EP2989389B1

EP2989389B1 - Sequential combustion with dilution gas

Info

Publication number: EP2989389B1
Application number: EP14708266.3A
Authority: EP
Inventors: Xianfeng GAO; Luis TAY WO CHONG HILARES
Original assignee: Ansaldo Energia Switzerland AG
Current assignee: Ansaldo Energia Switzerland AG
Priority date: 2013-04-25
Filing date: 2014-03-06
Publication date: 2018-08-01
Anticipated expiration: 2034-03-06
Also published as: EP2989389A1

Description

Technical field

The invention refers to a sequential combustor arrangement for a gas turbine with admixing dilution gas into the combustor arrangement. The invention additionally refers to a method for operating a gas turbine with admixing dilution gas into a combustor arrangement.

Background of the disclosure

Due to increased power generation by unsteady renewable sources like wind or solar existing gas turbine based power plants are increasingly used to balance power demand and to stabilize the grid. Thus improved operational flexibility is required. This implies that gas turbines are often operated at lower load than the base load design point, i.e. at lower combustor inlet and firing temperatures.
At the same time, emission limit values and overall emission permits are becoming more stringent, so that it is required to operate at lower emission values, keep low emissions also at part load operation and during transients, as these also count for cumulative emission limits.
State-of-the-art combustion systems are designed to cope with a certain variability in operating conditions, e.g. by adjusting the compressor inlet mass flow or controlling the fuel split among different burners, fuel stages or combustors. However, this is not sufficient to meet the new requirements.
To further reduce emissions and operational flexibility sequential combustion has been suggested in DE 10312971 A1 , which describes a sequential combustor arrangement according to the preamble of claim 1. Depending on the operating conditions, in particular on the hot gas temperature of a first combustion chamber it can be necessary to cool the hot gases before they are admitted to a second burner (also called sequential burner). This cooling can be advantageous to allow fuel injection and premixing of the injected fuel with the hot flue gases of the first combustor in the second burner.
Conventional cooling methods either require heat exchanger structures which lead to high pressure drops in the main hog gas flow or suggest injection of a cooling medium from the side walls. For injection of a cooling medium from the side walls a high pressure drop is required which is detrimental to the efficiency of a gas turbine operated with such a combustor arrangement and a controlled cooling of the whole flow is difficult.

