Combustor assembly for a gas turbine unit

Abstract

A combustor assembly (3) for a gas turbine unit (1) includes at least one combustor unit (7) having a bushing (16) extending substantially along the combustor axis (B); the combustor unit includes a first-stage combustor (8) and a second-stage combustor (9) arranged downstream of the first-stage combustor along the gas flow direction (G); the first-stage combustor includes a first-stage burner (11) and a first-stage combustion chamber (12), the first-stage burner being supplied with first-stage fuel and first-stage air, the first-stage fuel being burned in the first-stage combustion chamber; wherein the second-stage combustor includes a second-stage burner (13) and a second-stage combustion chamber (14); the second-stage burner is arranged downstream of the first-stage combustion chamber; the second-stage combustion chamber is supplied with hot gas exiting the first-stage combustion chamber and passing through the second-stage burner, is supplied with dilution air and is supplied with second-stage fuel; wherein the dilution air and the second-stage fuel are simultaneously injected into the second-stage burner.

Description

[0001] Cross-references to related applications This patent application claims priority to European Patent Application No. 24223722.0, filed on December 30, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to a combustor assembly for a gas turbine unit, and more particularly to a gas turbine unit for a power plant. The invention also relates to a method for operating the combustor assembly for a gas turbine unit. Background Technology

[0003] As is known, gas turbine units used in power plants include compressors, burner assemblies, and turbines.

[0004] Specifically, the compressor includes an inlet supplying air and multiple blades that compress the air passing through. The compressed air leaving the compressor flows into a chamber (i.e., a closed volume) and from there into a combustor assembly, where it mixes with at least one fuel and burns. The resulting hot gas leaves the combustor assembly and expands in a turbine to perform mechanical work.

[0005] Traditionally, the fuel supplied to the burner assemblies of gas turbine units is natural gas or oil.

[0006] The market requires gas turbine units to operate using fuels other than natural gas or oil in the future; in particular, gas turbine units should be able to operate correctly using highly reactive fuels (such as, for example, hydrogen (H2), hydrogen-containing mixtures), or low-reactive fuels (such as ammonia (NH3)), or mixtures of the above-mentioned fuels or various types of liquid fuels.

[0007] In addition, burner assemblies configured to operate using new fuels should also be able to meet pollution emission limits.

[0008] To reduce these emissions and improve operational flexibility, gas turbines that include combustor assemblies that perform sequential combustion cycles have been developed.

[0009] Generally, a sequential burner assembly consists of two burners connected in series, each equipped with a corresponding burner and combustion chamber. Along the direction of the main gas flow, the upstream burner, referred to as the "premixed" burner, is supplied with compressed air. The downstream burner, referred to as the "sequential" or "reheat" burner, is supplied with hot gas exiting the first combustion chamber. Furthermore, both burners can be supplied with the various types of fuels mentioned above.

[0010] Currently available sequential burner assemblies are relatively large (in terms of axial length) and therefore expensive. For example, the axial dimensions of these types of burner assemblies can cause space-related problems when they are retrofitted into existing gas turbine units.

[0011] In addition, large structures generally have higher initial costs and contain more parts that require cooling compared to more compact structures. Summary of the Invention

[0012] Therefore, the main objective of this invention is to provide a burner assembly that is efficient and cost-effective, and can also operate with highly reactive fuels without compromising the reliability of the burner unit, while ensuring that pollutant emissions are below legal limits.

[0013] According to the invention, this objective is achieved by a combustor assembly for a gas turbine unit, the combustor assembly comprising at least one combustor unit having a bushing extending substantially along a combustor axis; the combustor unit comprising a first-stage combustor and a second-stage combustor, the second-stage combustor being arranged downstream of the first-stage combustor in the gas flow direction; the first-stage combustor comprising a first-stage burner and a first-stage combustion chamber, the first-stage burner being supplied with first-stage fuel and first-stage air, the first-stage fuel being combusted in the first-stage combustion chamber; wherein the second-stage combustor comprises a second-stage burner and a second-stage combustion chamber; the second-stage burner being arranged downstream of the first-stage combustion chamber; the second-stage combustion chamber being supplied with hot gas exiting the first-stage combustion chamber and passing through the second-stage burner, with dilution air and second-stage fuel; wherein the dilution air and second-stage fuel are simultaneously injected into the second-stage burner.

