EP4133214B1 - Method for operating a buner assembly and burner assembly for carrying out the method - Google Patents

Description

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

A burner arrangement generally has a burner that is connected to the atmosphere via an exhaust system. Strong gusts of wind, such as those that occur during storms, can cause rapidly changing drafts or overpressure 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, calibration must be carried out when the burner is restarted after a flameout. Calibration is necessary in the event of a flameout in order to determine whether the burner control is functioning, as the cause of the flameout is not always clear. Calibration requires the burner to be forced to run at a high load level. In this case, a corresponding heat loss in the heating system must be ensured, which may require further control measures. From the documents EP2549187A2 , DE10058417A1 and DE101 13468A1 Methods for operating a burner arrangement are known from the prior art.

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 that is improved compared to the prior art and of specifying a method for operating a burner arrangement. In particular, flameout due to pressure surges should be prevented in order to avoid toxic emissions and mandatory calibration. The measures for preventing 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 further 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 carried out simultaneously. In particular, a fluid, i.e. gaseous or liquid fuel can be used as the fuel, for example natural gas or heating 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 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 target value for an ionization current is specified. The ionization current can be measured using an ionization electrode that is positioned 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 continues to operate in the first operating state. A small deviation exists in particular if the deviation is smaller than a specified limit. If the deviation exceeds the specified limit, the burner can be transferred 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 power 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 depending on the deviation. This can be done, for example, in such a way that the second power level is increased to a higher partial load if the deviation is greater than if the deviation is smaller. The control device can store corresponding values or an algorithm according to which the second power level is determined depending on the deviation.

By increasing 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 loss. Since the power level is determined depending on the measured deviation, a conventional burner arrangement with ionization electrode can react to pressure fluctuations without additional sensors in order to prevent flame loss. The method according to the invention can therefore also be implemented in older devices.

After a specified period of time has elapsed, the burner arrangement can be returned to the first operating state. The period of time can be determined, for example, depending on the measured deviation or can be a fixed value. This can prevent operation at an unnecessarily high power level for a long time. Since gusts of wind tend to be short-lived, a period of several seconds or a few minutes can be sufficient. In particular, the burner control device will try to transfer the burner to the lowest possible load level under the conditions, whereby the conditions can be determined from the deviation between the measured ionization current and 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 step by step over 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 immediately modulating to a high power level. After each step of increasing, 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 increase the power level any further or it can even be modulated back to a lower power level.

When transferring from the second to the first operating state, the following process steps can be carried out in each power level between the first and second power levels:
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, the burner can be transferred to the next higher power level. If the deviation does not exceed the limit, the burner can continue to operate at the current power level or, after a specified period of time, be transferred to the next lower power level.

The setpoint 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 setpoint value of the ionization current is generally dependent on the power level to be regulated.

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 flameout is to be avoided, it is advantageous to operate the burner as quickly as possible at a higher power level, particularly in the event of an external disturbance, for example due to a gust of wind. This can be achieved by increasing a control speed, which can be achieved, for example, by means of a coefficient (or a factor) to increase the modulation speed, which is described in more detail below.

The modulation speed of the burner is a change in the burner output over time. This can also be understood as the ability of the burner to react to changing thermal requirements. With a burner with a high modulation speed, the burner output can therefore be advantageously adapted particularly quickly to a changing thermal requirement. In other words, with a burner with a high modulation speed, the burner output can be regulated to a higher (or lower) value in a short time.

In order to change the burner output, the amount of air supplied and the corresponding amount of fuel (or gas) supplied must be changed synchronously, i.e. essentially at the same time and to an extent proportional to one another, so that the resulting air ratio changes as little as possible (or as little as possible). The amount of air supplied can be controlled, for example, by regulating the speed of a fan for supplying air to the combustion chamber.

If the change in the amount of air supplied and the change in the amount of fuel supplied were not synchronized, combustion could result in high levels of toxic CO emissions. In addition, the flame could leave an optimal range of combustion (threatened flame extinction), meaning that it could be blown out by a gust of wind, for example. This effect can be advantageously counteracted by adjusting the control speed.

A gust of wind can create a rapid back pressure in the burner's exhaust system. In this situation, a sudden, unexpected change, in particular a reduction, in the amount of air available for combustion can occur. Turning the fan up can primarily lead to an increase in the amount of air available for combustion and compensate for the reduction. In this case, modulating the burner at the normal speed (normal, low modulation speed designed for undisturbed normal operation) can be too slow to react appropriately to the suddenly changed conditions. This could, for example, lead to a flameout. or lead to inefficient combustion with high emission levels. To avoid these negative effects, the burner's modulation speed can be increased by means of a coefficient (factor). Operation without a coefficient in this situation could mean having to make a bad compromise between saving the flame and a shift in the air ratio during modulations.

