Method for servicing a combustor cap assembly for a turbine

According to one aspect of the invention, a method for servicing a combustor cap assembly of a turbine includes determining a defect is present in a center ring of the cap assembly, the center ring being disposed within a plurality of vanes, removing the center ring from the cap assembly. The method also includes placing a replacement center ring in the cap assembly, wherein dimensions of the replacement center ring are substantially the same as the center ring that has been removed and brazing the replacement center ring to the plurality of vanes.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbine engines. More particularly, the subject matter relates to servicing a cap assembly of a turbine engine.

In gas turbine engines, a combustor converts chemical energy of a fuel or an air-fuel mixture into thermal energy. The thermal energy is conveyed by a fluid, often air from a compressor, to a turbine where the thermal energy is converted to mechanical energy. These fluids flow downstream to one or more turbines that extract energy therefrom to produce the mechanical energy output as well as power to drive the compressor. Over time, turbine parts may experience wear and degradation due to extreme conditions caused by flow of heated fluid within the turbine engine.

For example, combustion dynamics and combustion temperatures in selected locations, such as the combustor and turbine nozzle assemblies, may lead to thermal stress and wear of parts in the assemblies. In some cases, repairing or replacing a single part of the assembly can lead to replacement of an entire assembly. Replacing an entire assembly due to a defect in a single part within the assembly is a costly and time consuming service process.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a method for servicing a combustor cap assembly of a turbine includes determining a defect is present in a center ring of the cap assembly, the center ring being disposed within a plurality of vanes, removing the center ring from the cap assembly. The method also includes placing a replacement center ring in the cap assembly, wherein dimensions of the replacement center ring are substantially the same as the center ring that has been removed and brazing the replacement center ring to the plurality of vanes.

According to another aspect of the invention, a method for servicing a combustor of a turbine, the combustor including a cap assembly, is provided. The method includes determining a defect is present in a center ring of the cap assembly, the center ring being disposed within a plurality of vanes, removing the center ring from the cap assembly by a process that does not substantially load the plurality of vanes, thereby enabling the plurality of vanes to remain structurally intact during the removing, placing a replacement center ring in the cap assembly, wherein dimensions of the replacement center ring are substantially the same as the center ring that has been removed and coupling the replacement center ring to the plurality of vanes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic diagram of an embodiment of a gas turbine system100. The system100includes a compressor102, a combustor104, a turbine106, a shaft108and a fuel nozzle110. In an embodiment, the system100may include a plurality of compressors102, combustors104, turbines106, shafts108and fuel nozzles110. As depicted, the compressor102and turbine106are coupled by the shaft108. The shaft108may be a single shaft or a plurality of shaft segments coupled together to form shaft108. Further, the system100may also include a plurality of compressors102and turbines106disposed about a turbine axis (not shown).

In an aspect, the combustor104uses liquid and/or gas fuel, such as natural gas or a hydrogen rich synthetic gas, to run the turbine engine. For example, fuel nozzles110are in fluid communication with a fuel supply112and pressurized air from the compressor102. The fuel nozzles110create an air-fuel mix, and discharge the air-fuel mix into the combustor104, thereby causing a combustion that creates a hot pressurized exhaust gas. The combustor104directs the hot pressurized exhaust gas through a transition piece into a turbine nozzle (or “stage one nozzle”), causing turbine106rotation as the gas exits the nozzle or vane and gets directed to the turbine bucket or blade. The rotation of turbine106causes the shaft108to rotate, thereby compressing the air as it flows into the compressor102. In an embodiment, combustion dynamics and associated temperatures can lead to thermal distress of components, such as components in the combustor104used for fuel and air distribution. In some cases, wear and thermal degradation of combustor104components leads to servicing and/or replacement of the components. Methods and systems that may be utilized for servicing a turbine component are discussed in detail below with reference toFIGS. 2-6.

As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the turbine. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The term “radial” refers to movement or position perpendicular to an axis or center line. It may be useful to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “radially inward” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it can be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. Although the following discussion primarily focuses on gas turbines, the concepts discussed are not limited to gas turbines and may apply to any suitable rotating machinery, including steam turbines. Accordingly, the discussion herein is directed to gas turbine embodiments, but may apply to other turbomachinery.

FIG. 2is a sectional side view of an exemplary combustor cap assembly202, where the section is formed by a plane that runs through an axis208. The combustor cap assembly202is disposed in a turbine combustor, such as combustor104. The cap assembly202includes a center stack210where a center ring212and vanes214are disposed in an annulus222of the center stack210. The cap assembly202also includes fuel nozzles216and218disposed about the center stack210. In an embodiment, the center stack210comprises a plurality of components that are coupled at joints from a base to an end220, including joints224, by a suitable process, such as brazing, welding or cladding. The center ring212is configured to receive a center fuel nozzle (not shown). The fuel nozzle supplies fuel to mix with air that swirls as it flows through vanes214, leading to combustion of the mixture downstream of the vanes214and center ring212. Over time, the center ring212is exposed to combustion dynamics and thermal stress. In some cases, the wear causes formation of a defect in the center ring212, where the center ring212requires servicing to ensure proper performance of the combustor200. In one embodiment described in detail below, the cap assembly202is placed on a servicing fixture where the entire center ring212is removed from the cap assembly202while the rest of the cap assembly remains assembled.

