Gas turbine unit

Abstract

A gas turbine unit includes a compressor (2), a turbine (5), a combustor assembly (3), and a fuel supply assembly (4); the combustor assembly (3) includes at least one combustor unit (7); the combustor unit (7) includes a first-stage combustor (8) and a second-stage combustor (9); the first-stage combustor (8) includes a first-stage incinerator (11) and a first-stage combustion chamber (12); the first-stage fuel is an amino fuel; wherein the second-stage combustor (9) includes a second-stage incinerator (13) and a second-stage combustion chamber (14); the fuel supply assembly (4) is configured to supply at least one first-stage fuel to the first-stage incinerator (11) such that the combustion stoichiometry of the first-stage incinerator (11) is unbalanced and there is an excess of first-stage fuel in the first-stage incinerator (11) to obtain unburned first-stage fuel reaching the second-stage incinerator (13).

Description

[0001] Cross-reference to related applications This patent application claims priority to European Patent Application No. 24223728.7, filed on December 30, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to a gas turbine unit, particularly a gas turbine unit for a power plant. The invention also relates to a method for operating the 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 it. The compressed air leaving the compressor flows into a chamber (i.e., a closed volume) and from there into a combustor assembly, where it is mixed with at least one fuel and combusted. The resulting hot gas leaves the combustor assembly and expands in a turbine, performing mechanical work.

[0005] Traditionally, the fuel supplied to the burner components of a gas turbine unit is natural gas or oil.

[0006] The market demands that gas turbine units operate on fuels other than natural gas or oil in the future; in particular, gas turbine units should be able to operate correctly on 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 comply with pollution emission limits.

[0008] To reduce these emissions and improve operational flexibility, gas turbines are being developed that include combustor components that perform sequential combustion cycles.

[0009] Generally, a sequential burner assembly comprises two burners connected in series, each with its own incinerator 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. Additionally, both burners can be supplied with the various types of fuels mentioned above.

[0010] Currently available sequential combustor assemblies are relatively bulky (in terms of axial length) and therefore expensive. The axial dimensions of these types of combustor assemblies can cause problems with available space, for example, when retrofitting them into existing gas turbine units.

[0011] In addition, generally speaking, larger structures 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 gas turbine unit that is efficient and cost-effective, and can also operate using different fuels, particularly ammonia fuels, without affecting the reliability of the combustor unit and ensuring that pollutant emissions are below legal limits.

[0013] According to the present invention, this objective is achieved by the gas turbine unit claimed in claim 1.

[0014] Another object of the present invention is to provide a method for operating a gas turbine unit using different fuels, particularly ammonia fuels. According to this object, the present invention relates to a method for operating a gas turbine unit as claimed in claim 9. 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 with a burner assembly according to the present invention, wherein 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 parts 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 2 A perspective view of the second detail of the burner assembly; Figure 5 This is a schematic side cross-sectional view of a burner assembly according to a variant of the invention, wherein parts have been removed for clarity; Figure 6 yes Figure 5 A perspective view showing the first detail of the burner assembly; Figure 7 This is a perspective view of the first detail of a modified 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 burner assembly 3, a fuel supply assembly 4, and a turbine 5. The compressor 2 and the turbine 5 extend along the main axis A.

[0018] In operation, the compressed air stream in compressor 2 mixes with fuel and is burned in burner assembly 3. Fuel is supplied by fuel supply assembly 4 (in... Figure 1 and Figure 2 (Only partially visible in the middle) is supplied to the burner assembly 3. The incinerated mixture then expands in the turbine 5 and is mechanically converted into power via the shaft 6 connected to the generator (not shown).

[0019] Burner assembly 3 is a sequential burner assembly and includes multiple units 7 ( Figure 1 (Only one 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, the terms "downstream" and "upstream" refer to the direction G of the main gas flow through the gas turbine.

