EP3978805B1 - Combustion device with air ratio regulation device, and heating apparatus - Google Patents

Description

State of the art

From the prior art, a combustion device for providing an air-fuel gas mixture stream consisting of an air stream and a fuel gas stream in a predeterminable air/fuel gas ratio, and for combustion of the mixture stream, is already known, in which a heating output is generated by the combustion and wherein an air conveying unit conveys an air stream, a fuel gas metering unit meters a fuel gas stream and a mixer unit mixes the mixture stream.

The WO2020/182902 A1 , on which the two-part form of claim 1 is based, discloses a burner system with a mechanism for specifying an air/fuel gas ratio, the air/fuel gas ratio depending at least in part on a heating output.

The EP1522790 A2 discloses a method for controlling a gas burner with an electronic control, which specifies a target signal for the amount of fuel gas and the amount of air for a predetermined burner output, with a fuel gas-air mixture being enriched and/or leaned in a defined manner over the modulation range.

The EP3182007 A1 discloses a heater system with a control and/or regulating unit, which is intended to set an air ratio parameter to a target air ratio parameter that is dependent on a heating output.

Disclosure of the invention

The invention relates to a combustion device, in particular a hydrogen combustion device, for a heater for heating at least one room and/or for heating at least one useful fluid. The combustion device serves to provide an air-fuel gas mixture stream consisting of an air stream and a fuel gas stream, in particular a hydrogen stream, with at least one predeterminable air ratio λ in the mixture stream, and to burn the mixture stream, with a heating output being generated by the combustion.

• die Brenngasdosiereinheit in Abhängigkeit der Heizleistung zu regeln, wobei die Brenngasdosiereinheit bei kleinerer Heizleistung einen relativ kleineren Brenngasstrom dosiert, und bei größerer Heizleistung einen relativ größeren Brenngasstrom dosiert, und/oder
• die Luftfördereinheit in Abhängigkeit der Heizleistung zu regeln, wobei die Luftfördereinheit bei kleinerer Heizleistung einen relativ größeren Luftstrom fördert, und bei größerer Heizleistung einen relativ kleineren Luftstrom fördert.

The combustion device comprises a control device, and a fuel gas metering unit and/or an air delivery unit, the control device being designed to:

• to regulate the fuel gas metering unit depending on the heating output, the fuel gas metering unit metering a relatively smaller fuel gas flow with a smaller heating output, and metering a relatively larger fuel gas flow with a larger heating output, and / or
• to regulate the air delivery unit depending on the heating output, whereby the air delivery unit promotes a relatively larger air flow with a smaller heating output, and promotes a relatively smaller air flow with a larger heating output.

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

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

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

to be regulated, whereby the interval limits of heating output-dependent air ratio limit curves λ-min(Q) and λ-max(Q) $$\mathrm{\lambda }-\min =0.15/\mathrm{Q}+1$$

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

be formed.

The air ratio λ characterizes a quantitative ratio of air to fuel gas and is calculated as a quotient of a quantity of air actually present in the mixture stream and a quantity of air required for stoichiometric combustion of the mixture stream. Q is the value of the relative heating power of the combustion device and is in the range 0.05 ≤ Q ≤ 1.

In particular, an air delivery unit promotes the air flow, in particular depending on a power requirement, a fuel gas metering unit meters the fuel gas flow, in particular depending on the air flow, and a mixer unit mixes the mixture flow.