According to the invention, the modulation speed of the burner can be increased with a coefficient (factor) in the range of preferably three to eight. An exemplary modulation speed in the lower load range (partial load range of the burner output up to approximately 10% of maximum output) is approximately 1% per second for burners with a modulation degree of, for example, 1:20. In the upper load range (partial load range of the burner output from approximately 30% to 100% of maximum output), modulation can take place with a modulation speed of 15% per second. Which value is selected for the coefficient (factor) can depend in particular on the specific burner behavior, as well as on the modulation speed in the lower load range, which for some burners can be lower values instead of 1% per second, for example 0.7% per second to 0.8% per second.

Furthermore, the duration of the deviation between the measured ionization current and the setpoint can be determined, in particular in order to determine the second power level depending on the duration of the deviation. A longer duration of the deviation is an indication of stronger gusts of wind, for example during storms. Since strong gusts of wind are to be expected more frequently during storms, the burner is preferably switched to a higher second power level in order to avoid flame loss.

The wind function described above can therefore regulate the burner's power level to a stable level if the flame is about to break off. Higher power levels result in higher pressure in the combustion chamber, which makes the flame more stable against flame break-off. The method according to the invention can therefore effectively prevent flame break-off.

BRIEF DESCRIPTION OF THE CHARACTERS

Further advantageous embodiments are described in more detail below with reference to an embodiment shown in the drawings, to which the invention is, however, not limited.

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

They show schematically:

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

DETAILED DESCRIPTION OF THE INVENTION USING EXEMPLARY EMBODIMENTS

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

Fig.1 illustrates an embodiment of a burner arrangement according to the invention, which can 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 control device 2 for air and a second control device 3 for gas. The first control device 2 can be, for example, an air blower (e.g. a speed-controlled fan). The second control 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 system.

An ionization electrode 5 is arranged near the burner 1 and is designed to measure an ionization current 9 and to output it to the control device 6 or the automatic firing system via a suitable signal line. When the burner 1 is in operation, i.e. during combustion, the ionization electrode 5 extends 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 probe 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 comprise further components, such as an ignition, exhaust gas paths and temperature sensors, which are not shown here because they are not necessary for the description of the present invention.

The combustion control unit 6 outputs control signals 7 and 8 for air and gas to the first 2 and second 3 control devices, so that the air ratio λ required for the respective application can be set during an operating phase and, if necessary, kept constant. The air ratio λ is a dimensionless parameter 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 stoichiometric air mass m _L,st that is required for complete combustion: $$\lambda =\frac{m_{L,\mathit{fact}}}{m_{L,\mathit{st}}},$$

If λ = 1, the combustion air ratio is stoichiometric. 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 present in the air. The case λ > 1 means an excess of air and is also referred to as a lean mixture.

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

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

To detect a dangerous wind influence, the ionization signal 9 is evaluated by the ionization electrode 5. Gusts of wind can cause large deviations of the measured value of the ionization signal 9 from the setpoint value specified by the control device 6.

In the following, the Fig.2 The operation of the burner 1 with the wind function is described in more detail in the flow chart shown, which illustrates the method according to the invention in a simplified manner.

In the first operating state BZ1, the burner 1 is operated in a first power level at partial load of, for example, 5.8% of the maximum load. The ionization electrode 5 measures the ionization current _I and outputs a corresponding ionization signal 9 to the automatic firing system 6, which simultaneously serves as a control device for regulating the combustion and carries out an evaluation of the ionization current.

The ionization signal 9 is compared with a specified target value I _target and a deviation δ = | I _actual - I _target | between the measured ionization current I _actual and the target value I _target is determined. The degree of deviation δ is determined using a specified limit value δ _max in order to determine the required increase in the burner load level. Pressure fluctuations due to wind have a negative influence on combustion and the measured ionization current can therefore deviate from the target value.

If the deviation is smaller than the limit (no in Fig.2 ), burner 1 continues to operate in the first operating state BZ1 at the first power level. However, if the deviation is greater than the specified limit (yes in Fig.2 ), burner 1 is transferred to a second operating state BZ2, in which burner 1 is operated at a higher load level. This increase is intended to prevent the flame from breaking off. A limit value can be specified, for example, as a deviation of 15% of the ionization current from the setpoint.

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 Fig.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 setpoint.

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 for the limit value to be exceeded in the deviation of the ionization current. In this case, a range of a lower time threshold, for example 0.1 seconds, up to an upper time threshold is divided linearly. The upper time threshold can be determined using a process timing that is specified by the automatic firing system 6. For example, a duration of twenty cycles of the automatic firing system 6 can be specified as the upper time threshold.

