EP2655971B1 - Method for stabilizing an operating behavior of a gas blower burner - Google Patents

Description

The invention relates to a method for stabilizing a performance of a power-modulating, air-frequency-controlled gas fan burner for the consideration of disturbances in the combustion air, fuel gas-air mixture path, Heizgasweg and / or exhaust path according to the preamble of claim 1.

Background of the invention are power modulating Gasgebläsebrenner with air ratio controlled combustion of a fuel. Such burners are often installed in heaters or boilers and are used, for example, the heat generation for domestic heating and / or domestic hot water. Its modulation range is limited by a lower modulation limit and an upper modulation limit. The lower modulation limit means a burner operation at low load where the blower operates at a lower allowable fan speed. Lower speeds are not adjustable. The upper modulation limit means burner operation at full load where the blower operates at an upper allowable blower speed. Higher speeds are also not adjustable.

In operation of such burners, a modulatable and / or switchable, e.g. Variable speed fan via an airway to a combustion air amount L and doses a modulatable and / or switchable fuel gas control valve a fuel gas amount G. In a mixing device combustion air and fuel gas are combined and processed into a homogeneous fuel gas-air mixture. At a burner mouth, e.g. a flat burner exit surface, the fuel gas-air mixture exits the burner is ignited and burns with heat. The resulting hot hot gases flow through a heat exchanger, transfer their heat to a heat transfer fluid and leave as cooled exhaust gases, the heater via an exhaust path in the area. An ionization electrode detects in the combustion zone an actual flame ionization signal I, which arises due to a voltage applied to a burner flame. A control device influences a supply of combustion air and / or fuel gas on the basis of operating data and / or target specifications.

In the burner design and the burner operation, there is an important requirement that the flame remains stable. This means that the flame or the flames neither strike back into the burner mouth nor lift off from the burner mouth. Both would be dangerous conditions with the potential risk of burner overheating, deflagration or other disruption. Flames of a lean fuel-air mixture tend to lift off, flames of a rich mixture tend to kick back. The size of the air flow delivered by the fan depends not only on the fan speed, but also on the flow resistance in the airway and the other pneumatically connected with the air flow paths through which the fuel gas-air mixture, the heating gas and finally the exhaust gas flow. These flow paths can be disturbed, which manifests itself in increased and reduced flow resistance. Possible exemplary causes of these disturbances are contamination of the Zuluftweges with leaves, reducing the outlet cross-section of the exhaust path to the open by icing or dead bird, deposits in the heat exchanger of corrosion products, damaged air or exhaust pipes with leakage, wind suction, wind pressure, and so on.

The ratio of fuel to combustion air is therefore of great importance for a trouble-free, but also for an efficient burner operation. With a view to optimized combustion with a stable flame, minimal pollutant emissions and high combustion efficiency even with changing fuel properties (fuel types, qualities, compositions), modern burners are operated with air-number-controlled combustion, wherein a fuel-air mixture of desired composition in the lean range with, for example, about 30% excess air compared with a stoichiometric mixture, ie an air ratio λ = λ _SOLL = 1.3.

The air ratio control is often based on a signal from the combustion, the so-called flame ionization signal. A suitable evaluation circuit makes use of the fact that flames conduct electricity when an electrical voltage is applied. The course of the ionization signal shows a clear dependence on the air ratio λ of the fuel-air mixture with a signal maximum at λ = 1.0 (stoichiometric reaction, Figure 1 left).

A known under the name SCOT (System Control Technology) evaluation circuit for air flow control is in the DE 44 33 425 C2 disclosed. In the corresponding control method, the measured in a flame of a fuel gas-air mixture I ionisation signal is driven at a predetermined operating point by controlling the amount of fuel gas or the combustion air quantity to be maximum signal I _MAX. In the In the subsequent calibration of the mixing device, the fuel gas-air mixture composition is controlled by a certain amount in the excess air until the adjusting Ionisationssignal I = I _SOLL is smaller by a predetermined factor than the measured maximum signal I _MAX . This SETPOINT setting then determines the power modulation behavior of the burner until the next calibration. For this method, independently adjustable devices for air and fuel gas delivery are required, so for example, a variable speed fan and an electronically adjustable gas valve - the gas valve is not pneumatically connected to the amount of combustion air, but receives its control signal from a device control. For air-gap controlled operation over a wider power modulation range, several correction factors are needed that take into account the effects of burner power dependency, fuel flow feasibility, and burner design.

