DE102020008001A1 - BURNER ARRANGEMENT, METHOD OF OPERATING A BURNER ARRANGEMENT, AND WIND FUNCTION - Google Patents

Abstract

The present disclosure relates to a method for operating a burner arrangement with a burner (1) which burns an air-fuel mixture. In one step of the method, a setpoint 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 by means of 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 performance level is higher than the first performance level. The second performance 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 which can prevent a flame out due to pressure fluctuations caused by wind.

A burner arrangement generally has a burner which is connected to the atmosphere via an exhaust system. Strong gusts of wind, such as those that occur in storms, can cause rapid changes in draft or overpressure in the exhaust system. This can cause pressure surges in the burner. Such pressure surges can lead to a flame out in the burner, which can result in toxic emissions. In addition, a calibration must be carried out when the burner is restarted after the flame has been interrupted. A calibration is necessary in the event of a flame failure in order to determine that the burner control is working, as the cause of the flame failure is not always clear. A calibration requires the burner to be forced to operate at a high load level. Here, a corresponding heat consumption in the heating system must be ensured, which may make further control measures necessary.

The present invention is based on the object of overcoming the problems known in the prior art and of providing a burner arrangement for a heating boiler which is improved over the prior art and of specifying a method for operating a burner arrangement. In particular, the aim is to prevent a flame out due to pressure surges in order to avoid toxic emissions and mandatory calibration. The measures to prevent the flame from stalling 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 which 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 performed at the same time. In particular, a fluid, that is to say gaseous or liquid fuel, for example natural gas or heating oil, can be used as the fuel.

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 level 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 setpoint value for an ionization current is specified. The ionization current can be measured by means of an ionization electrode which is arranged so that it is immersed in the flame.

The measured ionization current is then compared with the specified target value and a discrepancy 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 continues to operate in the first operating state. A small discrepancy exists in particular when the discrepancy is smaller than a predefined 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 at a higher partial load range than the first power level. The second performance level is therefore also referred to as "increased 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 level is raised to a higher partial load in the event of a greater deviation than in the event of a smaller deviation. Correspondingly, values or an algorithm according to which the second power level is determined as a function of the deviation can be stored in the control device.

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 act on the flame. This can prevent a flame out. Since the power level is determined as a function of the measured deviation, a conventional burner arrangement with ionization electrode can detect pressure fluctuations without additional sensors react in order to avoid the flame out. The method according to the invention can thus 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 time period can be determined as a function of the measured deviation, for example, or it can be a fixed value. This can prevent operation at an unnecessarily high power level over a long period of time. Since gusts of wind tend to be short-lived, a period of several seconds or a few minutes, for example, may be sufficient. In particular, the control device of the burner will attempt to transfer the burner to the lowest possible load level under the conditions, the conditions being able to be determined from the deviation between the measured ionization current and the nominal value.

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 via one power level or several power levels between the first and second power levels. By gradually increasing the power level, the burner arrangement can react to pressure fluctuations without modulating to a high power level. After each raising step, an ionization current can be measured again and compared with the nominal value. If the deviation is smaller than the limit value, it is possible to dispense with further raising the power level or even to modulate 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 compared again 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 output level. If the deviation does not exceed the limit value, the burner can continue to be operated in the current power level, or it can be transferred to a next lower power level after a predetermined period of time.

The nominal 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 nominal value of the ionization current is generally dependent on the power level to which the regulation is to take place.

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 out should be avoided, it is advantageous to operate the burner as quickly as possible at a higher output. This can be achieved by increasing a regulating 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 in the event of a storm. Since strong gusts of wind are to be expected more frequently during a storm, the burner is preferably switched to a higher, second power level in order to avoid a flame out.

The wind function described above can therefore regulate the burner's output level to a stable level if the flame threatens. Higher power levels require a higher pressure in the combustion chamber, which makes the flame more stable against flame detachment. The method according to the invention can therefore effectively prevent a flame out.

Figure list

Further advantageous configurations are described in more detail below with reference to an exemplary embodiment shown in the drawings, to which the invention is not limited, 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 a typical burner behavior under the influence of wind.

DETAILED DESCRIPTION OF THE INVENTION USING EXEMPLARY EMBODIMENTS

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

1 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 assembly has a burner 1 on, which has a first control device 2 for air and a second control device 3 for gas is supplied with a gas-air mixture. The first control device 2 can for example be an air blower. The second control device 3 can be designed as a proportional valve. At the burner 1 it is, for example, a 35kW gas burner. The burner 1 burns the gas-air mixture. Operation of the burner 1 is controlled by a control device 6th regulated or controlled with a burner control.

An ionization electrode 5 is near the burner 1 arranged and designed to generate an ionization current 9 to be measured and via a suitable signal line to the control device 6th or output the burner control. When operating the burner 1 During the combustion process, the ionization electrode protrudes 5 into the flame. The ionization electrode 5 is usually used for flame monitoring in gas burners, since the ionization current only flows when a flame is present 9 caused.

