BURNER ASSEMBLY, METHOD FOR OPERATING A BURNER ASSEMBLY, AND WIND FUNCTION

Abstract

The present disclosure relates to a method for operating a burner assembly comprising a burner (1) burning an air-fuel mixture. In a 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 specified power level. The ionization current (9) is measured using an ionization electrode (5). The measured ionization current (9) is compared with the predefined target value and a deviation is determined. When the deviation exceeds a predefined threshold value, the burner (1) is transitioned 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 as a function of the deviation.

Claims

1. A method for operating a burner assembly comprising a burner burning an air-fuel mixture, said method comprising the method steps of: specifying a target value for an ionization current; operating said burner in a first operating state at a first specified power level; measuring an ionization current by means of an ionization electrode; comparing the measured ionization current with the specified target value and determining a deviation; and when the deviation exceeds a specified limit: transitioning said burner to 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. The method according to claim 1, wherein said burner is transitioned back to the first operating state after a predetermined period of time has elapsed.

3. The method according to claim 1, wherein the transition from the first to the second operating state or from the second to the first operating state is carried out in steps via one power level or a plurality of power levels between the first and second power level.

4. The method according to claim 3, wherein the following method steps are 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 said burner at the current power level; measuring the ionization current; comparing the measured ionization current with the predetermined target value and determining the deviation; and when the deviation exceeds the specified limit value, transitioning said burner to the next higher power level.

5. The method according to claim 1, wherein the target value is specified as a function of the current power level.

6. The method according to claim 1, wherein a modulation rate of said burner when transitioning said burner to a higher power level is made faster by means of a coefficient.

7. The method according to claim 1, 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. A burner assembly for a heating boiler, said burner assembly comprising: a burner for burning an air-fuel mixture; an ionization electrode which is arranged on said burner, protrudes into a flame during combustion and outputs an ionization current; a control device for controlling the combustion process, wherein said control device is configured to carry out a method comprising: specifying a target value for an ionization current; operating said burner in a first operating state at a first specified power level; measuring an ionization current by means of the ionization electrode; comparing the measured ionization current with the specified target value and determining a deviation; and when the deviation exceeds a specified limit: transitioning said burner to 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Further advantageous developments are described in more detail below with reference to an exemplary embodiment illustrated in the drawings, to which the invention is not restricted, however.

[0027] In the figures:

[0028] FIG. 1 shows a burner assembly according to an exemplary embodiment of the invention.

[0029] FIG. 2 shows an exemplary embodiment of a method according to the invention.

[0030] FIG. 3 shows a diagram illustrating typical burner behavior under the influence of wind.

DETAILED DESCRIPTION OF THE INVENTION BASED ON EXEMPLARY EMBODIMENTS

[0031] In the following description of a preferred embodiment of the present invention, the same reference symbols designate the same or comparable components.

[0032] FIG. 1 illustrates an exemplary embodiment of a burner assembly according to the invention, which may be used for example in a boiler of a heating system for a building. The boiler may be, for example, a conventional gas boiler or a condensing boiler.

[0033] The burner assembly includes 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 may be, for example, an air fan (e.g., a speed-controlled fan). The second adjusting device 3 may be configured 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 unit.

[0034] An ionization electrode 5 is arranged in the vicinity of the burner 1 and is configured to measure an ionization current 9 and to output it to the control device 6 or the automatic firing control unit via a suitable signal line. When the burner 1 is in operation, i.e. 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.

[0035] Furthermore, a lambda probe 4 may 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 may 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.

[0036] The automatic firing unit 6 outputs control signals 7 and 8 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 characterizing the mass ratio of air to fuel in a combustion process. The combustion air ratio puts the air mass m.sub.L,tats actually available for combustion in relation to the minimum stoichiometric air mass m.sub.L,st necessary for complete combustion.

[00001]$\lambda =\frac{m_{L,\mathrm{tats}}}{m_{L,\mathrm{st}}},$

[0037] If λ=1, the combustion air ratio is stoichiometric. This occurs when all of the fuel molecules fully react 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.

[0038] The lambda probe 4 shown in FIG. 1 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.

[0039] The automatic firing unit 6 records the output signals from the lambda probe 4 and the ionization electrode 5 and processes them further in order to control the combustion. Therefore, the automatic firing unit 6 determines the control signals 7 and 8 for the first 2 and second 3 adjusting devices as a function of the signals 9 and 10. In particular, the automatic firing unit 6 may control a load level using the control signals.

[0040] The ionization signal 9 is evaluated by the ionization electrode 5 in order to detect dangerous wind influence. Wind gusts may cause large deviations in the measured value of the ionization signal 9 from the target value specified by the control device 6.

