PATTERN-ABRADABLE/ABRASIVE COATINGS FOR STEAM TURBINE STATIONARY COMPONENT SURFACES
A pattern-abradable seal assembly is provided for a stationary steam turbine component. The seal assembly, in use, is oriented in opposition to at least one seal tooth on a rotatable turbine component so as to inhibit leakage flow across the seal assembly in one direction, the seal assembly may include an annular seal carrier having at least one axially-oriented surface; a pattern-abradable/abrasive seal coating or insert at least partially covering the at least one axially-oriented surface, the pattern-abradable/abrasive seal coating having a pattern formed thereon adapted to face and be at least partially penetrated by the at least one seal tooth. A plurality of anti-swirl elements project radially beyond the pattern and are arranged to provide at least an axial component of flow across the abradable seal assembly. The coating or insert may also be used on other stationary turbine component surfaces to direct flow in a predetermined direction.
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The invention relates to pattern-abradable/abrasive seals in steam turbines and especially to abradable/abrasive coatings with patterns in the shape of sealing features, anti-swirl and/or guide seal features disposed radially outwardly of shrouded nozzle/buckets or on surfaces on stationary components axially adjacent to the nozzles/buckets to reduce leakage flow, reduce swirl and/or to aerodynamically guide the leakage flow to improve turbine efficiency.
It is well known to use abradable/abrasive materials which readily form seals between fixed and rotating parts of a turbine, whereby the rotating part erodes a portion of the fixed abradable material to form a seal having a very close tolerance. An important application of abradable seals in steam turbines where a rotor supporting a plurality of wheels, each of which mounts a plurality of blades or buckets rotating within a surrounding shroud. Utilizing abradable seals to minimize the clearance between the blade tips/nozzle root location and inner wall of the opposed shroud, makes it possible to reduce leakage of the working fluid which could be steam, across the blade tips and thereby enhance turbine efficiency.
Similar abradable/abrasive seals are also employed in turbines along the turbine rotor section to minimize leakage flow along the rotor shaft between higher and lower pressure regions. For example, conventional labyrinth seals provide a torturous path along the rotor shaft minimizing leakage flow, and generally, comprise a plurality of radial teeth extending from the rotor, with a small cold clearance between the teeth and the opposed, stationary abradable seal.
Typically, metal or ceramic abradable seals are spray-coated onto the stationary seal surface, and are effective to establish a radial clearance of about 15 mils.
There is a continuing need to improve efficiency by further reducing clearances, guiding the leakage flow at a favorable angle to adjacent nozzle/buckets and by minimizing the effect of swirl or tangential flow at the seal caused by the rotating component which decreases reliability, turbine efficiency and thus turbine performance.
BRIEF SUMMARY OF THE INVENTIONAccordingly, in one exemplary but nonlimiting embodiment, there is provided a pattern-abradable/abrasive seal assembly for a stationary steam turbine component, the seal assembly, in use, oriented in opposition to at least one seal tooth on a rotatable steam turbine component so as to inhibit leakage flow across the seal assembly and/or guide the leakage flow in a first direction, the seal assembly comprising an annular seal carrier having at least one axially-oriented, annular seal surface; a pattern-abradable/abrasive seal coating at least partially covering the at least one axially-oriented, annular seal surface, the pattern-abradable/abrasive seal coating having a pattern formed therein, adapted, in use, to face and be at least partially penetrated by the at least one opposed seal tooth; and a plurality of anti-swirl elements projecting radially beyond the pattern and arranged circumferentially about the at least one axially-oriented, annular seal surface.
In another exemplary but nonlimiting embodiment, there is provided a coating or insert for use on a surface of a stationary steam turbine component located along the steam path comprising: a first surface facing an adjacent rotating steam turbine component; and a first pattern-abradable/abrasive coating or insert having a pattern formed therein applied to the surface wherein the pattern is designed to direct leakage flow in a predetermined direction relative to the stationary steam turbine component.