FIG. 3is a top view of the center stack210portion of the cap assembly202shown inFIG. 2. As depicted, the vanes214are coupled to an inner burner tube301and center ring212via couplings300and302, respectively, where the coupling are formed by a suitable durable method, such as brazing, welding or cladding. In an exemplary servicing process, after a defect occurs in the center ring212, the entire center ring212is removed without substantial loading of the vanes214. Accordingly, the vanes214remain structurally intact during the removing process. In an embodiment, the center ring212with the defect is removed by a suitable process, such as electrical discharge machining (EDM), high speed milling, laser removal or waterjetting. In one embodiment, the center ring212is removed by high speed milling with a slow feed rate or by EDM, where the vanes214are substantially not loaded and retain their geometry during the removal process. In other embodiments, the loading of the vanes214during a removal process may alter a geometry of the vanes and adversely affect fuel-air mixing and turbine efficiency.

FIG. 4is a top view of the center stack210portion of the cap assembly202shown inFIGS. 2 and 3installed on a fixture400for servicing. The fixture400provides precise positioning of the cap assembly202for removal of the center ring212by a selected process. The fixture400includes a base402and supports404. The supports404each include alignment or orienting features configured to be placed in orienting holes406in the cap assembly202to provide precise positioning of the assembly during servicing. In an embodiment, the orienting features and orienting holes406enable the removal tool to find true center of the cap assembly202and center ring212, thereby enabling precise removal of the ring without structurally impacting the vanes214. In an embodiment, the fixture400is coupled to a suitable apparatus (not shown), such as an EDM machine, configured to precisely remove the center ring212after the cap assembly202is positioned in the fixture400.

FIG. 5is a side sectional view of the cap assembly202with a replacement center ring500on a fixture502positioned within the cap assembly202. The fixture502includes a base504, elongated support506and ring platform508, where the ring platform508positions the replacement center ring500for coupling to the vanes214. In an embodiment, the fixture502precisely positions the replacement center ring500relative to the vanes214and cap assembly202, thereby enabling the replacement center ring500to be coupled to the vanes214. In embodiments, the replacement center ring500is substantially identical in dimension and geometry to the original equipment center ring, thus providing the replacement center ring configured to operate with the assembly without substantial modification after installation. For example, the replacement center ring500is positioned in the cap assembly202and coupled to vanes214by a brazing process, where the replacement center ring500is not manually machined or modified after being coupled to the vanes214. Accordingly, the servicing process has reduced manual steps as compared to other processes, thus reducing repair time and the occurrence of defects after repair. Further, the servicing process uses a coupling method, such as brazing, to couple the center ring500to the vanes214that does not affect joints and couplings in other portions of the cap assembly202, such as joints224.

FIG. 6is a flow chart600of exemplary steps that may be included in a servicing process for a cap assembly, such as cap assembly202. The depicted blocks may be part of or in addition to another process and/or may be performed in any suitable order to provide a serviced and operational cap assembly. In block602, a determination is made that a defect is present in a center ring of a cap assembly. In an embodiment, the defect is a crack or worn portion of an inner sleeve surface of the center ring. In block604, the center ring is removed from the cap assembly by a suitable method, such as EDM, that has reduced loading of vanes coupled to the center ring. A fixture, such as the fixture400, may be used to position the cap assembly to enable precise removal of the center ring while enabling the vanes to remain structurally intact. Further, in embodiments, the removal of the center ring does not require disassembly of the cap assembly, thus simplifying the servicing process. In an embodiment, remnants of the removed center ring are removed by a process, such as de-burring. In block606, a replacement center ring is positioned in the cap assembly, where the replacement center ring has substantially the same dimensions and geometry as the original equipment center ring used during production of the turbine engine. In an embodiment, the replacement center ring is positioned in the cap assembly by a fixture, such as fixture502. In block608, the replacement center ring is coupled to the vanes by a suitable method to provide a durable bond, such as brazing. In an embodiment, the brazing process uses a suitable brazing material, such as a nickel alloy braze paste. For example, the braze paste may comprise a nickel alloy compound including but not limited to, AMDRY 103, AMDRY 915 or AMDRY 773. In one embodiment, the braze paste material is applied to each joint between the vanes and center ring and is then cycled through various heating stages to cure the coupling. For example, the assembly may be heated to about 1100 to 1300 Fahrenheit (F) for a first period of time, then heated to about 1850 to 2000 F for a second period of time, then heated to about 2060 to about 2160 F for a third period of time and finally cooled to finish the brazing process. In embodiments, the first, second and third periods of time are all the same. In other embodiments, the first, second and third periods of time are different.