[0021] The first-stage burner 8 includes: The first-stage incinerator 11 is supplied with first-stage fuel and first-stage air by the fuel supply assembly 4. The first-stage combustion chamber 12 is where the first-stage fuel is burned.

[0022] The second-stage burner 9 includes: The second-stage incinerator 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 optionally, second-stage fuel from the fuel supply assembly 4.

[0023] In the examples disclosed and shown herein, 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 variations not shown, the first-stage and second-stage burners may not be aligned along a single axis. The second-stage burner 14 may be cylindrical or annular.

[0024] Reference Figure 2 The second-stage incinerator 13 includes a mixing device 15, which is preferably a cyclone separator (in... Figure 2 In the middle, the cyclone separator 15 cuts along the axial plane. Diluted 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 expression "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 the inlet portion of the second-stage burner 13 and the mixing zone 18, and a diverging portion 17c defining the end portion of the mixing zone, subsequently connected to the second-stage combustion chamber 14. Therefore, the mixing zone 18 is preferably defined by a narrowing portion subsequently connected to an expansion portion facing the second combustion chamber 14.

[0028] The narrowing section has the effect of accelerating the passage of the combustion stream in order 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 large cross-sectional area. This allows the pressure loss of the hot gas leaving the first-stage combustion chamber 12 to remain low. Furthermore, as will be detailed below, positioning the second-stage burner 13 in the largest area of ​​the converging section 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 manner, dilution air, secondary fuel, and hot gas leaving the primary combustion chamber are simultaneously mixed in the mixing zone 18 downstream of the secondary burner 13.

[0031] The burner assembly 3 also preferably 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 across 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 incinerator 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 discharged, for example as film cooling, 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, the downstream portion of the central body 19 may 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, in this configuration, the central body is also open to allow air to be discharged into the second-stage combustion chamber 14.

[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 the dilution air preferably originate from a compartment (not shown in the figures). As is known, ambient air enters the compressor 2 and is compressed. The compressed air exits the compressor 2 and enters the compartment, which has a volume defined by the compartment 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] Reference Figure 2 The first-stage burner 11 of the first-stage burner 8 is schematically shown by a frame.

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

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

[0043] Reference Figures 2 to 4 The cyclone separator 15 includes a plurality of hollow struts 24 spaced circumferentially from each other about axis B. Each strut 24 extends radially from a central cylinder 19 to the outer casing 20. Each strut is defined along its radial direction r as originating 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 thereby initially separated from the hot gases from the first-stage combustion chamber 12.

[0045] Each strut 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] Cavity 30 is defined inside each support 24.

[0050] The sides 28a and 28b are respectively shaped to define the outer 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 variations, sides 28a and 28b may be shaped to define more than one concave surface. Preferably, sides 28a and 28b are also shaped to be internally curved.

[0053] 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 compensates for achieving uniform mixing among all three streams (hot gas-dilute air-secondary fuel).

[0054] Referring to the axial cross-sectional view showing a portion of the hydrocyclone 15 Figure 2 When viewed laterally on the trailing edge 27, the sides 28a and 28b are shaped into preferably circular sections 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.

[0055] In other words, the sides 28a and 28b are shaped such that they preferably form a right angle α with the bushing 16 at the trailing edge 27, and preferably a right angle β with the central cylinder 19.

[0056] Reference Figure 3 and 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 fluidly connected to the central cylinder 19, and specifically, is fluidly connected to the central second-stage fuel conduit 23b.

[0057] Depending on the variant, only some of the multiple struts house the corresponding second-stage fuel injection unit. (See reference...) Figure 4 The second-stage fuel injection unit 32 includes a finger 35 and a plurality of nozzles 36 extending from the finger 35.

[0058] The finger 35 is hollow and fluidly connected to the central body 19 (specifically, fluidly 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.

[0059] The nozzle 36 extends laterally from the finger 35 and supplies second-stage fuel through the finger 35.

