EP1010939A1 - Combustion chamber with acoustic damped fuel supply system - Google Patents

Abstract

The apparatus (17) prevent cyclic fluctuations occurring in the combustion chamber (11) leading to fluctuations of the fuel flow (12) in the fuel supply system (15,16). The cyclic fluctuations occurring in the combustion chamber (11) are acoustic vibrations, and these lie in the range of the acoustic natural oscillations of the combustion chamber.

Description

TECHNICAL AREA

The present invention relates to the field of burners, in particular the burner for use in gas turbines. It concerns a burner with a fuel supply system, in which the fuel supply system is fuel transported to the burner, the fuel in the burner into a combustion chamber is injected where the fuel is burned.

STATE OF THE ART

Burners of gas turbines serve the fuel and the combustion air in a controlled manner and controllably inject into a combustion chamber and there to burn the fuel. The burners can be used in many different ways Arrangement in the wall of the combustion chamber, and will be charged with fuel by means of a fuel supply system. The injection The fuel in the burner must be in order to optimally control the combustion process in the various operating states of the turbine ensure controllable and done in the best possible way. Just that in recent times, more and more strict regulations regarding emissions of combustion processes make a highly specialized and complicated injection and mixing of combustion air and fuel in the Burner essential.

EP-B1-0 321 809, for example, describes a so-called double-cone burner become known for liquid and gaseous fuels without a premix section, in which combustion air supplied from outside through at least two inlet slots tangentially between displaced, hollow half-cones enters and flows there towards the combustion chamber, and in which on the Combustion chamber facing away, tapered side of the half-cones fuel centrally or from distribution channels that run along the air inlet slots Rows of holes are injected transversely into the incoming air.

Problematic with the injection of the fuel and its subsequent Combustion includes acoustic oscillations, which also under the term "singing flame" are known. These are mostly oscillations, which results from the interaction of inflows of the combustion mixture and the actual combustion process in the combustion chamber. These largely coherently periodic pressure fluctuations can, for example with a burner of the type mentioned above under typical operating conditions to acoustic vibrations with frequencies of about 80 to 100 Hz to lead. Since these frequencies have typical fundamental eigenmodes of Combustion chambers of gas turbines can collapse, make them thermoacoustic Oscillations are a problem.

PRESENTATION OF THE INVENTION

The invention is therefore based on the object, a burner with at least a fuel supply system through which a fuel flow to the burner is supplied, the supplied fuel is injected via fuel nozzles, and then burned in a combustion chamber provide who is able to train and reinforce periodic To prevent pressure fluctuations in the combustion chamber at least partially.

This object is achieved in a burner of the type mentioned by Means are provided which prevent that occurring in the combustion chamber periodic pressure fluctuations to fluctuations in the fuel flow in the Lead fuel supply system. The extensive prevention of the coupling the periodic pressure fluctuations and fluctuations in the fuel flow can be the undesirable, rocking amplification of pressure fluctuations prevent by the fuel flow in the combustion chamber. In particular, if the periodic pressure fluctuations occurring in the combustion chamber are acoustic vibrations, and especially when these are in the range of the acoustic natural vibrations of the combustion chamber such funds are of great advantage. Are the fluctuations in the fuel flow periodically in the fuel supply system, and in particular the frequency this periodic fluctuations in the fuel flow in the range of acoustic Natural vibrations of the combustion chamber, then this can be rocking Effect extremely pronounced and prevention of the same is particularly indicated his.

A first preferred embodiment of the invention is characterized in that that the means at least a first, immediately upstream of the fuel nozzles arranged volume include, through which volume the fuel flow flows, and that this first volume is upstream over a first Narrowing with the fuel delivery system located further upstream communicates. This first volume is essentially preferred chosen smaller than a certain critical volume, and especially continues the cross-sectional area of the first narrowing is less than a certain critical Cross-sectional area formed. Each of these measures reduces the measure the coupling of the pressure fluctuations to the fluctuations in the fuel flow and the measures are also without major construction technology Effort can be installed or even retrofitted in common burners.

Another embodiment of the invention is characterized in that a second volume is arranged upstream of the first constriction which the fuel flow flows, and that this second volume upstream via a second constriction with the one located further upstream Fuel supply system is connected. This arrangement allows the effective prevention of coupling under special, essentially unchangeable Design specifications of the burner and the fuel supply system.

