Method of monitoring a burner and/or a burning behavior of a burner and burner assembly

Abstract

This invention relates to a method of monitoring a burner (2) and/or a burning behavior of a burner (2) by means of a measured ionization signal. The invention consists in that the ionization signal is measured between an ionization electrode (4, 4′) and a counter-electrode (3) spaced apart from a burner surface (2′) of the burner (2). Furthermore, the invention relates to a burner assembly.

Claims

1. (canceled)

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. A method of monitoring a burner and/or a burning behavior of a burner, wherein at least one ionization signal is measured, and wherein the measured ionization signal is used for monitoring the burner and/or the burning behavior of the burner, and wherein the ionization signal is measured between an ionization electrode and a counter-electrode spaced apart from a burner surface of the burner, wherein for a calibration and/or for a determination of parameters used when monitoring the burner ionization signals are measured during a hyperstoichiometric combustion, and that a local extremum of the ionization signal is determined during the hyperstoichiometric combustion in dependence on a lambda-value of an air-fuel mixture supplied to the burner and is used for the calibration and determination.

9. The method according to claim 8, wherein a heat exchanger is used as a counter-electrode.

10. The method according to claim 8, wherein the ionization signal is measured between the ionization electrode and the counter-electrode by electrically connecting the counter-electrode and the burner surface to ground.

11. A burner assembly comprising a burner, a heat exchanger, at least one ionization electrode, an air-fuel mixture supply unit for the burner, and a control device, wherein the control device is connected to the at least one ionization electrode, and wherein based on ionization signals measured by means of the at least one ionization electrode the control device monitors the burner and/or a burning behavior of the burner, wherein for monitoring the burner and/or a burning behavior of the burner the control device uses at least one ionization signal measured between the ionization electrode and the heat exchanger as a counter-electrode, wherein for a calibration and/or for a determination of parameters used when monitoring the burner, the control device leans the air-fuel mixture supplied to the burner via the air-fuel mixture supply unit, and evaluates ionization signals measured by means of the leaned air-fuel mixture, and that for the calibration or the determination of the parameters the control device determines a local extremum of the ionization signals by means off the leaned air-fuel mixture.

12. The burner assembly according to claim 11, wherein the ionization electrode is arranged in an area of plus/minus 20% around a mean distance between a burner surface and the heat exchanger.

Description

[0047] In detail, there is a wide variety of possibilities for designing and further developing the method and the burner assembly according to the invention. On the one hand, reference is made to the claims subordinate to the independent claims, and on the other hand to the following description of exemplary embodiments in conjunction with the drawing. In the drawing:

[0048] FIG. 1 shows a schematic block circuit diagram of a burner assembly according to the invention;

[0049] FIG. 2 shows a section through a schematic block circuit diagram of an alternative embodiment of a burner assembly according to the invention,

[0050] FIG. 3 shows two measurement curves of the ionization voltage for two ionization electrodes at different distances to the burner surface, wherein only the burner surface is connected to ground, and

[0051] FIG. 4 shows two measurement curves of the aforementioned two ionization electrodes, wherein the burner surface and the surrounding heat exchanger are connected to ground, and

[0052] FIG. 5 shows two measurement curves of the aforementioned two ionization electrodes, wherein only the heat exchanger surrounding the burner surface is connected to ground.

[0053] FIG. 1 schematically shows a burner assembly 1 comprising a burner 2 to which an air-fuel mixture is supplied via an air-fuel mixture supply unit 5. The fuel for example is a combustible gas such as propane or butane, or diesel that has been transferred into the gaseous state.

[0054] The air-fuel mixture is burnt by the burner 2, wherein here a—non-illustrated—flame is formed above the burner surface 2′ of the burner 2.

[0055] The burner surface 2′ is surrounded by a heat exchanger 3 in which the heat generated by the burning process—in the form of the flame and the flue gas generated—is transmitted to another medium, e.g. to water or a glycol-water mixture.

[0056] The heat exchanger 3 is designed to be electrically conductive at least partly and preferably on the inside facing the burner surface 2′. This conductivity allows to electrically connect the heat exchanger 3 to ground or to measure the ionization voltage via the at least one ionization electrode 4 opposite the heat exchanger 3.

