EP3978805A1 - Combustion device , method for operating a combustion device and heating apparatus - Google Patents

Abstract

The invention is based on a method for operating a combustion device to provide an air/fuel gas mixture flow from an air flow and a fuel gas flow, in particular a hydrogen flow, in at least one predeterminable air/fuel gas ratio, and for the combustion of the mixture flow, the combustion a heating output is generated, with an air conveying unit conveying an air flow, in particular depending on a power requirement, a fuel gas metering unit metering a fuel gas flow, in particular depending on the air flow, and a mixer unit mixing the mixture flow. The invention is characterized in that the air/fuel gas ratio is varied by means of a control device as a function of the heat output, the air/fuel gas ratio assuming a larger value with a smaller heat output and/or a smaller value with a larger heat output. In particular, an air ratio λ of the air/fuel gas mixture flow is regulated to a value within a selected air ratio value interval, the interval boundaries being formed by heat output-dependent air ratio curves λ=λ(Q).

Description

State of the art

A method for operating a combustion device for providing an air/fuel gas mixture flow from an air flow and a fuel gas flow in a definable air/fuel gas ratio and for burning the mixture flow is already known from the prior art, in which the combustion produces a Heat output is generated and wherein an air conveying unit promotes an air flow, a fuel gas metering unit meters a fuel gas flow and a mixer unit mixes the mixture flow.

Disclosure of Invention

The invention is based on a method for operating a combustion device to provide an air/fuel gas mixture flow from an air flow and a fuel gas flow, in particular a hydrogen flow, in at least one predeterminable air/fuel gas ratio, and for the combustion of the mixture flow, the combustion a heat output is generated.

The invention is characterized in that the air/fuel gas ratio is varied by means of a control device as a function of the heat output, the air/fuel gas ratio assuming a larger value with a smaller heat output and/or a smaller value with a larger heat output.

The invention also relates to a method for operating a combustion device to provide an air/fuel gas mixture flow from an air flow and a fuel gas flow, in particular a hydrogen flow, with at least one predeterminable air ratio λ in the mixture flow, and for the combustion of the mixture flow, with a heat output being generated by the combustion.

geregelt wird, wobei die Intervallgrenzen von heizleistungsabhängigen Luftzahlgrenzkurven λ-min(Q) und λ-max(Q) $$\mathrm{\lambda }\mathrm{-min}=\mathrm{0,15}/\mathrm{Q}+1$$

$$\mathrm{\lambda }\mathrm{-max}=\mathrm{0,175}/\mathrm{Q}+\mathrm{1,25}$$

gebildet werden.The invention is characterized in that the air ratio λ of the air/fuel gas mixture flow is adjusted to a value within the air ratio value interval by means of a control device $$0.15/\mathrm{Q}+1\le \mathrm{\lambda }\le 0.175/\mathrm{Q}+1.25$$

controlled, with the interval limits of heat output-dependent air ratio limit curves λ-min(Q) and λ-max(Q) $$\mathrm{\lambda }\mathrm{-min}=0.15/\mathrm{Q}+1$$

$$\mathrm{\lambda }\mathrm{-Max}=0.175/\mathrm{Q}+1.25$$

are formed.

In particular, an air conveying unit promotes the air flow, in particular as a function of a power requirement, a fuel gas metering unit meters the fuel gas flow, in particular as a function of the air flow, and a mixer unit mixes the mixture flow.

