Method for Controlling a Burner and Burner Arrangement having a Burner

Abstract

A method of regulating a burner which is supplied with an air-fuel mixture includes: determining a regulating variable based on an ionization signal, the air-fuel mixture being set depending on the regulating variable and a setpoint value; obtaining a spectrum from the ionization signal, from which a measure for a surface area is determined; and adjusting the setpoint value depending on the measure for the surface area. Also described is a burner arrangement including a burner.

Claims

1-6. (canceled)

7. A method of regulating a burner, the method comprising: supplying the burner with an air-fuel mixture; measuring an ionization signal; determining a regulating variable based on the ionization signal; setting the air-fuel mixture depending on the regulating variable and at least one setpoint value; obtaining, by a Fourier transformation, a spectrum from the ionization signal; determining a value of an area under the spectrum or under at least one frequency range of the spectrum; and adjusting the at least one setpoint value depending on the value of the area.

8. The method of claim 7, wherein determining the regulating variable based on the ionization signal comprises: determining at least one absolute value of an ionization voltage from the ionization signal; and using the at least one absolute value of the ionization voltage as the regulating variable.

9. The method of claim 8, wherein a plurality of individual absolute values of the ionization voltage is determined from the ionization signal, the method further comprising: determining a distribution of the individual absolute values; and adjusting the regulating variable depending on the distribution.

10. The method of claim 9, wherein an average value and the distribution are determined from the individual absolute values, and wherein the regulating variable is determined as a difference between the average value and the distribution.

11. The method of claim 7, wherein the air-fuel mixture is set depending on the regulating variable by a PID controller.

12. A burner arrangement, comprising: a burner; a heat exchanger; an ionization electrode configured to measure an ionization signal; an air-fuel-mixture supply configured to supply an air-fuel mixture to the burner; and a control device configured to: determine a regulating variable based on the ionization signal; act on the air-fuel-mixture supply to set the air-fuel mixture for the burner depending on the regulating variable and at least one setpoint value; obtain, by a Fourier transformation, a spectrum from the ionization signal; determine a value of an area under the spectrum or under at least one frequency range of the spectrum; and adjust the at least one setpoint value depending on the value of the area.

13. The burner arrangement of claim 12, wherein the control device is configured to determine at least one absolute value of an ionization voltage from the ionization signal and use the at least one absolute value of the ionization voltage as the regulating variable.

14. The burner arrangement of claim 13, wherein the control device is configured to determine a plurality of individual absolute values of the ionization voltage from the ionization signal, and wherein the control device is further configured to determine a distribution of the individual absolute values and adjust the regulating variable depending on the distribution.

15. The burner arrangement of claim 14, wherein the control device is configured to determine an average value and the distribution from the individual absolute values, and determine the regulating variable as a difference between the average value and the distribution.

16. The burner arrangement of claim 12, wherein the control device comprises a PID controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] More specifically, there are numerous possibilities for designing and further developing the method according to the invention and the burner arrangement according to the invention. For this purpose, reference is made, on the one hand, to the claims subordinate to the independent claims and, on the other hand, to the description below of example embodiments in conjunction with the drawing, in which:

[0029] FIG. 1 shows a schematic bloc diagram of a burner arrangement according to the invention,

[0030] FIGS. 2a) and b) show spectra without and with thermoacoustic effects,

[0031] FIGS. 3a) and b) show curve courses of the ionization voltage and the area number at different outputs of the burner,

[0032] FIG. 4 shows curve courses of the air ratio and the ionization voltage over time, and

[0033] FIG. 5 shows two curves with a value of the ionization voltage and a regulating variable determined therefrom as a function of the air ratio.

DETAILED DESCRIPTION

[0034] FIG. 1 schematically shows a burner arrangement comprising a burner 1 which is supplied with an air-fuel mixture via an air-fuel mixture supply 2. The fuel may be, for example, a combustible gas such as propane or butane. The flue gas generated by the combustion of the air-fuel mixture is supplied to a heat exchanger 3 which transfers the thermal energy to water or air. An ionization electrode 4 is provided for monitoring the combustion process, which is arranged relative to the burner 1 so as to project into the flame generated upon combustion. Depending on the design, an ionization voltage or an ionization current can be measured as an ionization signal via the ionization electrode 4. The ionization signal is fed to the control device 5 for evaluation. Based on the regulating variable thus obtained, the control device 5 acts on the air-fuel-mixture supply 2 by changing the fuel and/or air proportion, for example. This with the aim that the combustion takes place with as few emissions and as little noise as possible.

