EP2239505A1 - Method for analysing the tendency to hum of a combustion chamber and method for controlling a gas turbine - Google Patents

Abstract

The method involves identifying resonances of a characteristic variable by a spectrum, and determining amplitude values of the resonances. A stability parameter (9) is calculated as a function of the values. A lower distance value and/or upper distance value, on which the stability parameter lies above a lower threshold value and/or below an upper threshold value, are determined. The threshold values are selected such that the parameter lies on one of the threshold values if a combustion chamber is operated in an operating state with a humming tendency higher than a permissible value. Independent claims are also included for the following: (1) a method for operating a gas turbine (2) a control device for controlling operation of a gas turbine.

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.

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 may suddenly occur in such an intensity that the combustor structure itself or other components of the gas turbine may be damaged. To step Such operating conditions are conventionally relieved of the gas turbine with 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; Determine 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 threshold values are selected such that when the combustion chamber is in an operating state with a just barely tolerated buzz is operated, the stability parameter in this operating state is at one of the threshold values; Quantify the rumble slope using the lower distance value and / or the upper distance value.

The thresholds may 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. But if the relationship changes, then one approaches the borderline or moves away from it. By quantifying the rumble tendency, a tendency to approach the hum limit can be detected and thus timely countermeasures can be initiated be avoided, so that the reaching of the hum limit, with its adverse consequences for the operation is avoided.

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. Further, it is preferable 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 with the envelope of the entire possibly determined by spatial inhomogeneities operating state of the combustion chamber is represented. 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 locations at which the characteristics are measured, wherein the number of measurement points is reduced by utilizing the symmetry of waveforms. 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 averting 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 advantageously be prevented in advance of the occurrence of an inadmissibly high rumbling tendency, so that a possible continuous operation of the gas turbine is made 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 from its desired value and / or changes the temperature of the fuel in the combustion chamber as a control variable compared to their desired value is and / or the spatial distribution of the fuel supply is changed in the combustion chamber 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, the abscissa axis 4 of the coordinate system shows a frequency in [Hz], with the ordinate axis 5 of the coordinate system showing an amplitude as a dimensionless quantity. The spectra 1, 1 ', 1 "are the amplitude characteristics of a parameter over the frequency The characteristic 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 with one or more microphones in the combustion chamber become.

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 formed is taken from the first amplitude maximum 2, 2 ', 2 "and the second amplitude maximum 3, 3', 3".

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. Will now be the operation of the gas turbine turbine outlet temperature increases as it does in the 10-minute trajectory 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 humming has the consequence that the combustion chamber structure is strongly vibrated with the thus self-excited combustion vibrations, whereby the acceleration increases 14 to an acceleration peak 15 abruptly. 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. During operation of the gas turbine, the threshold value 16 becomes the stability parameter 6 falls below, it remains in accordance 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, the tendency to hum of the combustion chamber increases, 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 was the lowering the turbine outlet temperature 7 by 1 Kelvin 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 rises until a threshold 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 As a result of these interventions in the control of the operation of the gas turbine, on the one hand the hum of the combustion chamber is prevented, nevertheless a high power output of the gas turbine being 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 course 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 course 9 of the stability parameter 6 is decelerated and vice versa, so that finally the course 9 of the stability parameter 6 exceeds the threshold 16 'at 0.2 and then also exceeds the threshold 16 "at 0.4 Combustion chamber as low, so that the turbine outlet temperature 7 on the in 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 (13)

Method for analyzing the tendency to hum of a combustion chamber in an operating state, comprising the steps of: Operating the combustion chamber in the operating condition; 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 (1, 1 ', 1 ") of the characteristic in the operating state as the amplitude characteristic of the characteristic over time; Identifying a first resonance and a second resonance of the characteristic 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 ') is above a lower predetermined threshold value (16) and / or below an upper predetermined threshold value, wherein the threshold values (16) are selected such that if the combustion chamber is operated in an operating state with a barely permitted high rumbling tendency, the stability parameter (9, 9 ') in this operating state is at one of the threshold values (16); Quantify the rumble slope using the lower distance value and / or the upper distance value. Method according to claim 1,
wherein the stability parameter (9, 9 ') is calculated with the ratio value from the division of the amplitude value (2, 2', 2 ") of the first resonance and the amplitude value (3, 3 ', 3") of the second resonance. Method according to claim 1 or 2,
wherein the stability parameter (9, 9 ') is formed as the logarithm of the ratio value. Method according to one of claims 1 to 3,
wherein the stability parameter (9, 9 ') is attenuated over time with a damping function. Method according to one of claims 1 to 4,
where the parameter is measured at several points at the same time and the local spectrum is determined for each position,
where the local spectra have an envelope used as the spectrum (1, 1 ', 1 "). Method according to claim 5,
wherein the combustion chamber is formed as an annular combustion chamber rotationally symmetrical about an axis and having a plurality of points at which the parameters are measured, wherein the number of measuring points is reduced by utilizing the symmetry of waveforms. Method according to one of claims 1 to 6,
wherein the characteristic is the sound pressure in the combustion chamber and / or the acceleration of the combustion chamber structure. Method for controlling operation of a gas turbine with a combustion chamber, comprising the steps of: Performing the method for analyzing the tendency to hum of the combustion chamber of the gas turbine during its operation according to one of claims 1 to 7; once the quantification of the rumble tendency indicates that the stability parameter (9, 9 ') has reached at least one of the thresholds (16), reducing the output power of the gas turbine. Method according to claim 8, comprising the step: as soon as quantification of the rumbling tendency results, the stability parameter (9, 9 ') has a predetermined distance value (16 ') has reached at least one of the thresholds (16), controlling the operation of the gas turbine such that the rumble tendency is reduced. Method according to claim 9,
wherein for reducing the tendency to hum as a measure, the turbine outlet temperature (10) is reduced by changing the compressor air mass flow into the combustion chamber as a manipulated variable with respect to their desired value (10 ') and / or the temperature of the fuel is changed in the combustion chamber as a manipulated variable to its desired value and / or the spatial distribution of the fuel supply to the combustion chamber is changed as a manipulated variable to its desired value. Method according to claim 10,
wherein after the manipulation of the manipulated variable (10) and as soon as the quantification of the rumbling tendency shows that the rumbling tendency has further decreased, the manipulated variable (10) is reset to its desired value (10 '). Method according to one of claims 8 to 11, comprising the step: as soon as the quantification of the rumbling tendency indicates that the stability parameter (9, 9 ') has reached a predetermined and low rumble-defining distance value (16 ") to at least one of the thresholds (16), controlling the operation of the gas turbine such that the operation of the gas turbine Gas turbine is optimized in particular with regard to output power, emissions and / or fuel consumption. Control device for controlling an operation of a gas turbine, wherein the control device is arranged to perform a method according to one of claims 8 to 12.

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