A combustion device is to be understood here in particular as meaning a burner or a burner device, with the aid of which a combustible mixture flow can be provided and burned. The combustion device is used in particular in a heater, for example a heater for heating at least one room and/or for heating at least one useful fluid such as heating water and/or drinking water. The mixture flow is a gas flow comprising an air flow and a fuel gas flow. In particular, the air flow is taken from an installation environment of the combustion device or an exterior environment of a building in which the combustion device is installed. The fuel gas flow is in particular a fuel gas line or taken from a fuel gas tank. The combustion device is designed in particular for using the fuel gas hydrogen. Alternatively or additionally, the combustion device can also be designed to use other fuel gases. For its clean and efficient combustion, the mixture flow has a definable air/fuel gas ratio or an air ratio λ. An air/fuel gas ratio is to be understood here as a quantity ratio of air to fuel gas. The fact that the air/fuel gas ratio can be predetermined means in particular that the quantity ratio can be adjusted. The mixture flow is ignited in the combustion device and burned to form a flame. The combustion device comprises a burner mouth or burner surface, which acts as a flame holder: here the flame is intended to burn in a spatially stable manner. The energy (heat) released during combustion per unit of time is determined by the size of the mixture flow that is burned, in particular the size of the fuel flow that is burned. The energy released per unit of time characterizes the heat output of the combustion device. The heating output can be gradually or continuously modulated between a minimum heating output and a maximum heating output. The term heating output can be understood to mean both an absolute heating output (unit watt) and a relative heating output. The relative heating output is calculated as the actual absolute heating output in relation to the maximum absolute heating output. The relative heating power is a dimensionless variable with values generally between 0 and 1. However, since a real combustion device cannot usually be operated with 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 firing mode between 0.05 and 1, for example. An air conveying unit is understood to mean a device for conveying the air flow, which can in particular be an - in particular speed-controlled - air blower or air fan or an air valve . The air conveying unit is controlled in particular by an electrical signal. The air flow can be conveyed in particular as a function of a power requirement, for example a heating power requirement or a temperature requirement, to the combustion device and/or the heater. In particular, a size of the conveyed air volume flow in Depending on a size of a requested heating output. A required heating output is understood to mean, in particular, a theoretically required heating output that is used to meet a user's need for space heating and/or domestic hot water preparation. In contrast, an actual heating output is a measurable quantity that correlates with the quantity of the mixture flow that is used for combustion. A fuel gas dosing unit is understood to mean a device for dosing the flow of fuel gas, which can in particular be a fuel gas valve or a fuel gas fitting. The fuel gas metering unit is controlled in particular by an electrical and/or a pressure signal. The fuel gas flow can be metered in particular as a function of the air flow. In particular, the size of the metered fuel gas flow can be dependent on the size of the air flow. A mixer unit is understood to mean a device for bringing together and mixing the air flow and fuel gas flow and generating the air/fuel gas mixture flow, and this can in particular be a venturi mixer.

A control device is understood to mean a device for controlling and/or regulating at least one method step, in particular for varying the air/fuel gas ratio and/or the air ratio λ. Here, regulation is understood to mean control and/or regulation in the narrower sense. A regulation is understood here to mean a control and/or regulation in the narrower sense. With the variation, the air/fuel gas ratio and/or the air ratio λ is changed in a predetermined manner. A variable compound control for controlling the air/fuel gas ratio and/or the air ratio λ can be set up by means of the control device. A network means in particular that a target value of a first variable, for example the air flow, for example using an electrical signal, is specified, and that a target value of a subsequent variable, for example the fuel gas flow, for example using an electrical or a pressure signal, in the compound, adapted to the resulting actual value of the first variable is tracked. A variable combination means that the target value of the following variable is not only adapted to the actual value of the first variable, but that this adaptation is also varied as a function of a third variable, here the heating output. As a result, the value of the air/fuel gas ratio is controlled, so that a heat output-dependent air/fuel gas ratio is set. The fact that the air/fuel gas ratio is varied as a function of the heating output means that the size of the heating output at least partly determines the value of the air/fuel gas ratio.

The control device is designed in particular in such a way that the air/fuel gas ratio and/or the air ratio λ assumes a larger value with a smaller heating output and/or assumes a smaller value with a larger heating output. In this case, the control device intervenes in particular in the operation of the air conveying unit, the fuel gas metering unit and/or the mixer unit. In particular, the air/fuel gas ratio increases as the heating output decreases and decreases as the heating output increases. The variation of the air/fuel gas ratio over the heating output can have a stepped profile or a continuous profile. Increasing the air/fuel gas ratio is understood here to mean a leaning of the air/fuel gas mixture flow, ie a reduction in the fuel gas content in the mixture flow. Reducing the air/fuel gas ratio is understood here to mean enriching the air/fuel gas mixture flow, ie enriching the fuel gas content in the mixture flow. The air flow, the fuel gas flow and/or the mixture flow are variable in quantity and can be modulated stepwise or continuously between a respective minimum value and a respective maximum value.