[0057] For monitoring or controlling the burning process—in the illustrated embodiment—only one ionization electrode 4 is used, by means of which an ionization signal (here for example the ionization voltage) is measured. Alternatively, an ionization current can be measured.

[0058] For measuring the voltage (alternatively the current), either the burner surface 2′ of the burner 2 or the aforementioned, at least partly electrically conductive inner surface of the heat exchanger 3 is connected to ground so that the ionization electrode 4 is used for measuring the ionization voltage with respect to the burner 2 or with respect to the heat exchanger 3. In one embodiment it is also provided that the heat exchanger 3 and the burner surface 2′ are connected to the same ground so that the ionization signal is measured by the ionization electrode 4 opposite both of them as a counter-electrode.

[0059] Depending on the variant or method step, the ionization signal thus is measured by the at least one ionization electrode 4 by using the burner surface 2′, by using the heat exchanger 3 as a single counter-electrode, or by using the burner surface 2′ and the heat exchanger 3 as a common counter-electrode. These three ionization signals measured in different ways then are processed individually or jointly and used for monitoring the burner 2 or as a control variable of the burning behavior of the burner 2.

[0060] In one embodiment, the burner surface 2′ and the heat exchanger 3 are connected to the same ground so that the ionization signal is measured with respect to the burner surface 2′ and the heat exchanger 3. The possibilities between which components the electrical voltage is measured are indicated by the double arrows in the Figure.

[0061] The ionization electrode 4 is connected to the control device 6, which evaluates or processes the measurement signal (i.e. the ionization signal) and which acts on the air-fuel mixture supply 5 unit proceeding from the measured values. This is effected e.g. by regulating the fuel quantity or e.g. by controlling an air-conveying blower not shown here. The action of the control device 6 on the control of the burning process is indicated by the dashed arrow.

[0062] In one embodiment, the control device 6 acts on a—non-illustrated—starting device for starting a burning process, in case the ionization signal e.g. reveals that no flame is burning. Thus, the assembly 1 also allows monitoring of the flame.

[0063] The section of FIG. 2 shows a burner assembly 1 comprising two ionization electrodes 4, 4′ which are radially located at different distances between the burner surface 2′ and the inside of the heat exchanger 3. It can be seen that in this embodiment the burner surface 2′ has a circular cross-section that is surrounded by the inner wall of the circular cylindrical heat exchanger 3. The representation is not true to size.

[0064] In one embodiment, the burner surface 2′ has a diameter of 50 mm, wherein the distance between the burner surface 2′ and the inner edge of the heat exchanger 3 is 38 mm. The two ionization electrodes 4, 4′ in this exemplary embodiment have a distance between 5 mm and 9 mm (for the ionization electrode 4′ located closer to the burner surface 2′) or between 14 mm and 22 mm (for the ionization electrode 4 located further away from the burner surface 2′) to the outer surface of the burner surface 2′.

[0065] The position of the inner ionization electrode 4′ corresponds to the design known in the prior art. The small distance to the burner surface 2′ has the advantage that the probability is high that the ionization electrode 4′ projects directly into a flame. Thus, this relates in particular to the use of the ionization electrode 4′ for flame detection.

[0066] The radially further outer ionization electrode 4 here is located in an area around a mean distance between the burner surface 2′ and the inner edge of the heat exchanger 3.

[0067] For measuring the ionization signal, the inner wall of the heat exchanger 3 in one variant is connected to ground and the electrical ionization signal is measured via the ionization electrode 4 with respect to this ground.

[0068] The diagrams of FIGS. 3 to 5 show exemplary measurements that illustrate the course of the curves. The measured values are greatly dependent on the given dimensions of each of the components of the burner assembly or e.g. also on the power at which the burner is operated.

[0069] FIG. 3 shows two ionization voltages that have been measured by means of the two ionization electrodes 4, 4′ of the embodiment of FIG. 2.

[0070] The voltages (on the y-axis, the voltages are plotted with a negative sign) each have been measured with respect to the burner surface 2′, which was connected to ground. Thus, this measurement corresponds to the prior art. In the measurements, the heat exchanger 3 each was electrically isolated from the burner surface 2′. The x-axis shows the lambda value increasing from left to right. Thus, the mixture becomes leaner from left to right.