Summary of the disclosure

The object of the present disclosure is to propose a sequential combustor arrangement with a mixing section for dilution gas admixing between the first combustion chamber and the second burner. The dilution gas is admixed in the mixing section to provide proper inlet flow conditions for the second burner. In particular the hot gases are cooled to a predetermined temperature profile.
High local inlet temperatures may result in high emissions (in particular NOx, CO, and unburned hydrocarbons) and/or flashback in the second burner. Flashback and NOx are induced by the reduced self-ignition time for the injected fuel due to a high inlet gas temperature or high oxygen concentration, which causes earlier ignition (leading to flashback) or reduced time for fuel air mixing resulting in local hot spots during combustion and consequently increases NOx emission. Low temperature regions can cause CO emissions, due to the increased self-ignition time. This can reduce the time for CO to CO2 burnout, and a reduced local flame temperature, which is can further slowdown the CO to CO2 burnout. Finally local hot spots may lead to overheating of certain parts downstream of the mixer.
This object is achieved by a sequential combustor arrangement according to claim 1 and a method according to claim 13. A sequential combustor arrangement according to the disclosure comprises a first burner, a first combustion chamber, a mixing device for admixing a dilution gas to the hot gases leaving the first combustion chamber during operation, a second burner, and a second combustion chamber arranged sequentially in a fluid flow connection, wherein the mixer is adapted to guide combustion gases in a hot gas flow path extending between the first combustion chamber and the second burner comprising a duct having an inlet at an upstream end adapted for connection to the first combustion chamber and an outlet at a downstream end adapted for connection to the second burner.
A local high oxygen concentration can have a similar effect as a local high temperature, e.g. fast reaction reducing the time for mixing, high combustion temperatures, increased NOx emissions and possibly flash back. A local low oxygen concentration can have a similar effect as a local low temperature, e.g. slow reaction leading to increased CO and UHC (unburned hydrocarbon) emissions.
A high or low local inlet velocity can lead to increased or reduced residence time in the second burner and subsequent second combustion chamber, which has similar negative effects as inhomogeneous self-ignition times, e.g. a reduced residence time in the second burner can lead to incomplete mixing and high NOx. A reduced residence time in the second combustor can lead to incomplete combustion resulting in increased CO emissions. A reduced flow velocity in the second burner can lead to early ignition and flash back.
Further important requirements from the aerodynamic point of view are minimised pressure loss in the hot gas path and the dilution gas supply. Both can impact the performance of a gas turbine operating with such a sequential combustor arrangement.
The mixer comprises a plurality of injection tubes (also called injection pipe), which are pointing inwards from the walls of the duct for admixing the dilution gas to cool the hot flue gases leaving the first combustion chamber to provide appropriate inlet conditions to the second burner.
The diameter, length and number of these tubes are designed to admix dilution gas into the hot gas flow such that the required local mass flow and temperature drop are achieved with a low pressure drop. Typically the injection tubes allow admixing of dilution gas with a pressure drop of 0.4% to 2% of the total pressure of the dilution gas pressure before admixing. With a low pressure drop at the inlet of the injector tubes, a pressure drop of 0.2% to 1% of the total pressure of the dilution gas pressure before admixing can be sufficient. To reduce the inlet pressure drop rounded tube inlets can be used.
According to the invention, the sequential combustor arrangement comprises at least three groups of injection tubes pointing inwards from the side walls of the mixer for admixing the dilution gas to cool the hot flue gases leaving the first combustion chamber. The injection tubes of each group are arranged circumferentially distributed along the side wall of the mixer and the first injection tubes of the first group have a first protrusion depth into the hot gas flow path, the second injection tubes of the second group have a protrusion depth, and the third injection tubes of the third group have a third protrusion depth. As the tubes are arranged normal to the side wall, the length of the tubes extending into the hot gas path is equal to the protrusion depth.
According to another embodiment of the sequential combustor arrangement the distance in flow direction between the center point of first injection tube and center point of the second injection tube is between 0.1 and 2 times the diameter of the first injection tube.
According to yet another embodiment the distance in flow direction between the center point of second injection tube and center point of the third injection tube is between 0.1 and 2 times the diameter of the second injection tube.
Typically the injection tubes of two neighboring groups are not arranged directly downstream of each other but offset in circumferential direction, thus a distance in axial direction of less than the diameter of the injection tubes is possible.
According to one embodiment of the sequential combustor arrangement the duct wall is at least partly effusion cooled. Due to admixing of dilution gas the average temperature of the hot gas in the mixer is reduced downstream of the injection tubes. Typically, a reduced cooling requirement and less diffusion cooling are expected. However, due to locally increased turbulence the heat load on the side wall downstream of an injection tube can be increased. Therefore in first effusion cooled regions downstream of each first injection tube and upstream of an array of subsequent third injection tube the number of effusion cooling holes per unit area can be increased. It is for example at least 30% bigger than the number of effusion cooling holes per unit area in a second region extending upstream of the first injection tube. Typically the second region extends for one to three diameters of the first injection tube upstream of the first injection tube.
Downstream of the last injection tube the hot gas temperature can be reduced to a level where no diffusion cooling is required or other cooling methods are applied. Thus a third region without effusion cooling can be arranged towards the exit of the mixer.
According to another embodiment the first effusion cooled region has a trapezoidal shape with bases normal to the main flow direction of the hot gases, and wherein the downstream base of the trapezoidal first region is longer than the upstream base of the trapezoidal first region.
The length of the upstream base of the trapezoidal first region can for example be in the order of 1 to 2 times the diameter of the first injection tube.
