EP3486569A1

EP3486569A1 - Reheat burner for a gas turbine and gas turbine comprising such a reheat burner

Info

Publication number: EP3486569A1
Application number: EP18206809.8A
Authority: EP
Inventors: Yang Yang; Alexander Sergeevich MYATLEV; Eribert Benz
Original assignee: Ansaldo Energia Switzerland AG
Current assignee: Ansaldo Energia Switzerland AG
Priority date: 2017-11-17
Filing date: 2018-11-16
Publication date: 2019-05-22
Anticipated expiration: 2038-11-16
Also published as: CN110030582B; EP3486569B1; RU2017140045A; RU2747655C2; RU2017140045A3; CN110030582A

Abstract

A burner (22) for a gas turbine (1), the burner (22) comprising:
- gas flow channel (25) having an axis (24) parallel to the a main gas flow direction (M);
- at least a fuel injector (26) comprising at least a streamline body (28) extending straightly across the gas flow channel (25) along a first transverse direction (29) of a plane orthogonal to the gas flow direction (M);
wherein the streamline body (28) comprises a lobed shaped trailing edge (31) having turning points (34) and lobes pointing alternatively in opposite direction along a second transverse direction (33) orthogonal to first transverse direction (29) in the plane orthogonal to the gas flow direction (M).
wherein the lobed shaped trailing edge (31) has an apex portion (35) substantial parallel to the first transverse direction (29) and two side portions (36) connecting the turning points (34) to the apex portion (35).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Russian Patent Application No. 2017140045 filed on November 17, 2017 .

Field of the Invention

The present invention relates to a reheat burner for a gas turbine for power plants. In particular, the present invention relates to the shape of the trailing edge of the fuel injector of a reheat burner for a gas turbine. Moreover, the present application refers to a gas turbine having in series along the main gas flow a first burner, or premix burner, and a second burner, or reheat burner provided with the above mentioned fuel injector.

