DE102020008001B4 - BURNER ASSEMBLY, METHOD OF OPERATING A BURNER ASSEMBLY AND WIND FUNCTION - Google Patents

Abstract

The present disclosure relates to a method for operating a burner arrangement with a burner (1) that burns an air-fuel mixture. In one step of the method, a target value for an ionization current is specified. The burner (1) is operated in a first operating state at a first predetermined power level. The ionization current (9) is measured using an ionization electrode (5). The measured ionization current (9) is compared with the specified target value and a deviation is determined. If the deviation exceeds a predetermined limit value, the burner (1) is switched to a second operating state at a second power level. The second power level is higher than the first power level. The second power level is determined depending on the deviation.

Description

The present invention relates to a burner arrangement and a method for operating a burner arrangement. In particular, the present invention realizes a wind function that can prevent flameout due to pressure fluctuations caused by wind.

A combustor assembly generally includes a combustor that is connected to atmosphere through an exhaust system. Strong gusts of wind, such as those that occur during storms, can cause rapidly changing drafts or excess pressure in the exhaust system. This can cause pressure surges in the burner. Such pressure surges can lead to a flameout in the burner, which can result in toxic emissions. In addition, after a flame failure, a calibration must be carried out when the burner is restarted. In the event of a flame failure, calibration is necessary in order to determine whether the burner control is functioning, since the cause of the flame failure is not always clear. A calibration requires the burner to be forced to run at a high load level. Appropriate heat consumption in the heating system must be ensured here, which may necessitate further control measures.

The object of the present invention is to overcome the problems known in the prior art and to provide a burner arrangement for a heating boiler which is improved compared to the prior art and to specify a method for operating a burner arrangement. In particular, a flame failure due to pressure surges should be prevented in order to avoid toxic emissions and mandatory calibration. The measures for avoiding the flameout are also referred to below as the "wind function".

The object is achieved by a method for operating a burner arrangement according to claim 1. The solution is also achieved by a burner arrangement according to claim 8.

A method for operating a burner arrangement with a burner that burns an air-fuel mixture comprises the method steps described below. The order of the steps can be varied depending on the application. Some steps can also be executed simultaneously. In particular, a fluid, ie gaseous or liquid, fuel can be used as the fuel, for example natural gas or fuel oil.

In a first operating state, the burner is operated at a first predetermined power level. In particular, the burner is operated at partial load in the first operating state. A preferred partial load range of the first power stage can be, for example, between 3% and 10% of the maximum load, more preferably between 4% and 8% and particularly preferably between 5% and 7%.

In one step of the method, a target value for an ionization current is specified. The ionization current can be measured using an ionization electrode placed so that it is immersed in the flame.

The measured ionization current is then compared with the specified target value and a deviation between the measured ionization current and the specified target value is determined. For this purpose, for example, an electronic control device of the burner arrangement can be used, which in particular has a processor and a memory.

If the deviation is small, the burner will continue to operate in the first operating mode. A small deviation is present in particular when the deviation is less than a predetermined limit value. If the deviation exceeds the specified limit value, the burner can be switched to a second operating state at a second power level.

The second power level is in a higher partial load range than the first power level. The second power stage is therefore also referred to as "raised partial load". A preferred partial load range of the second power level can be, for example, between 20% and 40% of the maximum load, more preferably between 25% and 35% and particularly preferably between 28% and 33%.

In particular, the second power level can be determined as a function of the deviation. This can be done, for example, in such a way that the second power stage is raised to a higher partial load when the deviation is greater than when the deviation is smaller. Correspondingly, values or an algorithm can be stored in the control device, according to which the second power level is determined as a function of the deviation.

By raising the power level to the second power level, i.e. by operating the burner in a higher load range, stable combustion is achieved even if pressure fluctuations affect the flame. This can prevent flame failure. Since the power level depends on the measured If the deviation is determined, a conventional burner arrangement with an ionization electrode can react to pressure fluctuations without additional sensors in order to avoid the flameout. The method according to the invention can therefore also be implemented in older devices.

After a predetermined period of time has elapsed, the burner arrangement can be switched back to the first operating state. The period of time can be determined, for example, as a function of the measured deviation, or it can be a fixed value. In this way it can be avoided that operation takes place at an unnecessarily high power level over a longer period of time. Since gusts of wind tend to be of short duration, a period of several seconds or a few minutes may be sufficient, for example. In particular, the control device of the burner will try to transfer the burner to the lowest possible load stage under the conditions, with the conditions being able to be determined from the deviation of the measured ionization current from the setpoint.