In still another exemplary but nonlimiting embodiment, there is provided a turbine bucket and abradable seal assembly comprising a bucket having a tip shroud formed with plural radially-directed seal teeth; a stationary stator component surrounding the bucket and having plural abradable seals opposing respective ones of the plural radially-directed seals teeth; wherein each of the plural abradable seals includes an abradable seal coating having a pattern formed on a surface thereof facing a respective one of the plural, radially-directed seal teeth, and at least one an anti-swirl element projecting radially beyond the pattern and arranged to provide at least an axial component of flow across the seal assembly, the at least one anti-swirl element opposed to one of the plural radially-directed seal teeth, and adapted to be at least partially penetrated thereby.
The invention will now be described in detail in connection with the drawings identified below.
With reference initially to
More specifically, an abradable coating can be applied by thermal spraying, e.g., by plasma spraying the coating composition through a mask onto the stator shroud surface 34. Exemplary methods of producing an abradable coating on a substrate, utilizing, for example, an abradable ceramic coating composition, is described in commonly-owned U.S. Pat. No. 6,887,528.
Exemplary but non-limiting abradable patterns for the coating that forms the seal 26 are illustrated in
Typically, the rotating bucket teeth will penetrate from about 50 to about 100 percent of the seal thickness. For example, with a tight cold radial clearance between the bucket teeth 18, 20, 22 and the stator shroud 24, 26, 28 of about 15 mils, the abradable coating with a thickness of about 30-100 mils, may be penetrated by the teeth to a depth of about 10 to 25 mils during operation.
In the exemplary embodiments, the stationary; pattern-abradable/abrasive seal is used with shrouded buckets but it is not limited to that application, and in fact, may be used wherever seal teeth are employed on rotating turbine components.
It is also a feature of the invention to add anti-swirl features to the pattern-abradable/abrasive seal. These features help reduce swirl/tangential flow components and thus provide better rotor damping and improve overall turbine efficiency. For example, as illustrated in
Another exemplary but nonlimiting embodiment is illustrated in
A still further exemplary but nonlimiting embodiment is shown in
In this embodiment, the seal teeth engage the anti-swirl features, i.e., the anti-swirl features also serve as seal elements, and therefore, the base surface need not be patterned.
It will be appreciated that the combination of pattern-abradable/abrasive seals and anti-swirl features is applicable to other steam turbine bucket configurations, nozzle root seals and labyrinth packing seals. In this regard, attention is drawn to
In
It will be appreciated that any of the anti-swirl elements described in connection with
To demonstrate the significant reduction in tangential flow velocity achieved with the anti-swirl features described herein,
It is still another feature of the invention to utilize pattern-abradable/abrasive seal coatings or inserts on surfaces axially upstream or downstream of the rotatable components such as the blades/buckets described above,
By designing the pattern on the coating/insert to provide defined flow paths, it is possible to direct the leakage flow at a favorable angle to the adjacent rotating or stationary component.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims
1. A pattern-abradable/abrasive seal assembly for a stationary steam turbine component, the seal assembly, in use, oriented in opposition to at least one seal tooth on a rotatable steam turbine component so as to inhibit leakage flow across the seal assembly and/or guide the leakage flow in a first direction, the seal assembly comprising:
- an annular seal carrier having at least one axially-oriented, annular seal surface;
- a pattern-abradable/abrasive seal coating at least partially covering said at least one axially-oriented, annular seal surface, said pattern-abradable/abrasive seal coating having a pattern formed therein, adapted, in use, to face and be at least partially penetrated by the at least one opposed seal tooth; and
- a plurality of anti-swirl elements projecting radially beyond said pattern and arranged circumferentially about said at least one axially-oriented, annular seal surface.
2. The pattern-abradable/abrasive seal assembly of claim 1 wherein the abradable seal coating comprises a ceramic material or a metal alloy.
3. The pattern-abradable/abrasive seal assembly of claim 1 wherein said pattern has a depth of from about 50 to 100% of a total thickness of said abradable seal coating.
4. The pattern-abradable/abrasive seal assembly of claim 1 wherein said plurality of anti-swirl elements comprise a first plurality of substantially rectangular blocks, aligned and spaced about one circumferential edge of the said annular seal carrier, axially spaced from said at least one seal tooth, said rectangular blocks arranged at an acute angle relative to an axial centerline passing through said annular seal carrier.