[0014] Another object of the present invention is to provide a method for operating a burner assembly for a gas turbine unit as claimed in claim 15. Attached Figure Description

[0015] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments, in which: - Figure 1 This is a schematic diagram of a gas turbine unit equipped with a burner assembly according to the invention, wherein some parts have been removed for clarity; - Figure 2 This is a schematic side cross-sectional view of a burner assembly according to the invention, wherein some portions have been removed for clarity; - Figure 3 yes Figure 2 A perspective view showing the first detail of the burner assembly; - Figure 4 yes Figure 2A perspective view of the second detail of the burner assembly. Detailed Implementation

[0016] Figure 1 This is a schematic diagram of a gas turbine unit 1 for a power plant according to the present invention.

[0017] The gas turbine unit 1 includes a compressor 2, a combustor assembly 3, and a turbine 5. The compressor 2 and the turbine 5 extend along the main axis A.

[0018] In operation, the compressed airflow in compressor 2 is mixed with fuel and burned in combustor assembly 3. The combusted mixture expands in turbine 5 and is converted into mechanical energy via shaft 6 connected to generator (not shown).

[0019] Burner assembly 3 is a sequential burner assembly and includes multiple units 7 ( Figure 1 Only one unit is shown in the image. Each unit 7 includes a first-stage burner 8 and a second-stage burner 9 arranged sequentially along the gas flow direction G. In other words, the second-stage burner 9 is arranged downstream of the first-stage burner 8 along the gas flow direction G.

[0020] As used in this article, "downstream" and "upstream" refer to the direction G of the main airflow passing through the gas turbine.

[0021] The first-stage burner 8 includes: • First-stage burner 11, which supplies first-stage fuel and first-stage air, and • First-stage combustion chamber 12, where the first-stage fuel is burned.

[0022] The second-stage burner 9 includes: • The second-stage burner 13 is arranged downstream of the first-stage combustion chamber 12, and preferably at the outlet of the first-stage combustion chamber 12; • The second-stage combustion chamber 14 is supplied with hot gas exiting the first-stage combustion chamber 12, dilution air, and second-stage fuel.

[0023] In the disclosed and illustrated examples, each unit 7 extends along a corresponding axis B (i.e., the first-stage burner 8 and the second-stage burner 9 extend along the same axis B). However, according to a variant not shown, the first-stage and second-stage combustion chambers may not be aligned along a single axis. The second-stage combustion chamber 14 may be cylindrical or annular.

[0024] See Figure 2 The second-stage burner 13 includes a mixing device 15, which is preferably a cyclone separator (in... Figure 2 In the middle, the cyclone separator 15 is cut open along the axial plane. Diluent air and second-stage fuel are injected at the mixing device 15 of the second-stage burner 13.

[0025] In this manner, the second-stage combustion chamber 14 is supplied with dilution air, second-stage fuel, and hot gas that has left the first-stage combustion chamber 12 and passed through the mixing device 15.

[0026] The mixing unit 15 is located downstream of the outlet of the first-stage combustion chamber 12, and there is no injection of air and / or fuel between the first-stage combustion chamber 12 and the second-stage burner 13. The statement "no air injection" means that no air with a combustion function is injected. Cooling air may be injected between the first-stage combustion chamber 12 and the second-stage burner 13.

[0027] In other words, there is no mixer or mixing stage between the first-stage burner 8 and the second-stage burner 9. The burner assembly 3 includes a bushing 16 extending along the longitudinal axis B, and includes a substantially rotationally symmetric or even cylindrical portion 17a defining the first-stage combustion chamber 12; a converging portion 17b defining a portion of the second-stage burner 13 and the mixing zone 18; and a diverging portion 17c subsequently defining the end portion of the mixing zone of the second-stage combustion chamber 14. Thus, the mixing zone 18 is defined by a narrowing portion subsequently extending towards the second combustion chamber 14.

[0028] The narrowing section has the effect of accelerating the flow of combustion to enhance mixing and prevent backfire, while the expansion section has the effect of reducing pressure loss.

[0029] Advantageously, the second-stage burner 13 is arranged in a larger cross-sectional area. This allows for a lower pressure loss of the hot gas leaving the first-stage combustion chamber 12. Furthermore, as will be detailed below, positioning the second-stage burner 13 in the largest area of ​​the converging portion 17b also provides sufficient design space for the structure of the mixing unit 15 and for the injection of dilution air and second-stage fuel at the mixing unit 15.

