EP2103876A2 - Burner for gas turbine with scavenging mechanism for the fuel nozzles - Google Patents

Abstract

The burner has a fuel nozzle which is provided with multiple fuel outlets (23) that are connected with a fuel pipe through which selective fuel is conveyed. Different static pressures of air flow are formed between a fuel pipe with fuel flow and fuel pipes without fuel flow and between individual fuel outlets by selection of different pressures in the fuel pipes. The fuel outlets are arranged at regions of the burner with different static pressures. An air swirl device (12) is designed for producing differences of pressure between the individual fuel outlets. An independent claim is also included for a method for flushing fuel pipes and/or fuel outlets of a gas turbine burner.

Description

The invention relates to a gas turbine burner according to the features of the preamble of claim 1 and to a method for purging a fuel nozzle.

As a general state of the art for a burner for an aircraft gas turbine, for example, on the US Pat. No. 6,543,235 B1 directed.

To reduce the thermally induced nitrogen oxide emissions different concepts for fuel nozzles are known. One possibility is the operation of burners with a high air-fuel excess. Here, the principle is exploited that due to the lean mixture and at the same time ensuring sufficient spatial homogeneity of the fuel-air mixture, a reduction in the combustion temperatures and thus the thermally induced nitrogen oxides is favored.

In many such burners also an internal fuel staging is applied. This means that in addition to a designed for low NOx emissions main fuel injection in addition a pilot stage is integrated into the burner, which is operated with an increased fuel-air content and the stability of the combustion is to ensure a sufficient Brennkammerausbrand and ignition properties sufficient. The fuel for the main stage of such a lean burner can be introduced here as a closed film or by means of discrete fuel outlet holes as a multiple jet.

Particularly in the embodiments for discrete jet injections, there is a high risk due to the small bore diameter (usually D <1.0 mm) and the positioning of the fuel metering boreholes near components subjected to hot gas the fuel coking in the fuel outlet holes. The background to this is the process of thermal oxidation of the fuel, which starts with increasing heating of the fuel. From a fuel temperature of about 150 ° C and a corresponding temporal effectiveness of the thermal load, the incipient chemical processes can lead to a deposit formation.

The consequence of the formation of deposits is initially a change in the flow characteristics of the fuel in the affected fuel outlet holes due to an increased pressure drop. In addition, there may be a complete blockage of the fuel outlet holes. Both effects lead to a significant deterioration of the fuel-air mixture in the combustion chamber, associated with an increase in the emission values and a detrimental effect on the temperature distribution within the combustion chamber and the temperature traverse in the combustion chamber outlet. With a high deposit formation, the service life of the combustion chamber and of the turbine can thus be impaired.

The risk of fuel coking increases when the fuel line is shut off and some of the fuel lines are no longer continuously fueled. This is e.g. For tiered lean burners, it is possible to switch off main burners step by step or completely when passing between different load conditions. A portion of the fuel may remain in the fuel lines which are no longer continuously flowing and is then heated due to the high metal temperatures of the fuel lines and the radiation effect of the flame.

The invention has for its object to provide a gas turbine burner and a method for its flushing, which with a simple structure and simple, reliable application avoid a deposit of fuel and its reaction products in the area of the fuel nozzle.

According to the invention the object is achieved by the combination of features of the independent claims, the subclaims show further advantageous embodiments of the inventions.

In order to avoid the risk of coking of the fuel in the fuel outlet holes, a flush mechanism for the shut-off fuel lines of a burner is proposed, which allows a complete automatic emptying of the fuel lines. By way of a corresponding interconnection of individual fuel lines to one another, the basic principle is to impose different static pressures P _{a, i} in the outlet cross sections of the fuel lines and to generate pressure differences for the autonomous emptying of the fuel lines.

1. A. Profilierung der Oberflächenkontur strömungsführender Bauteile vor den Kraftstoffaustrittsbohrungen
2. B. Wahl geeigneter Ausbringungsorte für die Kraftstoffeindüsung mit unterschiedlichen statischen Drücken der Luftströmung
3. C. gestaffelte Anordnung der Kraftstoffaustrittsbohrungen
4. D. Anpassung der Schaufelstellung, -profilierung für Luftdraller
5. E. unterschiedliche Bohrungsdurchmesser der diskreten Eindüsung
6. F. Wegeventil im Brenner zur Luftspülung

To set different static discharge pressures in the fuel lines to support the emptying of the manifolds, fuel lines and / or fuel outlet holes, the following measures are proposed according to the invention:

1. A. Profiling the surface contour of flow-leading components in front of the fuel outlet holes
2. B. Choice of suitable application locations for the fuel injection with different static pressures of the air flow
3. C. Staggered arrangement of the fuel outlet holes
4. D. Adjusting the blade position, profiling for air swirlers
5. E. Different bore diameter of the discrete injection
6. F. Directional valve in the burner for air purge

Combinations of the measures A to E are also possible according to the invention. In addition, the use of a directional control valve with two switch positions is advantageous (measure F).