This type of burner operation is reliable only at full load (nominal power) Q _NENN or in a limited power modulation range minimum power Q _MIN (lower modulation _limit ) to nominal power Q _NENN (upper modulation _limit ) of about 1: 3 to 1: 4 possible. Below this, with smaller burner powers, the ionization signal I decreases sharply in intensity and loses its unambiguous assignment to the air ratio λ ( FIG. 2 ). This is due to the low area-based burner performance, the shorter flame lengths and the greater interaction of the flames with the burner mouth.

Today, preference is given to using burners with high power modulation ranges, which can satisfy very different heat requirements, such as those arising from domestic heating at different outside temperatures or from domestic hot water preparation for small and large dispensing volumes. We are looking for burners that can work right down to low heat requirements in a low-modulating continuous operation and without clocking in and out.

The DE 199 36 696 A1 discloses a method with which an air ratio control in the lower part load range is possible. Again, an ionization signal is generated in the flame and derived from the current air ratio, which is then compared with a predetermined air ratio and, if the current air ratio differs from the predetermined air ratio, the current air ratio is set to the value of the predetermined air ratio. The current air ratio is, however, determined at full load, since here is an area with a clear assignment between the ionization signal and the air ratio. In the partial load range of the burner is only controlled, ie unregulated operated.

One option for true air ratio control over the entire modulation range is the specification of a power modulation-dependent ionization setpoint I _SOLL (Q). To FIG. 2 For example, the ionization curve I (Q) for λ = 1.3 can be specified as a setpoint curve I _SOLL (Q), which assigns each burner output Q clearly a nominal flame ionization signal I _SOLL . If the actual flame ionization signal is always adjusted to the desired signal by adjusting the fuel gas / air mixture composition, the burner is operated over its entire modulation range with the air ratio λ = λ _SOLL = 1.3.

The relationship given in this characteristic curve I _SOLL (Q) can be determined with simple means on the laboratory test bench for a given burner. More difficult is the regulatory implementation in practice at the end user, since the affected burner usually have no determination of the power Q (ie the fuel gas flow G). The object of the power determination is solved by the relationship between the power Q and the amount of combustion air L, which can be represented as a fixed proportional relationship for a desired air ratio λ _SOLL . From characteristic I _SOLL (Q) FIG. 2 , a characteristic I _SOLL (L), FIG. 3 , The amount of combustion air L, whose direct measurement is not easy, can be expressed by the revolutions per minute (RPM) of the air-conveying blower, the air quantity L is usually directly proportional to the fan speed RPM. The blower speed can be measured by simple means. The characteristic I _SOLL (L) becomes a characteristic I _SOLL (RPM). In fact, the specified by a burner control flame ionization target signal is given as a function of the fan speed.

This results in the problem that the fan speed is proportional to the delivered air flow only as long as the flow resistance in the entire flow path (airway (eg supply air), fuel gas-air mixture path (eg burner), Heizgasweg (eg heat exchanger), exhaust path (eg Exhaust pipe, chimney)) are constant. However, this rule can be disturbed by suddenly occurring or slowly progressing blockages in the flow path. Causes may be wind, pollution and constipation due to corrosion, leaves and birds, as well as other disturbing influences. In these cases, less air is delivered at constant fan speed.