[0030] In this way, dilution air, secondary fuel, and hot gas leaving the primary combustion chamber are mixed simultaneously in the mixing zone 18 downstream of the secondary burner 13.

[0031] The burner assembly 3 preferably also includes an axisymmetric or even cylindrical central body 19 and a housing 20.

[0032] The central body 19 is preferably arranged along axis B and extends along the burner assembly 3 through at least a portion of the first-stage burner 8 and the second-stage burner 9.

[0033] In particular, the central body 19 preferably extends along the second-stage burner 13 and along the mixing zone 18 until it reaches the second-stage combustion chamber 14.

[0034] The central body 19 is supplied with at least a second stage of fuel.

[0035] Preferably, the central body 19 also includes a cooling system. The cooling system can be implemented by means of an annular duct 23a surrounding the central second-stage fuel duct 23b. Cooling air circulating in the annular duct 23a can be, for example, as film cooling, and discharged at the outer surface and / or end face of the central body 19 facing the second-stage combustion chamber 14.

[0036] According to a variant not shown in the figure, the downstream portion of the central body 19 can accommodate a Helmholtz damper to counteract thermoacoustic instabilities.

[0037] According to a variant not shown, the central body is not cylindrical, but shaped such that the cross-section of the mixing zone 18 decreases along axis B. Preferably, also in this configuration, the central body is open to allow air to be discharged into the second-stage combustion chamber.

[0038] The housing 20 surrounds at least a portion of the bushing 16 to define an annular chamber 22 around the bushing 16. The annular chamber 22 is supplied with a second stage of air (hereafter referred to as dilution air). The first stage air and dilution air preferably originate from a chamber (not shown in the figures). As is well known, ambient air enters the compressor 2 and is compressed. The compressed air exits the compressor 2 and enters the chamber, which is a volume defined by a chamber shell (not shown).

[0039] Specifically, the housing 20 surrounds the portion 17a of the bushing 16 that substantially defines the first-stage combustion chamber 12, and the converging portion 17b of the bushing 16. Cooling passages (not shown) may be implemented in the bushing portion 17c and supplied from said chamber.

[0040] See Figure 2 The first-stage burner 11 of the first-stage burner 8 is schematically shown by the frame.

[0041] As expected, the second-stage burner 13 includes a mixing device 15, which includes a cyclone separator.

[0042] Diluted air and second-stage fuel are supplied at cyclone 15, and preferably through cyclone 15.

[0043] See Figures 2 to 4 The cyclone separator 15 includes a plurality of hollow struts 24 spaced apart from each other circumferentially around the burner axis B. Each strut 24 extends radially from the central cylinder 19 to the housing 20. Each strut extends in a radial direction r defined from the burner axis B.

[0044] As will be detailed below, the mixing device 15 is configured such that the second-stage fuel stream is substantially embedded in the dilution air stream and thus initially separated from the hot gases from the first-stage combustion chamber 12.

[0045] Each support 24 includes a wall 25, which is shaped to define a leading edge 26 facing the first-stage combustion chamber 12 (in Figure 2 (This can be seen better in the image), and the trailing edge 27, which is arranged opposite to the leading edge 26 along the burner axis B and faces the second-stage combustion chamber 14.

[0046] Considering the gas flow direction G, the trailing edge 27 is positioned downstream of the leading edge 26.

[0047] The outer wall 25 is also shaped to define two sides 28a, 28b, which are respectively included between the leading edge 26 and the trailing edge 27.

[0048] The trailing edge 27 includes an outlet opening 29. Preferably, the outlet opening 29 extends the entire radial height of the trailing edge 27, and more preferably, extends the entire circumferential length of the trailing edge 27.

[0049] Each support 24 has a defined cavity 30.

[0050] Sides 28a and 28b are respectively shaped to define the external curved surface.

[0051] Preferably, each side portion 28a, 28b is shaped to define an outwardly curved surface that defines essentially a lobed flap.

[0052] Side 28a has a convex shape, while side 29a has a concave shape, or vice versa. In the example shown here, sides 28a and 28b are shaped to define a concave surface. According to a variation, sides 28a and 28b may be shaped to define more than one concave surface.

[0053] Preferably, the sides 28a and 28b are shaped so that they also curve inward.