Fig. 1:

eine schematische Darstellung eines Brenners für eine Fluggasturbine gemäß dem Stand der Technik,

Fig. 2:

eine schematische Darstellung von Hauptkomponenten für einen erfindungsgemäßen Magerbrenner mit kontrollierter Kraftstoffinhomogenität in der Hauptstufe,

Fig. 3:

eine schematische Darstellung der Positionierung der erfindungsgemäß vorgesehenen Maßnahmen zur Unterstützung des Spülvorgangs stehenden Kraftstoffs für die Hauptstufe eines Magerbrenners,

Fig. 4:

eine schematische Teildarstellung des erfindungsgemäßen Grundprinzips der Entleerung von Hauptkraftstoffleitungen durch eine Variation des anliegenden Drucks an den Austrittsöffnungen der Kraftstoffaustrittsbohrungen,

Fig. 5:

eine schematische Darstellung der Staffelung der Kraftstoffaustrittsöffnungen zur Ausnutzung unterschiedlicher anliegender Drücke an den Kraftstoffaustrittsöffnungen zur selbsttätigen Entleerung der Kraftstoffleitungen,

Fig. 6:

eine schematische Darstellung des Entleerungsvorgangs stehenden Kraftstoffs für die Hauptstufe eines Magerbrenners mit Hilfe eines Wegeventils in Schaltstellung 1 (Kraftstoffdurchfluss durch die Kraftstoffleitung zur Kraftstoffaustrittsbohrung, und

Fig. 7:

eine Darstellung, analog Fig. 6, in Schaltstellung 2 zur Durchleitung von Spülluft durch einen Teil der Kraftstoffleitung.

In the following the invention will be described by means of embodiments in conjunction with the drawing. Showing:

Fig. 1:

a schematic representation of a burner for an aircraft gas turbine according to the prior art,

Fig. 2:

a schematic representation of main components for a lean burn burner with controlled fuel inhomogeneity according to the invention in the main stage,

3:

a schematic representation of the positioning of the inventively provided measures to support the purging of standing fuel for the main stage of a lean burn burner,

4:

a schematic partial view of the basic principle according to the invention of the emptying of main fuel lines by a variation of the applied pressure at the outlet openings of the fuel outlet holes,

Fig. 5:

a schematic representation of the staggering of the fuel outlet openings for exploiting different applied pressures at the fuel outlet openings for the automatic emptying of the fuel lines,

Fig. 6:

a schematic representation of the emptying process of stationary fuel for the main stage of a lean burn burner by means of a directional control valve in switching position 1 (fuel flow through the fuel line to the fuel outlet bore, and

Fig. 7:

a representation, analog Fig. 6 , in switch position 2 for the passage of purging air through a part of the fuel line.

The Fig. 1 shows a schematic embodiment of an example of the prior art. In this case, a fuel nozzle 1 is provided, which comprises a burner axis 4 and a combustion chamber 2 is assigned, in which a combustion chamber flow 3 results. Reference numeral 17 exemplifies a pilot fuel injection.

In Fig. 2 For example, a prior art lean burn combustor with controlled fuel inhomogeneity for a main stage of a gas turbine combustor is shown in the prior art. The lean burn burner comprises an inner swirl generator 11 as well as a central swirl generator 12 and an outer swirl generator 13, which are assigned to an inner flow channel 14 and a central flow channel 15 and an outer flow channel 16. The reference numeral 17 shows a pilot fuel injection, a main fuel injection is designated 18. Furthermore, an inner downstream surface of the main fuel injection (film depositor) 19 is provided. Reference numeral 20 denotes an outer surface of the main fuel injection, the trailing edge of which is designated 21. The reference numeral 23 shows fuel discharge holes of the main fuel injection. 24 shows a flame stabilizer. Furthermore, an outer burner ring 27 (dome) is provided. Reference numeral 28 denotes the inner contour of the outer burner ring. Furthermore, a pilot fuel supply 29 and a main fuel supply 30 are provided. The reference numeral 33 shows an exit surface of the pilot fuel injection, while the reference numeral 34 shows an exit contour of the inner leg of the flame stabilizer.