[0060] Each nozzle 36 has an inlet 37 at a finger 35 and an outlet 38. The axial length of each nozzle 36 (intended to be the 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.

[0061] According to a variant not shown, the outlet 38 of each nozzle 36 is arranged upstream of the outlet opening 29.

[0062] 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 wall of the bushing 16 in the mixing zone 18.

[0063] 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.

[0064] Nozzles 36 may have the same diameter, or they may have different diameters, such as Figure 4 As shown in the example.

[0065] The diameter of the nozzle 36 can vary in order to generate the desired fuel mixture fraction distribution at the outlet opening 29.

[0066] 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 have varying distances.

[0067] The nozzles 36 are preferably connected to each other to create a “nozzle wall 39” that is substantially wavy.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] In fact, the convex lobe profiles of the sides 28a and 28b, as well as the convex lobe profile of the nozzle wall 39, have the effect of generating the vortices required to mix different flows.

[0072] Each pillar 24 cavity 30 is supplied with diluted air from the annular chamber 22 surrounding the bushing 16.

[0073] Reference Figure 3 The bushing 16 is preferably provided with a plurality of openings 40, each of the plurality of openings 40 connecting a corresponding cavity 30 to the annular chamber 22.

[0074] Preferably, each opening 40 is associated with at least one baffle 42, which, as will be described in more detail below, is configured to guide airflow inside the cavity 30. The purpose of the baffle 42 is primarily to ensure cooling of the leading edge 26.

[0075] Specifically, the baffle 42 is configured to guide the airflow behind the second-stage fuel injection unit 32 (see also...) Figure 2 In this manner, the dilution air exits the outlet opening 29 together with the second-stage fuel exiting the second-stage fuel injection unit 32, and specifically, the dilution air flow 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.

[0076] Depending on the variant not shown, each opening may be associated with more than one baffle.

[0077] To avoid direct contact between the undiluted first-stage hot gas and the second-stage fuel (which would likely cause backfire), the dilution air supply is configured such that the dilution air stream is positioned between the hot gas stream and the second-stage fuel stream.

[0078] Therefore, the second-stage flame temperature peaks that occur due to imperfect fuel mixing are at least partially compensated for by additional dilution air in such locations. Consequently, in the second-stage combustion chamber 14, even in relatively fuel-rich zones, the local flame temperature can be relatively low, and therefore, NO x The amount of emissions is low.

[0079] Therefore, the dilution air is injected axially as it exits 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 invention, the pressure loss of the burner assembly is reduced compared to conventional prior art burner assemblies.

[0080] Unlike the most common dilution air injection systems (which are 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 incinerator), 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.

[0081] In this way, the dilution air (which is a considerably larger volume of air compared to the air from the first-stage burner 8) keeps the highly reactive fuel in the dilution air core cold for a longer period of time 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.

[0082] Furthermore, the correct circumferential distance between each support 24 ensures that the vortices generated by each support 24 can better combine with those from adjacent lobed supports 24. This allows the claimed solution to also be applied to smaller incinerators.

[0083] Furthermore, the second-stage burner 9 features improved shielding of the second-stage fuel flow. In this way, the amount of fuel in the second-stage fuel nozzle 36 can be increased, providing excellent mixing of fuel with other flows.

[0084] Furthermore, the burner assembly of the present invention allows for the injection of most types of fuels, even amino or hydrogen-based fuels, at the first-stage burner 8. While in conventional burner assemblies, such fuels would present significant problems due to the high temperatures reached at the inlet of the second-stage burner, the present invention avoids this problem because dilution air is injected at the second-stage burner 13, thus causing a further increase in temperature downstream (primarily in the second-stage combustion chamber 14).

[0085] Finally, the burner assembly 3 of the present invention has a reduced axial length.

[0086] Figures 5 to 7 This illustrates a variation of the invention, wherein... Figures 1 to 4 The same reference numerals used in the figures are used to indicate the same or similar parts.