The transition from the first to the second operating state or from the second to the first operating state can be carried out in stages over one power level or multiple power levels between the first and second power level. By gradually increasing the power level, the burner arrangement can react to pressure fluctuations without immediately modulating to a high power level. After each increase step, an ionization current can be measured again and compared with the target value. If the deviation is smaller than the limit value, there is no need to raise the power level further or it can even be modulated back to a lower power level.

• Zunächst wird der Brenner bei der aktuellen Leistungsstufe betrieben und der Ionisationsstrom wird gemessen. Der gemessene Ionisationsstroms wird erneut mit dem vorgegebenen Sollwert verglichen und die Abweichung wird ermittelt. Falls die Abweichung den vorgegebenen Grenzwert überschreitet, kann der Brenner in die nächsthöhere Leistungsstufe überführt werden. Überschreitet die Abweichung den Grenzwert nicht, so kann der Brenner in der aktuellen Leistungsstufe weiterbetrieben werden, oder nach einem vorgegebenen Zeitraum in eine nächstniedrigere Leistungsstufe überführt werden.

When changing from the second to the first operating state, the following process steps can be carried out in each performance level between the first and second performance level:

• First, the burner is operated at the current power level and the ionization current is measured. The measured ionization current is again compared with the specified target value and the deviation is determined. If the deviation exceeds the specified limit value, the burner can be switched to the next higher power level. If the deviation does not exceed the limit value, the burner can continue to be operated at the current power level, or be transferred to the next lower power level after a specified period of time.

The target value of the ionization current can be specified depending on the current power level. Since the ionization current generated in the ionization electrode depends on the properties of the flame, in particular the temperature, the target value of the ionization current is generally dependent on the power level to which regulation is to be carried out.

A modulation speed of the burner can be accelerated by means of a coefficient when the burner is transferred to a higher power level. Since a flame failure is to be avoided, it is advantageous to operate the burner as quickly as possible at a higher output. This can be achieved by increasing a control speed, which can be achieved, for example, by means of a coefficient for accelerating the modulation speed.

Furthermore, a time duration of the deviation between the measured ionization current and the target value can be determined, in particular in order to determine the second power level as a function of the duration of the deviation. A longer duration of the deviation is an indication of stronger gusts of wind, for example during a storm. Since strong gusts of wind can be expected to occur more frequently during storms, the burner is preferably switched to a higher second power level in order to avoid a flame failure.

The wind function described above can thus regulate the output level of the burner to a stable level if the flame is about to die out. Higher power levels require higher pressure in the combustion chamber, which makes the flame more stable against flame loss. The method according to the invention can therefore effectively prevent flame failure.

character list

Further advantageous configurations are described in more detail below with reference to an exemplary embodiment which is illustrated in the drawings and to which the invention is not restricted, however.

• 1 zeigt eine Brenneranordnung gemäß einem Ausführungsbeispiel der Erfindung.
• 2 zeigt ein Ausführungsbeispiel eines erfindungsgemäßen Verfahrens.
• 3 zeigt ein Diagramm, das ein typisches Brennerverhalten unter Windeinfluss illustriert.

They show schematically:

• 1 shows a burner arrangement according to an embodiment of the invention.
• 2 shows an embodiment of a method according to the invention.
• 3 shows a diagram that illustrates typical burner behavior under the influence of wind.

DETAILED DESCRIPTION OF THE INVENTION ON THE BASIS OF EXEMPLARY EMBODIMENTS

In the following description of a preferred embodiment of the present invention, the same reference symbols designate the same or comparable components.

1 Figure 11 illustrates an embodiment of a burner arrangement according to the invention, which can thus be used, for example, in a boiler of a heating system for a building. The boiler can be, for example, a conventional gas boiler or a condensing boiler.

The burner arrangement has a burner 1 which is supplied with a gas-air mixture via a first adjusting device 2 for air and a second adjusting device 3 for gas. The first adjusting device 2 can be an air blower, for example. The second adjusting device 3 can be designed as a proportional valve. The burner 1 is, for example, a 35 kW gas burner. The burner 1 burns the gas-air mixture. The operation of the burner 1 is regulated or controlled by a control device 6 with an automatic firing device.

An ionization electrode 5 is arranged in the vicinity of the burner 1 and is designed to measure an ionization current 9 and to output it to the control device 6 or the burner control unit via a suitable signal line. When the burner 1 is in operation, ie during combustion, the ionization electrode 5 protrudes into the flame. The ionization electrode 5 is usually used for flame monitoring in gas burners, since only the presence of a flame causes the ionization current 9 to flow.

