Sequential burner for an axial gas turbine

A sequential burner for an axial gas turbine comprises: a burner body, which is designed as an axially extending hot gas channel and further comprises a fuel injection device, which extends into said burner body perpendicular to the axial direction. The manufacturing of the burner body is simplified and the fuel injection is stabilized by designing said fuel injection device as a mechanically stiff component, and fixing said fuel injection device to said burner body in order to keep it aligned with said burner body and to stiffen said burner body against creep.

BACKGROUND OF THE INVENTION

The present invention relates to the technology of gas turbines. It refers to a sequential burner for an axial gas turbine according to the preamble of claim1.

PRIOR ART

In order to achieve a high efficiency, a high turbine inlet temperature is required in standard gas turbines. As a result, there arise high NOx emission levels and high life cycle costs. These problems can be mitigated with a sequential combustion cycle (e.g. using a burner of the type as disclosed in U.S. Pat. Nos. 5,431,018 or 5,626,017 or in U.S. 2002/0187448, also called SEV combustor, where the S stands for sequential). Both combustors contain premixing burners, as low NOx emissions require high mixing quality of the fuel and the oxidizer.

An exemplary gas turbine of the applicant with sequential combustion, which is known as GT26, is shown inFIG. 1.

Gas turbine10ofFIG. 1comprises a rotor11with a plurality of blades rotating about a machine axis20and being surrounded by a casing12. Air is taken in at air inlet13and is compressed by compressor14. The compressed air is used to burn a first fuel in a first (annular) combustor15, thereby generating hot gas. The hot gas drives a first, high pressure (HP) turbine16, is then reheated in a second (annular, sequential) combustor17, drives a second, low pressure (LP) turbine18and exits gas turbine10through exhaust gas outlet19. While in the case of the gas turbine shown inFIG. 1said sequential combustor is arranged between a first and second turbine, the present invention is not restricted to this case but relates to sequential combustors and burners in general.

FIG. 2shows (inFIG. 2(b)) a prior art secondary combustor of a gas turbine of the kind depicted inFIG. 1, where an SEV fuel lance slides into the burner, but is not fixed to it. In this current configuration, the SEV lance is fixed at a flange to an outer casing. Therefore, the injection location moves radially relatively to the burner due to thermal expansions.

Document EP 2 522 912 A1 relates to a combined flow straightener and mixer as well as a burner for a combustion chamber of a gas turbine comprising such a mixing device. For a combined function of flow straightening and mixing at least two streamlined bodies are arranged in a structure comprising the side walls of the mixer. The leading edge area of each streamlined body has a profile, which is oriented parallel to a main flow direction prevailing at the leading edge position, and wherein, with reference to a central plane of the streamlined bodies the trailing edges are provided with at least two lobes in opposite transverse directions. The periodic deflections forming the lobes from two adjacent streamlined bodies are out of phase. The disclosure further relates to a burner for a combustion chamber of a gas turbine, comprising such a flow straightener and mixer as well as at least one nozzle having its outlet orifice at or in a trailing edge of the streamlined body. Further, it relates to the operation of such a burner.

Document EP 2 725 301 A1 relates to a burner for a combustion chamber of a gas turbine with a mixing and injection device, wherein the mixing and injection device is comprising a limiting wall that defines a gas-flow channel and at least two streamlined bodies, each extending in a first transverse direction into the gas-flow channel. Each streamlined body has two lateral surfaces that are arranged essentially parallel to the main-flow direction, the lateral surfaces being joined to one another at their upstream side to form a leading edge of the body and joined at their downstream side to form a trailing edge of the body. Each streamlined body has a cross-section perpendicular to the first transverse direction that is shaped as a streamlined profile. At least one of said streamlined bodies is provided with a mixing structure and with at least one fuel nozzle located at its trailing edge for introducing at least one fuel essentially parallel to the main-flow direction into the flow channel, wherein at least two of the streamlined bodies have different lengths along the first transverse direction such that they may be used for a can combustor.

In this case, the nozzles used for fuel injection are in a radial alignment. The difference to the fuel lance ofFIG. 2becomes apparent inFIG. 3:FIG. 3(a)relates to the case of a fuel lance21, which is inserted into but not fixed to the burner body27, which guides a hot gas flow29. The central injector25at the end of fuel lance21injects fuel through nozzles26perpendicular to hot gas flow29. The distance between nozzles26and the upper and lower walls is quite large and thus relatively insensitive to the radial location of fuel lance21.