[0054] Preferably, the sides 28a and 28b extend substantially radially so that the distance between the sides 28a and 28b increases radially. In this way, more cooling air is ejected at the larger radius compared to the smaller radius. In this way, the larger amount of hot gas from the larger radius is compensated for to achieve uniform mixing among all three streams (hot gas-dilute air-secondary fuel).

[0055] See the axial section view showing a portion of the hydrocyclone 15. Figure 2 When viewed in the lateral direction along the trailing edge 27, the sides 28a and 28b are preferably shaped into a circle to compensate for the converging bushing 16 and ensure proper mixing of the dilution air with the hot gas from the first-stage burner 8.

[0056] In other words, the sides 28a and 28b are shaped such that at the trailing edge 27, they preferably form a right angle α with the bushing 16 and preferably a right angle β with the central cylinder 19.

[0057] See Figure 3 and Figure 4 Each pillar 24 has a cavity 30 that houses a corresponding second-stage fuel injection unit 32, which is supplied with second-stage fuel. Preferably, the second-stage fuel is supplied to the second-stage fuel injection unit 32 through a central cylinder 19. In other words, the second-stage fuel injection unit 32 is oriented to the central cylinder 19, and more specifically, is oriented to the central second-stage fuel conduit 23b.

[0058] Depending on the variant, only some of the multiple struts house the corresponding second-stage fuel injection unit. See also Figure 4 The second-stage fuel injection unit 32 includes a finger 35 and a plurality of nozzles 36 extending from the finger 35.

[0059] The finger 35 is hollow and is flow-connected to the central body 19 (specifically, flow-connected to the central second-stage fuel conduit 23b). Preferably, the finger 35 is arranged radially and positioned substantially equidistant from the sides 28a and 28b in the cavity 30.

[0060] The nozzle 36 extends laterally from the finger 35 and supplies second-stage fuel through the finger 35.

[0061] Each nozzle 36 has an inlet 37 at the finger 35 and an outlet 38. The axial length of each nozzle 36 (intended as a length measured along the burner axis B) is defined such that the outlet 38 of each nozzle 36 is arranged at the outlet opening 29 of the corresponding support 24.

[0062] According to a variant not shown, the outlet 38 of each nozzle 36 is arranged upstream of the outlet opening 29.

[0063] Preferably, when viewed from the side, the nozzle 36 is arranged so that the second-stage fuel is ejected in a direction perpendicular to the trailing edge 27. In this way, the second-stage fuel will not impinge on the inner or outer wall of the bushing 16 in the mixing zone 18.

[0064] The inlet 37 of the nozzle 36 is aligned in a substantially radial direction on the surface of the finger facing the outlet opening 29.

[0065] Nozzles 36 may have the same diameter, or they may have different diameters, such as Figure 4 As shown in the examples.

[0066] The diameter of the nozzle 36 can vary in order to generate the desired fuel mixture fraction distribution at the outlet opening 29.

[0067] In the non-limiting example shown here, the nozzles 36 arranged in the intermediate region have a minimum diameter. Furthermore, these nozzles 36 may be equidistant along the trailing edge of the fuel injector 39, or may have varying distances.

[0068] The nozzles 36 are preferably connected to each other to create a "nozzle wall 39" that is substantially wavy.

[0069] Preferably, the nozzle wall 39 is shaped to be arranged substantially radially and has a wave shape similar to that of the sidewalls 28a and 28b.

[0070] The fuel nozzle 36 of the nozzle wall 39 preferably extends along a straight path that is inclined in all three directions to follow the shape of the sides 28a, 28b.

[0071] The wavy shape of the inner and outer surfaces of the sides 28a and 28b, as well as the wavy shape of the nozzle wall 39 including the nozzle 36, has the effect of improving the mixing of diluted air, secondary fuel and hot gas from the first-stage combustion chamber 12.

[0072] In fact, the convex petal-shaped profiles of the sides 28a and 28b, as well as the convex petal-shaped profile of the nozzle wall 39, have the effect of generating the vortices required to mix different flows.

[0073] Each pillar 24 cavity 30 is supplied with diluted air from the annular chamber 22 surrounding the bushing 16.

[0074] See Figure 3 The bushing 16 preferably has multiple openings 40, each opening 40 connecting the corresponding cavity 30 to the annular chamber 22.