[0087] according to Figures 5 to 7 In the variant shown, when the fuel supply assembly 4 supplies ammonia fuel as the first stage fuel, the second stage fuel is not supplied to the second stage burner 13, and only dilution air is supplied to the second stage burner 13.

[0088] In fact, Figures 5 to 7 In this configuration, the second-stage fuel supply assembly (including the second-stage fuel injection unit 32) is absent.

[0089] Specifically, in this case, the ammonia fuel supplied by the fuel supply assembly 4 is in excess relative to the first-stage air from the compressor 2. In this way, the unbalanced (i.e., fuel-rich) fuel / air mixture is burned in the first-stage combustion chamber 12. In this way, the unburned ammonia fuel reaches the inlet of the second-stage burner 13.

[0090] In other words, the amount of ammonia fuel supplied by the fuel supply assembly 4 to the first-stage incinerator 11 is adjusted so that the combustion stoichiometry of the first-stage incinerator 11 is unbalanced in terms of fuel.

[0091] Because there will be more ammonia fuel than available oxygen (rich combustion), the ammonia fuel cannot be completely burned in the first-stage combustion chamber 12. In this case, the NH3 of the ammonia fuel will either burn (4NH3 + 3O2 -> 6H2O + 2N2) or crack (2NH3 -> N2 + 3H2).

[0092] The dilution air injected at the second-stage incinerator 13 will allow the combustion of the remaining ammonia fuel (now in the form of hydrogen H2 generated in the first-stage combustion chamber 12).

[0093] Compared to the simple combustion of ammonia fuels, this method can significantly reduce NO. x The amount.

[0094] The amount of first-stage air supplied to the first-stage incinerator 11 and the amount of dilution air supplied to the second-stage incinerator 13 are preferably regulated by geometric features defined in the design steps, and therefore are substantially constant within the load and without active control.

[0095] Depending on variations not shown, the amount of air supplied to the first-stage incinerator 11 and the second-stage incinerator 13 may be actively controlled, taking into account factors such as the relative load of the engine, fuel composition, and environmental conditions (ambient temperature and humidity).

[0096] As already disclosed, when the fuel supply assembly 4 supplies ammonia fuel as the first-stage fuel, dilution air is supplied through the mixing unit 15, which has been detailed.

[0097] In particular, Figure 5 and 6 The mixing device 15 presented in the middle has the same as Figures 1 to 4 The same structure is detailed in the embodiments, but it does not include an injection unit for supplying second-stage fuel.

[0098] exist Figure 7 In, it is shown Figure 5 and 6 A variation of the mixing device 15, wherein the mixing element 132 is arranged in the cavity 30 of at least one support 24.

[0099] The mixing element 132 is shaped to define an appropriate velocity profile for the diluted air at the outlet opening 29.

[0100] In the non-limiting example shown herein, the hybrid element has the same characteristics as... Figure 3 and 4 The shape of the injection unit 32 is basically similar.

[0101] Therefore, refer to Figures 5 to 7 The publicly available alternative solutions focus particularly on ammonia fuels.

[0102] However, Figures 1 to 4 The solution disclosed can also be used with ammonia fuel, but caution is advised when setting the fuel supply assembly 4 to supply ammonia fuel as the first-stage fuel and not supply second-stage fuel. Only dilution air is supplied to the second-stage burner 13.

[0103] Figures 1 to 4 The solution disclosed herein can be seen as providing greater flexibility in the operation of burner assembly 3, since fuels other than ammonia fuels can be supplied to burner unit 7 without any necessary hardware modifications.

[0104] Finally, modifications and variations may be made to the components described herein without departing from the scope of the invention as defined in the appended claims.