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 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 is reached. (deviation smaller than the limit value) is reached. This means that burner 1 can be automatically regulated to the lowest possible partial load under the influence of wind.

A modulation speed when starting up the stable second load level can be accelerated with a coefficient, which can be a factor of 3 to 8, for example. This allows the burner 1 to be transferred more quickly to a higher load level in order to efficiently prevent the flame from breaking off. In other words, the modulation speed of the burner 1 is increased by the control device 6 (in particular for a short time) in order to operate the burner 1 at the optimum air ratio even in the event of an external disturbance (e.g. due to a gust of wind).

In practice, a higher load level can lead to an earlier achievement of the setpoint values of a heating system's flow temperature.

Fig.3 shows a diagram illustrating a typical course of the operating state of burner 1 under wind influence. In Fig.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 figures are in percent, whereby an ionization current of 100% is specified here for a load level of 30%.

After about 10 seconds, a load level of 30% is specified for burner 1. Combustion is started and after about 30 seconds, burner 1 reaches an ionization current of about 100%. The specified load level is then reduced to a first load level of 8%, which corresponds to the first operating state BZ1, and after about 60 seconds, the first operating state BZ1 is reached. After about 75 seconds, a first wind event A occurs and combustion is disrupted, so that a large deviation is determined between the measured ionization current and the specified target value. As a result, the control device transfers burner 1 to the second operating state BZ2 with a load level of 17.5%.

The second operating state BZ2 remains active for about 90 seconds. As can be seen in the diagram, the deviation between the measured ionization current and the specified Setpoint is 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 active for around 110 seconds and amount to 13% and 10.5% respectively. At around 400 seconds on the time axis, the burner is returned to the first operating state BZ1 at a load level of 8%.

At approximately 430 seconds on the time axis, a second wind event B occurs and the described process of transferring burner 1 to the second operating state BZ2 is carried out again. As a result, a flame break in the burner can be prevented. For the described control, evaluating the ionization current from the ionization electrode is sufficient. 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 embodiments were 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. By appropriate modification, the invention could also be used in an internal combustion engine.

The features disclosed in the above description, the claims and the drawings may be important both individually and in any combination for the realization of the invention in its various embodiments.

LIST OF REFERENCE SYMBOLS

1

burner

2

first control device for air

3

second control device for gas

4

Lambda sensor

5

ionization electrode

6

Burner control unit (control device)

7

Control signal for air

8th

Control signal for gas

9

ionization current

10

Current signal of the lambda sensor

Claims (8)

1. Method for operating a burner arrangement having a burner (1) which burns an air/fuel mixture, wherein the method comprises the following method steps:

   predefining a setpoint value for an ionization current;

   operating the burner (1) in a first operating state at a first predefined power level;

   measuring an ionization current (9) by means of an ionization electrode (5);

   comparing the measured ionization current (9) with the predefined setpoint value and determining a deviation; and

   if the deviation exceeds a predefined limit value:

   transferring the burner (1) into a second operating state at a second power level,

   wherein the second power level is higher than the first power level, and

   wherein the second power level is determined as a function of the deviation.
2. Method according to Claim 1, wherein the burner (1) is transferred back into the first operating state after a predefined time period has elapsed.
3. Method according to Claim 1 or 2, wherein the transfer from the first into the second operating state or from the second into the first operating state is carried out in stages via one power level or a plurality of power levels between the first and second power level.
4. Method according to Claim 3, wherein, during the transfer from the second into the first operating state in each power level between the first and second power level, the following method steps are carried out:

   operating the burner (1) at the current power level;

   measuring the ionization current (9);

   comparing the measured ionization current (9) with the predefined setpoint value and determining the deviation; and

   if the deviation exceeds the predefined limit value, transferring the burner (1) into the next higher power level.
5. Method according to one of the preceding claims, wherein the setpoint value is predefined as a function of the current power level.
6. Method according to one of the preceding claims, wherein a modulation speed of the burner (1) is accelerated by means of a coefficient during the transfer of the burner (1) into a higher power level.
7. Method according to one of the preceding claims, 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.
8. Burner arrangement for a heating boiler, wherein the burner arrangement comprises:

   a burner (1) for burning an air/fuel mixture;

   an ionization electrode (5) which is arranged on the burner (1) and which projects into a flame during the combustion and outputs an ionization current (9);

   a regulating device (6) for regulating the burning process, wherein the regulating device (6) is configured to carry out the method according to one of Claims 1 to 7.

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