Reduces due to increased flow resistance, the amount of combustion air, but the flame ionization _target signal I _SOLL (RPM) remains constant because of the unchanged fan speed ( FIG. 3 ). In the area of high air volumes L (high burner power Q), a reduction in the air volume has no or only slight effect on the air ratio, since the characteristic curve I _SOLL (L) runs approximately constant and a horizontal displacement of the operating point ( FIG. 3 , Shift AB) at constant speed and constant ionization setpoint therefore no air speed change causes. In the range of low air volumes L (low burner power Q), where the characteristic I _SOLL (L) has a significant gradient, reducing the air volume at a constant fan speed and constant ionization _{target signal} causes a large change in the air ratio. That after FIG. 3 , Shifting CD, fatter fuel gas-air mixture, as described above, has a negative effect on the burner operation. The released from the gas valve fuel gas sets in each case depending on the changed air volume and the constant ionisationssollsignal.

The US2005 / 0250061 A1 discloses a method according to the preamble of claim 1.

The cited prior art has the disadvantage that an air-frequency-controlled burner operation with a wide power modulation range is very susceptible to interference with respect to changed flow resistances in the air, mixture, heating gas and exhaust gas path.

The invention has for its object to provide a method for stabilizing the performance of a power modulating air ratio-controlled gas fan burner, are compensated with the interference due to changes in flow resistance in the air, mixture, Heizgas- and exhaust.

This is achieved by the objects with the features of claim 1 according to the invention. Advantageous developments can be found in the dependent claims.

An embodiment of the method according to the invention for stabilizing a performance of a power-modulating, air-frequency-controlled gas fan burner with a lower modulation limit and an upper modulation limit compensated with altered (eg increased) flow resistance disturbances in a supply air, fuel gas-air mixture, heating gas and / or exhaust path by adjusting the power modulation range. In a normal control operation of the gas-jet burner, a composition of a fuel gas-air mixture is adjusted as a function of an actual flame ionization signal and a nominal flame ionization signal by controlling the flame ionization actual signal to the nominal flame ionization signal and the nominal flame ionization signal can be specified as a function of a rotational speed of an air-conveying blower. Essential to the invention is at selected operating conditions of the gas fan burner and in deviation from the normal control mode, the fuel gas-air mixture temporarily and temporarily enriched with fuel gas and the flame ionization actual signal observed. From the difference between a maximum flame ionization actual signal (stoichiometric combustion) observed during the enrichment and the flame ionization actual signal measured before the enrichment, a so-called flame ionization signal stroke H is formed. Now, if this flame ionization signal H (short: signal swing) is smaller than a first tolerance amount T1 or greater than a second tolerance amount T2, a lower allowable fan speed associated with the lower modulation limit is increased. The burner control then returns to normal control mode. First (smaller) tolerance amount T1 and second (larger) tolerance amount T2 define a permissible flame ionization stroke interval ΔT ( FIG. 1 right).

Prior to the enrichment of the fuel gas-air mixture with fuel gas engages the normal control operation, the flame ionization actual signal is due to the regulation equal to the desired signal. The temporary and short-term enrichment or enrichment of the fuel gas-air mixture causes a change in the flame ionization actual signal. If the starting mixture (before enrichment) is significantly lean of stoichiometry or lean, the ionization signal will rise significantly when enriched. If the starting mixture is only slightly more than stoichiometric, the ionization signal grows only slightly. On the other hand, if the starting mixture is stoichiometric or substoichiometric, the ionization signal does not rise or even fall. The magnitude of the ionization signal lift (ionization signal increase) is determined by comparing the actual maximum flame ionization signal observed during enrichment with the original flame ionization actual signal prevailing before enrichment.

The measured ionization signals may be individual measurements or, to suitably account for statistically fluctuating measurements, averaged measurements (e.g., the moving average principle).

If the signal deviation is less than the first tolerance amount, then the original fuel gas-air mixture is diagnosed as being too fat. The signal deviation is outside the permissible signal stroke interval. This is attributed to an increase in the flow resistance in the flow path (air, mixture, Heizgas- and / or exhaust path).