On the other hand, when an injection head30is used with a radial inline series of injection points (FIG. 3(b)), the distance between the injector nozzles and the upper/lower walls of burner body31is much lower and therefore more sensitive to the radial location of the lance.

In existing secondary burners high creep resistant materials are used and the size of the burner is small in comparison with the new requirements. For these new requirements solutions could be found with more expensive materials or larger wall thickness that would increase the cost, worsen the LCF properties and possibly impose casting as manufacturing option.

The SEV burner is subject to a large pressure drop between its cold and hot side. It is also exposed to high temperatures. Also due to its mainly rectangular shape, the upper and lower walls can creep and its shape and robustness is compromised. The multipoint injection system shown inFIG. 3(b)is more sensitive to radial displacement of the lance relative to the burner body.

Although the problems have been discussed so far for a sequential burner with essentially rectangular cross-section, the problem and the solution to be found is not restricted to sequential burners with rectangular cross-section. In general, the cross-section can be for example rectangular, circular or trapezoidal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sequential burner, which avoids disadvantages of known sequential burners and allows a multipoint injection scheme without requiring new materials or designs for the burner body.

This and other objects are obtained by a sequential burner as claimed in claim1.

According to the invention, a sequential burner for an axial gas turbine comprises a burner body, which is designed as an axially extending hot gas channel, and further comprises a fuel injection device, which extends into said burner body perpendicular to the axial direction.

Said sequential burner is characterized in that said fuel injection device is designed as a mechanically stiff component, and that said fuel injection device is fixed to said burner body in order to keep it aligned with said burner body and to stiffen said burner body against creep.

According to an embodiment of the inventive sequential burner said fuel injection device is an injection head comprising a plurality of fingers extending parallel to each other and perpendicular to the axial direction between an upper end plate and a lower end plate, and said injection head is fixed with its upper endplate to an outer wall of said burner body, whereby its lower end plate is flush with an inner wall of said burner body.

Specifically, a burner flange is provided in said outer wall of said burner body, said injection head sits in said burner body with its upper end plate flush with said burner flange, and said upper end plate is fixed to said burner flange by means of sliding inserts.

More specifically, said upper and lower end plates of said injection head and said burner flange are circular, and said upper end plate is fixed to said burner flange by means of multiple inserts, which are distributed along the circumference of said burner flange and said upper end plate, respectively.

Even more specifically, each of said inserts is fixed to said burner flange by means of a fixing lug, and each of said inserts has a foot, which meshes on one side with a circumferential groove at said burner flange and on the opposite side with a related of a plurality of hooks being distributed along the circumference of said upper end plate.

Specifically, there is a gap provided within said series of distributed hooks for introducing an insert and sliding it from said gap to its final position along a circumferential path.

Alternatively, said upper and lower end plates of said injection head and said burner flange are non-circular with two parallel longitudinal sides, and said upper end plate is fixed to said burner flange by means of two straight inserts or wedges inserted at said longitudinal sides.

Specifically, each of said inserts meshes on one side with a slotted outer rail at said longitudinal sides of said burner flange and on the opposite side with a slotted inner rail at said longitudinal sides of said upper end plate.

According to another embodiment of the invention each of said fingers is configured as a streamlined body which has a streamlined cross-sectional profile, whereby said body has two lateral surfaces essentially parallel to the flow direction of the hot gas passing through said burner body, whereby said lateral surfaces are joined at their upstream side by a leading edge and at their downstream side forming a trailing edge, and whereby a plurality of nozzles for injecting a gaseous and/or liquid fuel mixed with air is distributed along said trailing edge.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

A basic idea of the present invention is to use the fuel injection head of a sequential burner as stiffening element for a more robust SEV design. At the same time, fixing the sequential burner injection head at the burner body keeps it centered (aligned) with the burner body.

In the prior art (seeFIG. 2) an injector lance is assembled into the SEV burner sliding into it from an SEV burner flange. The lance is fixed on the outer casing and it is kept free to radially move relatively to the burner body. For other engines, a different type of injector is used: the so called VG injection head. For this system (multipoint inline injection), the distance between the injector nozzles and the upper/lower walls in much lower and therefore more sensitive to the radial location of the lance (seeFIG. 3(b)).

The idea now is to fix the injection head to the top of the burner and flush with the bottom of it.

