EP2417395B1 - Method for analysing the humming tendency of a combustion chamber, and method for controlling a gas turbine - Google Patents

Description

The invention relates to a method for analyzing the tendency to hum of a combustion chamber and a method for controlling the operation of a gas turbine with a combustion chamber, provided that hum of the combustion chamber is prevented. Generic methods are for example from the document EP 1 327 824 A1 known.

When combustion of a combustion air / fuel mixture in a combustion chamber, in particular in a combustion chamber of a gas turbine, it may lead to the formation of combustion oscillations. The occurrence of combustion oscillations is also known as "combustion chamber hum". In particular, the combustor of the gas turbine tends to hum when the gas turbine is operated at a high turbine inlet temperature to achieve high thermal efficiency of the gas turbine. The high turbine inlet temperature can be achieved by a correspondingly high combustion temperature in the combustion chamber, whereby the combustion chamber tends to hum. When the combustion chamber hums, time-periodically correlated fluctuations of the combustion conversion and of the static pressure in the combustion chamber occur, the combustion vibrations being based on an interaction of the combustion air / fuel mixture flowing in the combustion chamber with the instantaneous combustion conversion in the flame. By changing the combustion conversion, for example, caused by an increase in the fuel supply to the combustion chamber, there may be pressure fluctuations, which in turn can lead to a change in the combustion conversion and thus to the formation of a stable pressure oscillation. The combustion vibrations cause increased mechanical and thermal stress on the combustion chamber structure and its suspension. The combustion vibrations can suddenly occur in such a Intensity occur that the combustion chamber structure itself or other components of the gas turbine can be damaged. When such operating conditions occur, the gas turbine is conventionally relieved of a high load gradient, thereby adversely reducing gas turbine output.

Remedy is the operation of the gas turbine with sufficient distance from the limit of self-excited combustion oscillations. For example, due to changing environmental conditions, however, the limit of the self-excited combustion vibrations can unfavorably shift, so that for the most unfavorable environmental conditions, a sufficient distance from the limit of self-excited combustion vibrations must be maintained. It is disadvantageous that thus the upper power range of the gas turbine must be excluded and can not be driven.

The object of the invention is to provide a method for analyzing the rumble tendency of a combustion chamber, a method for controlling an operation of a gas turbine with a combustion chamber and a control device for controlling an operation of a gas turbine, the method being able to effectively operate the combustion chamber with sufficiently low rumbling tendency ,

The method according to the invention for analyzing the rumble tendency of a combustion chamber in an operating state comprises the steps of: operating the combustion chamber in the operating state; Detecting a thermoacoustic size of the combustion chamber gas volume and / or a vibration magnitude of the combustion chamber structure in the operating state and determining a characteristic from the thermoacoustic variable and / or the vibration magnitude; Determining the spectrum of the characteristic in the operating state as the amplitude characteristic of the parameter over time; Identifying a first resonance and a second resonance of the characteristic using the spectrum; Determining the amplitude value of the first resonance and the amplitude value of the second resonance; Calculating the ratio value from the division of the amplitude value of the first resonance and the amplitude value of the second resonance as a stability parameter; Determining the lower distance value and / or the upper distance value by which the stability parameter is above a lower predetermined threshold and / or below an upper predetermined threshold, wherein the thresholds are selected such that when the combustor is in an operating state with just a high allowable Brumbling is operated, the stability parameter in this operating condition is at one of the threshold values; Quantify the rumble slope using the lower distance value and / or the upper distance value.

The threshold values can be selected depending on the operating and ambient conditions. The magnitude of the amplitude values of the parameter changes moderately with the combustion load of the combustion chamber and is only of limited significance for the analysis of the tendency to hum of the combustion chamber. Reaching the hum limit is often characterized by the fact that the amplitude values suddenly rise very sharply. It is therefore not recognized by the initially moderate course of the amplitude values that one approaches dangerously close to the hum. If the amplitudes rise suddenly when reaching the hum limit (usually in fractions of a second), the gas turbine can only be protected from mechanical damage by drastic measures which are disadvantageous from the point of view of the operator, such as immediate, significant load reduction. This is where the invention comes in: In certain cases, approaching the hum limit can be recognized by the fact that the shape of the spectrum of the parameter changes. For example, the ratio of the amplitudes of two frequency bands could be used to quantify the rumbling tendency. As long as the amplitude ratio remains constant when increasing the combustion load (despite the increase in the absolute amplitude values), there is no danger. Changes but the relation, one approaches the borderline or moves away from it. By quantifying the rumbling tendency, a tendency to approach the buzzing limit can be detected, and thus timely countermeasures can be taken so as to avoid reaching the buzz line with its adverse consequences for operation.