The first region can for example have the shape of an isosceles trapezoid.
In a further embodiment the effusion cooling holes have a diameter in a range from 0.5 to 1.2 mm. Further the distance between neighboring effusion cooling holes is in a range from 3 to 10 mm in the first region and in a range from 6 to 20 mm in the second region.
According to the invention, the first injection tubes are arranged upstream of the second injection tubes, and upstream of the third injection tubes. Further, the third injection tubes are arranged downstream of the second injection tubes. Such an arrangement allows the injection of dilution gas to different regions of the mixer with minimum interference between the dilution gas injected by different injection tubes.
In an arrangement where the shorter injection tubes are upstream of the longer injection tubes first the dilution gas injected by the short injection tubes reduces the heat load of the subsequent longer injection tubes. In particular if the long injection tubes are in the flow path of the dilution gas of an upstream injection tube the long injection tube is cooled due to a cool shower effect.
According to one embodiment of the sequential combustor arrangement the diameter of the first injection tube is larger than the diameter of the second injection tube. Further, in combination or as an alternative the diameter of the second injection tube can be larger than the diameter of the third injection tube.
In yet another embodiment of the sequential combustor arrangement the first injection tubes are arranged circumferentially distributed along the side wall of the mixer in a plane normal to the main flow direction of the hot gases flowing through the mixer, and the second injection tubes are arranged circumferentially distributed along the side wall of the mixer in one plane normal to the main flow direction of the hot gases flowing through the mixer.
Further, in one example, the number of second injection tubes can be equal to the number of first injection tubes. The second injection tubes can be arranged downstream or upstream of the first injection tubes wherein in radial direction they are in the center between two first injection tubes.
In a further embodiment the third injection tubes are arranged circumferentially distributed along the side wall of the mixer and staggered relative to a plane which is normal to the main flow direction of the hot gases flowing through the mixer. The stagger of the injection tubes reduces flow blockage due to the injection tubes. The stagger can for example be in a range of 0.1 to 3.5 times the diameter of the third injection tube.
The tubes of the mixer are exposed to the hot gases leaving the first combustion chamber. The tubes are inherently cooled by the dilution gas which is flowing through them. However, to increase life time of the tubes additional measures to reduce the temperature of the tubes can be applied.
Therefore, according to one embodiment of the sequential combustor arrangement at least part of the outer surface of the injection tubes is coated with TBC. Further, at least part of the inner surface of the side wall of the mixer can be coated with TBC to reduce the cooling requirements of the wall, and to thereby avoid cool peripheral regions in the hot gas flow leaving the mixer.
In one embodiment the heat transfer coefficient on the inside of the tube is increased. For increased heat transfer cooling ribs and/or a pin field can be arranged on the inner surface of the injection tubes.
According to a further embodiment the mixer additionally comprises injection holes arranged along the side wall. The first, second and third injection tubes are arranged to admix dilution gas towards the central region of the hot gas flow path and the injection holes are arranged to admix dilution gas into the wall regions of the hot gas flow path.
Besides the sequential combustor arrangement a gas turbine comprising such a sequential combustor arrangement is subject of the present disclosure. Such a gas turbine comprises at least a compressor, a sequential combustor arrangement with a first burner, a first combustion chamber, a mixing device for admixing a dilution gas to the hot gases leaving the first combustion chamber during operation, a second burner, and a second combustion chamber arranged sequentially in fluid flow connection, wherein the mixer is adapted to guide combustion gases in a hot gas flow path extending between the first combustion chamber and the second burner comprising a duct having an inlet at an upstream end adapted for connection to the first combustion chamber and an outlet at a downstream end adapted for connection to the second burner, and at least one turbine. The mixer comprises at least three groups of injection tubes pointing inwards from the side walls of the mixer for admixing the dilution gas to cool the hot flue gases leaving the first combustion chamber during operation. The injection tubes of each group are arranged circumferentially distributed along the side wall of the mixer and wherein the first injection tubes of the first group have a first protrusion depth into the hot gas flow path, the second injection tubes of the second group have a second protrusion depth, and the third injection tubes of the third group have a third protrusion. The mixer is arranged such that the dilution gas is admixed during operation to cool the hot gases.
The number of injection tubes in a group with a small protrusion depth can be larger than the number of injection tubes in a group with a high protrusion depth, e.g. if the second protrusion depth is bigger than the third protrusion depth the number of third injection tubes can be bigger than the number of second injection tubes. The number of injection tubes can for example be chosen such that the distance between the exit openings of neighboring injection tubes in two groups are similar. Similar in this context can mean that the distance between exit openings in the group with larger penetration depth one to three times the distance between exit openings of injection tubes of the group with smaller penetration depth. The distance between exit openings can further be increased with the exit diameter of the injection tubes. For example it can be proportional to the exit diameter.
Besides the gas turbine a method for operating such a gas turbine is subject of the present disclosure. Dilution gas can be admixed to the hot gases in the mixer such that the hot gases are cooled. According to the invention, dilution gas is admixed into different regions of the cross section of the mixer via the first, second and third injection tubes. According to the invention, the first injection tubes are arranged to admix dilution gas towards the central region of the hot gas flow path.
Effusion cooling might be used to cool the combustor walls and/or side walls of the mixing section.
Downstream of the dilution air injection mixing between dilution air and hot gas can be enhanced by a contraction of the flow path.
Referring to a sequential combustion the combination of combustors can be disposed as follows:

