METHOD FOR OPERATING A COMBUSTION SYSTEM

Abstract

A method for operating a combustion system of a combustion section of a gas turbine engine having at least one main burner arrangement and at least one pilot burner arrangement, wherein the at least one main burner arrangement and the at least one pilot burner arrangement are operated with an air-fuel mixture. The method includes: operating the at least one main burner arrangement with O.sub.2-lean air, enriching an air of the air-fuel mixture of the at least one pilot burner arrangement and/or a fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement with oxygen and preferably with pure oxygen.

Claims

1. A method for operating a combustion system of a combustion section of a gas turbine engine comprising at least one main burner arrangement and at least one pilot burner arrangement, wherein the at least one main burner arrangement and the at least one pilot burner arrangement are operated with an air-fuel mixture, wherein the method comprises: operating the at least one main burner arrangement with O.sub.2-lean air, enriching an air of the air-fuel mixture of the at least one pilot burner arrangement and/or a fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement with oxygen.

2. The method according to claim 1, further comprising: enriching the air of the air-fuel mixture of the at least one pilot burner arrangement and/or the fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement with oxygen so that an oxygen content of the air-fuel mixture burned by the at least one pilot burner arrangement is at least 5% higher than an oxygen content of the air feed to the at least one pilot burner arrangement beforehand of a mixing with the oxygen.

3. The method according to claim 1, wherein the air of the air-fuel mixture of the at least one pilot burner arrangement beforehand of the mixing with oxygen is O.sub.2-lean air.

4. The method according to claim 3, further comprising: providing the O.sub.2-lean air from an oxygen-extraction process.

5. The method according to claim 1, further comprising: mixing the air of the air-fuel mixture of the at least one pilot burner arrangement with the oxygen resulting in an O.sub.2-enriched working fluid, and further mixing the O.sub.2-enriched fluid with fuel resulting in the air-fuel mixture for operating the at least one pilot burner arrangement.

6. The method according to claim 1, further comprising: determining a feeding pressure of the oxygen and/or determining a feeding pressure of the fuel and, controlling a flame stability of a pilot flame of the at least one pilot burner arrangement due to the determined feeding pressure of the oxygen and/or the feeding pressure of the fuel.

7. The method according to claim 1, further comprising: controlling a feeding of an oxygen flow by at least one valve.

8. The method according to claim 1, further comprising: stopping a feeding of oxygen to the air of the air-fuel mixture of the at least one pilot burner arrangement and/or the fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement in case an oxygen content above 18% oxygen is detected in the air feed to the at least one pilot burner arrangement.

9. The method according to claim 1, further comprising: purging an oxygen feed line with a flow medium in case an oxygen content above 18% oxygen is detected in the air feed to the at least one pilot burner arrangement.

10. A combustion system of a combustion section of a gas turbine engine comprising: at least one main burner arrangement and at least one pilot burner arrangement, wherein the at least one main burner arrangement and the at least one pilot burner arrangement are operateable with an air-fuel mixture, wherein the air for operating the at least one main burner arrangement is O.sub.2-lean air, and at least one mixing device adapted to enrich oxygen in an air of the air-fuel mixture of the at least one pilot burner arrangement and/or in a fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or in the air-fuel mixture of the at least one pilot burner arrangement by mixing the air of the air-fuel mixture of the at least one pilot burner arrangement and/or the fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement with oxygen.

11. The combustion system according to claim 10, further comprising: at least one oxygen feed line at least one air feed line and/or at least one O.sub.2-enriched working fluid feed line and/or at least one fuel feed line, wherein an at least first mixing device is positioned to be feed with oxygen by the at least one oxygen feed line and with air by the at least one air feed line and/or wherein an at least second mixing device is positioned to be feed with the O.sub.2-enriched working fluid by the at least one O.sub.2-enriched working fluid feed line and with fuel by the at least one air feed line.

12. The combustion system according to claim 10, further comprising: at least one valve to control a feed of oxygen to the at least one feed line for the oxygen.