The Fig. 3 shows a schematic representation of different measures for impressing the different static pressures of the air supply (air flow) and for generating pressure differences. As a result, there is support for the purging process of stationary fuel for the main stage of a lean burn burner.

According to measure A, the surface contour of flow-guiding components is profiled in front of the fuel outlet bores 23, so that different pressures in the area of the fuel outlet bores 23 result, which lead to emptying (empty suction) of the fuel lines.

According to the measures B and C shown schematically, it is possible to choose the application locations and arrangements of the fuel outlet holes 23 so as to give different static pressures. In accordance with measure C, a staggered arrangement of the fuel outlet bores takes place along the burner axis 4.

According to measure D, it is possible to change the blade positions and / or the profiles of the air swirler (air swirler 12) in the middle flow channel 15. This results in different pressure conditions, which act on the individual fuel outlet holes differently and thus lead to a negative pressure (suction).

According to measure E, it is also possible to provide different bore diameter of the discrete fuel injection.

The Fig. 4 shows a schematic representation of the invention provided basic principle of emptying the main fuel lines by a variation of the applied pressure at the fuel outlet holes 23. In Fig. 4 an example is shown in which the use of a lower static pressure for every second, designated in the figure with I. Fuel outlet bore, which are provided alternately to fuel outlet holes II.

The Fig. 5 shows a schematic representation in which a staggering of the fuel outlet holes 23 along the burner axis 4 is provided. Out Fig. 5 result in the different pressure ratios when assigning the staggered fuel outlet holes 23 to a fuel line. 5

The 6 and 7 each show the use of a directional control valve 6 in the fuel line 5. The Fig. 6 shows a switching position of the directional control valve 6, in which fuel through the fuel line 5 in a free area of a subsequent fuel line 7, which is connected to the fuel outlet bore 23, is passed. A purge line 8 is out of action.

The Fig. 7 shows a switching position of the directional control valve 6, in which air is passed through the purge line 6 in the fuel line 7 and thus to the fuel outlet bore 23, while the supply of fuel through the fuel line 5 is suppressed. This measure corresponds to measure E.

It is thus to be stated as follows:

The location of the corresponding constructive measures for a burner is in Fig. 2 shown schematically. The measures can be transferred to any burner with a corresponding discrete fuel injection, for example, the application in Fig. 2 shown for a known lean burn burner.

The principle of emptying standing fuel by utilizing different static pressures on the components of the fuel nozzle or a specific local variation of the static Pressure at the fuel outlet holes is in Fig. 3 shown.

The aim of all measures described above is to position the different application locations for the fuel so that on the one hand different local static pressures of the air flow for emptying standing fuel can be used but also an optimized fuel-air mixture to ensure lowest emissions is possible. Due to the different static pressures of the air at the surface (wall pressures), it follows that air enters the one recess of the fuel line and thus flushes or expels the fuel from the other recess.

Measure A - Profiling of the surface contour in front of the fuel outlet holes and measure D - Adjustment of the blade position and profile:

By suitable design of a flow-pressurized component upstream of the fuel injection, e.g. by means of circumferential profiling of the surface geometry by a lamella shape, a variation of the static pressure can be achieved in the circumferential direction. By a targeted coordination of the surface contouring with the number and position of the outlet bores can then cause a depletion of the stationary fuel in a shutdown of the main fuel then applied pressure drop. A similar effect can be brought about by adapting the circumferential variation of the blade position of air swirlers in the flow channel of the main stage, in particular on the outer radius and by varying the blade profiling.

Measure B - Selection of suitable application locations for the fuel injection, taking advantage of the already existing variation of static pressures:

Another way to set different static pressure drop for the fuel holes is a suitable choice of application sites on the inner contour of the main stage. Here, the presence of an existing by the aerodynamics of the burner static pressure distribution is exploited to position the interconnected fuel outlet holes in areas high or low static pressures and to generate a necessary for the emptying of the stationary fuel pressure difference (s. Fig. 4 ).

Measure D - staggered arrangement of the fuel outlet holes:

As a further measure, a different interconnection of the fuel lines of e.g. proposed more than two fuel lines and / or different positioning of interconnected fuel outlet holes in the axial and circumferential directions.

Measure E - different bore diameters of the discrete injection:

Furthermore, it is proposed to set different pressure levels at the fuel outlet holes, in addition to the methods described above to provide different bore diameter for interconnected fuel lines to also allow by means of applied different static pressures an automatic emptying of fuel.