Both, the first and second combustors are configured as sequential can-can architecture.
The first combustor is configured as an annular combustion chamber and the second combustor is configured as a can configuration.
The first combustor is configured as a can-architecture and the secondary combustor is configured as an annular combustion chamber.
Both, the first and second combustor are configured as annular combustion chambers.

Brief description of the drawings

The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying drawings. Referring to the drawings:

Fig. 1a, 2a: show a generic gas turbine using sequential combustion with a mixer for admixing dilution gas;
Fig. 1b: shows a sequential combustor arrangement with a mixer with first, second, and third injection tubes;
Fig. 2b: shows a sequential combustor arrangement with a mixer with first, second, and third injection tubes;
Fig. 3: shows a mixer section with first, second, and third injection tubes;
Fig. 4: shows a mixer section with first, second, and third injection tubes;
Fig. 5: shows a section of mixer in an annular architecture with diffusion cooling;
Fig. 6: shows an injection tube.

Embodiments of the disclosure

Fig. 1a and 2a show a gas turbine 100 with a sequential combustor arrangement 104 according to the disclosure. It comprises a compressor 103, a sequential combustor arrangement 104, and a turbine 105. The sequential combustor arrangement 104 comprises a first burner 112, a first combustion chamber 101, and a mixer 117 for admixing a dilution gas to the hot gases leaving the first combustion chamber 101 during operation. Downstream of the mixer 117 the sequential combustor arrangement 104 further comprises a second burner 113, and a second combustion chamber 102. The first burner 112, first combustion chamber 101, mixer 117, second burner 113 and second combustion chamber 102 are arranged sequentially in a fluid flow connection. Fuel can be introduced into the first burner 112 via a first fuel injection 123, mixed with compressed air which is compressed in the compressor 103, and combusted in the first combustion chamber 101. Dilution gas is admixed in the subsequent mixer 117. Additional fuel can be introduced into the second burner via a second fuel injection 124, mixed with hot gases leaving the mixer 117, and combusted in the second combustion chamber 102. The hot gases leaving the second combustion chamber 102 are expanded in the subsequent turbine 105, performing work. The turbine 105 and compressor 103 are arranged on a shaft 106.
The remaining heat of the exhaust gas 107 leaving the turbine 105 can be further used in a heat recovery steam generator or boiler (not shown) for steam generation.
In the example shown here compressor exit gas is admixed as dilution gas. Typically compressor exit gas is compressed ambient air. For gas turbines with flue gas recirculation (not shown) the compressor exit gas is a mixture of ambient air and recirculated flue gas.
Typically, the gas turbine system includes a generator (not shown) which is coupled to a shaft 106 of the gas turbine 100.
Two different exemplary embodiments of the mixer 117 are shown in Figs. 1b and 2b as an enlarged section of the Fig. 1a and 2b Fig. 2a shows a first example with a mixer comprising first injection tubes 114 with length of second injection tube 11, second injection tubes 115 with a length of second injection tube 12, and third injection tubes 116 with a length of second injection tube 13. The second injection tubes 115 are arranged downstream of the first injection tubes 114, and the third injection tubes 116 are arranged downstream of the second injection tubes 115. The length of the injection tubes is decreasing in flow direction. In this example compressed gas from the compressor plenum is guided along the combustor liner in a connection duct 111 as dilution gas 110. From the connection duct 111 the dilution gas 110 is injected into the mixer via the first injection tubes 114, second injection tubes 115, and third injection tubes. The mixer 117 has a cross section with a height.
The mixer can be arranged with an annular cross section. For an annular mixer the height is the difference between the diameter of an outer wall of the annular flow section and the inner wall of the annular flow section. For a mixer with a cylindrical cross section (can-like mixer arrangement) the height is the diameter of the cross section. The length l1, l2, and l3 of the first, second and third injection tubes 114, 115, 116 are chosen such that good mixing of injected dilution gas 110 with the hot gas leaving the first combustion chamber 101 is assured.
Fig. 2b shows example which is based on the example of Fig. 1b. In this example the dilution gas 110 is directly supplied to the first injection tubes 114, second injection tubes 115, and third injection tubes 116 from the compressor plenum (downstream of the compressor 103). The first injection tubes 114, and second injection tubes 115 are extending into the compressor plenum and therefore dilution gas 110 with a higher pressure and lower temperature (no temperature pick-up due to the cooling of the combustor before use as dilution gas) is available.