Description of prior art

As known, a gas turbine for power plants (in the following only gas turbine) comprises a rotor provided with an upstream compressor sector, a combustor sector and a downstream turbine sector. The terms downstream and upstream refer to the direction of the main gas flow passing through the gas turbine. In particular, the compressor comprises an inlet supplied with air and a plurality of blades compressing the passing air. The compressed air leaving the compressor flows into a plenum, i.e. a closed volume, and from there into the combustor. Inside the combustor the compressed air is mixed with at least one fuel. The mixture of fuel and compressed air flows into a combustion chamber inside the combustor where this mixture are combusted. The resulting hot gas leaves the combustor and is expanded in the turbine performing work on the rotor.
In order to achieve a high efficiency, a high turbine inlet temperature is required. However, due to this high temperature, high NOx emissions are generated.
In order to reduce these emissions and to increase operational flexibility, today is known a particular kind of gas turbines performing a sequential combustion cycle.
In general, a sequential gas turbine comprises two combustors in series wherein each combustor is provided with the relative burner and combustion chamber. Following the main gas flow direction, the upstream combustor is called "premix" combustor and is fed by the compresses air. The downstream combustor is called "sequential" or "reheat" combustor and is fed by the hot gas leaving the first combustion chamber. According to a first kind of sequential gas turbines, the two combustors are physically separated by a stage of turbine blades, called high pressure turbine.
Following the main gas flow, this first kind of sequential gas turbines comprises a compressor, a first combustor, a high-pressure turbine, a second combustor and a low-pressure turbine. The compressor and the two turbines may be connected to a common rotor rotating around an axis and surrounded by a concentric casing.
Today is known a second kind of sequential gas turbines not provided with the high pressure turbine and wherein the premix and the reheat combustor are arranged directly one downstream the other inside a common casing, in particular a can-shaped casing. According to this kind of sequential gas turbines, a plurality of can combustors are provided arranged as a ring around the turbine axis. Each can-combustor is provided with a transition duct arranged downstream the second combustion chamber for guiding the hot gas leaving the combustor toward the turbine, in particular toward the first vane of the turbine.
As foregoing mentioned, the reheat combustor comprises a reheat burner provided with a single or dual fuel injector configured to delivery fuel (oil fuel and gas fuel) in the hot gas flow passing through the reheat burner. Moreover, the reheat combustor may be provided with mixing device that can be integrated in the fuel injector of the reheat burner. The reheat burner, in particular the casing of the reheat burner, defines a hot gas flow channel having an axis and housing the fuel injector. The axis of the burner is parallel to the hot gas flow direction so that in the following it is possible to refer indifferently to the burner axis or to the gas flow direction. The cross section of this hot gas flow channel, i.e. the section orthogonal to the gas flow direction, may be circular, square/rectangular or annular. For circular and square/rectangular configurations, the fuel may be fed to the fuel injector by a lance parallel but offset with respect reheat burner axis. In particular, the lance in this case is at least in part arranged outside the gas flow channel. For the annular configuration, the fuel lance is usually disposed along the burner axis.
The above described different kinds of gas turbines have been cited because the present invention can be applied in all these different gas turbines.
Today it is known to provide the reheat burner with a dual fuel injector comprising at least a streamline body having a leading edge and trailing edge along the gas flow direction and extending substantially straightly across the gas flow channel along a first transverse direction. This first transverse direction is orthogonal to the gas flow direction in a plane orthogonal to the gas flow direction. For hot gas channels having a circular or square/rectangular cross-section, the reheat burner comprises a plurality of dual fuel injectors as above defined and arranged parallel each-others along a common first transverse direction. For hot gas channel having an annular cross-section, the reheat burner comprises a plurality of dual fuel injectors radially arranged with respect to the burner axis. In this case, the first transverse direction corresponds to the radial direction with respect to the burner axis. The trailing edge of each streamline body is provided with a plurality of fuel nozzles. These nozzles may be dual fuel nozzles with moreover an additional channel for delivering carrying air or the injector trailing edge can comprise a first series of liquid fuel nozzles and a separated second series of gas fuel nozzles. The axis of these nozzles is usually parallel to the burner axis. However, in particular for the liquid fuel nozzles, the nozzle axis can be angled with respect to the burner axis in order to avoid interactions between liquid injected jets and the burner casing.
It is known to provide the reheat burner with mixing devices configured for mixing the injected fuel with the passing hot gas flow.
In order to integrate the mixing device in the fuel injector, it is known to provide the trailing edge of the streamline body with a lobed shape forming a wave along the first transverse direction. In particular, the apexes of this lobed shape point alternatively in opposite direction of a second transverse direction. This second transverse direction is orthogonal to the first transverse direction in the plane orthogonal to the gas flow direction. In the annular configuration, this second transverse direction correspond to the circumferential direction centered in burner axis. The lobes of adjacent fuel injectors may be in phase or out of phase. At the turning points of the lobed shape trailing edge are usually located the liquid or oil fuel nozzles whereas the gas nozzles are located along the remaining portions of the lobed shape trailing edge.
Today it is known to provide the trailing edge with a circular lobed shape or with a straight lobed shape. The straight lobed shape generates more shear type of injecting fuel flow with respect to the circular lobed shape that allows to generate only streamwise vortices. However, the straight lobed shape involves a higher pressure drop and moreover has design constrains for multiple point injection due to the geometrical restriction.
There is today the need to improve the lobed trailing edge of the reheat burner fuel injector in order to have an intermediate solution between the straight and the circular lobed shape.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a new lobed shape trailing edge of the fuel injector of a reheat burner for a gas turbine.
In order to achieve the objective mentioned above, the present invention provides a burner, in particular a reheat burner, for a gas turbine, wherein the burner comprises:

gas flow channel defining by the burner casing and having an axis parallel to the main gas flow direction;
at least a fuel or dual fuel injector comprising wherein each injector comprises a streamline body having a leading edge and a trailing edge along gas flow direction and extending straightly across the gas flow channel along a first transverse direction orthogonal to the gas flow direction in a plane orthogonal to the gas flow direction.