Measure F - directional valve:

Another method for automatic emptying is the integration of a directional valve with eg two switching positions in the burner (s. Fig. 5 ). In normal operation, the main fuel flows continuously through the directional valve. The shutdown of the fuel causes a movement of the directional control valve in a second switching position in which the continuous flow of the fuel is interrupted. Due to the presence of appropriate channel geometries, which can be located either in the middle air duct or upstream in the burner arm, then there is the possibility for continuous flow of purging air. This ensures complete emptying of the fuel lines. As soon as the fuel is to be switched on again, the movement of the directional control valve into the starting position causes the release of the pending fuel while the purge air channel is blocked.

• Vermeidung von Verkokungserscheinungen in den Kraftstoffkanälen von Brennern;
• Verhinderung einer Verschlechterung der Betriebseigenschaften der Brennkammer bzw. des Triebwerks (hinsichtlich Emissionen, Schwingungsneigung, Temperaturprofil im Austritt der Brennkammer, Lebensdauer von Brennkammer und Turbine etc.).

According to the invention, the following advantages arise, inter alia:

• Avoiding coking phenomena in the fuel channels of burners;
• Prevention of deterioration of the combustion chamber or engine operating characteristics (in terms of emissions, vibration tendency, temperature profile at the outlet of the combustion chamber, service life of the combustion chamber and turbine, etc.).

LIST OF REFERENCE NUMBERS

1

fuel nozzle

2

combustion chamber

3

combustor flow

4

Brenner

5

Fuel line

6

way valve

7

Fuel line

8th

flushing line

11

inner air swirl generator

12

medium air swirl generator

13

outer air swirl generator

14

inner flow channel

15

medium flow channel

16

outer flow channel

17

Pilot fuel injection

18

Main fuel injection

19

inner downstream surface of the main fuel injection, film layer

20

outer surface of the main fuel injection

21

Trailing edge of the main fuel injection

23

Fuel outlet holes of the main fuel injection

24

flame stabilizer

27

outer burner ring (dome)

28

inner contour of the outer burner ring

29

Pilot fuel supply

30

Main fuel supply

31, 32

33

Exit surface of the pilot fuel injection

34

Outlet contour of the inner leg of the flame stabilizer

Claims (13)

A gas turbine combustor for a gas turbine having a fuel nozzle (1) provided with a plurality of fuel discharge holes (23) each connected to a fuel line (5, 7, 29, 30) through which fuel is selectively passable, characterized in that between individual fuel outlet holes (23) are formed different static pressures of the air flow between the fuel line with fuel flow and fuel lines without fuel flow. Gas turbine burner according to claim 1, characterized in that the different static pressures by selecting different pressures in the fuel lines (5, 7, 29, 30) are formed. Gas turbine burner according to claim 1 or 2, characterized in that the surface contour of flow-guiding components in front of the fuel outlet openings (23) is formed contoured. Gas turbine burner according to one of claims 1 to 3, characterized in that the fuel outlet holes (23) are arranged at regions of the burner with different static pressures. Gas turbine burner according to one of claims 1 to 4, characterized in that the fuel outlet holes (23), relative to a burner axis (4), are arranged staggered. Gas turbine burner according to one of claims 1 to 5, characterized in that blades of a swirl generator (12) are designed to generate pressure differences between individual fuel outlet holes (23). Gas turbine burner according to claim 6, characterized in that the position of the blades of the swirl generator for generating pressure differences between individual fuel outlet holes (23) is configured. Gas turbine burner according to claim 6 or 7, characterized in that the profiling of the blades of the swirl generator for generating pressure differences between individual fuel outlet holes (23) is configured. Gas turbine burner according to one of claims 1 to 8, characterized in that the fuel outlet holes (23) have different bore diameters. Gas turbine burner according to one of claims 1 to 9, characterized in that selective fuel lines (5, 7) via one-way valve (6) can be acted upon with purge air. A method of purging fuel lines (5, 7, 29, 30) and / or fuel exit bores (23) of a gas turbine combustor for a gas turbine having a fuel nozzle (1), wherein different static pressures are imposed on individual fuel exit bores (23). A method according to claim 11, characterized in that the different static pressures by selecting different pressures in the fuel lines (5, 7, 29, 30) are formed. Gas turbine burner according to one of claims 11 or 12, characterized in that fuel lines (5, 7) are acted upon by scavenging air.

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