Fig. 3 shows an example of the mixer 117 of figs. 1b, 2b in detail. In this example the first injection tube 114 has a diameter of the first injection tube D1 which is bigger than the diameter of the second injection tube D2. Further, the second injection tube 115 has a diameter of the second injection tube D2 which is bigger than the diameter of the third injection tube D3. The second injection tube 115 is arranged downstream of the first injection tube 114 with a distance in flow direction a1 in the main flow direction of the hot gas 127. The third injection tube 116 is arranged downstream of the second injection tube 115 with a distance in flow direction a2.
Fig. 4 shows another example of a mixer 117. In this example the second injection tube 115 is arranged downstream of the short third injection tube 116. The long first injection tube 114 is arranged downstream of the second injection tube 115. The dilution gas 110 injected from the third injection tube 116 at least partly cools the first and/or second injection tube 114, 115. The dilution gas 110 injected from the second injection tube 115 at least partly cools the first injection tube 114.
Fig. 5 shows an example of a section of mixer in a can architecture. It shows a cut-out of a cylindrical side wall 119. First, second, and 3 injection tubes 114, 115, 116 are arranged on the cylindrical side wall 119. The second injection tubes 115 are arranged downstream of the first injection tubes 114 n the main flow direction of the hot gas 127. A staggered array of third injection tubes 116 is arranged downstream of the second injection tubes 115. Neighbouring third injection tubes 116 are staggered by a stagger s in direction of the main flow direction of the hot gas 127 relative to a plane normal to the hot gas flow direction.
The inlet to the injection tubes 114, 115, 116 is rounded to reduce the pressure loss of the dilution gas entering the injection tubes 114, 115, 116.
The side wall 119 of the mixer is diffusion cooled. Diffusion cooling holes 120 are distributed over a large area of the side wall 119. A trapezoidal first region 125 downstream of each first injection tube 114. A homogeneously cooled second region 126 the wall extends upstream of the first injection tubes 114. The first region 125 has an increased density of diffusion cooling holes 120 relative to the second region 126. The first region 125 has the shape of an isosceles trapezoid. The shorter base extends in a direction normal to the main flow direction of the hot gases 127 in both directions from the centre of the first injection tube 114. The legs of the trapezoid typically have an angle of about 30° to 45° relative to the main flow direction of the hot gases 127. In this example the first region 125 extends in the main flow direction of the hot gases 127 to the upstream side of subsequent third injection tubes 116.
Downstream of the third injection tubes 116 the hot gas temperature can be reduced to a level where no diffusion cooling is required or other cooling methods are applied. A third region 128 without effusion cooling is shown arranged towards the exit of the mixer 117.
The inner surface of the side wall 119 is protected by thermal barrier coating 122. In addition the outer surface of the first injection tube 114 is protected by thermal barrier coating 122.
Fig. 6 shows an injection tube 114, 115, 116 attached to the side wall 119. The outer surface of the injection tube 114, 115, 116 is coated with thermal barrier coating 122 to reduce the heat transfer to the hot gas flow. Ribs 121 are applied on the inner surface of the injection tube 114, 115, 116 to increase the heat transfer for better cooling of the injection tube 114, 115, 116.
The first combustion chamber 101 and the second combustion chamber 102 can be arranged in a combustor can-can-architecture, i.e. the first combustion chamber 101 and second combustion chamber 102 are can combustion chamber.
The first combustion chamber 101 and the second combustion chamber 102 can be arranged in a combustor can-annular-architecture, i.e. the first combustion chamber 101 is arranged as an annular combustion chamber and second combustion chamber 102 is arranged as can combustion chamber.
The first combustion chamber 101 and the second combustion chamber 102 can be arranged in a combustor annular-can-architecture, i.e. the first combustion chamber 101 is arranged as can combustion chamber and second combustion chamber 102 is arranged as an annular combustion chamber.
The first combustion chamber 101 and the second combustion chamber 102 can be arranged in a combustor annular-annular-architecture, i.e. the first combustion chamber 101 and second combustion chamber 102 are annular combustion chambers.
The mixing quality of the mixer 117 is crucial since the burner system of the second combustion chamber 102 requires a prescribed inlet temperature and inlet velocity profile.
All the explained advantages are not limited just to the specified combinations but can also be used in other combinations or alone without departing from the scope of the disclosure. Other possibilities are optionally conceivable, for example, for deactivating individual burners or groups of burners. Further, the dilution gas can be re-cooled in a cooling air cooler before admixing in the mixer 117. Further the arrangement of the injection tubes can be reversed.