It is preferable that the stability parameter is calculated with the ratio value from the division of the amplitude value of the first resonance and the amplitude value of the second resonance. With increasing combustion load of the combustion chamber, the frequency positions of the resonances shift, wherein for a present combustion chamber frequency bands in which the resonances occur during operation of the combustion chamber, for example, can be predetermined experimentally. In order to easily identify the resonances, it is thus possible, in particular, to examine these frequency bands so that it is not necessary to scan the entire frequency range of the spectrum.

Preferably, the stability parameter is formed as the logarithm of the ratio. It is further provided according to the invention that the stability parameter is attenuated over time with a damping function. In this way, excessive transient changes in the stability parameter can advantageously be contained. For example, an attenuation function may be formed such that at a time instant n the stability parameter is formed from the arithmetic mean of the ratio value at time n and the ratio value at time n-1.

It is preferred that at multiple locations the characteristic is measured at the same time and for each site the local spectrum is determined, the local spectra having an envelope used as the spectrum. Of the spectrum formed by the envelope is the entire possibly determined by spatial inhomogeneities operating state of Combustion chamber represents. As a result, the tendency to hum of the combustion chamber can advantageously be estimated in an operating state in which the combustion chamber is spatially inhomogeneously charged. The combustion chamber is preferably designed as an annular combustion chamber rotationally symmetrical about an axis and has a plurality of points at which the parameters are measured, wherein the number of measuring points is reduced by utilizing the symmetry of vibration modes. Furthermore, it is preferred that the parameter is the sound pressure in the combustion chamber and / or the acceleration of the combustion chamber structure.

The method according to the invention for controlling an operation of a gas turbine with a combustion chamber comprises the steps of: performing the previous method for analyzing the tendency to hum of the combustion chamber of the gas turbine during its operation; once the quantification of the rumble tendency indicates that the stability parameter has reached at least one of the threshold values, reducing the output power of the gas turbine.

Thus, the stability parameter can be used directly as a controlled variable for operating the gas turbine. The instantaneous load of the gas turbine is directly correlated to the stability parameter, so that with the stability parameter, a power control of the gas turbine with regard to the avoidance of the hum of the combustion chamber can be accomplished.

The method of controlling the operation of the gas turbine further includes the step of: once the quantification of the rumble tendency indicates that the stability parameter has reached a predetermined distance value to at least one of the threshold values, controlling the operation of the gas turbine to reduce the rumble tendency. As a result, a shutdown of the gas turbine can be advantageously prevented in the run-up to the occurrence of an inadmissibly high rumbling tendency, so that a possible continuous operation of the gas turbine is possible. It is preferred that to reduce the tendency to hum as a measure, the turbine outlet temperature is reduced by changing the compressor air mass flow into the combustion chamber as a manipulated variable compared to their target value and / or the temperature of the fuel is changed in the combustion chamber as a control variable to its desired value and / or spatial distribution of the fuel supply to the combustion chamber as a manipulated variable is changed from its desired value and / or - if more than one burner stages are available - the division is changed to different burner stages as a manipulated variable to its desired value. After the manipulation of the manipulated variable and as soon as the quantification of the rumbling tendency shows that the rumbling tendency has further decreased, the manipulated variable is preferably reset to its desired value.

Further, the method of controlling the operation of the gas turbine comprises the step of, once the quantification of the rumble tendency indicates that the stability parameter has reached a predetermined and low rumble-defining distance value to at least one of the thresholds, controlling the operation of the gas turbine such that the operation the gas turbine is optimized in particular with regard to output power, emission and / or fuel consumption.

A control device according to the invention for controlling an operation of a gas turbine is set up to carry out the aforementioned method.

FIG 1

ein Diagramm eines Spektrums einer Kenngröße der Brennkammer bei unterschiedlichen Betriebszuständen,

FIG 2

ein Diagramm des zeitlichen Verlaufs eines Stabilitätsparameters bei steigender Turbinenaustrittstemperatur,

FIG 3

ein Diagramm eines Steuerungsverlaufs für die Gasturbine bei sich ungünstig verändernden Umgebungsbedingungen und

FIG 4

ein Diagramm eines Steuerungsverlaufs für die Gasturbine bei Leistungsanhebung.

