Leaf seal for gas turbine stator shrouds and a nozzle band

This invention was made with Government support under Contract No. DE-FC21-95MC31176 awarded by the Department of Energy. The Government has certain rights in this invention.

The present invention relates to a seal for sealing between a stator shroud and a leading edge of a nozzle wall along the outer band of a nozzle segment defining in part the hot gas path through the gas turbine.

In an industrial gas turbine, shroud segments are fixed to turbine shell hooks in an annular array to form an annular shroud radially outwardly and adjacent the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Typically, nozzles are hooked into the radial slots in the shroud segments. However, the cavities forward and aft of the shroud segments are at a higher pressure than the pressure of the gas path and significant leakage into the hot gas path frequently occurs. These cavities are typically pressurized by compressor discharge air and leakage of this air is detrimental to turbine performance and emissions. The leakage is compounded in those nozzle stages having non-continuous nozzle leading edge hooks. That is, the gaps between the hooks and adjacent the edges of the shrouds provide large leakage paths for compressor discharge air to flow into the hot gas flow path. It is therefore desirable to provide a seal effective between the stator shroud segments and the nozzle wall, particularly in those turbines having non-continuous nozzle hooks, to minimize leakage flow into the hot gas path.

In accordance with a preferred embodiment of the present invention, there is provided a shroud system affording an effective seal between the shroud segments and the nozzle side wall band, particularly the leading edge side wall of the nozzle band. Particularly, inner and outer shrouds are provided with complementary hooks and grooves adjacent the leading and trailing edges of each shroud for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to a turbine shell hook. In a preferred embodiment, each shroud segment has one outer shroud and two inner shrouds. The shroud segments form an annular array thereof about the turbine rotor axis to form a shroud set. More particularly, the leading edge of the adjacent nozzle side wall band has a forward projection or “nub” for interfacing with a shroud leaf seal adjacent the trailing edge of the shroud segment. The leaf seal may be mounted on either the two inner shrouds or on the outer shroud. The leaf seal spans the circumference of the shroud segment and is spring-loaded in an aft direction by a pair of spring clips. The leaf seal and spring clips are pinned to the shroud segment in a radially outwardly extending groove along the shroud segment. To create the smallest leakage possible employing a leaf seal engaging against the nub or flange of the leading edge side wall of the outer band of the nozzle, the leaf seal is pivoted to the shroud segment such that it extends perpendicular to the turbine centerline during operation. The seals are also provided with overlaps such that each overlap seals between adjacent leaf seals of adjacent segments.

In a preferred embodiment according to the present invention, there is provided a seal for sealing between a stator shroud and a nozzle of a gas turbine to substantially preclude leakage between a pressurized cavity on one side of the seal and hot gases in a hot gas path of the gas turbine on the other side of the seal, comprising a shroud segment having a surface for, in part, defining the hot gas path and overlying tips of buckets forming part of a turbine rotor, an outer band for, in part, defining the hot gas path and forming part of the nozzle of the turbine, a leaf seal between the shroud segment and the nozzle outer band and a spring engaging the shroud segment and the leaf seal for biasing the leaf seal into sealing engagement with the nozzle outer band.

In a further preferred embodiment according to the present invention, there is provided a seal for sealing between a stator shroud and a nozzle of a gas turbine to substantially preclude leakage between a pressurized cavity on one side of the seal and hot gases in a hot gas path of the gas turbine on the other side of the seal, comprising a shroud segment having a surface for, in part, defining the hot gas path and overlying tips of buckets forming part of a turbine rotor, the shroud segment having a leading edge and a trailing edge, an outer band for, in part, defining the hot gas path and forming part of the nozzle of the turbine, a leaf seal between the trailing edge of the shroud segment and a leading edge side wall of the nozzle outer band, the shroud segment having a seat for receiving the leaf seal and a spring engaging the shroud segment and the leaf seal for biasing a portion of the leaf seal into sealing engagement with the leading edge side wall of the nozzle outer band.

FIG. 1 is a perspective view of a shroud segment with a leaf seal assembly constructed in accordance with a preferred embodiment of the present invention and illustrated with parts broken out for clarity;

FIG. 2 is a fragmentary side elevational view of a leaf seal assembly for use with an inner shroud of the shroud segment;

FIG. 3 is a view similar to FIG. 2 illustrating a leaf seal assembly for use with the outer shroud of the shroud segment illustrated in FIG. 3; and

FIG. 4 is an enlarged side elevational view of the leaf seal assembly of FIGS. 1 and 3 .