List of designations

100: Gas Turbine
101: First Combustor
102: Second Combustor
103: Compressor
104: Sequential combustor arrangement
105: Turbine
106: Shaft
107: Exhaust Gas
108: Compressed Air
109: Combustion Products
110: Dilution gas
111: Connecting Duct
112: First burner
113: Second burner
114: First injection tube
115: Second injection tube
116: Third injection tube
117: Mixer
118: Injection hole
119: Side wall
120: Effusion cooling holes
121: Rib
122: TBC
123: First fuel injection
124: Second fuel injection
125: First region
126: Second region
127: Main flow direction of the hot gases
128: Third region

a1: Distance in flow direction
a2: distance in flow direction
l1: length of first injection tube
l2: length of second injection tube
l3: length of second injection tube
D1: diameter of first injection tube
D2: diameter of second injection tube
D3: diameter of third injection tube
s: stagger

Claims

A sequential combustor arrangement (104) comprising a first burner (112), a first combustion chamber (101), a mixer (117) for admixing a dilution gas to the hot gases leaving the first combustion chamber (101) during operation, a second burner (113), and a second combustion chamber (102) arranged sequentially in a fluid flow connection, wherein the mixer (117) is adapted to guide combustion gases in a hot gas flow path extending between the first combustion chamber (101) and the second burner (113) comprising a duct having an inlet at an upstream end adapted for connection to the first combustion chamber (101) and an outlet at a downstream end adapted for connection to the second burner (113),
characterized in that the mixer (117) comprises at least three groups of injection tubes (114, 115, 116) pointing inwards from the side walls (119) of the mixer (117) for admixing the dilution gas to cool the hot flue gases leaving the first combustion chamber (101) wherein the injection tubes (114, 115, 116) of each group are arranged normal to the side wall (119) and circumferentially distributed along the side wall (119) of the mixer (117) and wherein the first injection tubes (114) of the first group have a first protrusion depth (11), the second injection tubes (115) of the second group have a second protrusion depth (12), and the third injection tubes (116) of the third group have a third protrusion depth (13); the second injection tubes (115) are arranged downstream of the first injection tubes (114), and the third injection tubes (116) are arranged downstream of the second injection tubes (115); the protrusion depth of the injection tubes (114, 115, 116) is decreasing or increasing in flow direction.
A sequential combustor arrangement (104) according to claim 1, characterized in that the distance (a1) in flow direction between the center point of first injection tube (114) and center point of the second injection tube (115) is between 0.1 and 2 times the diameter (D1) of the first injection tube (114).
A sequential combustor arrangement (104) according to claim 1 or 2, characterized in that the distance (a2) in flow direction between the center point of second injection tube (115) and center point of the third injection tube (116) is between 0.1 and 2 times the diameter (D2) of the second injection tube (115).
A sequential combustor arrangement (104) according to one of the claims 1 to 3, characterized in that the duct wall (119) is at least partly effusion cooled, and in that the number of effusion cooling holes (120) per unit area in first regions (125) downstream of each first injection tube (114) and upstream of an array of subsequent third injection tube (116) is at least 30% bigger than the number of effusion cooling holes (120) per unit area in a second region (126) extending upstream of the first injection tube (114).
A sequential combustor arrangement (104) according to claim 4, characterized in that the first region (125) has a trapezoidal shape with bases normal to the main flow direction of the hot gases, and wherein the downstream base of the trapezoidal first region (125) is longer than the upstream base of the trapezoidal first region (125).