13. The combustion system according to claim 10, adapted for operating a method comprising: operating the at least one main burner arrangement with O.sub.2-lean air, and enriching an air of the air-fuel mixture of the at least one pilot burner arrangement and/or a fuel of the air-fuel mixture of the at least one pilot burner arrangement and/or the air-fuel mixture of the at least one pilot burner arrangement with oxygen.

14. A gas turbine engine comprising: at least one combustion system according to claim 10.

15. The method according to claim 1, wherein the air is enriched with pure oxygen.

16. The combustion system according to claim 10, wherein the oxygen in the air of the air-fuel mixture is pure oxygen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be described with reference to drawings in which:

[0041] FIG. 1: shows a schematically and sectional view of a part of a gas turbine engine unit with an upper half of a gas turbine engine and a unit for an oxygen extraction process,

[0042] FIG. 2: shows in a perspective view a burner head of a combustion system of the gas turbine engine from FIG. 1,

[0043] FIG. 3: shows a sectional view through a part of a combustion chamber and the burner head of FIG. 2,

[0044] FIG. 4: shoes an enhanced view of a pilot burner arrangement of the burner head of FIG. 2 and

[0045] FIG. 5: shows a schematically and perspective view an exemplarily mixing device of the pilot burner arrangement of FIG. 4.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0046] The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow through the gas turbine engine 14 unless otherwise stated. If used and not otherwise specified, the terms axial, radial and circumferential are made with reference to a rotational axis 64 of the gas turbine engine 14.

[0047] FIG. 1 shows an example of a gas turbine engine unit 46 with a gas turbine engine 14 and a unit 48 for an oxygen extraction process in a sectional view. The gas turbine engine 14 comprises, in flow series of a working fluid, like air 22, 50 or a combustion gas 52, an air inlet 54 and a compressor section 56 with a compressor 58, a combustion section 12 with a combustion system 10 and a turbine section 60 with a turbine 62, which are generally arranged in flow series in the direction of a longitudinal or rotational axis 64. The gas turbine engine 14 further comprises a shaft 66 which is rotatable about the rotational axis 64 and which extends longitudinally through the gas turbine engine 14. The shaft 66 drivingly connects the turbine section 60 to the compressor section 56.

[0048] In operation of the gas turbine engine 14, air 50, which is taken in through the air inlet 54 is compressed by the compressor section 56 and delivered to the combustion section 12 or burner section. The compressed air 50 passing through the compressor section 56 is an O.sub.2-rich working fluid with about 21% O.sub.2 content. The combustion section 12 comprises a burner plenum 68, one or more combustion chambers 70 with a wall encasing the combustion chamber 70 and exemplarily one burner 72 fixed to the combustion chambers 70 defined by a double wall can 74 and at least one burner 72 fixed to each combustion chamber 70. The combustion chamber 70 and the burners 72 are located inside the burner plenum 68.

[0049] After traveling the compressor section 56 the O.sub.2-rich flow medium or air 50 enters a diffuser 76 of the compressor section 56 and is discharged from the diffuser 76 into a channel 78 extending through the combustion section 12 and connecting the gas turbine engine 14 or the combustion section 12 with the unit 48 for the oxygen extraction process. The unit 48 for the oxygen extraction process is embodied in such a way to extract O.sub.2 from the heated O.sub.2-rich air 50. Therefore, the extraction unit 48 comprises for example an ion transport membrane to perform the oxygen extraction process (not shown in detail).

[0050] After the oxygen is extracted the now O.sub.2-lean flow medium or air 22 has an O.sub.2 content of approximately 13% to 14%, depending on the efficiency of the extraction process. The gas turbine engine unit 46 comprises a return channel 80 connecting the extraction unit 48 and the gas turbine engine 12. Hence, after the extraction process the O.sub.2-lean flow medium or air 22 flows back to the gas turbine engine 14 travelling the return channel 80 to enter the combustion section 12. The channels 78 and 80 are sealed against one another to prevent a mixing of the O.sub.2-rich air 50 and the O.sub.2-lean air 22 (not shown in detail).

[0051] The O.sub.2-lean air 22 entering the combustion chamber 70 or the burners 74, respectively, is mixed with a gaseous or liquid fuel 24 (details see below). The resulting air-fuel mixture 20 is then burned and a resulting combustion gas 52 or working gas from the combustion is channelled via a transition duct 82 to the downstream turbine section 60.