Referring now to the drawings, particularly to FIG. 1, there is illustrated a shroud segment, generally designated 10 , comprised of an outer shroud 12 and a pair of inner shrouds 14 for securement to the outer shroud 12 . The inner shrouds have hooks 16 and 18 adjacent their leading and trailing edges 17 and 19 , respectively, for circumferential slidable engagement in grooves 20 and 22 of the outer shroud 12 in final assembly. The inner and outer shrouds also mount an impingement cooling plate 24 between the shrouds for impingement cooling of the wall surfaces 26 of the shroud segment, for example, by steam impingement cooling, which forms no part of the present invention. The outer shroud 12 has a radially outer dovetail groove 30 for receiving a hook 32 forming part of the fixed turbine shell for securing the shroud segment 10 to the shell. It will be appreciated that an annular array of shroud segments 10 are formed about the rotor of the gas turbine and about the tips of the buckets 35 on the rotor thereby defining an outer wall or boundary 31 for the hot gas flowing along the hot gas path 33 of the turbine.

Referring now particularly to FIGS. 1 and 3, a leaf seal assembly, generally designated 40 , is provided along the trailing edge of the shroud segment 10 and interfaces with a forward flange or nub 42 of a leading edge side wall 44 of a nozzle stage outer band 45 . The seal assembly 40 seals between the hot gas path 33 and a cavity 37 on the turbine shell side. In FIGS. 1 and 3, the leaf seal 40 is mounted on the outer shroud 12 . Particularly, the trailing edge of the outer shroud 12 includes a seat 46 , e.g., a groove, having a radially outwardly and circumferentially extending flange 48 for receiving the leaf seal assembly 40 . Particularly, the leaf seal assembly 40 includes a circumferentially elongated flat plate 50 received in the groove 46 . The plate 50 extends radially outwardly and engages along its trailing face the flange 42 of the leading edge side wall 44 of the nozzle band 45 . The leaf seal plate 50 includes a pair of openings 54 (FIG. 1) adjacent opposite ends. A pair of generally U-shaped spring clips 56 likewise have openings 58 passing therethrough. The spring clips 56 have a base and a pair of legs and are disposed in opposite ends of the groove 46 with the openings 58 thereof aligned with openings 54 of the leaf seal plate 50 . Pins 60 are extended through the plate 50 and spring clips 56 to engage in openings on the trailing edge face of the outer shroud 12 and within the groove 46 . The pins 60 are preferably tack-welded in place to secure the leaf seal plate 50 .

The plate 50 as illustrated in FIG. 4 has a bump or projection 57 along its aft face which lies in contact with the flange 48 at locations between the pins 60 and the outer edges of the spring clips 56 . The projection 57 serves as a pivot to ensure that the seal lies perpendicular to the centerline of the rotor during operation which, in turn, creates the smallest leakage past the seal. Also as illustrated in FIG. 1, one end of the seal plate 50 includes an overlap 66 for sealing between adjacent shroud segments. These overlaps 66 also include “suck down” holes to assure the overlap creates an effective seal.

To install the leaf seal assembly, the outer and inner shrouds are coupled to one another, with the impingement plate therebetween, using the respective complementary hooks 16 , 18 and grooves 20 , 22 . The leaf seal spring clips 56 are then installed in groove 46 , followed by the leaf seal plate 50 . The seal plate is disposed between the flange 48 and the trailing leg of the U-shaped clips 56 . Pins 60 are then inserted through the aligned openings 54 and 58 and into the outer shroud 12 and tack-welded in place. The shroud segment is then circumferentially received on the turbine shell hook 32 and pinned in place.

In FIG. 2, a similar leaf seal assembly is mounted on an inner shroud. In this form, the stator shroud segment 68 includes an outer shroud 70 having a pair of grooves 72 and 73 along respective leading and trailing edges thereof. The inner shroud 74 has a pair of flanges 76 and 78 for engaging in the respective grooves 72 and 73 of the outer shroud 70 . The leaf seal assembly, generally designated 80 , is secured in a seat 82 , e.g., a groove, formed along the trailing edge of the inner shrouds 74 . As in the prior embodiment, the seal assembly 80 includes a seal plate 84 and a pair of spring clips 86 , the spring clips and seal plate 84 having aligned openings for receiving pins 89 adjacent opposite ends of the groove for securing the seal assembly in the groove 82 of the inner shroud 74 . Also as in the previous embodiment, a bump 83 is formed along the aft face of the plate 84 and serves as a pivot point such that the plate is perpendicular to the turbine rotor axis for effective sealing engagement against the flange of the leading edge side wall 88 of the nozzle band 90 .

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.