[0075] Preferably, each opening 40 is associated with at least one baffle 42, which, as will be more detailed below, is configured to guide the flow of air within the cavity 30. The purpose of the baffle 42 is primarily to ensure cooling of the leading edge 26.

[0076] Specifically, the baffle 42 is configured behind the second-stage fuel injection unit 32 (see also...) Figure 2 The dilution airflow is guided. In this way, the dilution air leaves the outlet opening 29 together with the second-stage fuel leaving the second-stage fuel injection device 32, and in particular, the dilution airflow surrounds the second-stage fuel flow from the injection unit 32. In this way, the fuel-rich region at the outlet of the second-stage burner 13 has an average amount of dilution air.

[0077] Depending on the variant not shown, each opening may be associated with more than one baffle.

[0078] To prevent undiluted first-stage hot gas from coming into direct contact with second-stage fuel (which could potentially cause backfire), dilution air is supplied so that the dilution air stream is positioned between the hot gas stream and the second-stage fuel stream.

[0079] Therefore, the second-stage flame temperature peaks attributable to incomplete fuel mixing can be compensated at least partially by additional dilution air at such locations. Consequently, even in relatively fuel-rich zones within the second-stage combustion chamber 14, the local flame temperature may be relatively low, and therefore NO x Emissions are also low.

[0080] Therefore, the dilution air is injected axially as it flows out from the outlet opening 29 at the trailing edge 27. In this way, the dynamic portion of the total pressure does not dissipate as typically occurs in conventional prior art mixing stages arranged upstream of the second-stage burner. Therefore, according to the present invention, the pressure loss of the burner assembly is reduced compared to conventional prior art burner assemblies.

[0081] Unlike the most common dilution air injection systems (generally designed to inject dilution air into the hot gas in a "cross-flow injection" manner between the first-stage burner and the second-stage burner), the solution according to the invention is designed to inject dilution air through strut 24, which allows the dilution air to be injected parallel to the hot gas path. Specifically, the angle between the main flow direction of the hot air from the first-stage burner 8 and the dilution air flow at the outlet opening 29 of strut 24 is zero. Only some local mixing, due to the vortex shape of strut 24, generates some eddies, resulting in mixing in the downstream mixing zone 18.

[0082] In this way, the significantly larger volume of dilution air compared to the air from the first-stage burner 8 keeps the highly reactive fuel in the dilution air core at a lower temperature for a longer period and allows it to mix with the dilution air until it encounters the hot air from the first-stage burner 8, which leads to a chemical reaction. Advantageously, the shape of the swirler 15, and in particular the shape of each strut 24, allows for proper mixing of the hot gas flow from the first-stage burner 8 with the dilution air supplied through the swirler 15 and the second-stage fuel.

[0083] Furthermore, the correct circumferential distance between each support 24 ensures that the vortices generated by each support 24 can better combine with the vortices from the adjacent convex-shaped support 24. This allows the proposed solution to also be applied to small burners.

[0084] Furthermore, the features of the second-stage burner 9 improve the shielding effect of the second-stage fuel flow. In this way, the number of second-stage fuel nozzles 36 can be increased to provide excellent mixing of fuel with other flows.

[0085] Furthermore, the burner assembly of the present invention allows for the injection of most types of fuels, even ammonia or hydrogen-based fuels, at the first-stage burner 8. While in conventional burner assemblies, such fuels would cause significant problems due to the high temperatures reached at the second-stage burner inlet, the present invention avoids this problem because dilution air is injected at the second-stage burner 13, thus causing a temperature rise further downstream (primarily in the second-stage combustion chamber 14).

[0086] Advantageously, the burner assembly 3 of the present invention also has a reduced axial length.

[0087] Finally, modifications and variations of the components described herein can be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A combustor assembly (3) for a gas turbine unit (1), comprising at least one combustor unit (7) having a bushing (16) extending substantially along a combustor axis (B); the combustor unit (7) comprising a first-stage combustor (8) and a second-stage combustor (9), the second-stage combustor being arranged downstream of the first-stage combustor (8) along the gas flow direction (G); the first-stage combustor (8) comprising a first-stage burner (11) and a first-stage combustion chamber (12), the first-stage burner being supplied with first-stage fuel and The first stage air and the first stage fuel are burned in the first stage combustion chamber; wherein the second stage burner (9) includes a second stage burner (13) and a second stage combustion chamber (14); the second stage burner (13) is arranged downstream of the first stage combustion chamber (12); the second stage combustion chamber (14) is supplied with hot gas leaving the first stage combustion chamber (12) and passing through the second stage burner (13), is supplied with dilution air and is supplied with second stage fuel; wherein the dilution air and the second stage fuel are simultaneously injected into the second stage burner (13).