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

The air ratio λ is a special parameter used in combustion technology to characterize the air/fuel gas ratio of an air/fuel gas mixture flow. The air ratio λ is calculated as the quotient of the air quantity L actually present in the mixture flow and the air quantity L-st required for stoichiometric combustion of the mixture flow: $$\mathrm{\lambda }=\mathrm{L}/\mathrm{L-st}$$

The relative heating output Q is calculated as the quotient of the actual absolute heating output P and the maximum absolute heating output P-max: $$\mathrm{Q}=\mathrm{P}/\mathrm{P-max}$$

The formula expressions listed above for the limits of the air ratio value interval are mathematically defined for relative heating outputs Q from the interval: $$0<\mathrm{Q}\le 1$$

The fact that the removal of the value Q = 0 does not limit the validity of the specified air ratio value interval for combustion practice is clear from the above statements on real combustion devices, according to which the values of the relative heating output Q in real combustion operation are between Q-min, for example a value from a range between 0.05 and 0.1, and Q-max = 1, and only for the switched-off state (no mixture formation, no combustion, no meaningful air ratio definition possible) assume the value Q = 0.

The invention provides a method for operating a combustion device that is improved over the known prior art.

Air/fuel gas mixture flows with an air ratio λ from the value range mentioned above are particularly advantageous to burn. In particular, air-hydrogen mixture streams with an air ratio λ from the value range mentioned above can be burned particularly advantageously. The combustion of such an air-fuel gas mixture flow is characterized by reliable ignition, high flame stability (avoidance of rising flames and flashback), optimal thermal efficiency, complete combustion with low pollutant values, low noise and compatibility with commercially available pneumatic air-gas ratio controls.

An advantageous embodiment of the invention is characterized in that the control device regulates the fuel gas metering unit as a function of the heat output, with the fuel gas metering unit metering a relatively smaller fuel gas flow for a smaller heat output and a relatively larger fuel gas flow for a larger heat output.

The fuel gas metering unit can be regulated in particular by means of an electrical signal or a pressure signal which is output by the control device to the fuel gas metering unit.

The term "a relatively smaller (or larger) fuel gas flow" expresses the fact that the reduction (or increase) in the metering of the fuel gas flow with a smaller (or larger) heating output is not proportional, but disproportionate, so that the air/ Fuel gas ratio and the air ratio λ increases with a lower heating output and decreases with a higher heating output.

In particular, the control device regulates the fuel gas metering unit as a function of the heating output, so that an air ratio λ is set in the mixture flow within the above-mentioned air ratio value interval.

In particular, as a distributed system, the control device can also include parts that come into contact with the air flow, for example air throughput measuring devices or air pressure probes, which record a size of the air flow. The fuel gas flow is metered in accordance with the size of the air flow and depending on the heating output in such a way that an air ratio within the above-mentioned air ratio value interval is set in the mixture flow.

A further advantageous embodiment of the invention is characterized in that the control device regulates the air conveying unit as a function of the heating output, the air conveying unit conveying a relatively larger air flow with a smaller heating capacity and a relatively smaller air flow with a larger heating capacity.

The air conveying unit can be regulated in particular by means of an electrical signal or a pressure signal which is output by the regulating device to the air conveying unit.

The term "a relatively larger (or smaller) air flow" expresses the fact that the reduction (or increase) in the promotion of the air flow with a smaller (or larger) heating output is not proportional, but disproportionate, so that the air/ Fuel gas ratio and the air ratio λ increases with a lower heating output and decreases with a higher heating output.

In particular, the control device regulates the air conveying unit as a function of the heating output, so that an air ratio within the above-mentioned air ratio value range is set in the mixture flow.

In particular, the control device as a distributed system can also include parts that come into contact with the fuel gas flow, for example fuel gas throughput measuring devices or fuel gas pressure probes, which record a size of the fuel gas flow. The air flow is metered in accordance with the size of the fuel gas flow and depending on the heating output in such a way that an air ratio within the above-mentioned air ratio value range is set in the mixture flow.

A further advantageous embodiment of the invention is characterized in that the control device generates a mixture signal as a function of the heating power and outputs it to the fuel gas metering unit and/or the air conveying unit. The mixture signal is intended to meter a relatively smaller fuel gas flow and/or to promote a relatively larger air flow at a lower heating output; and metering a relatively larger flow of fuel gas and/or promoting a relatively smaller flow of air with a greater heating output. The heating power addressed here can be a detected actual heating power or a requested heating power.

The mixture signal can in particular be an electrical signal or a pressure signal. Including that the control device depending on the Heating power generates a mixture signal, it can be understood in particular that a correlation between heating power and mixture signal - in the form of a mechanism, a table of values, a mathematical function and/or an algorithm - can be called up in the control device, on which the generation of the mixture signal is based. The mixture signal comprises in particular a single signal or two partial signals, one for the air delivery unit and/or another for the fuel gas metering unit, and acts in particular on the air flow delivery of the air delivery unit and/or the fuel gas flow metering of the fuel gas metering unit.

