EP1050713A1 - Method for suppressing respectively controlling thermoacoustic vibrations in a combustion chamber as well as combustion chamber for carrying out the method - Google Patents

Abstract

The method involves detecting the oscillations in a closed control loop (24') and generating acoustic oscillations of a defi amplitude and phase depending on the detected oscillations for coupling into the combustion system. The amplitude of the generat acoustic oscillations is selected within the control loop in proportion to the amplitude of the detected oscillations. An Independent claim is also included for a combustion system for implementing the method.

Description

TECHNICAL AREA

The present invention relates to the field of combustion technology, as it plays a role in particular for gas turbines. The invention relates to a Process for the suppression or control of thermoacoustic vibrations in a combustion system according to the preamble of claim 1.

The invention further relates to a combustion system for performing the Method according to the preamble of claim 8.

Such a method or combustion system, for example from the article by Paschereit, CO, Osgood, E., and manner Stein, W., "Structure and Control of Thermal Acoustic Instabilities in a Gas Turbine Combustor", 36 ^th AIAA Aerospace Science Meeting and Exhibit , Reno, Nevada, January 12-15, 1998.

STATE OF THE ART

Thermoacoustic vibrations pose a threat to any type of combustion application or systems. They lead to higher pressure vibrations Amplitude, restricting the operating range, and can cause the unwanted Increase pollutant emissions. This is particularly true for combustion systems with low acoustic damping, as is usually the case with Gas turbines are available. To be high in terms of pulsations and emissions Enabling performance conversion across a wide operating range can be a active control or suppression of combustion vibrations necessary his.

Various active control systems have been proposed in the past which work on the principle of "anti-noise", i.e. the thermoacoustic Vibrations are detected and rotated in phase by 180 degrees and coupled into the system in an appropriately reinforced form in order to then due to superposition with the thermoacoustic vibrations out of phase leads to extinction. The anti-noise solutions have proven useful in low power combustion systems. In high-performance combustion systems with correspondingly strong ones Pressure fluctuations, however, are becoming increasingly difficult to achieve appropriate acoustic Generate and couple vibrations with reasonable effort.

In order to enable active control even at high outputs, one has therefore suggested either the burner flame itself via the fuel supply modulate depending on the detected instabilities (US-A-5,145,355), or a vibration generator in the form of a pulsed one Introduce auxiliary burner (US-A-5,428,951). In both cases, so can specifically generated fluctuations in the heat release the desired acoustic High power vibrations are generated. However, it is disadvantageous that this type of vibration generation massive interventions in the combustion system required and therefore, for example, with existing designs cannot be easily retrofitted. In addition, one can System because of the complexity of the combustion processes involved difficult to target and stable over a larger operating range influence and regulate.

In the publication mentioned at the beginning there is now an active control of the thermoacoustic Vibrations have been suggested that are not due to sound cancellation based, but intervenes in the formation of the vibrations and how can be described as follows: Coherent structures play a crucial role Role in mixing processes between air and fuel. The dynamics of this Structures therefore affect combustion and thus heat release. By influencing the shear layer between the fresh gas mixture and The recirculated exhaust gas can control the combustion instabilities. One way of influencing this is in the publication mentioned at the beginning described acoustic excitation. The acoustic excitation allows suppression the combustion-driven vibrations by doing the training coherent structures prevented. By preventing the emergence of Vortex structures at the burner outlet will release periodic heat and thus preventing the basis for the occurrence of thermoacoustic vibrations.

Unlike the principle of anti-noise, in which an existing sound field extinguished by introducing a phase-shifted sound field of the same energy this method is based on the direct influence of the shear layer. This direct influence on the shear layer has the advantage that the external disturbances in the shear layer itself are amplified and therefore less energy is needed to generate the disturbances than in the case the direct cancellation of a sound field by anti-sound. The shear layer can be excited both downstream and upstream of the burner. There only low power is required, the sound energy e.g. of acoustic Drivers, in particular loudspeakers or the like, introduced into the flow become. By choosing the correct phase difference between pulsation and acoustic excitation signal can reduce the coherence of the developing instability waves disturbed and the pulsation amplitudes can be reduced.

An exemplary combustion system, as described in the publication mentioned at the beginning has been used and is also suitable for the present invention represented schematically in Fig. 1. The combustion system 10 includes one (Swirl-stabilized) burner 11, which works in a combustion chamber 12. The burner 11 receives the necessary combustion air via an air supply 13. For the A corresponding fuel supply 14 is provided for the fuel supply. For the detection of thermoacoustic vibrations in the area of the flame 15 arise, sensors 20, .., 22 are provided which are connected to the air supply (sensors 20) and / or on the combustion chamber (sensors 21, 22) can be arranged. The sensors 20, .., 22 can be used for the direct detection of the pressure fluctuations or vibrations as (water-cooled) microphones or other dynamic Pressure transducers should be designed. The sensors 20, .., 22 can also be wholly or partly designed as optical sensors with which the Chemiluminescence e.g. the OH molecules the fluctuations in the heat release can be detected with the thermoacoustic vibrations are directly linked.