[0052] The turbine section 60 comprises a number of blade carrying discs 84 attached to the shaft 66. In the present example, the turbine section 60 comprises two discs 84 each carry an annular array of turbine blades 86. However, the number of blade carrying discs 84 could be different, i.e. only one disc 84 or more than two discs 84. In addition, guiding vanes 88 of a turbine cascade, which are fixed to a stator 90 of the gas turbine engine 14, are disposed between the turbine blades 86. Between the exit of the combustion chamber 70 and the leading turbine blades 86 inlet guiding vanes 94 are provided.

[0053] The combustion gas 52 from the combustion chamber 70 enters the turbine section 60 and drives the turbine blades 86 which in turn rotate the shaft 66. The guiding vanes 88, 92 serve to optimise the angle of the combustion or working gas 52 on to the turbine blades 86. The compressor section 56 comprises an axial series of guide vane stages 94 and rotor blade stages 96.

[0054] FIG. 2 shows a burner head 98 of the combustion system 10 of the combustion section 12. The burner head 98 comprises a main burner arrangement 16 (see FIG. 3) and a pilot burner arrangement 18 which are operateable with the air-fuel mixture 20 (see FIG. 4). The pilot burner arrangement 18 comprises several pilot burners 100 each having an injection nozzle 102 to inject the air-fuel mixture 20 in to the downstream combustion chamber 70 for ignition in the pilot flame 30 (see FIG. 3). O.sub.2-lean air 22 is injected through holes 104 or similar from the burner plenum 68 into the pilot burner arrangement 18.

[0055] In FIG. 3 the burner head 98 and a part of the combustion chamber 70 are shown in a simplified view. The main burner arrangement 16 is embodied as a central burner (not shown in detail) that is circumferentially surrounded by the pilot burners 100, which in turn are exemplarily embodied as external pilot burners 100. The main burner arrangement 16 and the pilot burner arrangement 18 are feed with the O.sub.2-lean air 22 from the oxygen extraction process. To stabilise the main flame 106 resulting after ignition of an air fuel mixture 20 of the main burner arrangement 16 the pilot burner arrangement 18 is embodied selectively for this purpose. As stated above, the pilot burner arrangement 18 is feed with O.sub.2-lean air 22. This may cause an unstable pilot flame 30 and the pilot burner 100 may lose his stabilising effect. By mixing the air 22 used for the pilot flame 30 with oxygen 26, especially with pure oxygen 26, a normal, 21% or higher oxygen mole fraction can be reached. Thus, the air 22 of the air-fuel mixture 20 of the pilot burner arrangement 18 beforehand of the mixing with oxygen 26 is O.sub.2-lean air 22.

[0056] As can be seen in FIG. 4, which shows an enhanced view of one pilot burner 100, the pilot burner arrangement 18 comprises a source for pure oxygen 26 and additional pieces to provide the oxygen 26 and to mix the oxygen 26 with the O.sub.2-lean air 22. The oxygen 26 is provided through an orifice 108 (not shown in FIG. 4, see FIG. 2) for example from the unit 46 or another source, into a manifold 110 shared by all pilot burners 100.

[0057] For mixing of the oxygen 26 with the O.sub.2-lean air 22 the combustion system 10 comprises a first mixing device 36 that is able to enrich oxygen 26 in the air 22 of theresultingair-fuel mixture 20 of the pilot burner arrangement 18. To provide the oxygen 26 and the air 22 for the first mixing device 36 the combustion system 10 comprises an oxygen feed line 34 and an air feed line 40, wherein the first mixing device 36 is positioned to be feed with oxygen 26 and with the O.sub.2-lean air 22 by the respective feed line 32, 40. After the mixing an O.sub.2-enriched working fluid 28 (air-oxygen mixture) is discharged from the first mixing device 36.