In particular, the control device regulates the air delivery unit and/or the fuel gas metering unit as a function of the heating output, so that an air ratio within the above-mentioned air ratio value range is established in the mixture flow.

A further advantageous embodiment of the invention is characterized in that the control device receives and processes a power signal characterizing the heating output, the power signal being based on a detection of an actual or requested heating output, the mixture flow, the fuel gas flow, the air flow, a fan speed of an air fan promoting the air flow and/or a combustion temperature of the combustion of the air/fuel gas mixture flow, the control device generating the mixture signal on the basis of the power signal.

The power signal can in particular be an electrical signal or a pressure signal. For this purpose, the combustion device comprises at least one measuring device, for example an electrical, electronic or pneumatic sensor, for detecting the heating output, the mixture flow, the fuel gas flow, the air flow, the fan speed of an air fan promoting the air flow, and/or the combustion temperature of the combustion of the air/fuel gas -mixed flow. A value of the power signal corresponds to a size of the heating power. The controller receives the power signal and translates it into the mixture signal.

A further advantageous embodiment of the invention is characterized in that a first detection unit detects the air/fuel gas ratio, in particular the air ratio λ, and outputs a corresponding first feedback signal to the control device, with the control device measuring the air/fuel gas ratio, in particular the air ratio λ, controls depending on the first feedback signal.

The first detection unit can in particular be a lambda sensor or an ionization electrode which measures a signal representing the air/combustion gas ratio, in particular the air ratio λ. By means of the first feedback signal, the control device can use a closed control circuit to control the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above.

A further advantageous embodiment of the invention is characterized in that a second detection unit detects the flame stability of the combustion and outputs a corresponding second feedback signal to the control device, with the control device controlling the air/fuel gas ratio, in particular the air ratio λ, 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 mouth or burner surface. In contrast, lifting of a flame from the burner mouth or burner surface means an unstable burning flame, increasing the distance and "flying" of the flame from the burner mouth or burner surface. This is accompanied by undesired burner extinguishing and discharge of unburned mixture and represents a hazardous condition that must be avoided and/or recognized. Flashback of a flame also means an unstable burning flame, reducing the distance and sitting of the flame on the burner mouth or burner surface, or even the flame propagating through the burner mouth or burner surface into an interior of the combustion device, for example up to the mixer unit. This goes with undesired overheating of the burner surface or other elements inside the combustor and represents a hazardous condition that must be avoided and/or recognized.

The second detection unit can in particular be a temperature sensor or an optical sensor. These measure a signal representing flame stability, for example a burner surface that is "too cold" (tendency to lift) or "too hot" (tendency to flashback), or a distance between the flame and the burner surface that is too large or too small. The temperature sensor can, for example, be arranged close to the burner surface. By means of the second feedback signal, the control device can use a control loop to control the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above, thereby ensuring reliable operation of the combustion device with stable flame formation.

If the control device determines, for example based on a signal from the second detection unit, that the flame is not burning stably, it can regulate the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above in such a way that a desired flame stability is restored.

A further advantageous embodiment of the invention is characterized in that a third detection unit detects a combustion noise of the combustion and outputs a corresponding third feedback signal to the control device, the control device controlling the air/fuel gas ratio, in particular the air ratio λ, depending on the second feedback signal .

The third detection unit can in particular be an acoustic sensor or a vibration sensor. These measure a signal representing the combustion noise, for example if the combustion is "too loud" or oscillates strongly (relative to a definable limit value). By means of the third feedback signal, the control device can set up a control circuit for controlling the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above, which ensures quiet operation of the combustion device.

A further advantageous embodiment of the invention is characterized in that the control device outputs an error message if a definable flame stability or a definable noise limit value or a definable vibration limit value is not reached within the air ratio value interval.

Since a deviation from the flame stability and/or the noise limit and/or the vibration limit can represent a dangerous condition that must be avoided, it can be useful to supplement the error message with a shutdown of the combustion device.

The invention also relates to a combustion device, in particular a hydrogen combustion device, for a heater for heating at least one space and/or for heating at least one useful fluid, the combustion device being designed to carry out a method according to one of the methods described above.

Such a combustion device ensures operation that is characterized by high flame stability, high efficiency, low pollutant values and low noise.