[0035] FIG. 2 to FIG. 5 exemplarily illustrate the evaluation of the ionization signal, wherein in particular thermoacoustic effects occur as disturbances. These noises are then avoided or at least reduced by changing the mixture ratio.

[0036] FIG. 2a) shows a spectrum of the ionization signal obtained by a FFT without audible thermoacoustic resonance. The frequency is plotted in Hz on the x-axis. The signal was obtained at an air ratio of 1.2. A signal of the mains voltage is appears at 50 Hz.

[0037] In FIG. 2b), a signal around 104 Hz appears in the spectrum, which is accompanied by an audible thermoacoustic resonance. The spectrum was obtained at an air ratio of 1.6.

[0038] According to one embodiment, a surface area is determined in a frequency range of the spectrum and used for a regulating variable during evaluation to reduce the resonance in the spectrum of FIG. 2b).

[0039] FIGS. 3a) and b) show the courses of the average values of the voltage values of the ionization signals (solid line and left y-axis) and the determined area numbers (dashed line and right y-axis) as a function of the air ratio. The graphs differ from each other in terms of the output obtained with the burner: in FIG. 3a), the power is 1 kW, and in FIG. 3b) 3,5 KW.

[0040] FIG. 3a) shows the case in which no thermoacoustic resonance is generated when the air ratio is changed. The higher the air ratio, the more the amount of the ionization voltage decreases. As no noises are generated, there is no additional signal in the spectrum so that the integral of the frequency range, i.e. the area number, remains constant.

[0041] In case of a higher power of the burner, the course changes significantly. In FIG. 3b), the amount of the ionization voltage decreases again, whereas a considerable increase in the area number can be seen at the air ratio of 1.6 (cf. FIG. 2b)). It has to be noted that in this range, the ionization voltage shows a very flat course. If the area number changes significantly, the setpoint value is corrected, with which the amount of the ionization voltage is used as a regulating variable for regulating the combustion process.

[0042] FIG. 4 shows the variations which result from the measured values of the ionization voltage if disturbances occur. The lambda value is plotted on the outer y-axis, and the amount of the ionization voltage is plotted on the inner y-axis. The time is plotted on the x-axis. The lambda values were increased in discrete steps, as can be seen in the staircase shape of the dashed line.

[0043] The curve generally shows that the ionization voltage decreases as the lambda value increases. It can also be seen that there is a direct correlation with the voltage for each air ratio set. However, it can also be seen that the voltage values can vary greatly if there are disturbances. In the test here, these are clearly audible thermoacoustic resonances which occur at lambda=1.6 and lambda=1.7 (from approx. 180 seconds). The variations even have a clearly recognizable effect on the average value. The distribution alone is therefore also an indicator for the presence of a disturbance.

[0044] Two curves are plotted in FIG. 5, one value being respectively plotted for the ionization voltage as a function of the lambda value.

[0045] In the solid curve, one unprocessed average value of the ionization voltage is respectively plotted. In the dashed curve, the difference between the average value and the associated distribution was calculated.

[0046] The decrease of the voltage is again recognizable from the solid curve. Due to the distribution in the range of the thermoacoustic effects, the average value in the range between lambda=1.5 and 1.6 is increased and remains nearly constant. The effect of this behavior on the regulation is indicated here. If, for example, the value of 1.4 V were specified as a setpoint value for the ionization voltage, two lambda values would thus be associated therewith. This means that the pure observation of the ionization voltage is not sufficient for regulation.

[0047] In the dashed curve, the distribution was respectively subtracted from the average value of the ionization voltage. The curve shifts downwards accordingly. A dramatic effect occurs in the range greater than 1.5 for lambda. The calculated value at lambda=1.6 differs significantly from the previous value at lambda=1.5. The increased distribution compensates for the increase in the average value. This results in a steadily decreasing course which allows clear regulation. Therefore, when the calculated voltage value decreases as a regulating variable in the range of the thermoacoustic resonance, the controller would determine that the regulating variable is smaller than a setpoint value and would then regulate the operating point in the rich range with a smaller lambda value.