Grouped reaction nozzle tip shrouds with integrated seals

Abstract

A reaction turbine stator vane segment comprising an integral grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud.

Description

BACKGROUND OF THE INVENTION

This invention relates to steam turbines having seals between rotating and non-rotating components, and more particularly, to seal configurations incorporated into integral tip shrouds of grouped stator vanes in a reaction turbine.

Each stage of a reaction steam turbine includes a plurality of circumferentially spaced buckets mounted on a drum rotor surrounded by a plurality of stationary reaction stator vanes. The buckets and nozzles form one stage of the turbine, and define the main steam flow path. By way of contrast, in an impulse turbine, the buckets are mounted on the periphery of rotor wheels and the nozzle partitions are supported in surrounding diaphragms. It is highly desirable in any case to minimize or eliminate as many steam leakage paths as possible that stem from the main steam flow path.

One source of leakage in a reaction turbine is a radial gap between grouped sets of reaction stator vanes provided with integral tip shrouds, and opposed radially outer portions of the rotor. One known technique for sealing this radial gap involves the utilization of insertable strip seals on the rotor that oppose seal lands on the reaction stator tip shrouds that have been sprayed with an abradable coating. Another prior technique involves the incorporation of radially projecting labyrinth teeth at the inner free ends of the nozzle or stator vanes that form labyrinth seals with radially opposed component parts of the turbine rotor. See, for example, commonly owned U.S. Pat. No. 6,786,699. The combination of labyrinth seal teeth with brush seals has also been utilized at the interface between diaphragm inner webs at the radially inner ends of nozzle partitions and rotor lands in impulse turbines. See, for example, commonly owned U.S. Pat. No. 6,669,443 and commonly owned U.S. Pat. No. 6,290,232.

There remains a need, however, for effective seal configurations for use with grouped reaction turbine stator vanes having integral tip shrouds that will effectively reduce the radial gap between the tip shrouds and the opposed rotor lands.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed toward novel seal configurations for grouped reaction stator vane segments with integral tip shrouds. The exemplary embodiments relate to integrated one-piece stator vane segments incorporating multiple vanes and seal configurations that may include a combination of strip seals, brush seals or integral seal teeth that oppose rotor seal lands in the assembled steam turbine.

For purposes of this invention, the term “grouped reaction stator vanes with integral tip shrouds” refers to a plurality (2 or more, and up to about 50) of reaction turbine stator vanes with integral cover shrouds that have been grouped together by machining as a one-piece or unitary group, where two or more groups make up a 360° ring; or by welding or brazing individual vanes to form a group, where two or more groups also make up a 360° ring.

In a first configuration, a machined one-piece stator vane segment includes a plurality of vanes, integral tip shroud and integral dovetail (or other mounting configuration). The stator tip shroud extends over the plurality of vanes, connecting the tips thereof, and is provided with a generally centered insert. The insert includes a brush seal, and the insert is flanked by conventional caulked strip seals upstream and downstream of the brush seal. In a second exemplary configuration, the integral stator tip shroud is provided with a generally axially centered (i.e., in a flow direction) insert having a brush seal with integral machined labyrinth seal teeth located upstream and downstream of the insert. In a third configuration, the stator tip shroud is machined to include a dovetail slot into which a seal strip assembly may be inserted. The insertable seal strip assembly is provided with an axially centered brush seal with integral labyrinth seal teeth upstream and downstream of the brush seal.

For all of the configurations, the opposed rotor surface may be machined to include a high-low-high land configuration or, a low-high-low land configuration to match a similar seal arrangement in the tip shrouds. In addition, the specific number of seals, opposed seal lands, and choice of specific seals and/or combination of seals may vary based upon specific application.

Accordingly, the present invention in its broader aspects relates to a reaction turbine stator vane segment comprising an integral grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud.

In another aspect, the invention relates to reaction turbine stator vane segment comprising a unitary machined grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud, wherein the plural seal components include a brush seal insert received in a groove in the tip shroud, with additional seal components on opposite sides of the brush seal.

The invention will now be described in detail in connection with the drawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a grouped reaction stator vane segment;

FIG. 2 is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a first exemplary embodiment of the invention;

FIG. 3 is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a second exemplary embodiment of the invention; and

FIG. 4 is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a third exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a grouped reaction stator vane segment 10 includes a plurality of reaction vanes 12, an integral, arcuate tip shroud 14 at the radially inner ends of the vanes, and a dovetail or other mounting configuration 15 at the radially outer ends of the vanes. While the figure shows a group of four vanes 12, it is to be understood that the segment may include other numbers of vanes, for example, 6, 8, 12, up to as many as 50 vanes or more, the latter forming a 180° segment. Together, two or more such segments form a closed 360° ring of reaction vanes.