In the following, a preferred embodiment of the inventive method for analyzing the rumbling tendency of a combustion chamber and a method for controlling the operation of a gas turbine is explained with reference to the accompanying schematic drawings. Show it:

FIG. 1

a diagram of a spectrum of a characteristic of the combustion chamber at different operating states,

FIG. 2

a diagram of the time profile of a stability parameter with increasing turbine outlet temperature,

FIG. 3

a diagram of a control curve for the gas turbine in unfavorable changing environmental conditions and

FIG. 4

a diagram of a control curve for the gas turbine with power boost.

In FIG. 1 A coordinate system is shown in which spectra 1, 1 'and 1 "are plotted, and the axis of abscissa 4 of the coordinate system shows a frequency in [Hz], where the ordinate axis 5 of the coordinate system shows an amplitude as a dimensionless variable The spectra 1, 1 ', 1 "are the amplitude curves of a characteristic over the frequency. The parameter is the sound pressure in a combustion chamber, which occurs during operation of the combustion chamber. The sound pressure in the combustion chamber can be measured, for example, with one or more microphones in the combustion chamber.

The spectrum 1 results when the Brummneigung the combustion chamber is low. If the operating state of the combustion chamber is changed in such a way that the tendency to humming increases, the spectrum 1 changes into the spectrum 1 '. If the operating state of the combustion chamber is further changed, that the rumbling tendency increases and reaches a just yet permissible limit range, the spectrum 1 'changes into the spectrum 1 ".As a first resonance, the spectra 1, 1', 1" first amplitude maximum 2, 2 ', 2 "and as a second resonance a second amplitude maximum 3, 3', 3" on.

As a stability parameter for quantifying the rumble tendency of the combustion chamber, the natural logarithm of the ratio is formed from the first amplitude maximum 2, 2 ', 2 "and the second amplitude maximum 3, 3', 3" taken.

In FIG. 2 a coordinate system is shown, over whose abscissa 8 the time from 0 to 2 minutes is plotted. The left ordinate 6 is the stability parameter and the right ordinate 7 is a turbine outlet temperature. At time 0 minutes, the curve 10 of the turbine outlet temperature is 579 ° C. This results in the operating state in the combustion chamber, in which the sound pressure prevails, the spectrum of 1 in FIG. 1 is shown. With the first amplitude maximum 2 and the second amplitude maximum 3, the stability parameter 6 for the spectrum 1 is 0.6, as it is in the in FIG. 2 shown diagram with the curve 9 at the time 0 minutes. Now, the turbine outlet temperature is increased to operate the gas turbine, as in the curve 10 in FIG. 2 is shown, then prevails after 0.75 minutes an operating condition in the combustion chamber, in which the sound pressure according to the spectrum 1 'in FIG. 1 prevails. From the spectrum 1 'results with the first amplitude maximum 1' and the second amplitude maximum 3 'of the stability parameter 6 with 0.3, as in the course curve 9 at time 0.75 minutes in FIG. 2 is shown. Finally, the course of the turbine outlet temperature 10 is raised to a first level 11. As it is in FIG. 2 is shown, the course 9 of the stability parameter 6 is decreasing over time, which is an indication of the combustion chamber's increased tendency to burn over time.

In FIG. 2 Furthermore, the course of the acceleration 14 of the combustion chamber structure is shown, which is substantially constant until the turbine outlet temperature 10 is raised to the first level 11. If the turbine outlet temperature 10 is increased to a second level 12, then the course 9 of the stability parameter 6 continues to drop and, in the combustion chamber, finally, hum occurs. The hum has the consequence that with it self-excited combustion vibrations, the combustion chamber structure is strongly vibrated, causing the acceleration 14 to abrupt acceleration peak 15 increases. The acceleration tip 15 is so high that damage to the combustion chamber structure is to be expected. Therefore, to prevent damage to the combustor structure, the gas turbine is shut down resulting in a rapid drop in the turbine discharge temperature curve 10 FIG. 2 shows.

In the in FIG. 2 a threshold 16 of the stability parameter 6 is plotted at 0.1. The course 9 of the stability parameter 6 falls below (in FIG. 2 17), threshold 16 at a first time 18, which is 1.55 minutes. The first time 18 is advanced 15 seconds from the second point in time 19, when the acceleration peak 15 occurs. If, during operation of the gas turbine, the threshold 16 is fallen below the stability parameter 6, then it remains FIG. 2 a reaction time of 15 seconds, during which the operation of the gas turbine is to be changed in such a way to attenuate the rumbling tendency that the hum of the combustion chamber and thus the resulting rapid shutdown of the gas turbine can be avoided.