The trailing edge of the above streamline body comprised a lobed shape along the first transverse direction having turning points and apexes of lobes pointing alternatively in opposite direction along a second transverse direction. This second transverse direction is orthogonal to first transverse direction in the plane orthogonal to the gas flow direction.
According the main aspect of the invention, the lobed shape of the injector trailing edge is a conic lobed shape having an apex portions substantial parallel to the first transverse direction and side portions connecting the turning points to the apex portions.
In particular, the above conic lobed shape is defined as a periodic quadratic equation controlled by five geometrical boundary conditions; wherein the five geometrical boundary conditions comprises two points explicitly defined, two points defined by a first geometric parameter a one defined by a second geometric parameter.
Preferably, the first geometric parameter is defined as the ratio of the length of the apex portion along the first transverse direction and the distance of two turning points. This first geometric parameter, or slope ratio, is comprised between 0,5 and 0,9 and preferably is 0,588.
Preferably, the second geometric parameter is defined as the ratio b/B. Given a first line L passing through a turning point and the apex; given a first tangent T1 to the lobed shape at the turning point, given a second tangent T2 to the apex, given a second line L2 perpendicular to the first line L and passing through the intersection between the first tangent T1 and the second tangent T2, b is defined as the distance between the first line L and the lobed shape measured on the second line L2 and B is defined as the distance between the first line L and the intersection between the first tangent T1 and the second tangent T2 measured on the second line L2.
This second geometric parameter, or conic parameter, is comprised between 0,5 and 0,75, and preferably is 0,504.
Advantageously, the lobed shape of the present invention allows to reduce the pressure drop, to increase the mixing between fuel and the hot gas and to mitigate the risk of flashback risks.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims.
The features of the invention believed to be novel are set forth with particularity in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.
The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

figure 1 is a schematic view of a gas turbine for power plants that can be provided with a burner according to the present invention;
figure 2 is a schematic view of a can combustor for a gas turbine for power plants provided in series with a premix and a reheat burner wherein such reheat burner can be configured according to the invention ;

figure 3 is a schematic view of the reheat burner of the can combustor of figure 2;
figures 4 and 5 are schematic views of alternative kinds of reheat burners that can be configured according to the invention;
figures 6 and 7 are schematic views of a fuel injector for a reheat burner that can be configured according to the invention;
figure 8 is a schematic view of a fuel injector having a trailing edge with conic lobed shape according to the invention;
figures 9 and 10 are schematic views of two geometrical parameters defining the conic lobed shape of the trailing edge of the reheat burner fuel injector according to the invention;
figure 11 is a schematic view of the influence of the geometrical parameter of figure 9 on the lobed shape of the trailing edge of the reheat burner fuel injector according to the invention;
figure 12 is a schematic view of the influence of the geometrical parameter of figure 10 on the lobed shape of the trailing edge of the reheat burner fuel injector according to the invention;
figure 13 is a schematic of the combine influence of the geometrical parameters of figures 9 and 10 on the lobed shape of the trailing edge of the reheat burner fuel injector according to the invention;
figures 14-17 are respectively schematic side and axial views of a comparison between a known lobed injector and a new lobed injector configured to avoid the oil impingement against the burner casing of the oil fuel delivered by the oil nozzles located at the lobe turning points.