2. The burner assembly according to claim 1, characterized in that, The second-stage burner (13) includes a mixing device (15); wherein the dilution air and the second-stage fuel are simultaneously injected at the mixing device (15).

3. The burner assembly according to claim 2, characterized in that, The mixing of the dilution air, the second-stage fuel, and the hot gas leaving the first-stage combustion chamber (12) takes place at the trailing edge of the mixing device (15) within the second-stage burner (13).

4. The burner assembly according to claim 2 or claim 3, characterized in that, The mixing device (15) includes a cyclone separator having a plurality of struts (24) arranged radially around the burner axis (B); dilution air and second-stage fuel are supplied through at least one of the plurality of struts (24).

5. The burner assembly according to claim 4, characterized in that, Each support (24) includes a wall (25) defined as follows: •Inner cavity (30); • Leading edge (26), which faces the first-stage combustion chamber (12) and includes an outlet opening (29); • The trailing edge (27) is arranged opposite to the leading edge (26) along the burner axis (B) and faces the second stage combustion chamber (14); • Two side portions (28a; 28b) are respectively included between the leading edge (26) and the trailing edge (27).

6. The burner assembly according to claim 5, characterized in that, The dilution air and the second-stage fuel are supplied through at least one of the pillars (24) such that at the trailing edge of each pillar (24), the second-stage fuel flow is embedded in the dilution air flow.

7. The burner assembly according to claim 5, characterized in that, The burner assembly includes a plurality of second-stage fuel injection units (32); wherein the cavity (30) of each of the plurality of struts (24) accommodates a corresponding second-stage fuel injection unit (32) supplied with second-stage fuel.

8. The burner according to claim 7, characterized in that, The second-stage fuel injection unit (32) includes a finger (35) supplied with second-stage fuel and a plurality of nozzles (36), each of which extends laterally from the finger (35) and is supplied with second-stage fuel through the finger (35).

9. The burner assembly according to claim 7, characterized in that, The bushing (16) is provided with at least two openings (40), each of which connects the cavity (30) of the corresponding support (24) to a dilution air source (22); wherein each opening (40) is preferably associated with the at least one baffle (42) configured to guide the flow of air within the cavity (30).

10. The burner according to claim 5, characterized in that, The sides (28a, 28b) are respectively shaped to define an outer curved surface; wherein each side (28a, 28b) is shaped to define an outer curved surface, the outer curved surface defining at least one lobe.

11. The burner according to claim 5, characterized in that, The sides (28a, 28b) are shaped to form a right angle (α) with the bushing (16) at the trailing edge (27).

12. The burner assembly according to claim 5, characterized in that, The burner assembly includes a central body (19) supplied with at least a second stage of fuel; the second stage fuel injection unit (32) is connected in circulation to the central body (19).

13. The burner according to claim 12, characterized in that, The sides (28a, 28b) are shaped to form a right angle (β) with the central body (19) at the trailing edge (27).

14. A gas turbine unit comprising a compressor (2), a turbine (4), and a burner assembly (3) according to claim 1.

15. A method for operating a burner assembly (3) of a gas turbine unit (1); the burner assembly (3) comprising at least one burner unit (7) having a bushing (16) extending substantially along a burner axis (B); the burner unit (7) comprising a first-stage burner (8) and a second-stage burner (9), the second-stage burner being arranged downstream of the first-stage burner (8) along the gas flow direction (G); the first-stage burner (8) comprising a first-stage burner (11) and a first-stage combustion chamber. The first stage burner (12) is supplied with first stage fuel and first stage air, and the first stage fuel is burned in the first stage combustion chamber; wherein the second stage burner (9) includes a second stage burner (13) and a second stage combustion chamber (14); the second stage burner (13) is arranged downstream of the first stage combustion chamber (12) and is supplied with hot gas leaving the first stage combustion chamber (12) and passing through the second stage burner (13); the method includes simultaneously injecting dilution air and second stage fuel into the second stage burner (13).

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