If the signal swing is greater than the second tolerance amount, then the original fuel gas-air mixture is diagnosed as too lean. The signal deviation is outside the permissible signal stroke interval. This is attributed to a reduction in the flow resistance in the flow path (air, mixture, Heizgas- and / or exhaust path).

In both cases, the burner control changes a parameter set on which the control is based by increasing the lower allowable fan speed. This corresponds to an increase in the associated lower modulation limit or an adaptation (restriction) of the power modulation range of the gas-jet burner to a flow resistance that is changed compared to a design state in the flow path. With this adaptation, operating points accessible to the burner control are limited to a higher power modulation range, operating points in the lower modulation range can no longer be approached. Thus, the formation of a fuel gas-air mixture with desired composition at target air and thus a more stable performance of the gas blower burner is achieved because the burner flame neither rests on the outlet surface and these overheats, still stands out from the burner and tends to extinguish, causing excessive pollutant emissions. This results from the flatter characteristic I _SOLL (L) at the higher power modulation range ( FIG. 3 ), Like previously described. With this adjusted parameter set, the control returns to the normal control mode.

If the Ionisationssignalhub in the permissible Signalhubintervall, that is greater than or equal to the first tolerance amount and less than or equal to the second tolerance amount, the original fuel gas-air mixture is thus diagnosed as "good". The burner control returns to the normal control mode without intervention in a parameter set on which the control is based.

After increasing the lower allowable fan speed again the normal control operation, that is, that the burner meets the heat demands placed on him by a heating system to be supplied within the now available, adjusted modulation range and thereby executes the air ratio control described.

The steps of temporarily, briefly enriching the mixture with fuel gas, comparing the ionization signal stroke with the first amount of tolerance, and optionally increasing the lower allowable fan speed, may be repeated and progressively adjusting the power modulation range lead the gas fan burner. Thus, for example, with increasing flow resistance in the flow path, the lower permissible fan speed can be increased step by step and thus the power modulation accessible to the burner control system can be increasingly limited to higher ranges. On the other hand, when the flow resistance has been eliminated, the lower permissible fan speed can be lowered again, and thus the power modulation range accessible to the burner control unit can be expanded again.

The repetition rate of repeated steps may be in minutes or hours. The frequency can also be selected as a function of the Ionisationsshubhubes observed during enrichment of the fuel gas-air mixture, for smaller strokes, the frequency may for example be higher than for larger strokes.

The described steps for checking and possibly adjusting the power modulation range of the gas-fired burner are carried out at selected operating conditions of the gas-fired burner and in deviation from the normal control operation, the fuel gas-air mixture. Such selected operating states may be, for example, operating points of medium and low power modulation, since, according to experience, the largest gradients of the ionization signal setpoint curve are present here. The steps can also be performed only at those operating points that are unchanged during a predetermined minimum period, so for example, after a five-minute burner operation at low load. When carrying out the steps, the burner operation must deviate from the normal control mode in order to enrich the mixture differently from the nominal air number.

An embodiment of the method according to the invention is characterized in that the observed maximum flame ionization actual signal is a measured maximum flame ionization actual signal. This means that when enriching, the mixture composition is at least enriched to stoichiometry.

An alternative embodiment to this is characterized in that the observed maximum flame ionization actual signal is an expected maximum flame ionization actual signal which can be derived from the observed time profile of the flame ionization actual signal in a forward-looking manner (time t). The derivation of the expected actual signal is based on a model over the course of the ionization signal, this is the in FIG. 1 represented parabolic-like course over the air ratio λ, which reaches its maximum at λ = 1.0. The expected course and the maximum can be measured from the enrichment Predictive course can be calculated without the stoichiometric operating point is actually achieved. Thus, all the disadvantages with regard to burner overheating and pollutant formation, which entails a stoichiometric operating point, are avoided.