A combustion device is to be understood here in particular as a burner or a burner device, with the aid of which a combustible mixture stream 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 stream is a gas stream comprising an air stream and a fuel gas stream. The air flow is taken in particular from an installation environment of the combustion device or from an outside environment of a building in which the combustion device is installed. The fuel gas stream is taken in particular from a fuel gas line or a fuel gas tank. The combustion device is designed in particular to use the fuel gas hydrogen. Alternatively or additionally, the combustion device can also be designed to use other fuel gases. For clean and efficient combustion, the mixture flow has a predeterminable air/fuel gas ratio or an air ratio λ. An air/fuel gas ratio here means a quantitative ratio of air to fuel gas. The fact that the air/fuel gas ratio can be specified means in particular that the quantitative ratio is adjustable. The mixture stream is ignited in the combustion device and burned to form a flame. The combustion device includes a burner mouth or burner surface that acts as a flame holder: here the flame should burn in a spatially stable manner. The energy (heat) released during combustion per unit of time is determined by the size of the burned mixture stream, in particular the size of the fuel flow burned. The energy released per unit of time characterizes the heating output of the combustion device. The heating output can be modulated gradually or continuously 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 based on the maximum absolute heating output. The relative heating power is a dimensionless quantity with values generally between 0 and 1. However, since a real combustion device generally cannot 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. An air delivery unit is understood to mean a device for conveying the air flow; this can in particular be an - in particular speed-controlled - air blower or air fan or an air valve. The air delivery unit is controlled in particular by an electrical signal. The air flow can be promoted in particular depending on a power requirement, for example a heating power requirement or a temperature requirement, on the combustion device and/or the heater. In particular, a size of the air volume flow conveyed can depend on a size of a requested heating power. A requested heating output is understood to mean, in particular, a theoretically required heating output that serves 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 size of the mixture flow that is used for combustion. A fuel gas metering unit is understood to mean a device for metering the fuel gas stream; this can in particular be a fuel gas valve or a fuel gas fitting. The fuel gas metering unit is regulated in particular by an electrical and/or a pressure signal. The fuel gas flow can be metered in particular depending on the air flow. In particular, the size of the metered fuel gas flow can be determined depending on the size of the air flow. A mixer unit is a device for combining and mixing air flow and Fuel gas flow and generation of the air-fuel gas mixture stream are understood, 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 process step, in particular for varying the air/fuel gas ratio and/or the air ratio λ. Here, regulation is understood to mean controlling and/or regulating in the narrower sense. A regulation here is understood to mean a control and/or regulation in the narrower sense. By varying, the air/fuel gas ratio and/or the air ratio λ is changed in a predeterminable manner. Using the control device, a variable compound control system can be set up to regulate the air/fuel gas ratio and/or the air ratio λ. A composite means in particular that a setpoint of a first variable, for example the air flow, is specified, for example based on an electrical signal, and that a setpoint of a subsequent variable, for example the fuel gas flow, for example based on an electrical or a pressure signal, in the composite, adapted to the resulting actual value of the first variable is tracked. A variable combination means that the setpoint of the following variable is not only adjusted to the actual value of the first variable, but this adjustment is also varied depending on a third variable, here the heating output. As a result, the value of the air/fuel gas ratio is regulated so that a heating output-dependent air/fuel gas ratio is established. The fact that the air/fuel gas ratio is varied depending on the heating output means that the size of the heating output at least 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. The control device also intervenes in particular in the operation of the air delivery unit, the fuel gas metering unit and/or the mixer unit. In particular, the air/fuel gas ratio is increased as the heating power decreases and is reduced as the heating power increases. The variation of the air/fuel gas ratio over the heating output can have a stepped course or a continuous course. Under enlarge The air/fuel gas ratio is understood here as a leaning of the air/fuel gas mixture stream, i.e. a reduction in the fuel gas content in the mixture stream. Reducing the air/fuel gas ratio here means enriching the air/fuel gas mixture stream, i.e. enriching the fuel gas content in the mixture stream. The air flow, the fuel gas flow and/or the mixture flow are variable in quantity and can be modulated in stages 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 device”. The control device can alternatively or additionally (in the sense of a distributed system) also be designed as part of the air delivery 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 stream. The air ratio λ is calculated as the quotient of the amount of air L actually present in the mixture stream and the amount of air L-st required for stoichiometric combustion of the mixture stream: $$\mathrm{\lambda }=\mathrm{L}/\mathrm{L}-\mathrm{st}$$

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

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 represent a restriction on the validity of the specified air ratio value interval for combustion practice, becomes clear from the above statements on real combustion devices, according to which the values of the relative heating power Q in real combustion operation lie between Q-min, for example a value from a range between 0.05 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 creates an improved method for operating a combustion device compared to the known prior art.

Air-fuel gas mixture streams with an air ratio λ from the above-mentioned range of values are particularly advantageous to burn. In particular, air-hydrogen mixture streams with an air ratio λ from the above-mentioned value range are particularly advantageous to burn. The combustion of such an air-fuel gas mixture stream is characterized by reliable ignition, high flame stability (avoidance of lifting flames and flashback), optimal thermal efficiencies, complete combustion with low pollutant levels, low noise and compatibility with commercially available pneumatic air-gas systems. Ratio controllers. The control device can regulate the fuel gas metering unit depending on the heating output, with the fuel gas metering unit metering a relatively smaller fuel gas flow with a smaller heating output and metering a relatively larger fuel gas flow with a larger heating output.