Furthermore, a lambda probe 4 can be arranged in the exhaust gas flow of the burner 1 . A lambda sensor 4 is used to measure the residual oxygen content in the exhaust gas. A more detailed description of the lambda probe 4 and its function is omitted below. In addition, the burner 1 can include other components, such as an ignition, exhaust gas paths and temperature sensors, which are not shown here since they are not necessary for the description of the present invention.

The automatic firing system 6 outputs control signals 7 and 8 for air and gas to the first 2 and second 3 adjusting device, so that the air ratio λ desired for the respective application can be set during an operating phase and, if necessary, kept constant. The air ratio λ is a dimensionless number that characterizes the mass ratio of air and fuel in a combustion process. The combustion air ratio sets the air mass m _L , _tαts actually available for combustion in relation to the minimum stoichiometric air mass m _L , _st required for complete combustion: $$\lambda =\frac{m_{L,tats}}{m_{L,st}},$$

If λ = 1, the combustion air ratio is stoichiometric. This is the case when all of the fuel molecules react completely with the oxygen in the air, leaving no oxygen in the exhaust gas and no unburned fuel. The case λ < 1 means lack of air. This is also referred to as a rich mixture. There is more fuel in the air-gas mixture than can react with the oxygen in the air. The case λ > 1 means excess air and is also referred to as a lean mixture.

In the 1 shown lambda probe 4 is not required for the present invention. The method according to the invention does not evaluate the signals from the lambda probe 4 . The method can therefore also be used for burners that do not have a lambda probe.

The automatic firing device 6 records the output signals from the lambda probe 4 and the ionization electrode 5 and processes them further in order to regulate the combustion. The automatic firing device 6 therefore determines the control signals 7 and 8 for the first 2 and second 3 actuating device as a function of the signals 9 and 10. In particular, the automatic firing device 6 can control or set a load stage using the control signals.

The ionization signal 9 is evaluated by the ionization electrode 5 in order to detect a dangerous wind influence. Gusts of wind can cause large deviations in the measured value of the ionization signal 9 from the desired value specified by the control device 6 .

In the following, based on the in 2 shown flow chart, which represents the method according to the invention in simplified form, the operation of the burner 1 with the wind function is described in more detail.

In the first operating state BZ1, the burner 1 is operated in a first power level at part load of, for example, 5.8% of the maximum load. The ionization electrode 5 measures the ionization current I actual and emits a corresponding ionization signal 9 to the automatic firing device 6, which _is the same temporarily serves as a control device for controlling the combustion and carries out an evaluation of the ionization current.

The ionization signal 9 _is compared with a specified desired _value I setpoint and a deviation δ=|I _{actual −I setpoint} 1 between the measured ionization current I actual and the setpoint I _{setpoint is} determined. The degree of deviation δ is evaluated using a specified limit value δ _max in order to determine from this a required increase in the burner load stage. Pressure fluctuations due to wind have a negative impact on combustion and the measured ionization current can therefore deviate from the target value.

If the deviation is smaller than the limit value (no in 2 ), the burner 1 continues to be operated in the first operating state BZ1 at the first power level. However, if the deviation is greater than the specified limit value (yes in 2 ), the burner 1 is transferred to a second operating state BZ2, in which the burner 1 is operated at a higher load level. This lifting is intended to prevent an imminent flameout. For example, a deviation of 15% of the ionization current from the target value can be specified as a limit value.

The power range from the first power level to the increased partial load (second power level) can, for example, be divided into five intermediate levels (in 2 not shown). The burner 1 can be operated at each stage for a period of, for example, (at least) one minute before a new check is carried out to determine whether the measured ionization current deviates from the desired value.

The raised partial load is, for example, 30% of the maximum load. The wind function according to the invention can also determine the duration of the exceeding of the limit value in the deviation of the ionization current. In this case, a range of a lower time threshold, for example 0.1 seconds, is subdivided linearly up to an upper time threshold. The upper time threshold can be determined on the basis of a process cycle that is specified by the automatic firing device 6 . For example, a duration of twenty revolutions of the automatic firing device 6 can be specified as the upper time threshold.

Thus, the wind function raises the lower limit of the burner capacity. This remains active for a defined period of time, after which burner 1 can modulate to lower load levels again. The lower partial load can also be released in stages. If another wind event occurs, the control device 6 can regulate the burner 1 again to a higher load level until a level with stable combustion (deviation smaller than the limit value) is reached. The burner 1 can thus be automatically regulated to the lowest possible partial load under the influence of the wind.

A modulation speed when approaching the stable second load level can be accelerated with a coefficient, which can be a factor of 3, for example. In this way, the burner 1 is transferred more quickly to a higher load level in order to efficiently prevent the flameout.