The temporary enrichment of the fuel gas / air mixture with fuel gas includes enrichment and subsequent leaning to the original mixture composition prior to enrichment. According to one embodiment, this is done by a fuel gas supply of the gas fan burner dominant electronic gas valve at constant fan speed temporarily and briefly releases about 10% to 50% more fuel gas. The control of the gas valve is controlled and not in response to a current heat request. The activation of the gas valve and / or the enrichment of the mixture can take place in the manner of a jump function or a ramen function. Likewise, the enrichment can be achieved by changing the fan speed and changing the amount of air at a constant amount of gas.

The enrichment of the mixture takes place in another embodiment of the method by the flame ionization target signal influencing the composition of the fuel gas-air mixture is temporarily increased at constant fan speed by about 10% to 30%. The dependence of the nominal flame ionization signal on the speed of the fan is temporarily suspended. The increase of the desired signal in turn causes an opening of the gas valve and thus an enrichment of the mixture.

According to a further embodiment of the method, a duration of the temporary, short-term enrichment of the fuel gas-air mixture with fuel gas is about 0.1 second to 10 seconds. Thus, on the one hand, the described adverse effects associated with the enrichment, are very limited in time and therefore are not significant. On the other hand, the additional amount of heat released by combustion of the additional amount of gas is very low and can be easily absorbed and mitigated by the thermal storage capacity of the component masses involved.

According to one embodiment, the increase in the lower allowable fan speed always takes place by a fixed, proportionate amount of about 5% to 30% of a currently available speed range.

According to an alternative or complementary embodiment, the amount of increase in the lower allowable fan speed depends on the Flammenionisationssignalhub when enrichment. This amount increases with increasing difference between Flammenionisationssignalhub and the respectively associated tolerance amount. A small distance of the flame ionization signal stroke from the first or second tolerance amount (ie, a signal stroke lying only slightly outside the signal stroke interval) results in a slight increase in the lower allowable fan speed. A large distance of the flame ionization signal stroke from the first and second tolerance amounts (ie, a signal swing far out of the signal stroke interval) results in a large increase in the lower allowable fan speed.

An embodiment of the method is characterized in that the first tolerance amount is about 10% to 30% of the nominal flame ionization signal, and that the second tolerance amount is about 30 to 50% of the nominal flame ionization signal. This means that an actual flame ionization signal of a combustible fuel gas / air mixture having the desired composition (nominal air ratio) is smaller by the corresponding amount than the maximum ionization signal observed during stoichiometric enrichment. The exact values of the tolerance amounts also depend on the design, operating and / or installation conditions.

An embodiment of the invention is characterized in that the increase in the lower allowable fan speed after each burner-off or after pressing a reset button or after a predetermined increase period is reset. Resetting to the design state means that the entire power modulation range is available again. Subsequent to the provision, the method according to the invention can then be carried out again. Already at the first or only at a repeated increase of the lower allowable fan speed, a warning message can be issued, which signals to a user or installer that there is a fault in the flow path.

Figur 1

den charakteristischen parabelförmigen Zusammenhang zwischen dem Ionisationssignal I und der Luftzahl λ,

Figur 2

den beispielhaften Zusammenhang zwischen dem Ionisationssignal I und der Brennerleistung Q für verschiedene Luftzahlen λ,

Figur 3

den beispielhaften Zusammenhang zwischen dem Ionisationssignal I und der Verbrennungsluftmenge L für verschiedene Luftzahlen λ und

Figur 4

den schematischen Zusammenhang zwischen Anreicherung des Brenngas-Luft-Gemischs und beobachtetem Ionisationssignal.

The drawings illustrate the physical relationships of the invention and show in the figures:

FIG. 1

the characteristic parabolic connection between the ionization signal I and the air ratio λ,

FIG. 2

the exemplary relationship between the ionization signal I and the burner power Q for different air numbers λ,

FIG. 3

the exemplary relationship between the ionization I and the combustion air quantity L for different air numbers λ and

FIG. 4

the schematic relationship between enrichment of the fuel gas-air mixture and observed ionization signal.

