Patent Application
20100054911
The subject matter disclosed herein relates to gas turbines and, more particularly, to methods and systems for adjusting clearance between bucket or blade tips and a shroud assembly connected to a turbine shell.
In order to improve efficiency, gas turbines, such as those used in power generation or aviation, utilize a turbine “shroud” disposed in a turbine shell. The shroud provides for a reduced clearance between the tips of buckets disposed on the turbine rotor and the shroud in comparison to a clearance between the bucket tips and the turbine shell. Such reduced clearance provides enhanced efficiency by maintaining a reduced threshold clearance between the shroud and tips of the buckets to prevent unwanted “leakage” of hot gas over tips of the buckets. Increased clearances can lead to gas leakage which can reduce turbine efficiency.
Current shroud systems employ solely segmented shrouds connected to the turbine shell and held together by, for example, turbine shell hooks. The clearance between the bucket tips and the shroud is simply driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Initial bucket tip/shroud clearances may be set high enough to prevent rubbing, but such clearances cannot be actively controlled in transient or in steady state conditions. Both turbine shell out-of-roundness and transient bucket/shroud rubbing play a major role in increased steady state clearances. Cold-built clearances, i.e., clearances set prior to operation, can be set high enough to mitigate rubbing, but, in effect, this will drive up steady state clearances, and thereby reduce engine efficiency and output. Accordingly, there is a need for improved systems and methods for controlling clearance between bucket tips and shrouds in a gas turbine, such as during transient and/or steady state operation of the turbine.
A system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets, constructed in accordance with exemplary embodiments of the invention includes: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an elongated member extending from the turbine shell. The at least one shroud segment is attached to an end of the elongated member, the elongated member configured to move in response to a temperature change to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.
Other exemplary embodiments of the invention include a method of adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets. The method includes: disposing a shroud assembly on a turbine shell, the shroud assembly including a shroud segment attached to one end of an elongated member; extending the elongated member from the turbine shell and disposing the shroud segment in an interior of a turbine shell; and applying a thermal source to the shroud assembly to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.
Additional features and advantages are realized through the techniques of exemplary embodiments of the invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features thereof, refer to the description and to the drawings.
There is provided a system and method for displacing a component in a turbine or other system. The system includes a thermally actuated member that is configured to move in response to a temperature change. In one embodiment, a coefficient of thermal expansion (“CTE”) of the thermally actuated member is different than the CTE of one or more structures attached thereto. A method is provided that includes heating or cooling the thermally actuated member to cause movement of the member. In one embodiment, the thermally actuated member is an elongated member such as a rod or cylinder.
In one embodiment, the system includes the thermally actuated member connected at one end to a turbine shell or other body, and connected at another end to a movable member such as a turbine shroud, to adjust a clearance between bucket tips and one or more shrouds located on a gas turbine. Although bucket tips are described herein, the system may be utilized with any type of bucket, blade or other device for causing movement of a turbine rotor. The elongated member is described herein as a generally cylindrical rod or tube, but may be any suitable shape having a dimension in the radial direction. As used herein, the term “radial” refers to a direction extending from the center of the turbine rotor or a rotational axis of the turbine rotor, and perpendicular to the major axis or the rotational axis of the turbine rotor. Although the thermally actuated member is described herein in conjunction with turbine assemblies, the thermally actuated member may be utilized in conjunction with any system or apparatus utilizing displacement of components.
With reference to
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In one embodiment, the elongated member 32 has a coefficient of thermal expansion (“CTE”) that is different from the CTE of the protrusion 46 and or the turbine shell 12. For example, as shown in
Referring to
In one embodiment, the shroud assembly 30 includes any number of segments 31, and each segment 31 includes at least one elongated member 32 and at least one of the shrouds, 34, 38, 40. In the example shown in
In one embodiment, an inlet 50 is included to allow heated air or steam from the interior of the turbine shell 12 or allow other heating or cooling sources. Such sources may include air, gas and steam.
In one embodiment, a securing or adjusting mechanism 52 is attached to the elongated member 32. The mechanism 52 is connectable to the protrusion 46 to allow the elongated member 32 to be manually or mechanically moved or removed from the shroud assembly 30.
In another embodiment, insulation 54 is provided to thermally isolate the elongated member 32 from the protrusion 46, and heating or cooling sources can be applied to the elongated member 32 via the inlet 50. Alternatively, this embodiment allows for air from the interior of the turbine shell 12 to maintain the elongated member 32 at a specified temperature, and retract the elongated member 32 by applying heat to the protrusion 46 and causing the protrusion 46 to expand and thereby retract the elongated member 32. For example, during transient operation, the electric heater 48 is turned on at the time of maximum pinch between the bucket tip and the inner shroud 40 to expand the protrusion 46 and cause the elongated member 32 to retract. In this embodiment, the elongated member 32 has a CTE that is less than the CTE of the protrusion 46.
Referring to
In one example, the elongated member 32 has a radial height of nine inches, the turbine shell has a radial height of six inches, and the outer shroud has a radial height of three inches.
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In another embodiment of the shroud assembly 30, the outer shroud 34 is pocketed and includes a pin 66 or other fastening mechanism that attaches the outer shroud 34 to the turbine shell 12. The pin 66 is removable in an axial direction, to in turn allow the outer shroud 34 to be removed axially so that components such as the inner shroud 40 can be accessed. Additional pins or other fastening mechanisms are included to attach the intermediate shroud 38 to the elongated member 32.