A sequential combustor arrangement (104) according to claim 4 or 5, characterized in that the effusion cooling holes (120) have a diameter in a range from 0.5 to 1.2 mm, wherein the distance between neighboring effusion cooling holes (120) is in a range from 3 to 10 mm in the first region (125) and in a range from 6 to 20 mm in the second region (126).
A sequential combustor arrangement (104) according to anyone of the foregoing claims, characterized in that the diameter of the first injection tube (D1) is larger than the diameter of the second injection tube (D2), and/or in that the diameter of the second injection tube (D2) is larger than the diameter of the third injection tube (D3).
A sequential combustor arrangement (104) according to one of the claims 1 to 7, characterized in that the first injection tubes (114) are arranged circumferentially distributed along the side wall (119) of the mixer (117) in a plane normal to the main flow direction of the hot gases flowing through the mixer (117), and the second injection tubes (115) are arranged circumferentially distributed along the side wall (119) of the mixer (117) in a plane normal to the main flow direction of the hot gases flowing through the mixer (117).
A sequential combustor arrangement (104) according to one of the claims 1 to 8, characterized in that the third injection tubes (115) are arranged circumferentially distributed along the side wall (119) of the mixer (117) and staggered relative to a plane normal to the main flow direction of the hot gases flowing through the mixer (117), wherein the stagger is between 0.1 and 3.5 times the diameter of the third injection tube (D3).
A sequential combustor arrangement (104) according to one of the claims 1 to 9, characterized in that at least part of the outer surface of the injection tubes (114, 115, 116) and/or at least part of the inner surface of the side wall (119) of the mixer (117) is coated with TBC (122).
A sequential combustor arrangement (104) according to one of the claims 1 to 10, characterized in that cooling ribs (121) and/or a pin field is arranged on the inner surface of the injection tubes (114, 115, 116).
Gas turbine (100) with at least one compressor (103), a combustor, and at least one turbine (105), characterized in that it comprises a sequential combustor arrangement (104) according to one of the claims 1 to 11.
Method for operating a gas turbine (100) with at least a compressor (103), a sequential combustor arrangement (104) comprising a first burner (112), a first combustion chamber (101), a mixer (117) for admixing a dilution gas to the hot gases leaving the first combustion chamber (101) during operation, a second burner (113), and a second combustion chamber (102) arranged sequentially in a fluid flow connection, wherein the mixer (117) is adapted to guide combustion gases in a hot gas flow path extending between the first combustion chamber (101) and the second burner (113) comprising a duct having an inlet at an upstream end adapted for connection to the first combustion chamber (101) and an outlet at a downstream end adapted for connection to the second burner (113),
wherein the mixer (117) comprises at least three groups of injection tubes (114, 115, 116) pointing inwards from the side walls (119) of the mixer (117) for admixing the dilution gas to cool the hot flue gases leaving the first combustion chamber (101) wherein the injection tubes (114, 115, 116) of each group are arranged normal to the side wall (119) and circumferentially distributed along the side wall (119) of the mixer (117) and wherein the first injection tubes (114) of the first group have a first protrusion depth (11), the second injection tubes (115) of the second group have a second protrusion depth (12), and the third injection tubes (116) of the third group have a third protrusion depth (l3); ); the second injection tubes (115) are arranged downstream of the first injection tubes (114), and the third injection tubes (116) are arranged downstream of the second injection tubes (115); the protrusion depth of the injection tubes (114, 115, 116) is decreasing or increasing in flow direction; characterized in that the dilution gas (110) is admixed into different regions of the cross section of the mixer (117) via the first, second and third injection tubes (114, 115, 116).