FIG. 1 schematically shows the typical parabolic shape of a lonisationssignales I as a function of the air ratio λ. The ionization signal I as a signal from the combustion is often the basis for air-fuel control. A suitable evaluation circuit makes use of the circumstance that flames conduct a so-called ionization current when an electrical voltage is applied. The course of the ionization signal shows a clear dependence on the air ratio λ of the fuel-air mixture with a signal maximum at λ = 1.0 (stoichiometric combustion). The ionization signal falls in the direction of rich mixtures (λ <1) and lean mixtures (λ> 1). An enrichment of a fuel gas-air mixture, starting from a superstoichiometric to a stoichiometric composition, is on the left side of FIG FIG. 1 represented by the successive (mixing) points along a time axis t. On the right side of the FIG. 1 exemplary ionization strokes H are shown as they may result in an enrichment. Also shown is a permissible flame ionization stroke interval ΔT, which is limited by a first tolerance amount T1 and a second tolerance amount T2. If, in carrying out the method according to the invention, a flame ionization signal stroke H smaller than T1 or greater T2 is observed, the lower permissible blower speed is increased. The burner control then returns to normal control mode. On the other hand, if the signal swing is within the allowable interval ΔT, the burner control returns to normal control operation without any change in the fan speed.

FIG. 2 shows schematically exemplary Ionisationssignalverläufe I at three different air ratios λ as a function of a burner power Q. It can be seen that the ionization signals I are higher in rich combustion (eg λ = 1.1) and the lean mixture range (eg λ = 1.3 .. 1.5). Conspicuous are the constant air ratio (example λ = 1.3) in intensity significantly decreasing ionization in the range of small burner power Q _MIN - here the ionization signal I loses its unique allocation to the air ratio λ. A function assignment of the ionization signal to power and air ratio is still given in this area - due to the declining and converging curves but here is a reliable control, based on the specification of a lonisationsssollsignals, depending on the fan speed, difficult. Disturbances in the flow channel lead to greater deviations in the set air ratio in this area than would be the case in the area of higher power.

A modulation range of a power modulating burner is limited by a lower modulation _limit ( _low load, Q _MIN ) and an upper modulation _limit (full load or rated power, Q _NOM ). An air-fuel ratio control, for example, the here average ionization curve, which results in an air ratio λ = 1.3, be specified as a setpoint curve.

FIG. 3 shows schematically exemplary Ionisationssignalverläufe I at three different air ratios λ depending on a combustion air amount L and illustrates the underlying this invention problem. In this case, the amount of combustion air L is the amount of air that is required to achieve a burner power Q at a given air ratio. It can be seen once again that the ionization signals I are higher during rich combustion (eg λ = 1.1) and decrease towards the lean mixture range (eg λ = 1.3 ... 1.5). Noticeable are the constant air ratio (example λ = 1.3) in intensity significantly decreasing ionization in the range of small air volumes L _MIN (equivalent to small burner power Q _MIN ). A modulation range of a power modulating burner is limited by a lower modulation limit (minimum air volume, L _MIN ) and an upper modulation limit (maximum or nominal air volume, L _NOM ). An air-fuel ratio control, for example, the here average ionization curve, which results in an air ratio λ = 1.3, be specified as a setpoint curve.

In fact, the burner control is given an ionization curve with respect to the RPM (revolutions per minute) fan speed as the setpoint curve. With increased flow resistance in the air, mixture, Heizgas- and / or exhaust path, the combustion air quantity L decreases for example along the paths AB and CD. However, the fan speed does not change or does not change significantly. However, since the flame ionization setpoint curve is formulated as a function of the blower speed, the ionization setpoint does not change either. In the high modulation range, this reduction in the air volume has no significant effect on the air ratio of the fuel gas-air mixture, compare way AB. In the range of low power modulation, however, there is one significant change in the air ratio compared to the target composition of the fuel gas-air mixture, for example the path CD, with a much richer composition. This greasy mixture composition D as an effect of disturbance in the flow path (increase in flow resistance) is undesirable for reasons described above.