Further embodiments of the burner with fuel supply system result themselves from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

zeigt eine schematische Darstellung einer Drossel zwecks Einführung der im weiteren verwendeten Terminologie;

Fig. 2

zeigt schematisch in a) eine Drossel mit vorgeschalteter Verengung und in b) eine Drossel vorgeschaltetem Volumen;

Fig. 3

zeigt eine schematische Darstellung eines Brenners des Typs EV17i der Anmelderin mit akustischen Dämpfungsmitteln im Brennstoffversorgungssystem;

Fig. 4

zeigt das Ankopplungsverhalten zwischen Druckschwankungen und Brennstoffstromschwankungen für einen Brenner des Typs EV17i der Anmelderin ohne akustische Dämpfungsmittel im Brennstoffversorgungssystem;

Fig. 5 und 6

zeigen das Ankopplungsverhalten zwischen Druckschwankungen und Brennstoffstromschwankungen für einen Brenner des Typs EV17i der Anmelderin mit verschiedenen akustischen Dämpfungsmitteln im Brennstoffversorgungssystem;

Fig. 7

zeigt schematisch eine Drossel mit zwei vorgeschalteten Volumina;

Fig. 8

zeigt schematisch einen Brenner des Typs EV18 der Anmelderin, wie er in einer Turbine des Typs GT26 der Anmelderin eingebaut ist, mit akustischen Dämpfungsmitteln im Brennstoffversorgungssystem; und

Fig. 9

zeigt das Ankopplungsverhalten zwischen Druckschwankungen und Brennstoffstromschwankungen für einen Brenner des Typs EV18 der Anmelderin, wie er in einer Turbine des Typs GT26 der Anmelderin eingebaut ist, mit akustischen Dämpfungsmitteln im Brennstoffversorgungssystem.

The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawings.

Fig. 1

shows a schematic representation of a throttle for the purpose of introducing the terminology used in the further;

Fig. 2

shows schematically in a) a throttle with upstream constriction and in b) a throttle upstream volume;

Fig. 3

shows a schematic representation of a burner of the type EV17i from the applicant with acoustic damping means in the fuel supply system;

Fig. 4

shows the coupling behavior between pressure fluctuations and fuel flow fluctuations for a burner of the type EV17i from the applicant without acoustic damping means in the fuel supply system;

5 and 6

show the coupling behavior between pressure fluctuations and fuel flow fluctuations for a burner of the type EV17i of the applicant with various acoustic damping means in the fuel supply system;

Fig. 7

shows schematically a throttle with two upstream volumes;

Fig. 8

shows schematically a burner of the type EV18 of the applicant, as it is installed in a turbine of the type GT26 of the applicant, with acoustic damping means in the fuel supply system; and

Fig. 9

shows the coupling behavior between pressure fluctuations and fuel flow fluctuations for a burner of the type EV18 from the applicant, as it is installed in a turbine of the type GT26 from the applicant, with acoustic damping means in the fuel supply system.

WAYS OF CARRYING OUT THE INVENTION

It turns out that especially when switching between different operating modes a gas turbine, such as when switching between premix and pilot mode, the fuel supply system become acoustically "soft" can, i.e. that pressure fluctuations in the combustion chamber affect the flow of the fuel and thus a mutually rocking coupling can take place. When switching, this can lead to pressure fluctuations large amplitude and thus lead to loud acoustic vibrations. This happens especially when injectors are almost closed or have a leak. Without measures to acoustically harden the fuel supply system But it can also happen that the instabilities are critical in almost the entire switching range. The instabilities fall in their frequency together with eigenmodes of combustion chambers, so these acoustic vibrations can become a serious problem.

The possibilities for acoustic hardening of a fuel supply system are initially to be rationalized based on some theoretical considerations and are explained, then the technical exemplary embodiments described by the applicant's burners EV17i and EV18.

In the simplest case, the fuel supply system can be viewed acoustically as shown in FIG. 1 as a throttle, ie as an opening 10 with a negligible length and cross-sectional area A _F , through which fuel the density ρ _F from a large volume at pressure p _F to another large one Volume, the combustion chamber 11, flows at pressure p _I. It is assumed that the following applies: p _F > p _I. In addition, it is assumed that the fuel supply volume has a constant pressure p _F , while the pressure in the injection space p _I can be subject to fluctuations. Under these conditions, the laws of fluid mechanics result in the following relationship between fluctuations in the pressure in the injection space, Δ p _I , and fluctuations in the fuel injection speed Δ u _F : Δ p I. = -ρ F u F Δ u F .