[0041] The operation of the burner 1 with the wind function is described in more detail below with reference to the flow chart shown in FIG. 2, which shows the method according to the invention in a simplified manner.

[0042] In the first operating state BZ1, the burner 1 is operated at a first power level at partial load of, for example, 5.8% of the maximum load. The ionization electrode 5 measures the ionization current list and outputs a corresponding ionization signal 9 to the firing control unit 6, which at the same time serves as a control device for controlling the combustion and evaluates the ionization current.

[0043] The ionization signal 9 is compared with a specified target value I.sub.soil and a deviation δ=|I.sub.ist−I.sub.soil| between the measured ionization current I.sub.ist and the target value I.sub.soil is determined. The degree of deviation δ is evaluated using a specified limit value δ.sub.max in order to determine a required increase in the burner load level therefrom. Pressure fluctuations due to wind have a negative impact on combustion and the measured ionization current may therefore deviate from the target value.

[0044] When the deviation is less than the limit value (No in FIG. 2), the burner 1 continues to operate in the first operating state BZ1 at the first power level. However, when the deviation is greater than the specified limit value (Yes in FIG. 2), then the burner 1 is transitioned to a second operating state BZ2 in which burner 1 is operated at a higher load level. This raise is intended to prevent an imminent flameout. For example, a deviation of 15% of the ionization current from the target value may be specified as a limit value.

[0045] The power range from the first power level to the increased partial load (second power level) may be divided into five intermediate levels, for example (not shown in FIG. 2). The burner 1 may be operated at each level 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 target value.

[0046] The increased partial load is, for example, 30% of the maximum load. The wind function according to the invention may also determine the duration of the excess 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 may be determined on the basis of a process clock that is specified by the automatic firing unit 6. For example, a duration of twenty revolutions of the automatic firing unit 6 may be specified as the upper time threshold.

[0047] Thus, the wind function raises the lower limit of the burner power. This remains active for a defined period of time after which the burner 1 may modulate to lower load levels again. The enabling of the lower partial load may also happen in steps. If another wind event occurs, the control device 6 may control 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 controlled to the lowest possible partial load under the influence of the wind.

[0048] A modulation rate when approaching the stable second load level may be accelerated with a coefficient, which may be a factor of 3 to 8, for example. In this way, the burner 1 is transitioned more quickly to a higher load level in order to efficiently prevent the flameout. In other words, the modulation rate of the burner 1 is increased by the control device 6 (in particular for a short time) in order to operate the burner 1 with an optimal air ratio even in the event of an external disturbance (e.g., due to a gust of wind).

[0049] In practice, a higher load level may result in target values for a flow temperature of a heating system being reached earlier.

[0050] FIG. 3 shows a diagram that illustrates a typical course of the operating state of the burner 1 under the influence of wind. In FIG. 3, the ionization current generated and measured in the ionization electrode 5 (dotted line), the target value specified for the ionization current (solid line) and the load level (dashed line) to which the burner is controlled are plotted over time. The information is in percent, with an ionization current of 100% being specified at a load level of 30% here.

[0051] After approximately 10 seconds, a load level of 30% is specified for burner 1. Combustion is started and, after about 30 seconds, the burner 1 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 about 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 transitions the burner 1 to the second operating state BZ2 with a load level of 17.5%.

[0052] The second operating state BZ2 remains active for approximately 90 seconds. As is apparent in the diagram, the deviation between the measured ionization current and the specified target value remains relatively small so that the control device reduces the load level back to the first operating state in a stepwise manner.

[0053] 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 approximately 110 seconds and amount to 13% and 10.5%, respectively. At around 400 seconds on the time axis, the burner is transitioned back to the first operating state BZ1 with a load level of 8%.

[0054] At about 430 seconds on the time axis, a second wind event B occurs and the described process of transitioning the burner 1 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 control described. Since such an ionization electrode is present in most burners, the method according to the invention can be used for most burners without a retrofit with special sensors being necessary.

[0055] Although the exemplary embodiments have been described in relation to a gas boiler for a heating system, the method according to the invention for testing and calibrating a lambda probe may also be used in other applications in which a fuel is burned. The burner assembly according to the invention is also not limited exclusively to the combustion of a gaseous fuel. The invention may also be used in an analogous manner in relation to 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.

[0056] The features disclosed in the above description, the claims and the drawings may be significant for the implementation of the invention in its various configurations both individually and in any combination.

LIST OF REFERENCE SYMBOLS

[0057] 1 burner [0058] 2 first adjusting device for air [0059] 3 second adjusting device for gas [0060] 4 lambda probe [0061] 5 ionization electrode [0062] 6 automatic firing unit (control device) [0063] 7 control signal for air [0064] 8 control signal for gas [0065] 9 ionization current [0066] 10 current signal of lambda probe