In the preferred arrangement, the segment 10 is machined from a single block of metal material, preferably a stainless steel alloy, but individual vanes may also be grouped by welding, brazing or other suitable means to form a segment.

Turning now to FIG. 2, the segment 10 and, specifically, the tip shroud 14 is provided with a combined strip and brush seal arrangement. Specifically, a brush seal insert 16 is slidably received within a groove 18 formed in a radially inner face 19 of the tip shroud 14. The insert incorporates brush seal elements 20 that extend radially inward to a location closely adjacent a land 22 on the turbine rotor 24. A pair of strip seals 26, 28 are seated in respective grooves 30, 32 in the face 19 of the tip shroud on opposite sides of the brush seal insert, and secured by, for example, peening. These strip seals extend inwardly with the tips closely adjacent respective lands 34, 36 of the rotor 24. Note that the strip seals 26, 28 lie, respectively, upstream and downstream of the generally axially centered brush seal 16 (relative to the direction of steam flow), in a high-low-high arrangement vis-à-vis the turbine lands. It will be understood that the turbine land configuration could be reversed, with appropriate relocation of seal tips in a low-high-low configuration.

FIG. 3 illustrates an alternative arrangement in connection with a reaction stator vane segment 38. In this embodiment, the tip shroud 40 is fitted with a generally axially centered brush seal insert 42, seated in a groove 43 formed in the radially inner face 44 of the tip shroud, with brush seal elements 45 similar to the insert 16 in FIG. 2. Labyrinth seal teeth 46, 48, respectively, are formed integrally with the tip shroud 40 and lie upstream and downstream of the brush seal insert 42, interacting with lands 50 and 52 on the rotor 54. The brush seal elements 44 extend inwardly to a turbine land 56. Here again, a high-low-high land configuration is illustrated but, as in the case of FIG. 2, that configuration may be reversed to a low-high-low arrangement.

FIG. 4 illustrates yet another embodiment of the invention where the reaction vane segment 58 includes an integrated tip shroud 60, the radially inner face 61 of which is formed with a dovetail-like groove 62 that receives an arcuate seal strip assembly insert 64. The insert 64 is provided with a generally axially centered brush seal 66 having brush seal elements 68 that extend inwardly to a location closely adjacent the turbine land 70. The insert 64 is also formed with integrated upstream and downstream labyrinth seal teeth 72, 74 which extend radially inwardly to a location closely adjacent respective lands 76, 78 of the rotor 80. As in the prior embodiments, the high-low-high land configuration may be reversed to a low-high-low configuration, with suitable modification of the sealing elements. It will be appreciated that the labyrinth seal teeth 72, 74 could be replaced with strip seals similar to those in FIG. 2.

The above-described seal configurations reduce the radial gap between the rotor and the reaction stator vane tip shrouds, and at the same time reduce assembly time for the rotor and eliminate the need for an abradable coating on the reaction stator's integral tip shroud. It will be appreciated that the tip shrouds may incorporate seals and/or seal inserts with any combination of strip seals, brush seals, or labyrinth seal teeth.

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

1-15. (canceled)

16. A method of forming a one-piece reaction turbine stator vane segment comprising: (a) providing a stainless steel alloy block; and (b) machining said block to include an integral grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes.

17. The method of claim 16 including adding plural seal components extending radially inwardly from said tip shroud.

18. The method of claim 17 wherein said plural seal components include a combination of strip seals and brush seals.

19. The method of claim 17 wherein said plural seal components include a combination of labyrinth seal teeth and brush seals.

20. The method of claim 17 wherein said plural seal components include a pair of strip seals, one on either side of a brush seal.

21. The method of claim 17 wherein said plural seal components include a pair of labyrinth seal teeth, one on either side of a brush seal.

22. The method of claim 17 wherein said plural seal components are mounted in an arcuate insert and said method further comprises installing said arcuate insert within a groove in said tip shroud.

23. The method of claim 17 wherein said plural seal components include a brush seal flanked by a pair of labyrinth seal teeth.

24. The method of claim 17 wherein said plural seal components include a brush seal insert received in a groove in said tip shroud, with additional seal components on opposite sides of said brush seal insert.

25. The method of claim 24 wherein said additional seal components comprise strip seals.

26. The method of claim 24 wherein said additional seal components comprise labyrinth seal teeth.