FIG. 4shows an embodiment for the case of a burner body with circular burner flange, with the associated mounting procedure sketched inFIG. 5.

InFIG. 4, a burner body31, which extends in axial direction between a burner inlet32and a burner outlet33and has in this example an essentially rectangular cross section with an outer (or upper) wall52and an inner (or lower) wall53, has a circular opening34in the outer wall52surrounded by a burner flange (37inFIG. 5). The opening34receives a circular injection head30. Injection head30comprises in this example 3 parallel fingers, which extend perpendicular to the direction of hot gas flow29between a circular upper end plate35and a circular lower end plate51.

Each of said fingers36is configured as a streamlined body which has a streamlined cross-sectional profile, whereby said body has two lateral surfaces essentially parallel to the flow direction of the hot gas passing through said burner body31. Said lateral surfaces are joined at their upstream side by a leading edge and at their downstream side forming a trailing edge. A plurality of nozzles (not shown in the Figures) for injecting a gaseous and/or liquid fuel mixed with air is distributed along said trailing edge.

Injection head30is configured such that the upper end plate35is flush with the burner flange37and the lower end plate51is flush with the inner wall53, when injection head30, after sliding into burner body31(FIG. 4(a)) is in the end fully inserted into burner body31(FIG. 4(b)).

When injection head30has been fully inserted into burner body31, it is fixed at burner flange37according to a procedure shown inFIG. 5: Ring-like burner flange37is provided with a circumferential groove37aon its inner side. At its outer side multiple bulges are provided and distributed along the circumference, each comprising a tapped hole38. Corresponding to these multiple bulges and tapped holes38, upper end plate35of injection head30is provided with multiple hooks39, which are distributed accordingly along the periphery of upper end plate3and have each a recess39a, which is opposite to and corresponds with groove37aof the burner flange37.

Injection head30is fixed to the burner body and balcony with inserts40,40′ as shown inFIG. 5(b). Inserts40correspond to hooks39and are distributed along the circumference of burner flange37and upper end plate35, respectively. Each of said inserts40,40′ is fixed to burner flange37with a threaded bolt by means of a fixing lug40b. Each of said inserts40,40′ has a (horizontal) foot40a, which meshes on one side with circumferential groove37aat said burner flange37and on the opposite side with a related hook39and its recess39a. Inserts40,40′ thus slide around burner flange37and fix injection head30to the burner body with bolts.

As shown inFIGS. 5(c) to 5(f), there is a gap41provided within said series of distributed hooks39for introducing an insert40′ and sliding it clockwise or counter-clockwise from said gap41to its final position along a circumferential path, where it is fixed with a threaded bolt.

If an injection head has more than three fingers, e.g. four fingers, a non-round solution is needed. In this case, the injection head can also slide into the burner body, but the shape has two long straight slits (or slotted rails) used to fix the burner with straight inserts or wedges.

FIG. 6shows an embodiment with such a non-round balcony and the related fixation concept. Injection head42ofFIG. 6with its four fingers has upper end plate44and a lower end plate and can be inserted into burner body43. Burner flange47of burner body43is non-circular with two parallel longitudinal sides, whereby upper end plate44is fixed to said burner flange47by means of two straight inserts or wedges50inserted at said longitudinal sides. Thereby, each of said inserts50meshes on one side with a respective slotted outer rail48,49at said longitudinal sides of said burner flange47and on the opposite side with a respective slotted inner rail45,46at said longitudinal sides of upper end plate44(seeFIGS. 6(d) and 6(e)). At the same time, the lower end plate is flush with the inner wall of burner body43, as explained for the circular injection head, before.

The side view ofFIG. 7makes clear that said stiff injection head42stiffens the burner body43in that creep deformation is prevented, whereby the fingers act as stiffening elements against burner body creep.

To sum up, fixing the burner on top and preventing the bottom to deform inwards, the injection head not only serves its fuel injection purposes but also prevents the upper and lower walls to creep because of their high temperatures and the strong pressure difference between the cold and the hot side. At the same time the injection head is always centered and aligned with the burner body.

The advantages of the invention are:It allows the use of cheaper material (e.g. HastX instead of Haynes230);It allows lower wall thickness and therefore lower cost, as the burner body can be fabricated by welded metal sheet;It prevents flashback and high emission due to radial misalignment of the lance with the burner.

LIST OF REFERENCE NUMERALS