[0071] It is shown how proceeding from a maximum (designated by an arrow) in the region of lambda=1, the voltage values each become smaller with increasing lambda value—hence a lean fuel-air ratio. This course of the signal falling from a maximum is reproducible in general and is known from the prior art.

[0072] FIG. 4 shows the courses of the voltage values when the voltages are measured between the respective ionization electrode 4, 4′ on the one hand and both the burner surface 2′ and the surrounding heat exchanger 3 of the embodiment of FIG. 2 on the other hand. In contrast to the measurements of FIG. 3, the burner surface 2′ and the heat exchanger 3 are electrically connected to each other and thus to the same ground.

[0073] The upper curve was measured by means of the ionization electrode 4′, which is positioned closer to the burner surface 2′. The lower curve originates from the measurement by the ionization electrode 4 located further away from the burner surface 2′.

[0074] It can be clearly seen that the voltage of the ionization electrode 4′ located closer to the burner surface 2′ shows the known falling course of the ionization signal.

[0075] The ionization signal of the ionization electrode 4 located further away initially is falling proceeding from the maximum at lambda=1, in order to then rise again after a local minimum—which here accordingly is the local extremum sought for. In the further—non-illustrated—course of the measurement curve, the amplitude of this ionization signal, too, is falling towards zero like in the curve of the ionization electrode 4′ located closer to the burner surface 2′.

[0076] Thus, in this leaned area a local minimum is obtained, which is used for calibration. In the Figure, this minimum is designated by an arrow.

[0077] A number of experiments have revealed that the local minimum mostly occurs between lambda=1.4 and lambda=1.6. In the measurement shown here, the minimum approximately lies at lambda=1.55.

[0078] The ionization signal increases again after passing through the minimum, in order to then decrease again. These larger lambda values also show a strong lift-off of the flame from the burner surface.

[0079] Experiments have shown that the position and the expression of the minimum in the lean range also depend on the surface load of the burner (quotient of supplied energy and usable burner surface). In one embodiment it therefore is provided that with each change of the power at which the burner 2 is operated, a new determination of the control parameters, i.e. a new calibration, is made.

[0080] A method for calibration—and hence for example as part of the method of monitoring the burner or of controlling the burning process—consists in that the air-fuel mixture is leaned and that a local minimum of the ionization signal between the ionization electrode and the heat exchanger as an example for a surrounding counter-electrode is sought for. The minimum then is used for calibration in order to be able to finally monitor the burning behavior of the burner by means of the calibration data or to control the burning process. A great advantage consists in that the calibration is made in the leaned area.

[0081] Alternatively, a setpoint value is calculated proceeding from the minimum, which—in particular in dependence on the performance or surface load of the burner—is higher by a previously fixed value, and is then used as a control variable.

[0082] FIG. 5 shows the course of the ionization voltages measured by means of the two ionization electrodes 4, 4′ for the case that only the heat exchanger 3 as a counter-electrode to the respective ionization electrode 4, 4′ is electrically connected to ground and galvanically separated from the burner surface 2′. Like in the two preceding Figures, the negative voltage is plotted on the y-axis and the lambda value increasing from left to right is plotted on the x-axis.

[0083] The upper curve belongs to the ionization electrode 4′ of FIG. 2, which is located closer to the burner surface 2′. There is the known maximum around the area with lambda=1 and the decrease in the direction of increasing lambda values.

[0084] What is different therefrom is the course of the lower curve which has been measured by means of the ionization electrode 4 located centrally between the burner surface 2′ and the counter-electrode 3. Here as well, a maximum is present at lambda=1. In the lean area, the amount of the amplitude of the measured voltage decreases in order to pass a minimum as an extremum in the area indicated with the arrow. After this minimum, the curve rises again in order to again fall off towards zero in the area—not shown here—with larger lambda values.

[0085] Thus, an extremum appears here as well, which can serve the calibration and determination or correction of the control parameters.

LIST OF REFERENCE NUMERALS

[0086] 1 burner assembly

[0087] 2 burner

[0088] 2′ burner surface

[0089] 3 heat exchanger

[0090] 4, 4′ ionization electrode

[0091] 5 air-fuel mixture supply

[0092] 6 control device