The invention also relates to a heater with a combustion device according to the invention.

drawings

Figur 1

zeigt ein erstes Ausführungsbeispiel einer Verbrennungsvorrichtung,

Figur 2

zeigt ein zweites Ausführungsbeispiel einer Verbrennungsvorrichtung,

Figur 3

zeigt ein drittes Ausführungsbeispiel einer Verbrennungsvorrichtung,

Figur 4

zeigt einen Grenzkurvenverlauf der Luftzahlwerte λ in einem ausgewählten Werteintervall in Abhängigkeit der relativen Heizleistung Q.

Further refinements and advantages result from the following description of the drawings. Exemplary embodiments of the invention are shown in the drawing. The drawing, the description and the claims contain numerous features in combination. The professional will Appropriately, features should also be considered individually and grouped together to form further meaningful combinations.

figure 1

shows a first embodiment of a combustion device,

figure 2

shows a second embodiment of a combustion device,

figure 3

shows a third embodiment of a combustion device,

figure 4

shows a limit curve of the air ratio values λ in a selected value interval as a function of the relative heating output Q.

Those described below Figures 1, 2 and 3 (Special features are each highlighted) each show a combustion device 100 for providing an air/fuel gas mixture flow M from an air flow A and a fuel gas flow G, in particular a hydrogen flow G, in at least one specifiable air/fuel gas ratio, and for burning the mixture flow M , whereby a heat output is generated by the combustion. The combustion device 100 comprises an air conveying unit 102, a fuel gas metering unit 104, a mixer unit 106, a burner surface 108 or a burner mouth 108, a control device 110, and lines for air, fuel gas, mixture or signal-conducting connection of the aforementioned components.

The air delivery unit 102 is used to draw in an air flow A, in particular from an installation environment 1 of the combustion device 100, and to deliver the air flow A to the mixer unit 106. The air delivery unit 102 is, for example, a speed-controllable air blower 102. The air delivery unit 102 is of control device 110, for example on the basis of a signal S1 of a requested heating output, by means of a specification of a setpoint delivery value S20, in particular a setpoint fan speed S20. On the air handling unit 102 after figure 3 a power signal S21, in particular an actual delivery value such as an actual fan speed, is detected, which describes a size of the heating output (here in particular the actually delivered air flow A).

The fuel gas metering unit 104 serves to meter a fuel gas flow G, with the fuel gas flow G being fed into the mixer unit 106 . For example, the fuel gas metering unit 104 is a pneumatically controllable fuel gas valve 104 (in particular figure 1 ) or electronically controllable fuel gas valve 104 (in particular figures 2 and 3 ). A mixture signal S3 specifies a control value for the fuel gas metering unit 104, on the basis of which the fuel gas flow G is metered.

The mixer unit 106 serves to combine the air flow A and the fuel gas flow G and to mix them to form a mixture flow M. The mixer unit 106 is a Venturi nozzle 106, for example figure 1 a power signal S21, in particular an actual air flow signal such as an air pressure, is detected, which describes a size of the heating power (in this case in particular the actually conveyed air flow A). On the basis of the power signal S21, the fuel gas metering unit 104 figure 1 regulated.

The mixture flow M emerges at the burner surface 108 into a combustion chamber 2 (not shown here), is ignited and burned while flames F are formed.

$$\mathrm{\lambda }\mathrm{-max}=\mathrm{0,175}/\mathrm{Q}+\mathrm{1,25}$$

Combustion device 100 also includes a control device 110 that is set up to vary the air/fuel gas ratio as a function of the heating output, with the air/fuel gas ratio assuming a larger value for a smaller heating output and/or a smaller value for a larger heating output assumes Control device 110 is set up in particular to regulate an air ratio λ, which describes the air/fuel gas ratio of the mixture flow M, to a value from a selected air ratio value interval, with the air ratio value interval being defined by a lower air ratio limit curve λ-min and a upper air ratio limit curve λ-max is defined as follows: $$\mathrm{\lambda }\mathrm{-min}=0.15/\mathrm{Q}+1$$

$$\mathrm{\lambda }\mathrm{-Max}=0.175/\mathrm{Q}+1.25$$

The values of the lower air ratio limit curve λ-min and the upper air ratio limit curve λ-max depend on the heating output value. Q stands for the value of the relative heating power of the combustion device 100.

In particular, an air ratio value λ that is actually regulated is at best essentially in the middle between the lower and upper air ratio limits. The air ratio limit curves λ-min and λ-max thus represent the permissible deviations of the air ratio λ from an ideal value.

