Title of Invention

METHOD FOR THE ACTIVE DAMPING OF COMBUSTION OSCILIATION AND COMBUSTION APPARATUS

Abstract

The invention relates to a method for the active damping of combustion oscillation in a combustion chamber (4) by means of at least two actuating members)8). The method is distinguished in that control of the actuating members (8) necessitates measurement of the combustion oscillation at fewer points than there are actuating members (8). This is achieved, in particular, by utilizing the symmetry of natural acoustic oscillation (30) in the combustion chamber (4).

Full Text

Description The invention relates to a method for the active damping of combustion oscillation in a combustion chamber and to a combustion apparatus. The article "Aktive Dämpfung selbsterregter Brennkammerschwingungen (AIC) bei Druckzerstäuberbrennern durch Modulati on der flüssigen Brennstoffzufuhr" [ "Active Damping of Self-excited Combustion-Chamber Oscillation's (AIC) in Pressure Atomizer Burners by Modulating the Liquid Fuel Supply"] by J. Herrmann, D. Vortmeyer and S. Gleiß, VDI Reports No. 1090, 1993, describes how combustion oscillation occurs in a combustion chamber and how it can be actively damped. During combustion in a combustion chamber, for example- of a turbine, self-excited combustion oscillation may occur, this also being referred to as combustion instability. Such combustion oscillation arises as a result of the interaction between a fluctuating release of power during combustion and the natural oscillations of the combustion chamber. Combustion oscillation is often accompanied by high noise emission and mechanical load on the combustion chamber, which may lead to structural parts being destroyed. Active damping of combustion oscillation is achieved by modulating by means of an actuating member {piezoelectric actuator) the fuel quantity which is supplied to a burner. A microphone records the acoustic oscillations in the combustion chamber, A regulating signal for regulating the modulation of the fuel quantity supplied is derived from the microphone signal in such a way that the modulation of the fuel quantity supplied takes place anticyclically to the combustion oscillation. The object of the invention is to specify a simple method for the active damping of combustion - 2 - oscillation in a combustion chamber. A further object of the invention is to specify a combustion apparatus in which active damping of combustion oscillation is possible in a simple way. The object directed at the method is achieved by specifying a method for the active damping of combustion oscillation in a combustion chamber, the combustion oscillation being damped by means of at least two actuating members which each influence a regulating variable, and a measured variable being determined at at least one measuring point, the actuating members being controlled via a number of measured variables which is smaller than the number of actuating members. This method makes it possible, at a low outlay in terms of measurement, to carry out regulation for the active damping of combustion oscillation. By regulating variable is meant a system variable which is described by a physical variable, for example a fuel quantity supplied at a specific point. In this sense, another regulating variable would, for example, be a fuel quantity supplied at another point or, for example, a quantity of combustion air supplied. An actuating member is accordingly not necessarily to be interpreted as a unit of equipment. The term "actuating member" may also embrace two or more means which jointly influence a regulating variable, for example two loud-speakers which jointly modulate a combustion-air mass flow. Fuel and combustion air are supplied for combustion, a quantity of fuel supplied for combustion and/or a quantity of combustion air supplied for combustion preferably being used as a regulating variable, although other regulating variables may also be used at the same time. The fuel mass flow and/or the combustion-air mass flow is preferably modulated. It is consequently possible to carry out the active damping of combustion oscillation via the modulation of the fuel quantity supplied and/or of the combustion-air quantity supplied. - 3 - In combustion oscillation, natural acoustic oscillation or a sound field forms in the combustion chamber. A sound field is characterized by characteristic sound-field variables, such as, for example, sound pressure and sound velocity, the time profiles of which have particular periodic regularities. A sound field typically has spatial regions, within which the sound-field variables oscillate periodically at different amplitudes. Sound-field variables in different spatial regions of the sound field are shifted relative to one another in time in their oscillations in a way which is characteristic of the sound field, that is to say they have a characteristic phase shift. If the spatial regions described have some regularity in their features, this is referred to as symmetry of the sound field. Preferably, exactly as many measured variables as are necessary for characterizing the natural oscillation are determined. Preferably, furthermore, the control of at least one actuating member is determined via the symmetry of the natural acoustic oscillation. The natural acoustic oscillation is characterized with the aid of a number of measured variables. The regulation of the actuating members is derived from this knowledge of the existing sound field via the symmetry of the natural acoustic oscillation in the combustion chamber, by taking into account the respective spatial