Referring to
In another embodiment, the securing or adjusting mechanism includes a locking feature 70 attached to an alignment feature 71, which allows the elongated member to be mechanically or manually aligned within the tube 44 and/or allows the elongated member 32 to be advanced or retracted radially to adjust the clearance between the inner shroud 40 and the bucket tips. In another embodiment, the elongated member 32 is a solid elongated member.
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In one embodiment, if there are two or more elongated members 32 per shroud assembly 30, the elongated members 32 extend parallel to one another. The average of the angular deviation of each elongated member 32 from a radial line extending from the rotational axis is equal to zero. This orientation helps to prevent possible binding during operation. For example, if a third elongated member 32 is placed half way between the first two elongated members 32, the third elongated member 32 is oriented along the radial line, and all of the elongated members 32 are parallel to one another.
Referring to
In one embodiment, the system 90 includes a computer 91 coupled to a device such as the displacement senor 92 to measure the clearance between the bucket tip and the shroud assembly 30. Exemplary components include, without limitation, at least one processor, storage, memory, input devices, output devices and the like. As these components are known to those skilled in the art, these are not depicted in any detail herein.
In one embodiment, the computer 91 is configured to automatically retract the inner shroud 40 to an initial position upon detection of a malfunction in the shroud assembly 30.
Generally, some of the teachings herein are reduced to instructions that are stored on machine-readable media. The instructions are implemented by the computer 91 and provide operators with desired output.
In the first stage 101, the shroud assembly 30 is disposed on the turbine shell 12. The elongated member 32 is extended through at least a portion of the wall of the turbine shell 12 and the inner shroud is positioned in the interior of the turbine shell 12.
In the second stage 102, the elongated member 32 is initially disposed to a selected radial distance from the interior of the turbine shell 12. In one embodiment, this is accomplished by disposing the shroud assembly 30 and designating the radial distance of the outer shroud 34, the intermediate shroud 38 and/or the inner shroud 40 so that a selected minimum distance is set. In one embodiment, this may be accomplished by moving the elongated member 32 radially through the tube 44. In one embodiment, the minimum distance is selected based on the maximum pinch between the bucket tip and the inner shroud 40, that is, the closest approach between the bucket tip and the inner shroud 40.
In the third stage 103, the turbine 10 is activated. Activation in turn causes rotation of the turbine rotor and the buckets 39.
In the fourth stage 104, a thermal source such as the electric heater 46, steam, air and gas is applied to the shroud assembly 30 to move the inner shroud 40 and change a clearance between the inner shroud 40 and at least one of the plurality of buckets tips. In one embodiment, a thermal source is applied to the elongated member 32 to raise the temperature of the elongated member, causing it to expand and advance the inner shroud 40 toward the interior of the turbine shell 12 to reduce the clearance between the inner shroud 40 and the bucket tips. In another embodiment, the thermal source is applied to the elongated member 32 to reduce its temperature to retract the inner shroud 40 away from the interior of the turbine shell 12.
In one embodiment, the electric heater 46 is activated to elevate the temperature of the protrusion 46 and/or the elongated member 32. In response, the elongated member expands and extends in the radial direction to decrease the clearance between the inner shroud and the bucket tip. In one embodiment, a thermal source is applied to the elongated member via the protrusion 46 and/or the inlet 50, to extend or retract the inner shroud 40. As discussed above, applying a heating source will raise the temperature of the elongated member and extend the inner shroud 40, and applying a cooling source will lower the temperature of the elongated member and retract the shroud 40.
In one embodiment, the elongated member is maintained at a selected temperature, such as by applying air from the interior of the turbine shell 12 through the conduit 50, and the elongated member 32 is retracted by applying heat to the protrusion 46 and causing the protrusion 46 to expand and thereby retract the elongated member 32. For example, during transient operation, the electric heater 48 is turned on at the time of maximum pinch between the bucket tip and the inner shroud 40 to expand the protrusion 46 and cause the elongated member 32 to retract.
Although the systems and methods described herein are provided in conjunction with gas turbines, any other suitable type of turbine may be used. For example, the systems and methods described herein may be used with a steam turbine or turbine including both gas and steam generation.
The system and method described herein provide numerous advantages over prior art systems. For example, the systems and methods provide the technical effect of allowing active control of the clearance between the bucket tip and the shroud, which will allow a user to run the turbine engine at tighter clearances than prior art systems. These systems and method are a simple and inexpensive means of moving the shrouds independently to control clearances and to account for manufacturing differences.
The systems and methods described herein allow for tighter clearances than prior art systems, which increases overall efficiency relative to prior art designs. Prior art systems employ solely segmented shrouds held together by turbine shell hooks. The clearance is simple driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Bucket tip/shroud clearances may be set high enough to prevent rubbing, but clearances may not be actively controlled in transient, nor in steady state conditions. The systems and methods described herein are advantageous in that they provide for active control of the shroud assembly during both transient and steady state conditions.
The capabilities of the embodiments disclosed herein can be implemented in software, firmware, hardware or some combination thereof As one example, one or more aspects of the embodiments disclosed can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has embodied therein, for instance, computer readable program code means for providing and facilitating the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately. Additionally, at least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform the capabilities of the disclosed embodiments can be provided.
In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of exemplary embodiments of the invention if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