The sensors 20, .. 22 are connected to a control 23, the output side controls different speakers 16, .., 19, which are symmetrical to the axis of the Combustion system 10 optionally in the area of the air supply 13 and / or the combustion chamber 12 are arranged. The speakers 16, .., 19 produce after Provided the regulation 23 acoustic vibrations, which then enter the combustion system 10 are coupled and there the shear layers described influence. The combustion system 10 according to the prior art with the Sensors 20, .., 22 and the loudspeakers 16, .. 19 forms - if the vibrations are detected at the combustion chamber 12 - the closed one shown in FIG. 2 Control loop 24. Those detected by sensors 21 and / or 22 Vibrations in the combustion chamber 12 are in a subsequent filter 25 filtered and possibly amplified and then by means of a phase shifter 26 with predefinable phase setting 29 in the phase by a desired amount postponed. The phase-shifted signal then triggers a signal generator 27, whose output signal in a power amplifier 28 with a predeterminable amplitude setting 30 amplified and used to control the speakers 16, .., 19 becomes. With this known scheme, in which the acoustic vibrations are generated synthetically and the amplitude of these vibrations is fixed is already a suppression (weakening) in the system used of the combustion-driven vibrations by up to 6 dB.

However, it would be desirable to have one with an arrangement according to FIG to achieve better oppression.

PRESENTATION OF THE INVENTION

It is therefore an object of the invention to provide a method of acoustic thermoacoustic control Specify vibrations, which using the principle of acoustic excitation of the shear layer a significantly improved suppression enables, as well as a combustion system for performing such a method specify.

The object is achieved by the entirety of the features of claims 1 and 8. The essence of the invention is, within the closed control loop, through the combustion system with the sensors and acoustic Excitation means (e.g. loudspeakers) is formed, a proportional regulation to provide, i.e., the amplitude of the acoustic vibrations generated directly to be proportional to the amplitude of the detected vibrations. By the proportional regulation surprisingly results in values for suppression, which can be up to 20 dB in a system according to FIG. 1. A preferred embodiment of the method according to the invention is thereby characterized that for the detection of thermoacoustic vibrations either the associated pressure fluctuations are measured acoustically, or the associated fluctuations in heat release measured optically be used for optical measurement of the fluctuations in the heat release in particular the fluctuations in the chemiluminescence of the OH molecules be measured.

Another preferred embodiment of the method according to the invention is characterized by the fact that it generates acoustic vibrations Speakers are used which acoustically connect to the combustion system are coupled.

The sensors used in the combustion system according to the invention can according to a preferred embodiment, either as pressure fluctuations receiving pressure sensors, in particular as a microphone, or as optical sensors for measuring chemiluminescence.

Further embodiments result from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

die schematische Darstellung eines Verbrennungssystems mit akustischer Kontrolle der thermoakustischen Schwingungen nach dem Stand der Technik, wie es beispielhaft auch zur Realisierung der vorliegenden Erfindung eingesetzt werden kann;

Fig. 2

das aus dem Stand der Technik bekannte Regelschema des Systems nach Fig. 1;

Fig. 3

ein bevorzugtes Ausführungsbeispiel eines Regelschemas für das System nach Fig. 1, wie es bei dem Verfahren nach der Erfindung Anwendung findet; und

Fig. 4

beispielhafte Messkurven, welche die Unterdrückung einer Druckschwingung im 100 Hz-Bereich in einem System nach Fig. 1 mit einem Regelschema gemäss Fig. 3 zeigen.

The invention will be explained in more detail below on the basis of exemplary embodiments in connection with the drawing. Show it

Fig. 1

the schematic representation of a combustion system with acoustic control of the thermoacoustic vibrations according to the prior art, as can be used for example to implement the present invention;

Fig. 2

the known from the prior art control scheme of the system of FIG. 1;

Fig. 3

a preferred embodiment of a control scheme for the system of Figure 1, as used in the method according to the invention. and

Fig. 4

exemplary measurement curves which show the suppression of a pressure oscillation in the 100 Hz range in a system according to FIG. 1 with a control scheme according to FIG. 3.

WAYS OF CARRYING OUT THE INVENTION

3 shows a preferred exemplary embodiment of a control scheme, that in the context of the invention instead of that of the prior art known control schemes (Fig. 2) used in a combustion system of FIG. 1 can be used to improve the suppression of thermoacoustic To achieve vibrations. With the closed control loop with proportional control in deviation from FIG. 2, the sensors 21, 22, detection signals characteristic of the thermoacoustic vibrations passed on to a P-controller 31, which amplifies the signals and around delayed a predetermined period of time. The delay - that of the phase shift 2 corresponds - can be done directly in the P controller 31, or - as shown in Fig. 3 - in a downstream delay circuit 32 with Delay time setting 33. The pre-amplified, delayed signal will then given directly to the input of a power amplifier 28 ', which it for the control of the speakers 16, .., 19 required performance level amplified. The proportional control causes the amplitude of the acoustic generated Vibrations with the amplitude of the detected combustion vibrations increases and decreases proportionally. This direct control-technical connection of the two Vibrations now surprisingly leads to the fact that an essential results in better suppression of the combustion vibrations.