The pressure fluctuations in the injection space therefore have a directly linear effect to fluctuations in fuel injection speed 12 and vice versa, i.e. there is a direct coupling of the two sizes. Actually behave the fuel supply systems of the GT24 gas turbines and Applicant's GT26 in the area of eigenmodes of the combustion chambers, i.e. around oscillation frequencies of 100 Hz according to the equation above. As a result, instabilities arise in the system consisting of the fuel supply system, Burner and combustion chamber on once the fuel injection speed 12 falls below a value of approximately 125 m / s.

More complicated fuel supply systems can be described using the following formula: α (ω) Δ p I. = ρ F u F Δ u F , where ω is the angular frequency of the periodic pressure oscillations and α = α (ω) is a complex-valued function of the angular frequency, the magnitude of which applies: | α (ω | ≤1. Consequently, compared to simple injection systems, the critical fuel injection speed u _{FC can} at least be reduced to that Value | α (ω) | u _FC One way to achieve arbitrarily small values for α at any oscillation frequency is, for example, the use of check valves with a second, upstream opening of variable cross-sectional area. In this case, even for very small ones Fuel injection speeds of pressure drop across the fuel supply system are kept to a minimum.

führt, wobei c_F die Schallgeschwindigkeit im Brennstoffgas darstellt. Die komplewertige Responsefunktion α(ω) ist somit gegeben durch

und es ist leicht ersichtlich, dass eine solche Leitung zu einer perfekten akustischen Härtung des Brennstoffversorgungssystems führt, dies aber nur bei im Bereich der diskreten Frequenzwerte ω = (2N + 1) πcF 2L , für ganzzahlige Werte von N It can now be shown that a fuel nozzle of cross-sectional area _AF with an upstream fuel supply line of length L and cross-sectional area _AT , as is shown schematically in FIG. 2a), forms an acoustic coupling of the shape

leads, where c _{F represents} the speed of sound in the fuel gas. The complete response function α (ω) is thus given by

and it is easy to see that such a line leads to a perfect acoustic hardening of the fuel supply system, but only in the range of the discrete frequency values ω = (2nd N + 1) π c F 2nd L , for integer values of N

Acoustic hardening in a whole frequency range can only be achieved if the quotient A F c F A T u F is less than or equal to 1 in size. Consequently, in view of the fact should that the Mach number M = u _F / c _F is for critical fuel injection typically range from 0.25 to 0.3, the cross-sectional area A _T of the fuel line is not more than 3 to 4 times as large as the cross-sectional area _F of the Be fuel nozzle. In other words, the fuel flow rate in the line should be at least a quarter to a third of the fuel injection rate u _FC in the fuel nozzle 10. Unfortunately, this requirement cannot usually be met in practice without serious disadvantages.

In addition, it must be noted that each volume between the fuel line 15 and the fuel _nozzle 10 must be small compared to a critical volume V _CRIT , which is given by:

Normally, none of these conditions is met, as the following example is intended to demonstrate: FIG. 3 schematically shows a burner of the applicant's type EV17i, such as is installed in a gas turbine of the applicant's type GT26. The fuel is supplied to the burner 14 via a fuel supply line 15. The line 15 initially opens into an annular distribution space 16, from which fuel distribution channels run along the conical outer surface of the double-cone burner. On the side facing the burner, these distribution channels have a plurality of fuel nozzles 10, through which the fuel can flow into the burner and thus into the combustion chamber 11. Assuming typical switching conditions for such a burner, it can be seen that the volume between the fuel supply line 15 and the fuel nozzles 10, which is formed by the annular distribution space 16 and the distribution channels and is approximately 650 cm ^3, is the critical volume under these conditions V _CRIT of 271cm ³ _exceeds by a factor of 2. Likewise, the diameter of the fuel feed 15 is approximately 38 mm, although it should not be more than 21 mm according to the above criterion.

A simple way of acoustically hardening the specified structure, which is associated with a small outlay in terms of construction, is the introduction of a Helmholtz volume with a suitable cross-sectional area e A and length L between the fuel supply line 15 and the fuel nozzles 10, as is shown schematically in FIG. 2b). It is of great advantage to set the dimensioning of the volume and the constriction in such a way that at least one resonance of the fuel supply system coincides with the most important fundamental acoustic natural frequency of the combustion chamber.