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

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

In particular, the control device regulates the fuel gas metering unit depending on the heating output, so that an air ratio λ is established in the mixture flow within the air ratio value interval mentioned above.

In particular, the control device as a distributed system can also include parts that come into contact with the air flow, for example air flow measuring devices or air pressure probes that detect a size of the air flow. The fuel gas flow is metered according to the size of the air flow and depending on the heating output so that an air ratio is achieved in the mixture flow within the air ratio value interval mentioned above.

The control device can regulate the air delivery unit depending on the heating power, with the air delivery unit promoting a relatively larger air flow with a smaller heating power and a relatively smaller air flow with a larger heating power.

The air delivery unit can be controlled in particular by means of an electrical signal or a pressure signal which is output by the control device to the air delivery unit.

The term "a relatively larger (or smaller) air flow" expresses that the reduction (or increase) in the delivery 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 becomes larger with a lower heating output or smaller with a higher heating output.

In particular, the control device regulates the air delivery unit depending on the heating output, so that an air ratio is established in the mixture flow within the air ratio value interval mentioned above.

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 flow meters or fuel gas pressure probes that record a size of the fuel gas flow. The air flow is metered according to the size of the fuel gas flow and depending on the heating output so that an air ratio is achieved in the mixture flow within the air ratio value interval mentioned above.

An advantageous embodiment of the invention is characterized in that the control device is set up to detect the heating power, to generate a mixture signal depending on the heating power and to output it to the fuel gas metering unit and/or the air delivery 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 with greater heating power, to meter a relatively larger fuel gas flow and/or to promote a relatively smaller air flow. The heating output mentioned here can be a recorded actual heating output or a requested heating output.

The mixture signal can in particular be an electrical signal or a pressure signal. The fact that the control device generates a mixture signal depending on the heating power can be understood in particular to mean 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 the generation of the mixture signal is used as a basis. The mixture signal includes 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 in particular acts 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 depending on the heating output, so that an air ratio is established in the mixture flow within the air ratio value interval mentioned above.

A further advantageous embodiment of the invention is characterized in that the control device is set up to receive and process a power signal characterizing the heating power, the power signal being based on a detection of an actual or requested heating power, the mixture flow, the fuel gas flow, the air flow, etc Fan speed of an air blower promoting the air flow and / or a combustion temperature of the combustion of the air-fuel gas mixture flow, the control device being set up to generate the mixture signal based on 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 power, the mixture flow, the fuel gas flow, the air flow, the fan speed of an air blower promoting the air flow, and / or the combustion temperature of the combustion of the air-fuel gas -Mixture flow. A value of the power signal corresponds to a size of the heating output. The control device receives the power signal and translates it into the mixture signal.

A further advantageous embodiment of the invention is characterized by a first detection unit, the first detection unit being set up to detect the air ratio λ and to output a corresponding first feedback signal to the control device, the control device being set up to determine the air ratio λ depending on the first to regulate the feedback signal.

The first detection unit can in particular be a lambda sensor or an ionization electrode, which measures a signal representing the air/fuel gas ratio, in particular the air ratio λ. By means of the first feedback signal, the control device can use a closed control loop to regulate 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 by a second detection unit, wherein the second detection unit is set up to detect flame stability of the combustion and to output a corresponding second feedback signal to the control device, the control device being set up to determine the air ratio λ depending on the second feedback signal.

Flame stability here is understood to mean, in particular, a spatially permanent presence of the flame at a desired target distance from the burner mouth or burner surface. In contrast, lifting a flame from the burner mouth or burner surface means an unstable burning flame, increasing the distance and "flying away" of the flame from the burner mouth or burner surface. This is accompanied by undesirable extinguishing of the burner and escape of unburned mixture and represents a dangerous condition that must be avoided and/or recognized. A flashback of a flame also means a flame that does not burn stably, a reduction in the distance and the flame resting on the burner mouth or burner surface, or even a penetration of the flame through the burner mouth or burner surface into an interior of the combustion device, for example to the mixer unit. This results in undesirable overheating of the burner surface or other elements inside the combustion device and represents a dangerous 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 off) or “too hot” (tendency to flashback), or a flame distance from 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 set up a control loop for regulating the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above use, which ensures safe 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 so that a desired flame stability is established again.