DETAILED DESCRIPTION OF THE INVENTION

In cooperation with the attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to preferable embodiments, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention.
Reference will now be made to the enclosed drawings to describe the present invention in detail.
Reference is now made to Fig. 1 that is a schematic view of a gas turbine for power plants that can be provided with a burner according to the present invention. In particular, figure 1 discloses a gas turbine 1 having an axis 9 and comprising a compressor 2, a combustor sector 4 and a turbine 3. As known, ambient air 10 enters the compressor 2 and compressed air leaves the compressor 2 and enters in a plenum 16, i.e. a volume define by an outer casing 17. From the plenum 16, the compressed air 37 enters in the combustor that comprises a plurality of can combustors 4 annularly arranged around the axis 9. The terms annular, radial, axial, inner and outer refer to the axis 9 whereas the terms downstream and upstream refer to the gas main flow. Each can combustor 4 comprises at least a first burner 5 where the compressed air 37 is mixed with at least a fuel. This mixture is then combusted in a combustion chamber 6 and the resulting hot gas flows in a transition duct 7 downstream connected to the turbine 3. The turbine 3 comprises a plurality of vanes 12, i.e. stator blades, supported by a vane carrier 14, and a plurality of blades 13, i.e. rotor blades, supported by a rotor 8. In the turbine 3, the hot gas expands performing work on the rotor 8 and leaves the turbine 3 in form of exhaust gas 11.
Reference is now made to figure 2 that is schematic view of a can combustor that can be applied in the gas turbine of figure 2. In particular, figure 2 disclose a can combustor 4 housed in a relative portal hole of an outer casing 17 defining the plenum 16 where the compresses air are delivered by the compressor 2. The can combustor 4 has an axis 24 and comprises in series along the gas flow M a first combustor, or premix combustor 18, and a second combustor, or reheat combustor 19. In particular, the first combustor 18 comprises a first or premix burner 20 and a first combustion chamber 21. The reheat combustor 19 comprises a reheat burner 22 and a second combustion chamber 23. The burner axis 24 is parallel to the gas flow direction M and the casing of the reheat burner 22 defines a channel 25 (disclosed in figure 3-5) for the gas flow. The reheat burner comprises a plurality of fuel injectors 26, in particular dual fuel and carrying air injectors, arranged across the channel 25 for injecting the fuel in the passing hot gas. According to the embodiment of figure 2, the fuel is fed to the fuel injectors 26 by a fuel lance 27 axially extending through the first combustion chamber 21 up to the reheat burner 22. Downstream the second combustion chamber 23 the can combustor 4 comprises a transition duct 28 for guiding the hot gas flow to the turbine 3.
Reference is now made to figure 3 that is a schematic view of the reheat burner of the can combustor of figure 2. In particular, figure 3 shows a downstream view of the reheat burner 22 along a plane orthogonal to the axis 24 and to the hot gas flow direction. In view of the presence of the lance 27 arranged in the axis, the reheat channel 25 is define as an annular channel (i.e. having an annular cross section orthogonal to the can axis 24) and the fuel injectors 26 are radially arranged along the direction 29 with respect to the can axis.. The lobed shape of the fuel injectors 26 of figure 3 and the direction 29 will be described in detail in the following description of figures 6 and 7.
Reference is now made to the figures 4 and 5 that are schematic views of alternative kinds of reheat burners that can be configured according to the invention. According to the embodiment of figure 4, the reheat burner comprises a channel 25 having a square/rectangular cross section and the fuel injectors are arranged parallel along the first transverse direction 29. According to the embodiment of figure 5 the reheat burner comprises a channel 25 having a circular cross section and also in this embodiment the fuel injectors are arranged parallel along a transverse direction 29 in a plane orthogonal to the hot gas direction. In these embodiments of figures 4 e 5, the fuel is fed to the fuel injectors by a lance passing outside the burner casing.
Reference is now made to the figures 6 and 7 that are schematic views of a lobed fuel injector for a reheat burner that can be configured according to the invention. The fuel injector comprising a streamline body 28 having a leading edge 30 and a trailing edge 31 along the main flow direction M. The streamline body 28 is extending straightly across the entire cross-section of the reheat channel 25 from a first point to an opposite point along the first transverse direction 29 orthogonal to the gas flow direction. The trailing edge 31 of the streamline body 28 has a lobed shape along the transverse direction 29. The apexes 32 of lobes point alternatively in opposite direction of a second transverse direction 33 orthogonal to the first transverse direction 29. Lobes of adjacent fuel injectors may be in or out of phase and the turning points 34 of the lobed shape are located preferably along the central plane of the injector. The lobes progressively extend from leading edge 30 to the trialing edge 31. The lobed trailing edge 31, in particular at least at turning points 34, is provided with a plurality of fuel nozzles or dual fuel nozzles and/or air nozzles.
In case of dual fuel injector, at the turning points 34 are located the liquid or oil nozzles and at the remaining portion of the lobed edge is located a plurality of gas nozzles.
Reference is now made to figure 8 that is a schematic view of a fuel injector having a trailing edge with a conic lobed shape according to the invention. According to the invention, the lobed shape is defined as a conic lobed shape that can be considered as an intermediate between a lobed circular shape and a lobed straight shape. Indeed, as reported in the summery of invention, in the cross-section orthogonal to the burner axis, the claimed conic lobed shape comprises an apex portion 35, i.e. the portion comprising the apex 32 or middle point of the apex portion 35, that is substantial parallel to the first transverse direction 29 and two side portions 36 connecting the turning points 34 to the apex portion 35.