In practice, a higher load level can lead to setpoint values for a flow temperature of a heating system being reached earlier.

3 shows a diagram that illustrates a typical course of the operating state of the burner 1 under the influence of wind. In 3 the ionization current generated and measured in the ionization electrode 5 (dotted line), the setpoint value specified for the ionization current (solid line) and the load level (dashed line) to which the burner is regulated are plotted against time. The information is in percent, with an ionization current of 100% being specified here at a load level of 30%.

After approx. 10 seconds, a load level of 30% is specified for the burner. Combustion is started and after about 30 seconds the burner reaches an ionization current of about 100%. The specified load level is now reduced to a first load level of 8%, which corresponds to the first operating state BZ1, and the first operating state BZ1 is reached in approximately 60 seconds. At about 75 seconds, a first wind event A occurs and the combustion is disrupted, so that a large deviation between the measured ionization current and the specified target value is determined. As a result, the control device transfers the burner to the second operating state BZ2 with a load level of 17.5%.

The second operating state BZ2 remains active for approximately 90 seconds. As can be seen in the diagram, the deviation between the measured ionization current and the specified target value remains relatively small, so that the control device gradually reduces the load level back to the first operating state.

The two load levels illustrated here between the first load level of the first operating state BZ1 and the second load level of the second operating state BZ2 are each for about 110 seconds active and amount to 13% and 10.5% respectively. At around 400 seconds on the time axis, the burner is switched back to the first operating state BZ1 at a load level of 8%.

At about 430 seconds on the time axis, a second wind event B occurs and the described process of transferring the burner to the second operating state BZ2 is carried out again. As a result, flameout in the burner can be prevented. An evaluation of the ionization current from the ionization electrode is sufficient for the regulation described. Since such an ionization electrode is present in most burners, the method according to the invention can be used with most burners without it being necessary to retrofit them with special sensors.

Although the exemplary embodiments have been described in connection with a gas boiler for a heating system, the method according to the invention for testing and calibrating a lambda probe can also be used in other applications in which a fuel is burned. The burner arrangement according to the invention is also not limited exclusively to the combustion of a gaseous fuel. The invention can also be used in an analogous manner in connection with an oil burner or a heating boiler in which wood is used as fuel. Appropriate modification would also make it possible to use the invention in an internal combustion engine.

The features disclosed in the above description, the claims and the drawings can be important both individually and in any combination for the implementation of the invention in its various configurations.

Reference List

1

burner

2

first adjusting device for air

3

second control device for gas

4

lambda probe

5

ionization electrode

6

Burner control (control device)

7

Control signal for air

8th

Gas control signal

9

ionization current

10

Lambda sensor current signal

Claims (7)

Method for operating a burner arrangement with a burner (1) that burns an air-fuel mixture, the method comprising the following method steps: Predetermining a target value for an ionization current; Operating the burner (1) in a first operating state at a first predetermined power level; measuring an ionization current (9) by means of an ionization electrode (5); Comparing the measured ionization current (9) with the predetermined target value and determining a deviation; and If the deviation exceeds a specified limit: Transferring the burner (1) to a second operating state at a second power level, where the second power level is higher than the first power level, wherein the second power level is determined as a function of the deviation, and a time duration of the deviation being determined and the second power level being determined as a function of the duration of the deviation. procedure after claim 1 , wherein the burner (1) is transferred back to the first operating state after a predetermined period of time has elapsed. procedure after claim 1 or 2 , wherein the transition from the first to the second operating state or from the second to the first operating state is carried out in stages via a power level or multiple power levels between the first and second power level. procedure after claim 3 , wherein the following method steps are carried out when transferring from the second to the first operating state in each power level between the first and second power level: operating the burner (1) at the current power level; measuring the ionization current (9); Comparing the measured ionization current (9) with the predetermined target value and determining the deviation; and If the deviation exceeds the predetermined limit value, transferring the burner (1) to the next higher power level. Method according to one of the preceding claims, in which the target value is specified as a function of the current power level. Method according to one of the preceding claims, in which a modulation speed of the burner (1) is accelerated by means of a coefficient when the burner (1) is transferred to a higher power level. A burner arrangement for a heating boiler, the burner arrangement comprising: a burner (1) for burning an air-fuel mixture; an ionization electrode (5) arranged on the burner (1) which protrudes into a flame during combustion and emits an ionization current (9); a control device (6) for controlling the combustion process, wherein the control device (6) is configured, the method according to one of Claims 1 until 6 to execute.

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