The controller 110 after figure 1 regulates the fuel gas flow G on the basis of a power signal S21, in particular an air pressure signal, which is detected at the mixer unit 106 and describes the size of the heating power (here in particular the air flow A flowing through the mixer unit). The power signal S21 acts on the control device 110. The control device 110 then uses a mixture signal S3 to meter an adapted combustion gas flow G, so that the air ratio λ in the mixture flow M assumes values from the selected value interval.

The fuel gas metering unit 104 and at least parts of the control device 110 figure 1 can be formed in particular by a pneumatic air/fuel gas ratio regulator 112 . A pneumatic air/combustion gas ratio controller 112 can be understood in particular as a fitting made up of a control device 110 and a combustible gas metering unit 104 combined to form a structural unit. The air/fuel gas ratio controller 112 receives a power signal S21 describing an air flow A, for example an air pressure signal, translates this into a mixture signal S3, for example an actuating signal for a fuel gas pressure, opens the gas valve in particular for setting a fuel gas pressure in correlation to the air pressure, and meters a Fuel gas flow G corresponding to air flow A. The aforementioned correlation is defined by adjustments made to the air/fuel gas ratio controller 112 (e.g. an offset adjustment to the ratio, in particular difference, of fuel gas pressure and air pressure).

The controller 110 after figure 2 controls both the air flow A and the fuel gas flow G by means of two mixture signals S3 based on one requested heating power S1. This regulation takes place in such a way that the air ratio λ in the mixture flow M assumes values from the selected value interval. The mixture signals S3 can be based on a table of values, a parameterized function equation or another calculation algorithm that is stored in the control device 110 and produces a correlation with the requested heating power S1.

The controller 110 after figure 3 regulates the air flow A based on the requested heating output S1. The fuel gas flow G is metered by means of a mixture signal S3 on the basis of a power signal S21 detected at the air delivery unit 102, in particular an actual delivery value such as an actual fan speed, which describes a size of the air flow A actually delivered. This regulation takes place in such a way that the air ratio λ in the mixture flow M assumes values from the selected value interval. The mixture signal S3 can be based on a value table, a parameterized functional equation or another calculation algorithm that is stored in the control device 110 and produces a correlation with the power signal S21.

The combustion device 100 according to FIG figure 3 shows an optional first detection unit 114 for detecting the actual air/fuel gas ratio, in particular the actual air ratio λ, and for outputting a corresponding first feedback signal S4 to the control device 110, with the control device 110 measuring the air/fuel gas ratio, in particular the air ratio λ , as a function of the first feedback signal S4 so that the actual air ratio λ in the mixture flow M assumes values from the selected value interval. The first detection unit 114 can include a lambda probe or an ionization electrode. The air/combustion gas ratio is regulated in particular by regulating the combustion gas metering unit 104 . The first feedback signal S4 influences the mixture signal S3 output by the control device 110 .

Furthermore, the combustion device 100 according to FIG figure 3 an optional second detection unit 116 for detecting a flame stability of the combustion and for outputting a corresponding second feedback signal S6 to the control device 110, wherein the control device 110 Air/fuel gas ratio, in particular the air ratio λ, as a function of the second feedback signal S6 so that the air ratio λ in the mixture flow M assumes values from the selected value interval. The second sensing unit 116 may include a temperature sensor in or at the plane of the burner surface 108 . With this temperature sensor, a distance D of the flame F from the burner surface 108, which characterizes the flame stability, can be detected and compared with a target distance. The air/fuel gas ratio is regulated in particular by controlling the fuel gas metering unit 104. The setpoint distance can then also be set again via the air/fuel gas ratio or the air ratio λ. The second feedback signal S6 influences the mixture signal S3 output by the control device 110 .

The first detection unit 114 and the second detection unit 116 attached to the combustion device 100 according to figure 3 , can also be used with the combustion devices 100 according to FIG Figure 1 or Figure 2 be used.

figure 4 shows the limit curves λ-min and λ-max of the selected lower and upper air ratio limits as a function of the relative heating output Q.

A total modulation range of the relative heat output Q of the combustion device 100 between a minimum value Q-min>0 and a maximum value Q-max=1 can be divided into three operating sections in an advantageous view.

The curves of the limit curves λ-min and λ-max of the selected lower and upper air ratio limits are designed as a function of the relative heating output Q based on these three operating sections under consideration, which each have restrictions in the direction of larger and/or smaller air ratio values and a permissible minimum and /or Set a maximum air ratio at a specific relative heating output.