A third detection unit can be set up to detect a combustion noise of the combustion and to output a corresponding third feedback signal to the control device, the control device being set up to regulate 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 combustion that is “too loud” or strongly oscillating (based on a predeterminable limit value). By means of the third feedback signal, the control device can use a control loop to regulate the air/fuel gas ratio, in particular the air ratio λ, within the limits defined above, thereby ensuring quiet operation of the combustion device.

A further advantageous embodiment of the invention is characterized in that the control device is set up to output an error message if a predefinable flame stability or a predefinable noise limit value or a predefinable vibration limit value is not achieved within the air ratio value interval.

Since a deviation from the flame stability and/or the noise limit and/or vibration limit can represent a dangerous condition that must be avoided, it may make sense to supplement the error message with switching off the combustion device.

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

The invention further 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 drawing. The drawing shows exemplary embodiments of the invention. The drawing, description and claims contain numerous features in combination. The specialist will It is advisable to consider features individually and combine them into further sensible combinations.

Figure 1

shows a first exemplary 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 depending on the relative heating output Q.

Those described below Figures 1, 2 and 3 (Special features are highlighted in each case) show a combustion device 100 for providing an air-fuel gas mixture stream M from an air stream A and a fuel gas stream G, in particular a hydrogen stream G, in at least one predeterminable air/fuel gas ratio, and for combustion of the mixture stream M , whereby combustion generates heating power. The combustion device 100 comprises an air delivery 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 connecting the aforementioned components in an air, fuel gas, mixture or signal-conducting manner.

The air delivery unit 102 is used to suck in an air flow A, in particular from an installation environment 1 of the combustion device 100, and to convey the air flow A to the mixer unit 106. For example, the air delivery unit 102 is a speed-controllable air blower 102. The air delivery unit 102 is from the control device 110, for example based on a signal S1 of a requested heating power, by specifying a target delivery value S20, in particular a target fan speed S20. At the air delivery unit 102 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 power (here in particular the actually delivered air flow A).

The fuel gas metering unit 104 serves to meter a fuel gas stream G, the fuel gas stream 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 gives the fuel gas metering unit 104 a control value, based on which the fuel gas flow G is metered.

The mixer unit 106 is used to combine air stream A and fuel gas stream G and mix them to form a mixture stream M. For example, the mixer unit 106 is a Venturi nozzle 106. On the mixer unit 106 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 (here in particular the air flow A actually conveyed). The fuel gas metering unit 104 is based on the power signal S21 Figure 1 regulated.

At the burner surface 108, the mixture stream M exits into a combustion chamber 2 (not shown here), is ignited and burned to form flames F.

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

The combustion device 100 further comprises a control device 110, which is set up to vary the air/fuel gas ratio depending on 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 accepts. The control device 110 is in particular set up 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, 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: $$\mathrm{\lambda }-\min =0.15/\mathrm{Q}+1$$

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

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

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

The control device 110 according to Figure 1 regulates the fuel gas flow G based on a power signal S21, in particular an air pressure signal, which is detected at the mixer unit 106 and describes the magnitude 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 fuel 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 according to Figure 1 can be formed in particular by a pneumatic air-fuel gas ratio controller 112. A pneumatic air-fuel gas ratio controller 112 can be understood in particular as a fitting consisting of a control device 110 and a fuel gas metering unit 104 combined into 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 a control signal for a fuel gas pressure, opens the gas valve in particular to set a fuel gas pressure in correlation to the air pressure, and doses one Fuel gas flow G corresponding to the air flow A. The aforementioned correlation is defined by settings made on the air-fuel gas ratio controller 112 (for example an offset setting to the ratio, in particular difference, of fuel gas pressure and air pressure).

The control device 110 according to Figure 2 controls both the air flow A and the fuel gas flow G using two mixture signals S3 based on one requested heating output S1. This control is carried out in such a way that the air ratio λ in the mixture flow M assumes values from the selected value interval. The basis of the mixture signals S3 can be a table of values, a parameterized functional equation or another calculation algorithm that is stored in the control device 110 and establishes a correlation with the requested heating power S1.