Reference is now made to figure 9 and 10 that are schematic views of two geometrical parameters that allow to geometrically define the conic lobed shape according to the invention. The first parameter, disclosed in figure 9, is called "slope ratio" or SL and it is defined by the ratio of the half of the wavelength λ of the lobed shape, i.e. the distance of two turning points 34, and the length A of the apex portion 32 along the first transverse direction 29. The parameter SL is comprised from 0, wherein the lobed shape is a triangular shape and the length A of the apex portion 32 along the first transverse direction 29 is 0, and 1 wherein the lobed shape is a straight shape and the length A of the apex portion 32 along the first transverse direction 29 is equal to the distance of two turning points 34. The second parameter, disclosed in figure 10, is called "conic parameter" or K and it is defined by the ratio b/B. Given a first line L passing through a turning point 34 and the apex 32; given a first tangent T1 to the lobed shape at the turning point 34, given a second tangent T2 to the apex 32, given a second line L2 perpendicular to the first line L and passing through the intersection between the first tangent T1 and the second tangent T2, b is defined as the distance between the first line L and the lobed shape measured on the second line L2 and B is defined as the distance between the first line L and the intersection between the first tangent T1 and the second tangent T2 measured on the second line L2. The parameter K describes the inclination of the side portion 36 with respect to the second transverse direction 33. Also the parameter K is comprised form 0 to 1.
By using the above described two parameters, the conic lobed shape of the present invention can be defined as a periodic quadratic equation controlled by 5 geometrical boundary conditions. These 5 geometrical boundary conditions comprises two points explicitly defined (i.e. the turning points), two points defined by the SL parameter and 1 point defined by the K parameter.
Reference is now made to figure 11 that is a schematic view of the influence of the geometrical parameter SL on the lobed shape having K parameter equal to 0,6.
Reference is now made to figure 12 that is a schematic view of the influence of the geometrical parameter K on the lobed shape having SL parameter equal to 0,7.
Reference is now made to figure 13 that is a schematic diagram of the combined influence of the geometrical parameters SL and K on the lobed shape according to the invention.
With constant K, by increasing SL a sharp corner appears on the summit of lobe. With constant SL, by increasing SL the lobed shape becomes a triangle shape. By increasing SL and K, the shape goes from curved lobe to straight lobe.
As foregoing described, in case of dual fuel injector, at the turning points 34 are located the liquid or oil nozzles whereas along the remaining portions of the lobed edge is located a plurality of gas nozzles. It is known to provide the liquid or oil nozzles with a nozzle axis angled or inclined with respect to the burner axis in order to avoid interactions between the liquid injected jets and interactions between liquid injected jets and the burner casing. However, also with these inclined liquid or oil nozzles an oil impingement against the burner casing can occur.
Reference is now made to figures 14-17 that are respectively schematic side and axial views of a comparison between a known lobed injector and a new lobed injector for a reheat burner. This new lobed injector is configured to avoid the oil impingement against the burner casing of the oil fuel delivered by the oil nozzles located at the turning points.
Figures 14 and 16 disclose a known lobed injector 26 having two oil nozzles, respectively an outer and inner oil nozzle with respect to the burner axis 24, located at the two turning points 34 in the injector trailing edge 31. Since the lobed shape progressively extends from leading edge 30 to the trialing edge 31, starting from the oil nozzles at the turning points 34 it is possible to define a lobe turning line 37 extending from the trailing edge 31 to the leading edge 30. In case of two oil nozzles, namely an outer and inner oil nozzles, the lobed injector 26 comprises an outer and an inner turning line 37. According to the prior art practice of figure 14 and 16, both the outer and the inner turning lines 37 are parallel to the burner axis 24. In this embodiment, to avoid the oil impingement of the fuel oil against the burner casing it is necessary to provide the oil nozzle with a nozzle axis inclined with respect to the turning line 37. In particular, the nozzle axis is inclined toward the burner axis 24. Unfortunately, this angled configuration is expensive and involves negative effects on the nozzle lifetime.
Figure 15 and 17 disclose a lobed injector 26 having two oil nozzles, respectively an outer and inner nozzle with respect to the burner axis 24. Also for this lobed injector 26 it is possible to define an inner and an outer turning line 37 as foregoing described. In particular, at least at the trailing edge 31 these turning lines 37 are not parallel to the burner axis 24 but are inclined toward the burner axis 24. In view of this angled configuration, the turning lines 37 can be at least partially seen also in the axial view of figure 17. As discloses in figure 15, the virtual linear prosecutions of each turning line 37 downstream the training edge 31 forms an angle α, β with respect to the burner axis 24. Preferably, the angle α of the outer turning line 37 is higher that the angle β of the inner turning line 37 because the oil injected by the outer nozzle has a higher risk of impact against the burner casing. The solution of figures 15 and 17 allows to realize oil nozzles at the turning points 34 having nozzle axis aligned to the relative turning line 37. Therefore, according this solution the nozzles are easy to be realized, ensure a higher lifetime and at the same time are suitable to avoid the oil impingement against the burner casing. Of course, also the oil nozzles of the figure 15 and 17 can be provided with an axis inclined with respect to the relative inclined turning line 37. This solution further improves the effect of avoiding the oil impingement against the burner casing. The solution with inclined turning lines 37 can be applied both in the conic lobed shape injectors of the present invention and in the common circular lobe shape injectors.
Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.