[0058] For mixing of the O.sub.2-enriched working fluid 28 with the fuel 24 the combustion system 10 comprises a second mixing device 38. The O.sub.2-enriched working fluid 28 is led via an O.sub.2-enriched working fluid feed line 42 and the fuel 24 via a fuel feed line 44 to the second mixing device 38. The fuel 24 is provided from a separate manifold 112 shared by all pilot burners 100. The resulting air-fuel mixture 20 is than discharged from the second mixing device 38 to the nozzle 102 to be injected into the combustion chamber 70 where the oxidation process occurs in the pilot flame 30.

[0059] The main flame 106 is feed by an air-fuel mixture 20 that contains the same air 22 with reduced oxygen content (O.sub.2-lean) as the air 22 feed to the pilot burner arrangement 18 but this mixture 20 is not doped with extra oxygen.

[0060] The first and second mixing devices 36, 38 can be embodied as a pre-mixer or as a swirler. In FIG. 5 one embodiment of one useable mixing device is exemplarily shown. A mixing cavity 114 that receives the respective flow medium (air 22, oxygen 26; O.sub.2-enriched working fluid 28, fuel 24) has two swirler wings 116 that are arranged in close proximity to the respective nozzle 102, 102 for injection in the combustion chamber 70 or the O.sub.2-enriched working fluid feed line 42 (see FIG. 4).

[0061] The method for operating the combustion system 10 comprises the following steps: Enriching the O2-lean air 22 of the air-fuel mixture 20 of the pilot burner arrangement 18 with oxygen 26 and advantageously pure with oxygen 26, and specifically, enriching the air 22 of the air-fuel mixture 20 of the pilot burner arrangement 18 with oxygen 26 so that an oxygen content of the air-fuel mixture 20 burned by the pilot burner arrangement 18 is at least 5% higher or about 8% higher than an oxygen content of the air 22 feed to the pilot burner arrangement 18 beforehand of the mixing with the oxygen 26. Advantageously, the air 22 is enriched so that the oxygen content of the resulting air-fuel mixture 20 is about 21%.

[0062] The mass flow of the air 22 is not specifically controlled. It is dependent on the pressure drop over the burner(s) which depends on the engine load. A mass flow of the oxygen 26 and a mass flow of the fuel 24 are controlled by each feeding pressure which gives two parameters to control the stability of the pilot flame 30 and thus the main flame 106. Hence, the method comprises the steps of: Determining a feeding pressure of the oxygen 26 and controlling a flame stability of the pilot flame 30 of the pilot burner arrangement 18 due to the determined feeding pressure of the oxygen 26. Thus, the combustion system comprises a sensor to detect the feeding pressure of the oxygen 26 (not shown) and a valve 32, located in or at the oxygen feed line 34, to control a feed of oxygen 26 to the feed line 34 for the oxygen 26.

[0063] It may be also possible to determine a feeding pressure of the fuel 24 by a sensor and to control the flame stability of the pilot flame of the pilot burner arrangement due to the determined feeding pressure the fuel 24. Therefore, a further valve may be located in or at the fuel feed line (not shown).

[0064] The oxygen content in the air 22 feed to the pilot burner arrangement 18 can vary over time and might in some cases become as high as in a normal gas turbine operation, e.g. 21%. In such cases the flow of oxygen 26 can be eliminated and replaced by a small amount of purge air 22. The pilot burner 100 then works as a standard pilot burner. Hence, the method may comprise the step of: Stopping the feeding of oxygen 26 to the air 22 of the air-fuel mixture 20 of the pilot burner arrangement 18 in case an oxygen content above 18% oxygen is detected in the air 22 feed to the pilot burner arrangement 18. Moreover, in that case the method may comprise the further step of: Purging the oxygen feed line 34 with a flow medium, like the air 22.

[0065] Alternatively, it may be possible to add the oxygen to the fuel or to mix the oxygen with the fuel and subsequently mix the resulting fuel-oxygen mixture with the O.sub.2-lean air. It might be also possible to mix only the fuel with oxygen without adding O.sub.2-lean air after the mixing of the fuel with the oxygen. In such a case a mass flow of the O.sub.2-lean air provided for the pilot burner arrangement would be 0. This might be controlled by a valve. It may be also possible to add the oxygen to the already mixed air-fuel mixture (not shown).

[0066] It should be noted that the term comprising does not exclude other elements or steps and a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

[0067] Although the invention is illustrated and described in detail by the preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.