The control device 110 according to Figure 3 regulates the air flow A based on the requested heating output S1. The fuel gas flow G is metered using a mixture signal S3 based on 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 actually delivered air flow A. This control is carried out in such a way that the air ratio λ in the mixture flow M assumes values from the selected value interval. The basis of the mixture signal S3 can be a table of values, a parameterized functional equation or another calculation algorithm that is stored in the control device 110 and establishes a correlation with the power signal S21.

The combustion device 100 after 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, the control device 110 determining the air/fuel gas ratio, in particular the air ratio λ , depending on the first feedback signal S4, regulates so that the actual air ratio λ in the mixture flow M assumes values from the selected value interval. The first detection unit 114 may include a lambda sensor or an ionization electrode. The air/fuel gas ratio is regulated in particular by regulating the fuel 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 shows Figure 3 an optional second detection unit 116 for detecting flame stability of the combustion and for outputting a corresponding second feedback signal S6 to the control device 110, the control device 110 being the Air/fuel gas ratio, in particular the air ratio λ, is controlled depending on 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 detection unit 116 may include a temperature sensor in or on 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 recognized and compared with a target distance. The air/fuel gas ratio is regulated in particular by regulating the fuel gas metering unit 104. The target 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, which are connected to the combustion device 100 Figure 3 shown can also be used with the combustion devices 100 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 depending on the relative heating output Q.

An overall modulation range of the relative heating power Q of the combustion device 100 between a minimum value Q-min = 0.05 and a maximum value Q-max = 1 can be advantageously divided into three operating sections.

The courses of the limit curves λ-min and λ-max of the selected lower and upper air ratio limits are designed depending on the relative heating output Q on the basis of 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 the maximum value for the air ratio at a certain relative heating output.

In a first operating phase, between a minimum relative heating power Q-min = 0.05 and approximately 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 phase, the ignitability of the air-fuel gas mixture stream M and the safe 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 excess pressures due to sudden ignition of the mixture flow M can be safely controlled and sufficiently quiet. The low flame speed helps to prevent the flame from flashing back. 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 a quick 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 phase, approximately between the relative heating outputs Q = 0.15 and Q = 0.4, the air ratio value interval ensures the avoidance of flashback.

To avoid flashback, the air ratio value λ should be so high that an interaction between the exit speed of the mixture stream M on the burner surface 108 and the flame speed in the mixture stream M excludes a flashback. To ensure this, the exit velocity must be higher than the flame speed. Stoichiometric mixture flows (air ratio λ = 1) have the highest flame speed. By increasing the air ratio, the flame speed is reduced. On the other hand, increasing the air ratio simultaneously increases the exit velocity of the mixture flow because the mixture volume flow is increased. In this way, flashback can be avoided even with relatively low heating outputs.

In a third operating section, approximately between the relative heating output Q = 0.4 and a maximum relative heating output Q-max = 1 (nominal heating output of the combustion device 100), the air ratio value interval is guaranteed optimal thermal efficiency, complete combustion, elimination of flying flames and compatibility with pneumatic air-fuel gas ratio controllers 112.

In this third operating section, thermal efficiency of the combustion, complete combustion of the mixture flow M and the compatibility of the air ratio value interval with the possibilities of pneumatic air-fuel gas ratio controllers 112 are crucial. Pneumatic air-gas ratio control relies on flow restrictions and a nominally set regulated gas pressure from the gas valve. This physically limits one form of air ratio limit curves that the regulated air-fuel gas system can provide. Compatibility means that the shape of the limit curve can be brought into agreement with the physical behavior of a pneumatic air-fuel gas ratio controller 112. Another important aspect is to avoid the flame lifting. The air ratio value λ must continue to be so low that a heater 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 to ensure complete combustion of the mixture stream M, in particular the fuel gas stream G. The air ratio λ must therefore be set optimally in order to form a framework (which specifies both an upper and a lower limit to the claimed operating conditions) that meets all of the above requirements and also through an air-fuel gas ratio controller 112 for regulating the air / fuel gas ratio can be done. Air-fuel gas ratio controllers 112 are, in particular, passive physical systems whose possible behavior is limited 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 adapting the air ratio λ from the selected air ratio value interval, depending on the heating output Q, was found, which meets all of these different, sometimes competing requirements . The safe combustion of hydrogen is much more difficult than other fuels such as methane, propane or butane. This is due to the combustion properties of flame speed, ignition energy and ignition limits. The method and the selected air ratio limits were adapted in particular to the very specific requirements of a hydrogen-burning combustion device 100.