Claims

1. A gas turbine unit comprising a compressor (2), a turbine (5), a combustor assembly (3), and a fuel supply assembly (4) configured to supply at least one first-stage fuel to the combustor assembly (3); the combustor assembly (3) 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 (9) being arranged downstream of the first-stage combustor (8) along a gas flow direction (G); the first-stage combustor (8) comprising a first-stage incinerator (11) and a first-stage combustion chamber (12), the first-stage incinerator (11) being supplied with first-stage air from the compressor (2) and first-stage fuel from the fuel supply assembly (4), The first-stage fuel is burned in the first-stage combustion chamber (12); the first-stage fuel is an amino fuel; 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), and is supplied with dilution air; the fuel supply assembly (4) is configured to supply the at least one first-stage fuel to the first-stage burner (11) such that the combustion stoichiometry of the first-stage burner (11) is unbalanced and there is an excess of first-stage fuel in the first-stage burner (11) to obtain unburned first-stage fuel reaching the second-stage burner (13).

2. The gas turbine unit according to claim 1, wherein, The second-stage incinerator (13) includes a mixing device (15); wherein the dilution air is injected at the mixing device (15).

3. The gas turbine unit according to claim 2, wherein, The mixing of the diluted air, the unburned first-stage fuel, and the hot gas leaving the first-stage combustion chamber (12) is completed at the trailing edge of the mixing device (15) within the second-stage burner (13).

4. The gas turbine unit according to claim 2 or 3, wherein, The mixing device (15) includes a cyclone separator having a plurality of supports (24) arranged radially around the burner axis (B); The dilution air supply passes through at least one of the plurality of pillars (24).

5. The gas turbine unit according to claim 4, wherein, Each pillar (24) includes a wall (25) whose shape is defined as follows: Inner cavity (30); Leading edge (26), which faces the first stage combustion chamber (12); The trailing edge (27) is arranged opposite to the leading edge (26) along the burner axis B and includes an outlet opening (29) facing 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 gas turbine unit according to claim 5, wherein, 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 at least one baffle (42) configured to guide airflow inside the cavity (30).

7. The gas turbine unit according to claim 5 or 6, wherein, The sides (28a, 28b) are respectively shaped to define an outward curved surface; wherein each side (28a, 28b) is shaped to define an outward curved surface, which defines at least one lobe.

8. The gas turbine unit according to claim 5 or 6, wherein, The sides (28a, 28b) are shaped to form a right angle (α) with the bushing (16) at the rear edge (27).

9. A method for operating a gas turbine unit (1); the gas turbine unit (1) comprising a compressor (2), a turbine (5), a combustor assembly (3), and a fuel supply assembly (4) configured to supply at least one first-stage fuel to the combustor assembly (3); wherein the combustor assembly (3) comprises 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 (9) being arranged downstream of the first-stage combustor (8) along the gas flow direction (G); the first-stage combustor (8) comprising a first-stage incinerator (11) and a first-stage combustion chamber (12); wherein the second-stage combustor (9) comprises a second-stage incinerator (13) and a second-stage combustion chamber (14); the second-stage incinerator (13) being arranged downstream of the first-stage combustion chamber (12); the method comprising: The first-stage air is supplied to the first-stage incinerator (11); The first-stage fuel is supplied to the first-stage incinerator (11) so that the combustion stoichiometry of the first-stage incinerator (11) is unbalanced and there is an excess of the first-stage fuel in the first-stage incinerator (11); the first-stage fuel is an ammonia fuel. Diluted air is supplied to the second-stage incinerator (13).

10. The method according to claim 9, wherein, The step of supplying dilution air to the second-stage incinerator (13) includes injecting dilution air at the mixing device (15) arranged in the second-stage incinerator (13).

11. The method according to claim 10, wherein, The mixing of the dilution air, the unburned first-stage fuel, and the hot gas leaving the first-stage combustion chamber (12) is completed at the trailing edge of the mixing device (15) within the second-stage burner (13).

12. The method according to claim 10 or 11, wherein, The mixing device (15) includes a cyclone separator having a plurality of struts (24) arranged radially about the burner axis (B); dilution air is supplied through at least one of the plurality of struts (24).

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