position in which an actuating member influences the combustion oscillation. The phase and amplitude of the combustion oscillation at the point of action of an actuating member are known from the characterization of the natural acoustic oscillation. The regulation of each actuating member, as is necessary for damping the combustion oscillation, is thus obtained. The number of measuring points is therefore determined solely by the number of measuring points necessary for characterizing the natural oscillation. Preferably, furthermore, the actuating members are controlled anticyclically to the combustion oscilla- - 4 - tion. Anticyclic control brings about a particularly-efficient damping of the combustion oscillation. Anticyclic control denotes a regulating variable fluctuation which is inverted in relation to the self-excited combustion oscillation. For harmonic combustion oscillation, this means that the regulating variable is applied with the same frequency, but in phase opposition. Preferably, the method is employed in an annular combustion chamber of a gas turbine. An annular combustion chamber of a gas turbine has a relatively large number of burners which may each excite combustion oscillation. It is desirable to have the possibility of carrying out active damping of combustion oscillation for each burner by means of its own actuating member. The number of measured variables to be determined for these actuating members may be kept small. The object directed at a combustion apparatus is achieved by specifying a combustion apparatus with at least one burner in a combustion chamber and with at least one modulating device which comprises: a) a sensor for recording a measured variable characterizing the combustion oscillation, b) a controller for converting a signal from the sensor into a regulating signal, and c) a actuating member for modulating a regulating variable, altogether at least two actuating members, for modulating one regulating variable each, being present, and the number of sensors being smaller than the number of actuating members. In this case, two or more actuating members may be present due to the fact that a modulating device comprises two or more actuating members or to the fact that two or modulating devices are present. By means of this combustion apparatus, it is possible to reduce the necessary number of controllers and sensors and thus - 5 - carry out active damping of combustion oscillation at a low outlay in terms of design. The saving of sensors and controllers which is achieved in this way leads to considerable cost savings. Preferably, a burner has in each case a fuel supply and a combustion-air supply, at least one actuating member being connected to the fuel supply or to the combustion-air supply. It is consequently possible to carry out the damping of combustion oscillation by regulating the fuel quantity supplied or the combustion-air quantity supplied. At the same time, one actuating member or a plurality of actuating members may also modulate another regulating variable or other regulating variables. Preferably, the burners are hybrid burners, each comprising a premixing burner and a pilot burner. The principle of a hybrid burner is described in the article "Progress in NOX and CO Emission Reduction of Gas Turbines", H. Maghon, P. Behrenbrink, H. Termuehlen and G. Gartner, ASME/IEEE Power Generation Conference, Boston, October 1990, to which reference is hereby made explicitly. Preferably, the combustion chamber is an annular combustion chamber of a gas turbine. The method for the active damping of combustion oscillation and the corresponding combustion apparatus are explained in more detail by way of example with reference to the accompanying drawing. The single Figure shows diagrammatically a gas turbine 33 directed along an axis 31- A compressor 2 is flow-connected to a turbine 3. A combustion apparatus 1 is connected between the compressor 2 and turbine 3. The combustion apparatus 1 consists of a combustion chamber 4, into which hybrid burners 5 open. Each hybrid burner 5 is composed of a conical premixing burner 6 which at the same time forms a combustion-air supply 6a. The premixing burner 6 surrounds a pilot burner 7 having its - 6 - own combustion-air supply 7a. Fuel 28 is supplied to each premixing burner 6 via a fuel supply conduit 23. Fuel 28 is supplied to each pilot burner 7 via a fuel supply conduit 24. The hybrid burners 5 are arranged partly in the combustion chamber 4 and partly in a prechamber 4a adjacent to the combustion chamber 4. An actuating member 8 is built into each fuel supply conduit 24 of the pilot burners 7. The actuating members 8 are connected electrically to a common logical control unit 9. The latter is connected electrically to a controller 10. The controller 10 is, in turn, connected electrically to a pressure sensor 11, in particular a piezoelectric pressure transducer 11. The pressure sensor 11 is arranged at a measuring point 11a in the combustion chamber 4. When the gas turbine 1 is in operation, combustion air 2 9 is compressed in the compressor 2 and is conducted into the prechamber 4a via a duct 21. The combustion air 2 9 passes out of the prechamber 4a into the air supply ducts 6a,7a of the premixing burners 6 and of the pilot burners 7. Fuel 28 is supplied to the pilot burners 7 via the fuel supply conduits 24 and is burnt in the combustion air 29 as a pilot flame. Fuel 28 is supplied to the premixing burners 6 via the fuel supply conduits 23 and is mixed with the combustion air 29. The fuel/air mixture entering the combustion chamber 4 is ignited at the