FIG. 4 shows the schematic relationship between the enrichment of the fuel gas-air mixture with fuel gas G and the observed ionization signal I over time t. A fuel gas-air mixture is enriched according to the invention temporarily and briefly with fuel gas, the fuel gas is released, for example, by a suitably driven fuel gas valve. The ionization signal I is observed, it follows the fuel gas enrichment G. According to the fuel gas enrichment results depending on the air ratio of the original mixture a larger or smaller Ionisationssignalhub H, which is subjected to an analysis according to the invention, the result of which then follow the inventive method steps described above. When the ionization signal stroke H is smaller than a first tolerance amount T1 or larger than a second tolerance amount T2, the lower allowable fan speed is increased. Subsequently, the control returns to the normal control mode, according to the invention now only a limited power modulation range is available.

Claims (10)

1. Method for stabilizing an operating behaviour of a power-modulating, air ratio-controlled gas blower burner with a lower modulation limit and an upper modulation limit, for making allowance for disturbances in a combustion air path, mixture path, heating gas path and/or waste gas path, wherein, during normal controlling operation of the gas blower burner,

   • a composition of a burnable gas/air mixture is set in dependence on an actual flame ionization signal and a setpoint flame ionization signal,

   • the actual flame ionization signal is controlled to the setpoint flame ionization signal and the setpoint flame ionization signal is preset in dependence on a rotational speed of an air-delivering blower,

   wherein, during selected operating states of the gas blower burner and as a departure from the normal controlling operation,

   • the burnable gas/air mixture is temporarily and briefly enriched with burnable gas and the actual flame ionization signal is observed, and

   • the control is subsequently returned to normal controlling operation,

   characterized in that, in the aforementioned selected operating states of the gas blower burner and in the aforementioned departure from the normal controlling operation, a lower permissible blower speed that is assigned to the lower modulation limit is increased if a flame ionization signal stroke, that is the difference between a maximum actual flame ionization signal observed during enriching and the actual flame ionization signal measured before enriching, is smaller than a first tolerance amount or greater than a second tolerance amount.
2. Method according to Claim 1,
   characterized in that the observed maximum actual flame ionization signal is a measured maximum actual flame ionization signal.
3. Method according to Claim 1,
   characterized in that the observed maximum actual flame ionization signal is an expected maximum actual flame ionization signal, which can be predictably derived from the observed progression of the actual flame ionization signal.
4. Method according to one of Claims 1 to 3,
   characterized in that the temporary enriching of the burnable gas/air mixture with burnable gas comprises enriching and subsequent leaning and takes place by an electronic gas valve that controls the supply of burnable gas to the gas blower burner temporarily releasing approximately 10% to 50% more burnable gas at a constant blower speed.
5. Method according to one of Claims 1 to 3,
   characterized in that the temporary enriching of the burnable gas/air mixture with burnable gas comprises enriching and subsequent leaning and takes place by the setpoint flame ionization signal that controls the composition of the burnable gas/air mixture being temporarily increased by approximately 10% to 30% at a constant blower speed, the dependence of the setpoint flame ionization signal on the speed of the blower being suspended.
6. Method according to one of the preceding claims,
   characterized in that a period of temporarily briefly enriching the burnable gas/air mixture with burnable gas is approximately 0.1 second to 10 seconds.
7. Method according to one of the preceding claims,
   characterized in that the increase of the lower permissible blower speed takes place by an amount of approximately 5% to 30% of a speed range available at the time.
8. Method according to one of the preceding claims,
   characterized in that the amount of the increase of the lower permissible blower speed depends on the flame ionization signal stroke and grows with an increasing difference between the flame ionization signal stroke and the respectively assigned tolerance amount.
9. Method according to one of the preceding claims,
   
   characterized in that the first tolerance amount is approximately 10% to 30% of the setpoint flame ionization signal, and the second tolerance amount is approximately 30% to 50% of the setpoint flame ionization signal.
10. Method according to one of the preceding claims,
    characterized in that the increase of the lower permissible blower speed is reset after every burner switchoff or after actuation of a reset button or after a predeterminable increasing period.

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