If one takes typical switching conditions for an EV17i burner, as listed in Table 1, and as they occur in a gas turbine of the type GT26B, the response function α (ω) can be calculated. Size unit value print bar 18th Cross-sectional area of the nozzle m ² 0.000111 Temperature of methane K 323 Mass flow of methane kg / s 0.167 Length of the line m 2nd Diameter of the pipe m 0.038 Length of the first volume m 0.1 Cross-sectional area of the first volume m ² 6.5e-3

The damping factor α (ω) (attenuation factor) as a function of the frequency of the pressure fluctuations under consideration for the conditions listed in Table 1 is shown in FIG. A value of α (ω) = 1 as the upper limit corresponds to a normal throttle according to the schematic illustration in FIG. 1, and thus a maximum coupling of the pressure fluctuations in the combustion chamber 11 to the fuel flow, which means a value of α (ω) = 0 that a pressure fluctuation Δ p _I in the combustion chamber 11 is unable to cause a change in the fuel injection speed, Δ u _F. It can be seen in FIG. 4 that the damping only occurs in narrow areas around the resonance frequencies of the fuel supply system. It can also be clearly seen from FIG. 4 that, particularly in the region of the eigenmodes of the combustion chamber under consideration, that is to say at approximately 90 Hz, the fuel supply system behaves like a simple and almost completely undamped throttle, and thus the resonance behavior of the fuel supply system does not at all match that of the combustion chamber is coordinated.

If a line constriction 17, as also shown in FIG. 3, is introduced into the fuel supply line 15, the resonance frequency of the fuel supply system shifts and widens in the range from 90 to 100 Hz and the minimum value of α at this frequency is approximately 0.35-0.4. This is done with a simple use of a slide-in device 17 (or a constriction caused in another way) of 300 mm in length and an inner diameter of 21 mm. A further improvement can be achieved with the values given in table 2 by increasing the length of the insert 17 from 300 mm to 500 mm and additionally reducing the first volume from 650 cm ³ to 400 cm ³ . Size unit value print bar 18th Cross-sectional area of the nozzle m ² 0.000111 Temperature of methane K 323 Mass flow of methane kg / s 0.167 Length of the line m 0.5 Diameter of the pipe m 0.021 Length of the first volume m 0.1 Cross-sectional area of the first volume m ² 4.0e-3

The absorption profile for the values from Table 2 is shown in FIG. 5. Essentially The minimum value changes as a result of these further measures from α at the frequency of 90 to 100Hz to a value of 0.2, which is a doubling corresponds to the absorption efficiency in comparison to the first example.

A further improvement can be achieved with the values from Table 3, namely by doubling the length of the constriction 17 again and halving the volume again. Size unit value print bar 18th Cross-sectional area of the nozzle m ² 0.000111 Temperature of methane K 323 Mass flow of methane kg / s 0.167 Length of the line m 1 Diameter of the pipe m 0.021 Length of the first volume m 0.05 Cross-sectional area of the first volume m ² 2.0e-3

The resulting absorption profile is shown in FIG. 6, it shows in the resonance range from 90 to 100Hz an absorption of remarkable 90% in Compared to the simple throttle.

As a further exemplary embodiment, the acoustic hardening of a burner of the type EV18 from the applicant, as is installed in a gas turbine of the type GT26, is to be used. In such a gas turbine, as already shown in FIG. 8 with acoustic hardening, the fuel is supplied to the burner 14 via annular fuel distribution lines 18, which jointly supply the burners arranged in a ring in the annular combustion chamber of the turbine. The fuel branches off from the annular fuel distribution line 18 via a second constriction 19 and enters a volume which is normally formed by the volumes 20 and 22 without the partition 23 shown in FIG. 8 and the first constriction 21. The fuel is guided through the fuel distribution channels 22 along the cone of the burner 14 and passes through the fuel nozzles 10 into the combustion chamber 11, where it is mixed with combustion air. For practical reasons, a solution to acoustic hardening must now be found here, in which the fuel distribution system has to be changed as little as possible. The easiest way to do this is to arrange two volumes upstream of the fuel nozzle 10 and connected to the fuel supply line via two constrictions, as is shown schematically in FIG. A possible technical implementation is shown in Figure 8. A partition 23 separates the large volume into the fuel distribution channels 22 and a second volume 20, and a constriction 21, which is wound around the burner and is designed as a line, connects the two volumes. If the first constriction 21 is a line of 1.2 m length and 20 mm inside diameter and typical switching conditions in such a gas turbine, as shown in Table 4, the absorption characteristic in FIG. 9 is obtained. Size unit value print bar 18th Cross-sectional area of the nozzle m ² 9.08e-5 Temperature of methane K 323 Mass flow of methane kg / s 0.133 Length of the second narrowing m 0.04 Cross-sectional area of the second constriction m ² 0.000314 Second volume m ³ 0.0015 Length of the first narrowing m 1.2 Cross-sectional area of the first constriction m ² 0.000314 First volume m ³ 0.00015

As can be seen from FIG. 9, this arrangement and dimensioning are used of two volumes connected in series a perfect damping of the acoustic coupling with the natural frequency of the combustion chamber of approx. 90 Hz a considerable width of the resonance condition, with a deviation of approx. ± 30Hz namely 2/3 are still absorbed by the resonance condition.