pilot flame. Combustion oscillation may occur as a result of interaction with the acoustics of the combustion chamber 4. Such combustion oscillation causes natural acoustic oscillation 30 or a sound field 30 in the combustion chamber 4. This natural acoustic oscillation 30 is measured by the pressure sensor 11. The pressure sensor 11 emits a measurement signal. This measurement signal is converted into a regulating signal in the controller 10. Control of the actuating members 8 is determined from this regulating signal with the aid of the logical control unit 9. In this case, the control is - 7 - derived from the spatial position of a burner 5 and from the symmetry of the natural acoustic oscillation 30. The supply of fuel for the pilot burners 7 is regulated anti-cyclically to the combustion oscillation, that is to say the fuel mass flow of each pilot burner 7 is modulated in such a way that the fuel quantity injected into the combustion chamber 4 changes in time at the location of the flame or the combustion zone of the respective pilot burner 7 in phase opposition and with the same frequency as the combustion oscillation at the location of the flame. This results in damping of the combustion oscillation. The control of the actuating members 8 thus necessitates measurement at only one measuring point 11a. One sensor 11 and one controller 10 are saved. A simple method for the active damping of combustion oscillation and a combustion apparatus of simple design, in which active damping of combustion oscillation can be carried out, are obtained. The method is also suitable, in particular, for a combustion chamber 4 with more than two burners 5, for example for an annular combustion chamber, or for a silo combustion chamber with, for example, eight burners. The number of sensors 11 and controllers 10 is preferably as large as is just necessary for characterizing the natural acoustic oscillation 30. 8. WE CLAIM 1. Method for the active damping of combustion oscillation in a combustion chamber (4), the combustion oscillation being damped by means of at least two actuating members (8) which each influence a regulating variable and a measured variable being determined at atleast one measuring point (11a), characterized in that the actuating members (8) are controlled via a number of measured variables which is smaller than the number of actuating members (8)- 2. Method as claimed in claim 1, wherein a quantity of fuel (28) supplied for combustion or a quantity of combustion air (29) supplied for combustion is used as a regulating variable. 3. Method as claimed in claim 1 or 2, wherein natural acoustic oscillation (30) forms in the combustion chamber (4), exactly as many measured variables as are necessary for characterizing the natural oscillation being determined. 4. Method as claimed in one of the preceding claims, wherein natural acoustic oscillation (30), which is characterized via a number of measured variables, forms in the combustion chamber (4), the control of at least one actuating member (8) being determined via the symmetry of the natural acoustic oscillation (30). 9 5. Method as claimed in one of the preceding claims, wherein the actuating members (8) are controlled anti-cyclically to the combustion oscillation. 6. Combustion apparatus (1) for carrying out the method as claimed in claim 1, the apparatus comprising at least one burner (5) in a combustion chamber (4); and at least one modulating device, the modulating device comprising: a) a sensor (11) for recording a measured variable characterising the combustion oscillation, b) a controller (10) for converting a signal from the sensor (11) into a regulating signal, and c) an actuating member (8) for modulating a regulating variable, altogether at least two actuating members (8), for modulating a regulating variable each, being present, characterized in that the number of sensors (11) is smaller than the number of actuating members (8). b) 10. 7. Combustion apparatus (1) as claimed in claim 7, wherein each burner (5) has in each case a fuel supply (23,24) and a combustion-air supply (6,7), at least one actuating member (8) being connected to one of the fuel supply (23,24) and to the combustion-air supp1y (6,7). 8. Combustion apparatus (1) as claimed in claim 7 or 8, wherein the at least one burner (5) is a hybrid burner (5) which in each case comprises a premixing burner (6) and a pilot burner (7). 9. Combustion apparatus (1) as claimed in one of claims 7 to 9, wherein the combustion chamber (4) is an annular combustion chamber (4) of a gas turbine (33). Dated this 20th day of January 1998 OF L.S.DAVAR & CO APPLICANTS' A6ENT The invention relates to a method for the active damping of combustion oscillation in a combustion chamber (4) by means of at least two actuating members)8). The method is distinguished in that control of the actuating members (8) necessitates measurement of the combustion oscillation at fewer points than there are actuating members (8). This is achieved, in particular, by utilizing the symmetry of natural acoustic oscillation (30) in the combustion chamber (4).

Documents:

00106-cal-1998-abstract.pdf

00106-cal-1998-claims.pdf

00106-cal-1998-correspondence.pdf

00106-cal-1998-description (complete).pdf

00106-cal-1998-drawings.pdf

00106-cal-1998-form-1.pdf

00106-cal-1998-form-2.pdf

00106-cal-1998-form-3.pdf

00106-cal-1998-form-5.pdf

00106-cal-1998-gpa.pdf

00106-cal-1998-priority document others.pdf

00106-cal-1998-priority document.pdf

106-CAL-1998-(15-10-2012)-FORM-27.pdf

106-CAL-1998-CORRESPONDENCE.pdf

106-CAL-1998-FORM-27.pdf

106-CAL-1998-PA.pdf