Another advantage of the method, in particular the air ratio value interval found, is that the method can also be implemented with known pneumatic air-fuel gas ratio controllers 112 with the appropriate setting.

In 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 can be achieved 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 setting can be made using an adjusting screw on the 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 offset pressure delivered by the gas valve varies over the modulation range, its size increases with increasing heating power. However, this follows a linear relationship to heating output and maintains a very small amount (a few tens of Pascals). Due to its small size, the influence of the offset pressure is negligible at high heating powers (where the Venturi effect and the throttling of the fuel gas flow G are high). Conversely, the influence of the offset pressure is very strong at low heating outputs and allows the air ratio to vary greatly over the heating output, as shown in the air ratio limit curves λ-min and λ-max.

Claims (7)

1. 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, 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, having at least one predefinable air ratio λ in the mixture stream (M), and for combusting the mixture stream (M), wherein a heating power is generated by the combustion,
   wherein the combustion device (100) comprises a control device (110) and a combustion gas metering unit (104) and/or an air delivery unit (102), wherein the control device (110) is designed

   · to control the combustion gas metering unit (104) depending on the heating power, wherein the combustion gas metering unit (104) meters a relatively smaller combustion gas stream (G) at a relatively low heating power, and meters a relatively larger combustion gas stream (G) at relatively high heating power, and/or

   · to control the air delivery unit (102) depending on the heating power, wherein the air delivery unit (102) delivers a relatively larger air stream (A) at a relatively low heating power, and delivers relatively smaller air stream (A) at a relatively high heating power,

   characterized in that the control device (110) is further designed to control the air ratio λ of the mixture stream (M) depending on a value Q of the relative heating power of the combustion device (100) for the entire modulation range 0.05 <= Q <= 1 to a value within the air ratio value interval $$0.15/\mathrm{Q}+1\le \mathrm{\lambda }\le 0.175/\mathrm{Q}+1.25,$$

   

   wherein the air ratio λ characterizes a quantity ratio of air to combustion gas and is calculated as a quotient of a quantity of air actually present in the mixture stream (M) and a quantity of air required for stoichiometric combustion of the mixture stream (M).
2. Combustion device according to Claim 1, characterized in that the control device (110) is designed to detect the heating power, to generate a mixture signal (S3) depending on the heating power and to output the mixture signal to the combustion gas metering unit (104) and/or the air delivery unit (102), wherein the mixture signal (S3) is intended to meter a relatively smaller combustion gas stream (G) and/or to deliver a relatively larger air stream (A) at a relatively low heating power; and to meter a relatively larger combustion gas stream (G) and/or to deliver a relatively smaller air stream (A) at a relatively high heating power.
3. Combustion device according to Claim 1 or 2, characterized in that the control device (110) is designed to receive and to process a power signal (S21) characterizing the heating power,

   wherein the power signal (S21) is based on detection of an actual or requested heating power, the mixture stream (M), the combustion gas stream (G), the air stream (A), a blower rotation speed of an air blower delivering the air stream (A) and/or a combustion temperature of the combustion of the mixture stream (M),

   wherein the control device (110) is designed to generate the mixture signal (S3) on the basis of the power signal (S21) .
4. Combustion device according to one of the preceding claims, characterized by a first detection unit (114), wherein the first detection unit is designed to detect the air ratio λ and to output a corresponding first feedback signal (S4) to the control device (110), wherein the control device (110) is designed to control the air ratio λ depending on the first feedback signal (S4) .
5. Combustion device according to one of the preceding claims, characterized by a second detection unit (116), wherein the second detection unit is designed to detect a flame stability of the combustion and to output a corresponding second feedback signal (S6) to the control device (110),
   wherein the control device (110) is designed to control the air ratio λ depending on the second feedback signal (S6) .
6. Combustion device according to one of the preceding claims, characterized in that the control device (110) is designed to output a fault message when a predefinable flame stability cannot be achieved within the air ratio value interval.
7. Heater, having a combustion device (100), characterized in that the combustion device (100) is designed according to one of the preceding claims.

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