5. The pattern-abradable/abrasive seal assembly of claim 4 wherein said plurality of anti-swirl elements further comprise a second plurality of substantially rectangular blocks, aligned and spaced about an opposite circumferential edge of said annular seal carrier, said second plurality of said rectangular blocks arranged at substantially the same acute angle as said first plurality of substantially rectangular blocks.
6. The pattern-abradable/abrasive seal assembly of claim 1 wherein said plurality of anti-swirl elements comprise three or more axially-spaced, circumferential rows of substantially rectangular blocks.
7. The pattern-abradable/abrasive seal assembly of claim 1 wherein said plurality of anti-swirl elements comprise plural, circumferentially-staggered rows of substantially rectangular blocks.
8. The pattern-abradable/abrasive seal assembly of claim 1 wherein said pattern comprises a criss-cross mesh pattern.
9. The pattern-abradable/abrasive seal assembly of claim 1 wherein said pattern comprises a plurality of substantially rectangular brick-shapes.
10. The pattern-abradable/abrasive seal assembly of claim 7 wherein said rectangular blocks are oriented in an axial direction.
11. A stationary steam turbine component located along a gas path comprising: a first surface facing an adjacent rotating steam turbine component; and a first pattern-abradable/abrasive coating or insert having a pattern formed therein applied to said surface wherein said pattern is designed to direct leakage flow in a predetermined direction relative to said stationary steam turbine component.
12. The stationary steam turbine component of claim 11 wherein said stationary steam turbine component comprises a turbine vane or nozzle and said rotatable steam turbine component comprises a turbine bucket.
13. The stationary steam turbine component of claim 12 wherein said turbine vane nozzle is located axially upstream of said turbine bucket.
14. The stationary steam turbine component of claim 12 wherein said turbine vane or nozzle is located axially downstream of said turbine bucket.
15. The stationary steam turbine component of claim 12 wherein said turbine bucket is formed with a tip shroud supporting on or more radially-outwardly directed seal teeth, and a stationary stator surface surrounding said tip shroud is provided with a second pattern-abradable/abrasive coating or insert facing said one or more radially outwardly directed seal teeth.
16. The stationary steam turbine component of claim 15 and wherein said second pattern-abradable/abrasive coating includes one or more anti-swirl features projecting radially beyond said pattern abradable/abrasive coating or insert.
17. A turbine bucket and abradable seal assembly comprising:
- a bucket having a tip shroud formed with plural radially-directed seal teeth;
- a stationary stator component surrounding said bucket and having plural abradable seals opposing respective ones of said plural radially-directed seal teeth; wherein each of said plural abradable seals includes an abradable seal coating having a pattern formed on a surface thereof facing a respective one of said plural, radially-directed seal teeth, and at least one an anti-swirl element projecting radially beyond said pattern and arranged to provide at least an axial component of flow across the seal assembly, said at least one anti-swirl element opposed to one of said plural radially-directed seal teeth, and adapted to be at least partially penetrated thereby.
18. The turbine bucket and abradable seal assembly of claim 17 wherein said at least one anti-swirl element comprises plural circumferentially-arranged rows of anti-swirl elements.
19. The turbine bucket and abradable seal assembly of claim 18 wherein said plural circumferentially-arranged rows of anti-swirl elements are axially-spaced and staggered in the circumferential direction.
20. The turbine bucket and abradable seal assembly of claim 18 wherein each anti-swirl element of said plural circumferentially-arranged rows of anti-swirl elements is arranged at an acute angle to an axis of rotation of said bucket.
Type: Application
Filed: Jul 14, 2011
Publication Date: Jan 17, 2013
Applicant: GENERAL ELECTRIC COMPANY (Schenectady, NY)
Inventors: Sulficker ALI (Bangalore), Vasanth MURALIDHARAN (Bangalore)
Application Number: 13/182,829
International Classification: F01D 11/00 (20060101); F01D 5/14 (20060101);