Furthermore, a lambda probe 4th in the exhaust gas flow of the burner 1 be arranged. A lambda probe 4th is used to measure the residual oxygen content in the exhaust gas. For a more detailed description of the lambda probe 4th and their function is waived in the following. In addition, the burner can 1 further 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 burner control 6th gives control signals 7th and 8th for air and gas to the first 2 and second 3 adjusting devices, 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, tats} actually available for combustion in relation to the minimum necessary stoichiometric air mass m _{L, st} that is required for complete combustion: $$\lambda =\frac{m_{\mathrm{L.},tats}}{m_{\mathrm{L.},st}},$$

If λ = 1, there is a stoichiometric combustion air ratio. This is the case when all fuel molecules react completely with the oxygen in the air, so that no oxygen remains in the exhaust gas and no unburned fuel. The case λ <1 means a 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 4th is not required for the present invention. The method according to the invention evaluates the signals from the lambda probe 4th not from. The method can therefore also be used for burners that do not have a lambda probe.

The burner control 6th records the output signals of the lambda probe 4th and the ionization electrode 5 and processes them further in order to regulate the combustion. The burner control 6th thus determines the control signals 7th and 8th for the first 2 and second 3 setting devices depending on the signals 9 and 10 . In particular, the burner control 6th control a load stage by means of the control signals or

The ionization signal 9 from the ionization electrode is used to detect a dangerous wind effect 5 evaluated. Gusts of wind can cause large deviations between the measured value of the ionization signal 9 and that obtained by the control device 6th cause specified setpoint.

In the following, the in 2 flowcharts shown, which represent the method according to the invention in a simplified manner, the operation of the burner 1 described in more detail with the wind function.

In the first operating state BZ1, the burner 1 operated in a first power level at partial load of, for example, 5.8% of the maximum load. The ionization electrode 5 measures the ionisation current _is I and outputs a corresponding ionization signal 9 to the automatic heating 6th which simultaneously serves as a control device for regulating the combustion and evaluates the ionization current.

The ionization signal 9 is compared with a predetermined nominal value I _soll and a Deviation δ = | I _is -I _should | _is between measured ionisation current I and setpoint value I _soll is determined. The degree of the deviation δ is evaluated on the basis of a predetermined limit value δ _max in order to determine from this a necessary increase in the burner load level. Pressure fluctuations due to wind have a negative influence on the 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 ) so will the burner 1 continued to operate 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 ) so will the burner 1 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 impending flameout. For example, a deviation of 15% of the ionization current from the nominal value can be specified as the limit value.

The performance range from the first performance level to the increased partial load (second performance 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 nominal value.

The increased partial load is, for example, 30% of the maximum load. The wind function according to the invention can also determine a time duration in which the limit value in the deviation of the ionization current is exceeded. A range of a lower time threshold, for example 0.1 seconds, is linearly subdivided up to an upper time threshold. The upper time threshold can be determined on the basis of a process cycle that is generated by the automatic firing system 6th is specified. For example, a duration of twenty revolutions of the automatic furnace can be used as the upper time threshold 6th can be specified.

The wind function thus raises the lower limit of the burner output. This remains active for a defined period of time, after which the burner can 1 modulate again to lower load levels. The lower part load can also be released in stages. If another wind event occurs, the control device can 6th the burner 1 Regulate to a higher load level until a level with stable combustion (deviation less than the limit value) is reached. Thus, the burner can 1 can be independently regulated to the lowest possible partial load under the influence of 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. This enables faster transfer of the burner 1 reached in a higher load level in order to efficiently prevent the flame from stalling.

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

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

After approx. 10 seconds, the burner is given a load level of 30%. The combustion is started and after approx. 30 seconds the burner reaches an ionization current of approx. 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 at approx. 60 seconds. A first wind event A occurs at approx. 75 seconds and the combustion is disturbed, so that a large discrepancy 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 approx. 90 seconds. As can be seen in the diagram, the deviation between the measured ionization current and the specified setpoint value remains relatively small, so that the control device carries out a gradual lowering of 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 active for about 110 seconds and amount to 13% and 10.5%, respectively. At approx. 400 seconds on the time axis, the burner is switched back to the first operating state BZ1 at a load level of 8%.

At approx. 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, a flame out in the burner can be prevented. 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 in most burners without the need for retrofitting 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. A use of the invention in an internal combustion engine would also be conceivable through appropriate modification.

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.

List of reference symbols

1

burner

2

first control device for air

3

second adjusting device for gas

4th

Lambda probe

5

ionization electrode

6th

Burner control system

7th

Control signal for air

8th

Control signal for gas

9

Ionization current

10

Current signal of the lambda probe

Claims (7)

A method for operating a burner arrangement with a burner (1) which burns an air-fuel mixture, the method comprising the following method steps: Specifying a setpoint 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 nominal value and determining a deviation; and If the deviation exceeds a specified limit value: Transferring the burner (1) to a second operating state at a second power level, where the second performance level is higher than the first performance level, wherein the second performance level is determined as a function of the deviation, and wherein a time duration of the deviation is determined and the second power level is determined as a function of the duration of the deviation. Procedure according to Claim 1 , the burner (1) being returned to the first operating state after a predetermined period of time has elapsed. Procedure according to 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 one power level or several power levels between the first and second power levels. Procedure according to Claim 3 , the following method steps being carried out during the transition 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 nominal 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, wherein the target value is specified as a function of the current power level. Method according to one of the preceding claims, wherein 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 burning process, wherein the control device (6) is configured, the method according to one of Claims 1 until 6th to execute.

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