LIST OF DESIGNATIONS

10th

Fuel nozzle

11

Combustion chamber

12th

Fuel injection speed, fuel flow

13

first volume

14

burner

15

Fuel supply line

16

annular distribution space

17th

Line narrowing

18th

annular fuel distribution line

19th

second narrowing

20th

second volume

21

first narrowing

22

Fuel distribution channel, first volume

23

partition wall

Claims (12)

Burner (14) with at least one fuel supply system (15, 16, 18, 20, 22), through which a fuel flow (12) is fed to the burner (14), the fuel supplied is injected via fuel nozzles (10), and then in a combustion chamber (11) is burned,
characterized in that
Means (17, 21, 23) are provided which prevent periodic pressure fluctuations occurring in the combustion chamber from leading to fluctuations in the fuel flow (12) in the fuel supply system (15, 16, 18, 20, 22). Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to claim 1, characterized in that in the combustion chamber (11) occurring periodic pressure fluctuations acoustic Vibrations are, and that these are in the area of acoustic Natural vibrations of the combustion chamber (11) lie. Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to claim 2, characterized in that the fluctuations the fuel flow (12) in the fuel supply system (15,16,18,20,22) are periodic, and that in particular the frequency these periodic fluctuations in fuel flow (12) in the area of the acoustic natural vibrations of the combustion chamber (11) lies. Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to one of claims 1 to 3, characterized in that the means at least a first, immediately upstream of the Volume (16, 22) arranged in the fuel nozzles (10), through which volume (16, 22) the fuel stream (12) flows, and that this first volume (16,22) upstream over a first Narrowing (17.21) with that located further upstream Fuel supply system (15,18,20) communicates. Burner (14) with a fuel supply system (15, 16, 18, 20, 22) according to claim 4, characterized in that the first volume (16, 22) is smaller than a critical volume (V _crit ), and that the critical volume ( V _crit ) is approximately given as the quotient of the product of the cross-sectional area (A _F ) of the opening of the fuel nozzle (10) and the square of the speed of sound (c _F ) in the first volume (16,22), and the product of the angular frequency (ω ) the acoustic vibration and the flow velocity (u _F ) of the fuel stream (12). Burner (14) with fuel supply system (15,16,18,20,22) according to any one of claims 4 or 5, characterized in that the first constriction (17,21) has a cross sectional area (A _T) which is substantially smaller or equal to the product of the cross-sectional area (A _F ) of the fuel nozzle (10) and the inverse Mach number ( 1 / M = c F / u F ) is. Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to one of claims 4 to 6, characterized in that the dimensions of the first volume (16, 22) and the first narrowing (17,21) are chosen such that a resonance of the absorption of the fuel supply system essentially in the area the eigenmodes of the combustion chamber (11). Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to one of claims 4 to 7, characterized in that the first volume (16) through an annular distribution space and by downstream, at least partially outside the distribution channels of the burner (14) are formed, and that the fuel from the distribution channels through the fuel nozzles (10) flows into the combustion chamber (11). Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to claim 8, characterized in that the first constriction (17) through a tubular insert in an upstream of the first volume (16) arranged fuel supply line (15) or through a tapered line section between the fuel supply line (15) and the first volume (16) becomes. Burner (14) with a fuel supply system (18, 20, 22) according to a of claims 4 to 7, characterized in that upstream a second volume (20) is arranged in the first constriction (21) through which the fuel stream (12) flows, and that this second volume (20) upstream via a second constriction (19) with the fuel supply system located further upstream (18) communicates. Burner (14) with fuel supply system (15, 16, 18, 20, 22) according to claim 10, characterized in that the dimensions of first volume (22) and second volume (20) and first Constriction (21) and second constriction (19) are selected such that resonate the absorption of the fuel supply system essentially in the area of the mode of the combustion chamber (11) lies. Burner (14) with a fuel supply system (18, 20, 22) according to a of claims 10 or 11, characterized in that the first constriction (21) is formed as a line of small cross-section which is the first volume (22) with that of the first volume (22) with a partition (23) separated second volume (20) connects.

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