In a first operating section, between a minimum relative heating power Q-min (e.g. in the range Q-min = 0.05...0.1) and approx Q = 0.15, the air ratio value interval ensures a low flame speed and low ignition energy in the mixture flow M.

In this first operating section, the ignitability of the air/fuel gas mixture flow M and the reliable ignition of the flame F are of central importance. The air ratio value λ should be so high that a flame speed of the mixture flow M is so low that overpressures resulting from sudden ignition of the mixture flow M can be safely controlled and are sufficiently quiet. The low flame speed helps to avoid flame flashback. On the other hand, the air ratio value λ should also be so low that the ignition energy of the mixture flow M is so low that rapid and reliable ignition of a flame is possible. Low ignition energy means that the mixture flow ignites easily and ensures reliable, instantaneous and safely controllable ignition.

In a second operating section, approximately between the relative heating powers Q = 0.15 and Q = 0.4, the air ratio value interval ensures that flashback is avoided.

To avoid flashback, the air ratio value λ should be so high that an interaction of the outlet speed of the mixture flow M on the burner surface 108 and the flame speed in the mixture flow M rules out a flashback. To ensure this, the exit velocity must be higher than the flame velocity. Stoichiometric mixture flows (air ratio λ = 1) have the highest flame speed. Increasing the air ratio reduces the flame speed. On the other hand, by raising the air ratio, the outlet speed of the mixture flow is increased at the same time because the mixture volume flow is increased. In this way, a flashback can be avoided even with relatively low heat outputs.

In a third operating section, approximately between the relative heating power Q=0.4 and a maximum relative heating power Q-max=1 (rated heating power of the combustion device 100), the air ratio value interval ensures optimum thermal efficiency, complete combustion, avoidance of uplifted flames and compatibility with 112 pneumatic air/fuel gas ratio regulators.

In this third operating section, a thermal efficiency of the combustion, a complete combustion of the mixture flow M and the compatibility of the air ratio value interval with the possibilities of the pneumatic air/combustion gas ratio controller 112 are decisive. Pneumatic air-gas ratio control relies on flow restrictions and a nominally fixed regulated gas pressure from the gas valve. This physically limits one form of the air ratio limit curves that the controlled air-fuel gas system can provide. Compatibility means that the shape of the limit curve can be made to match the physical behavior of a pneumatic air/fuel gas ratio controller 112 . Another important aspect is avoiding the flame lifting. The air ratio value λ must also be so low that a heating device comprising a combustion device 100 according to the invention achieves the highest possible thermal efficiency. In addition, the air ratio λ must be sufficiently higher than λ=1.0 in order to ensure complete combustion of the mixture flow M, in particular the fuel gas flow G. The air ratio λ must therefore be set optimally in order to form a framework (giving both an upper and a lower limit to the claimed operating conditions) that meets all of the above requirements and also by an air/fuel gas ratio controller 112 for controlling the air / fuel gas ratio can be done. In particular, air/fuel gas ratio controllers 112 are passive physical systems whose possible behavior is restricted by physical laws. For example, the curve must be strictly monotonic and either convex or concave.

Through extensive research and experiments, the method described above for varying the air/fuel gas ratio, in particular for adjusting the air ratio λ from the selected air ratio value interval, as a function of the heating output Q was found that meets all these different, sometimes competing requirements . The safe combustion of hydrogen is incomparably more difficult accomplish than those of other fuels such as methane, propane or butane. This is due to the combustion properties of flame speed, ignition energy and ignition limits. In particular, the method and the selected air ratio limits were adapted to the very specific requirements of a combustion device 100 that burns hydrogen.

A further advantage of the method, in particular of the air ratio value interval found, is that the method can also be implemented with known pneumatic air/combustion gas ratio controllers 112 if the setting is appropriate.

With known pneumatic air/fuel gas ratio controllers 112, the selected air ratio value interval or the selected air ratio limit curves λ-min and λ-max can be figure 4 in particular for air-hydrogen combustion by setting a higher amount for the, in particular negative, offset pressure than is usual, for example for hydrocarbon-based fuel gases (although the curve is still in the modulation range of existing gas valves). This offset adjustment can be made using a set screw on controller 112. The air ratio λ achieved in this way is influenced by a negative pressure triggered by the mixer unit 106, a throttling of the fuel gas flow G (including the adjustable throttle valve in the gas valve, if present) and the offset pressure. The actual gas valve offset pressure delivered varies over the modulation range, its magnitude increasing as the heater output increases. However, this follows a linear relationship with heating power and maintains a very small amount (a few tens of pascals). Due to its small size, the influence of offset printing is negligible at large heating powers (where the Venturi effect and the throttling of the fuel gas flow G are high). Conversely, the influence of offset printing is very strong at low heating outputs and enables the air ratio to vary greatly over the heating output, as is shown in the air ratio limit curves λ-min and λ-max.