The diagrams in 3 and 4 are similar to the diagram in FIG. 2 and show an operation of the gas turbine under the condition of preventing hum of the combustion chamber. The Brummneigung the combustion chamber may increase, for example, that decreases in a compressor of the gas turbine due to wear or contamination, the pressure ratio. Further, the Brummneigung the combustion chamber may increase by the fact that the ambient temperature and thus the compressor inlet temperature increases during operation of the gas turbine. For example, let the gas turbine operate at a turbine exhaust temperature level, as does the trajectory 10 at the origin of the abscissa in FIG FIG. 3 shows. Caused by, for example, one of the aforementioned Influences increase the Brummneigung the combustion chamber, so that the course 9 of the stability parameter 6 drops. Without intervention in the operation of the gas turbine, this process would continue until eventually the combustion chamber starts to hum. In FIG. 3 a second threshold 16 'is plotted at 0.2 which is above the first threshold 16 (threshold 16 at 0.1). As soon as the curve 9 of the stability parameter 6 has reached the threshold value 16 ', the fuel supply into the combustion chamber is reduced at a third time 20 by means of a control device for the gas turbine such that the curve 10 of the turbine outlet temperature within 3 seconds at the fourth time 21 7 lowers by 1 Kelvin. As a result, the lowering of the curve 9 of the stability parameter 6 is decelerated and vice versa, so that finally the curve 9 of the stability parameter 6 exceeds the threshold value 16 'again at the fifth time point 22. For example, to reduce the humming of the combustion chamber, the lowering of the turbine outlet temperature 7 by 1 Kelvin was not sufficient to achieve a sufficiently large distance to the hum of the combustion chamber, so falls after the fifth time 22, the curve 9 of the stability parameter 6 again and falls below the threshold 16 '. In an analogous measure as at the third time 20, the curve 10 of the turbine outlet temperature 7 is now lowered again by 1 Kelvin, which in turn decelerates the course 9 of the stability parameter 6 and vice versa, until finally the curve 9 of the stability parameter 6 has exceeded the threshold value 16 ' ,

The course 9 of the stability parameter 6 now increases until a threshold value 16 "at 0.4 is reached. In this operating state, the tendency of the combustion chamber to hum is considered low, so that the level of the turbine outlet temperature 7 gradually returns to its level in FIG original level can be raised through this Interventions in the control of the operation of the gas turbine on the one hand, the hum of the combustion chamber is suppressed, yet a high power output of the gas turbine is achieved.

In the in FIG. 4 The diagram shown, the operation of the gas turbine is shown, in which a segregation of the output power of the gas turbine by increasing the turbine outlet temperature 10 is to be achieved. By increasing the curve 10 of the turbine outlet temperature, the profile 9 of the stability parameter 6 drops until it has reached the threshold value 16 '. By resetting the ramp-shaped course 10 of the turbine outlet temperature 7 by 1 Kelvin, it is prevented that the stability parameter 6 reaches the threshold value 16. If this lowering of the turbine outlet temperature 7 by 1 Kelvin was not carried out, the curve 9 'of the stability parameter 6 would be such that the threshold value 16 is reached at 0.1, which would result in an early shutdown of the gas turbine. By lowering the curve 10 of the turbine outlet temperature 7 by 1 Kelvin, the drop of the curve 9 of the stability parameter 6 is decelerated and vice versa, so that finally the curve 9 of the stability parameter 6 exceeds the threshold value 16 'at 0.2 and thereafter the threshold value 16 " 0.4 in this operating state, the tendency of the combustion chamber to hum is considered low, so that the turbine outlet temperature 7 exceeds that in FIG FIG. 4 Course shown 10 can be nachgefahren to the required level required 10 ', wherein the tendency to hum of the combustion chamber always remains so low that an emergency shutdown of the gas turbine need not be made.