4 shows exemplary measurement results which show the suppression (in dB) of a pressure oscillation in the 100 Hz range in a combustion system 1 with a proportional control according to FIG. 3. The normalized amplitudes are shown as a function of the phase shift (in degrees) between the detected and generated vibrations for acoustic detection using a microphone (open circles) and optical detection via OH chemiluminescence (filled circles). You can see that in In both cases the maximum suppression of more than 20 dB is approximately the same with a phase shift of about 50 degrees.

It goes without saying that the necessary optimal time delay or Phase shift depends on the respective combustion system. Significant is in any case that the acoustic vibrations generated with one power and can be coupled in which is several powers of ten smaller than the thermal performance of the combustion system. From the acoustic stimulants (Loudspeakers 16, .., 19) is to be requested that - if it is the combustion system 10 is that of a gas turbine - that in gas turbines must withstand the usual preheating temperatures of approx. 400 ° C. Farther they should approx. 0.001% of the thermal output per burner 11 (with several Burners) to the respective gas (air or fresh mixture when excited upstream; Exhaust gas can give off excitation downstream of the burner 11).

REFERENCE SIGN LIST

10th

Combustion system

11

Burner (swirl stabilized)

12th

Combustion chamber

13

Air supply

14

Fuel supply

15

flame

16, .. 19

speaker

20th

Sensor (air supply)

21.22

Sensor (combustion chamber)

23

regulation

24.24 '

Control loop

25th

filter

26

Phase shifter

27

Signal generator

28.28 '

Power amplifier

29

Phase adjustment

30th

Amplitude adjustment

31

P controller

32

Delay circuit

33

Delay time setting

Claims (12)

Process for the suppression or control of thermoacoustic Vibrations, which in a combustion system (10) with one in a Combustion chamber (12) working burner (11) by forming coherent or Vortex structures and the associated periodic heat release arise with which method in a closed control loop (24 ') Vibrations detected and depending on the detected vibrations acoustic vibrations of a certain amplitude and phase generated and in the combustion system (10) are coupled in, characterized in that within the control loop (24 ') the amplitude of the acoustic generated Vibrations selected proportional to the amplitude of the detected vibrations becomes. A method according to claim 1, characterized in that for detection the thermoacoustic vibrations the associated pressure fluctuations be measured acoustically. A method according to claim 1, characterized in that for detection of the thermoacoustic vibrations the associated fluctuations in the heat release can be measured optically. A method according to claim 3, characterized in that for optical Measuring the fluctuations in the heat release the fluctuations in the Chemiluminescence of the OH molecules can be measured. Method according to one of claims 1 to 4, characterized in that that loudspeakers (16, .., 19) are used to generate the acoustic vibrations which are acoustically coupled to the combustion system (10) are. Method according to one of claims 1 to 5, characterized in that that generates and couples the acoustic vibrations with one power that are several powers of ten smaller than the thermal output of the Combustion system (10). Combustion system for performing the method according to claim 1, which combustion system (10) a burner (11), a combustion chamber (12), an air supply (13) for supplying combustion air to the burner (11), at least one sensor (20, .., 22) for detecting the thermoacoustic vibrations and means (16, .., 19) for generating and coupling the acoustic Vibrations in the combustion system (10), the at least a sensor (20, .., 22) and the means (16, .., 19) for generating and coupling the acoustic vibrations arranged in a closed control loop (24 ') are characterized in that in the control loop (24 ') between the at least a sensor (20, .., 22) and the means (16, .., 19) for generation and coupling the acoustic vibrations, a P controller (31) is provided. Combustion system according to claim 7, characterized in that the at least one sensor (21) absorbing pressure fluctuations Pressure sensor, in particular as a microphone, is formed. Combustion system according to claim 7, characterized in that the at least one sensor (22) as an optical sensor for measuring chemiluminescence is trained. Combustion system according to one of claims 7 to 9, characterized in that that the means for generating and coupling the acoustic Vibrations are designed as speakers (16, .., 19). Combustion system according to claim 10, characterized in that a power amplifier (28 ') within the control loop (24') the P controller (31) is connected downstream, which controls the speakers (16, .., 19). Combustion system according to one of claims 7 to 11, characterized in that that in the control loop (24 ') before the means for generating and Coupling the acoustic vibrations or in front of the loudspeakers (16, .., 19) Means (32) are provided for the adjustable time delay of the control signal are.

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