means that the shape of the limit curve can be brought into line with the physical behaviour of a pneumatic air/combustion gas ratio regulator 112. A further important aspect is avoiding the rising of the flame. The air number value A must also be so low that a heating unit comprising a combustion device 100 according to the invention achieves a highest possible thermal effectiveness. The air number A must also be sufficiently higher than A = 1.0 in order to ensure complete combustion of the mixture stream M, in particular the combustion gas stream G. The air number A must thus be optimally set in order to form a range (which indicates both an upper and a lower limit to the required operational conditions), which fulfils all above requirements and can also be carried out by an air/combustion gas ratio regulator 112 to regulate the air/combustion gas ratio. Air/combustion gas ratio regulators 112 are in particular passive physical systems, whose possible behaviour is restricted by laws of physics. For example, the curve must be strictly monotone and either convex or concave.

Through comprehensive research and experiments, the method described above was found to vary the air/combustion gas ratio, in particular to adapt the air number A from the -24 -selected air number value interval as a function of the heating power Q which meets all these different, partially concurrent requirements. In this case, the safe combustion of hydrogen is much more difficult to achieve than the other fuels such as methane, propane or butane. This is due to the combustion-related properties of flame speed, ignition energy and ignition limits. The method and the selected air number limits are in particular adapted to the quite particular requirements of a combustion device 100 10 burning hydrogen.

A further advantage of the method, in particular the found air number value interval, is that the method can be implemented in the case of corresponding setting even with known pneumatic air/combustion gas ratio regulators 112.

In the case of known pneumatic air/combustion gas ratio regulators 112, the selected air number value interval or the selected air number limit curves A-min and A-max according to Figure 4 can usually be achieved in particular for air/hydrogen combustion by setting a higher amount for the, in particular negative, offset pressure than for example for hydrocarbon-based combustion gases (although the curve can still be in the modulation range of existing gas valves). This offset setting can be carried out by means of an adjusting screw on the regulator 112. The thus achieved air number A is influenced by an underpressure triggered by the mixer unit 106, a throttling of the combustion gas stream G (including the settable throttle valve in the gas valve, if present) and the offset pressure. The actually delivered offset pressure of the gas valve varies over the modulation range, its size is increased with increasing heating power. However, this follows a linear relation to the heating power and contains -25 -a very small amount (a few tenths of a pascal). Due to its small size, the influence of the offset pressure in the case of high heating powers (in which the Venturi effect and the throttling of the combustion gas stream G are high) is negligible. Conversely, the influence of the offset pressure in the case of low heating powers is very strong and enables the large variation of the air number over the heating power, as is reflected in the air number limit curves A-min and A-max.

Claims

-26 -Claims 1. Method for operating a combustion device (100) to provide an air/combustion gas mixture stream (M) composed of an air stream (A) and a combustion gas stream (G), in particular a hydrogen stream, in at least one predefinable air/combustion gas ratio and to burn the mixture stream (M), wherein heating power is generated by the combustion, characterised in that the air/combustion gas ratio is varied by means of a regulating apparatus (110) as a function of the heating power, wherein the air/combustion gas ratio adopts a higher value in the case of lower heating power and/or adopts a lower value in the case of higher heating power.
2. Method for operating a combustion device (100) to provide an air/combustion gas mixture stream (M) composed of an air stream (A) and a combustion gas stream (G), in particular a hydrogen stream, with at least one predefinable air number A in the mixture stream (M) and to burn the mixture stream (M), wherein heating power is generated by the combustion, characterised in that the air number A of the mixture stream (M) is regulated to a value within the air number value interval by means of a regulating apparatus (110) 0.15 / Q + 1 A 0,175 / 1,25 wherein the air number A characterises a quantity ratio of air to combustion gas and is calculated as a quotient from an air quantity actually present in the mixture stream (M) and an air quantity required for a stoichiometric combustion of the mixture stream (M) and wherein Q is the -27 -value of the relative heating power of the combustion device (100) and is in the range 0 < Q 1.
3. Method according to any one of the preceding claims, 5 characterised in that the regulating apparatus (110) regulates the combustion gas metering unit (104) as a function of the heating power, wherein the combustion gas metering unit (104) meters a relatively smaller combustion gas stream (G) in the case of lower heating power and 10 meters a relatively larger combustion gas stream (G) in the case of higher heating power.
4. Method according to any one of the preceding claims, characterised in that the regulating apparatus (110) regulates the air conveying unit (102) as a function of the heating power, wherein the air conveying unit (102) conveys a relatively larger air stream (A) in the case of lower heating power and conveys a relatively smaller air stream (A) in the case of higher heating power.
S. Method according to any one of the preceding claims, characterised in that the regulating apparatus (110) detects the heating power, generates a mixture signal (53) as a function of the heating power and outputs it to the combustion gas metering unit (104) and/or the air conveying unit (102), wherein the mixture signal (53) is provided, in the case of lower heating power, to meter a relatively smaller combustion gas stream (G) and/or to convey a relatively larger air stream (A); and, in the case of higher heating power, to meter a relatively larger -28 -combustion gas stream (G) and/or to convey a relatively smaller air stream (A).
6. Method according to any one of the preceding claims, characterised in that the regulating apparatus (110) receives and processes a power signal (521) characterising the heating power, wherein the power signal (521) is based on detection of an actual or required heating power, the mixture stream (M), the combustion gas stream (G), the air 10 stream (A), a blower speed of an air blower conveying the air stream (A) and/or a combustion temperature of the combustion of the mixture stream (M), wherein the regulating apparatus (110) generates the mixture signal (53) based on the power signal (521).
7. Method according to any one of the preceding claims, characterised in that a first detection unit (114) detects the air/combustion gas ratio, in particular the air number A and outputs a corresponding first feedback signal (54) to the regulating apparatus (110), wherein the regulating apparatus (110) regulates the air/combustion gas ratio, in particular the air number A as a function of the first feedback signal (54).
8. Method according to any one of the preceding claims, characterised in that a second detection unit (116) detects a flame stability of the combustion and outputs a corresponding second feedback signal (56) to the regulating apparatus (110), wherein the regulating apparatus (110) regulates the air/combustion gas ratio, in particular the -29 -air number A as a function of the second feedback signal
9. Method according to claim 8, characterised in that the regulating apparatus (110) outputs an error message when a predefinable flame stability cannot be achieved within the air number value interval.
10. Combustion device (100), in particular a hydrogen combustion device for a heating unit to heat at least one room and/or to heat at least one service fluid, characterised in that the combustion device (100) is designed to carry out the method according to any one of the preceding claims.
11. Heating unit, comprising a combustion device (100), characterised in that the combustion device (100) is designed according to claim 10.