Claims (11)

Method for operating a combustion device (100) to provide an air/fuel gas mixture flow (M) from an air flow (A) and a fuel gas flow (G), in particular a hydrogen flow, in at least one predeterminable air/fuel gas ratio, and for the combustion of the mixture flow (M), whereby a heat output is generated by the combustion,
characterized in that the air/fuel gas ratio is varied by means of a control device (110) as a function of the heating output, the air/fuel gas ratio assuming a larger value with a smaller heating output and/or a smaller value with a larger heating output. Method for operating a combustion device (100) to provide an air-fuel gas mixture flow (M) from an air flow (A) and a fuel gas flow (G), in particular a hydrogen flow, with at least one predeterminable air ratio λ in the mixture flow (M), and for Combustion of the mixture flow (M), with the combustion generating a heat output,
characterized in that by means of a control device (110) the air ratio λ of the mixture flow (M) to a value within the air ratio value interval $$0.15/\mathrm{Q}+1\le \mathrm{\lambda }\le 0.175/\mathrm{Q}+1.25$$

is regulated,
where the air ratio λ characterizes a volume ratio of air to fuel gas and is calculated as the quotient of the air volume actually present in the mixture flow (M) and the air volume required for stoichiometric combustion of the mixture flow (M) , and where Q is the value of the relative heating output of the combustion device (100) and is in the range 0 < Q ≤ 1. Method according to one of the preceding claims,
characterized in that the control device (110) regulates the fuel gas metering unit (104) as a function of the heat output, the fuel gas metering unit (104) metering a relatively smaller fuel gas flow (G) for a lower heat output and a relatively larger fuel gas flow (G) for a larger heat output . Method according to one of the preceding claims,
characterized in that the control device (110) regulates the air conveying unit (102) depending on the heating output, the air conveying unit (102) conveying a relatively larger air flow (A) with a smaller heating output and a relatively smaller air flow (A) with a larger heating output . Method according to one of the preceding claims, characterized in that the control device (110) detects the heating output, generates a mixture signal (S3) as a function of the heating output and outputs it to the fuel gas metering unit (104) and/or the air delivery unit (102), wherein the mixture signal (S3) is intended to meter a relatively smaller fuel gas flow (G) and/or to promote a relatively larger air flow (A) at a lower heating output; and metering a relatively larger fuel gas flow (G) and/or promoting a relatively smaller air flow (A) with a greater heating output. Method according to one of the preceding claims, characterized in that the control device (110) receives and processes a power signal (S21) characterizing the heating output, the power signal (S21) being based on a detection of an actual or requested heating output, the mixture flow (M), the fuel gas flow (G), the air flow (A), a fan speed of an air fan conveying the air flow (A), and/or a combustion temperature of the combustion of the mixture flow (M), wherein the control device (110) based on the power signal (S21) the mixture signal (S3) is generated. Method according to one of the preceding claims, characterized in that a first detection unit (114) detects the air/fuel gas ratio, in particular the air ratio λ, and outputs a corresponding first feedback signal (S4) to the control device (110), wherein the control device (110) controls the air/fuel gas ratio, in particular the air ratio λ, as a function of the first feedback signal (S4). Method according to one of the preceding claims, characterized in that a second detection unit (116) detects a flame stability of the combustion and outputs a corresponding second feedback signal (S6) to the control device (110), wherein the control device (110) controls the air/fuel gas ratio, in particular the air ratio λ, as a function of the second feedback signal (S6). Method according to claim 8,
characterized in that the control device (110) outputs an error message if a definable flame stability cannot be achieved within the air ratio value interval. Combustion device (100), in particular a hydrogen combustion device, for a heater for heating at least one room and/or for heating at least one useful fluid,
characterized in that the combustion device (100) is designed to carry out the method according to any one of the preceding claims. A heater comprising a combustion device (100),
characterized in that the combustion device (100) is designed according to claim 10.

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