Claims

A burner for a gas turbine (1), the burner (22) comprising:
- gas flow channel (25) having an axis (24) parallel to the a main gas flow direction (M);

- at least a fuel injector (26) comprising at least a streamline body (28) extending straightly across the gas flow channel (25) along a first transverse direction (29) of a plane orthogonal to the gas flow direction (M);
wherein the streamline body (28) comprises a lobed shaped trailing edge (31) having turning points (34) and apexes (32) of lobes pointing alternatively in opposite direction along a second transverse direction (33) orthogonal to first transverse direction (29) in the plane orthogonal to the gas flow direction (M);
characterized in that the lobed shaped trailing edge (31) is a conic lobed shaped trailing edge (31) wherein each lobe comprises an apex portion (35) substantial parallel to the first transverse direction (29) and two side portions (36) connecting the turning points (34) to the apex portion (35).
Burner as claimed in claim 1, wherein the lobed shaped trailing edge is geometrically defined as a shape passing through two turning points (34) and controlled by five geometrical boundary conditions; wherein the five geometrical boundary conditions comprises two points explicitly defined, two points defined by a first geometric parameter a one defined by a second geometric parameter.
Burner as claimed in claim 2, wherein the first geometric parameter is defined as the ratio between the distance of two turning points (34) and the length (A) of the apex portion (35) along the first transverse direction (29) .
Burner as claimed in claim 3, wherein the first geometric parameter is comprised between 0,5 and 0,9.
Burner as claimed in claim 4, wherein the first geometric parameter is 0,588.
Burner as claimed in any one of the foregoing claims from 2 or 5, wherein the second geometric parameter is defined as defined by the ratio b/B; given a first line (L) passing through a turning point (34) and the apex (32); given a first tangent (T1) to the lobed shape at the turning point (34), given a second tangent (T2) to the apex (32), given a second line (L2) perpendicular to the first line (L) and passing through the intersection between the first tangent (T1) and the second tangent (T2), b is defined as the distance between the first line (L) and the lobed shape measured on the second line (L2) and B is defined as the distance between the first line (L) and the intersection between the first tangent (T1) and the second tangent (T2) measured on the second line (L2).
Burner as claimed in claim 6, wherein the second geometric parameter is comprised between 0,5 and 0,75.
Burner as claimed in claim 7, wherein the second geometric parameter is 0,504.
Burner as claimed in any one of the foregoing claims, wherein the gas flow channel (25) comprises a circular cross section.
Burner as claimed in any one of the foregoing claims, wherein the gas flow channel (25) comprises a square or rectangular cross section.
Burner as claimed in any one of the foregoing claims, wherein the gas flow channel (25) comprises an annular.
A gas turbine for power plant; the gas turbine (1) having an axis (9) and comprising following the gas flow direction:
- a compressor sector (2) for compressing ambient air,

- a combustor (4) for mixing and combusting the compressed with at least a fuel

- at least a turbine (3) for expanding the combusted hot gas flow leaving the combustors (4) and performing work on a rotor (8);
wherein the combustor (4) comprises an upstream burner and a downstream burner; the downstream burner being realized according to any one of the foregoing claims.
Gas turbine as claimed in claim 12 wherein, the gas turbine (1) comprises an high pressure turbine and a low pressure turbine, the downstream burner being arranged between the high pressure turbine and the low pressure turbine.
Gas turbine as claimed in claim 12 wherein, the combustor (4) is a can combustor housing in series the upstream and the downstream burner.