Claims (15)

1. Method for analyzing the humming tendency of a combustion chamber in an operating state, comprising the steps of:

   operating the combustion chamber in the operating state;

   detecting a thermoacoustic variable of the combustion chamber gas volume and/or a vibration variable of the combustion chamber structure in the operating state and determining a characteristic variable from the thermoacoustic variable and/or the vibration variable;

   determining the spectrum (1, 1', 1") of the characteristic variable in the operating state as the amplitude profile of the characteristic variable over time;

   identifying a first resonance and a second resonance of the characteristic variable with the aid of the spectrum (1, 1', 1") ;

   determining the amplitude value (2, 2', 2") of the first resonance and the amplitude value (3, 3', 3") of the second resonance;

   calculating a stability parameter (9, 9') as a function of the amplitude value (2, 2', 2") of the first resonance and the amplitude value (3, 3', 3") of the second resonance;

   determining the lower distance value and/or the upper distance value by which the stability parameter (9, 9') lies above a lower predetermined threshold value (16) and/or below an upper predetermined threshold value, the threshold values (16) being chosen such that, if the combustion chamber is operated in an operating state with a humming tendency that is just about at a permissible level, the stability parameter (9, 9') in this operating state lies at one of the threshold values (16);

   quantifying the humming tendency by means of the lower distance value and/or the upper distance value, the stability parameter (9, 9') being damped over time by a damping function.
2. Method according to Claim 1,
   wherein the stability parameter (9, 9') is calculated with the ratio value from dividing the amplitude value (2, 2', 2") of the first resonance and the amplitude value (3, 3', 3") of the second resonance.
3. Method according to Claim 1 or 2,
   wherein the stability parameter (9, 9') is formed as the logarithm of the ratio value.
4. Method according to one of Claims 1 to 3,
   wherein the characteristic variable is measured simultaneously at a number of locations and the local spectrum is determined for each location,
   wherein the local spectra have an envelope that is used as the spectrum (1, 1', 1").
5. Method according to Claim 4,
   wherein the combustion chamber is formed rotationally symmetrically about an axis as an annular combustion chamber and has a number of locations at which the characteristic variables are measured, the number of measuring locations being reduced by using the symmetry of forms of oscillation.
6. Method according to one of Claims 1 to 5,
   wherein the characteristic variable is the acoustic pressure in the combustion chamber and/or the acceleration of the combustion chamber structure.
7. Method for controlling operation of a gas turbine with a combustion chamber, comprising the steps of:

   carrying out the method for analyzing the humming tendency of the combustion chamber of the gas turbine during its operation according to one of Claims 1 to 6;

   reducing the output power of the gas turbine as soon as the quantifying of the humming tendency shows that the stability parameter (9, 9') has reached at least one of the threshold values (16).
8. Method according to Claim 7,
   wherein the stability parameter is used directly as a controlled variable for operating the gas turbine.
9. Method according to Claim 8,
   wherein the momentary load of the gas turbine is in direct correlation with the stability parameter, so that with the stability parameter a closed-loop control of the power of the gas turbine with a view to averting humming of the combustion chamber is accomplished.
10. Method according to one of Claims 7-9, comprising the step of:
    controlling the operation of the gas turbine in such a way that the humming tendency is reduced as soon as the quantifying of the humming tendency shows that the stability parameter (9, 9') has reached a predetermined distance value (16') from at least one of the threshold values (16).
11. Method according to Claim 10,
    wherein, as a measure for reducing the humming tendency, the turbine outlet temperature (10) as a manipulated variable is lowered with respect to its setpoint value (10') by changing the compressor air mass flow into the combustion chamber and/or the temperature of the fuel into the combustion chamber as a manipulated variable is changed with respect to its setpoint value and/or the spatial distribution of the fuel supply into the combustion chamber as a manipulated variable is changed with respect to its setpoint value.
12. Method according to Claim 11,
    wherein there are a number of burner stages, the apportionment among different burner stages as a manipulated variable being changed with respect to its setpoint value.
13. Method according to Claim 12,
    wherein the manipulated variable (10) is reset to its setpoint value (10') after the manipulation of the manipulated variable (10) and as soon as the quantifying of the humming tendency shows that the humming tendency has reduced further.
14. Method according to one of Claims 7 to 13, comprising the step of:
    controlling the operation of the gas turbine in such a way that the operation of the gas turbine is optimized, in particular with regard to output power, emissions and/or fuel consumption, as soon as the quantifying of the humming tendency shows that the stability parameter (9, 9') has reached a distance value (16") from at least one of the threshold values (16) that is predetermined and defines a low humming tendency.
15. Control device for controlling operation of a gas turbine, wherein the control device is designed for carrying out a method according to one of Claims 7 to 11.

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