Bushing retention system for cooling tubes in a gas turbine rotor

Abstract: Bushings are provided in counterbores for wheels and spacers for supporting thermal medium cooling tubes extending axially adjacent the rim of the gas turbine rotor. The retention system includes a retaining ring (62) disposed in a groove adjacent an end face of the bushing and which retaining ring projects radially inwardly to prevent axial movement of the bushing in one direction. The retention ring has a plurality of circumferentially spaced tabs (69) along its inner diameter whereby the ring is supported by the lands of the tube maintaining its bushing retention function, notwithstanding operation in high centrifugal fields and rotation of the ring in the groove into other circular orientations.

Description: The present invention relates to gas turbines having rotational components cooled by a thermal medium flowing in axially extending supply and return tubes within and adjacent the rim of the rotor and particularly relates to retention rings for retaining the bushings about the thermal medium carrying tubes against axial displacement. In an advanced gas turbine design such as that shown in EPO 735 238, a closed cooling circuit is provided for supplying a thermal medium, e.g., cooling steam, generally in an axial direction along the rim of the rotor to turbine buckets to cool the buckets and for returning the spent thermal medium in an opposite, generally axial direction for flow from the rotor, for example, to the steam turbines of a combined cycle system. Generally, in that design, cooling steam is supplied via an axial bore tube assembly, radially outwardly extending tubes and a plurality of axially extending tubes along the rims of the wheels and spacers for supplying steam to the buckets. Spent cooling steam is returned from the buckets through additional axially extending return tubes, radially inwardly extending tubes and the central bore of the bore tube assembly. The axially extending supply and return tubes adjacent the rotor rim are fixed at their aft ends and grow thermally in an axial direction relative to tube-carrying bushings in the wheels and spacers upon turbine startup. Upon turbine shutdown, the tubes thermally contract in an axial direction. There has developed a need for a bushing retention system which will prevent dislodgement of the steam tube bushings as a result of axial thermal growth of the tubes, as well as having the capability to perform their retention function in a very substantial transverse high centrifugal field. In accordance with a preferred embodiment of the present invention, there is provided a bushing retention system for preventing displacement of the bushings in an axial direction during turbine operation and having the capability of operating in a high centrifugal field. It will be appreciated that each bushing comprises an annular member disposed in a counterbore formed in the openings through the wheel and spacer which receive the steam delivery and return tubes. The inner diameter of the bushing is less than the diameter of the openings through the wheels and spacers and the interior surface of the bushing engages lands formed on the tubes to support the tubes in the openings. An axial face of the bushing engages a shoulder or base of the counterbore, preventing axial movement of the bushing toward that face. To preclude axial movement of the bushing in the opposite axial direction, the retention system hereof includes a retainer ring for reception in an annular groove of the counterbore at an axial location beyond the adjacent face of the bushing. The retention ring is a split ring, i.e., having a circumferential extent terminating in ends spaced from one another which enables reduction of the outer diameter of the ring to locate the ring in the groove. Once located, the ring projects radially inwardly of the counterbore to afford a stop for the bushing, preventing dislodgement of the bushing in an axial direction. The lands of the tubes support the ring in the high centrifugal field which otherwise tends to drive the ring out of the groove. Particularly, a plurality of circumferentially spaced tabs project radially inwardly from the inner diameter of each ring and preferably have arcuate faces for engaging the tube lands. In this manner, each ring remains sufficiently in the groove, notwithstanding high centrifugal forces, to continue its function of preventing dislodgement of the bushings. Further, the width of the ring in a radial direction decreases in directions circumferentially toward the ends of the ring. This enables the use of a tool inserted into openings at the ends of the rings to readily and easily reduce the diameter of the ring for subsequent expansion and installation in the groove. In a preferred embodiment according to the present invention, there is provided a bushing retention system in a gas turbine, comprising a gas turbine rotor having a plurality of axially aligned wheels and spacers, a plurality of axially aligned openings through the wheels and spacers with one of the wheels and spacers having counterbores in the openings, a plurality of tubes extending through the openings in the wheels and spacers at circumferentially spaced locations about the rotor for flowing a thermal medium, each counterbore having a radial extending groove thereabout, a bushing in each counterbore of the one wheel and spacer for supporting the tube therein, a retainer ring in each counterbore groove and projecting radially inwardly sufficiently to prevent movement of the bushing in one axial direction, each ring having a circumferential extent terminating in ends spaced from one another enabling reduction of the outer diameter of the ring to locate the ring in the groove, the ring having radial inward tabs for engaging the tube when the ring is subject to substantial centrifugal forces upon rotation of the rotor to maintain the ring within the groove and prevent axial displacement of the bushing in one axial direction. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a fragmentary cross-sectional view of a portion of the turbine section of a gas turbine rotor having an axial retention system in accordance with the present invention; FIGURE 2 is an fragmentary cross-sectional view illustrating a preferred form of an axial retention system hereof; FIGURE 3 is an end elevational view of a retainer ring forming part of the axial retention system hereof; FIGURE 4 is a cross-sectional view thereof taken generally about on line 4-4 in Figure 3; and FIGURE 5 is a perspective view of the retaining ring of Figure 3. Referring to Figure 1, there is illustrated a turbine section, generally designated 10, of a gas turbine rotor, generally designated R. Rotor R includes in the present example a number of stages, represented by wheels 12, 14, 16 and 18 carrying a plurality of circumferentially spaced buckets or blades 20, 22, 24 and 26, respectively. The wheels are arranged alternately between spacers 28, 30 and 32. The outer rims of spacers 28, 30 and 32 lie in radial registration with a plurality of stator blades or nozzles 34, 36 and 38, respectively, with a first set of nozzles, not shown, lying forwardly of the buckets 20. Consequently, it will be appreciated that a four-stage turbine is illustrated, at least in part, wherein the first stage comprises nozzles, not shown, and buckets 20; the second stage, nozzles 34 and buckets 22; the third stage, nozzles 36 and buckets 24; and the fourth and final stage, in this representative example, of nozzles 38 and buckets 26. Fewer or more stages may be provided. As is conventional, rotor wheels and spacers are secured one to the other by a plurality of circumferentially spaced bolts 40 passing through aligned openings in the wheels and spacers. It will be appreciated that the nozzles and buckets lie in a hot gas path of the turbine section and the energy of the hot gases of combustion are imparted to the buckets to rotate the rotor. At least one, and preferably both of the sets of buckets 20 and 22 of the first two stages are provided with a thermal medium for cooling the buckets, the thermal medium preferably being cooling steam. The cooling steam is provided in a plurality of circumferentially spaced tubes extending axially through the aligned wheels and spacers adjacent the rim of the rotor. Circumferentially spaced return tubes extend axially adjacent the rim of the rotor for returning spent cooling steam from the cooled buckets to a bore tube assembly, not shown. Only a return tube 42 is illustrated in Figure 1, the supply tubes and remaining return tubes being substantially similar. The retention system of the present invention applies equally to the supply and return tubes and will be described with respect to the illustrated return tube 42. Each of the tubes includes an elongated, thin-walled sleeve 44 having raised lands 46 at axially spaced locations therealong for engagement by bushings carried adjacent opposite ends of the openings through the aligned wheels and spacers. In the specific disclosed embodiment, a pair of bushings 48 and 50 are disposed in counterbores in the aft face of the 1-2 spacer 28 and the counterbore of the forward face of wheel 14. The bushings of the wheels and spacers aft of the illustrated bushings are retained by other means, not part of this invention, although it will be appreciated that where bushings are employed, the retention system hereof may be utilized. Referring now to Figure 2, there is illustrated the forwardmost bushing 48 disposed in a counterbore 54 in the aft face of the spacer 28 and the opening 56 through spacer 28 which receives the forward end of the return tube 42. A spoolie 58 is also illustrated in connection with the forward end of tube 42 for directing return steam from the first and second-stage buckets into the return tube 42. From a review of drawing Figure 2, it will be appreciated that the bushing on its annular forward face abuts a shoulder 60 forming the base of counterbore 54. To preclude dislodgement of the bushing 48 in an aft direction, a retention ring 62 is provided for substantially preventing axial movement of bushing 48 in that direction. The retention ring 62 is disposed in an annular groove 64 formed at a location in the counterbore 54 closely adjacent the aft end face of the bushing 48. With the retention ring 62 disposed in the groove 64 and projecting radially inwardly in axial registration with the aft end face of the bushing, the bushing is retained against axial movement. Referring to Figures 3-5, the retaining ring 62 comprises a split ring having a circumferential extent terminating in closely spaced, circumferentially opposed ends 66. From a review of Figure 3, it will be seen that the width of the ring in a radial direction (with the exception of tabs 69 described below) decreases in opposite directions from a medial location 65 along the ring toward the ends 66 of the ring. Particularly, the inner diameter 68 of the ring increases in a direction toward the ends 66 such that the maximum thickness in a radial direction of the ring lies substantially 180° from the ends 66 and the minimum thickness lies adjacent ends 66. To provide support for the rings 62 from the lands of the tube, a plurality of circumferentially spaced, radially inwardly directed tabs 69 are provided along the interior surface of the ring. The inner faces 70 of the tabs 69 are preferably arranged on a constant inner diameter of the ring and are preferably curved or arcuate to correspond to the curvature of the tube land. Thus, the distance x (Figure 3) between the faces 70 of the tabs 69 and the outer diameter of the ring are substantially identical. As a consequence of this construction, the ring ends 66 may be engaged in their illustrated openings 71 by a suitable tool and the outer diameter of the ring reduced such that the ring can be inserted into the groove 64 to retain the bushing against axial displacement. When the rotor is operating in the high centrifugal field and each ring is therefore subject to high centrifugal forces, the tabs 69 engage the land of the associated tube. The ring is thus supported by the tube land for retention in the groove 64. Additionally, because of the radially upwardly projecting tabs, the retaining ring is retained in the groove for all orientations of the ring about the groove. That is, the ring may rotate within the groove when subjected to certain forces. The circular orientation of the ring in the groove, however, does not affect its ability to retain the bushing in its counterbore or to be retained in the groove 64.

Claims: A bushing retention system in a gas turbine, comprising: a gas turbine rotor (R) having a plurality of axially aligned- wheels (12, 14, 16, 18) and spacers (28, 30, 32), a plurality of axially aligned openings through said wheels (12, 14, 16, 18) and spacers (28, 30, 32) with one of said wheels (12, 14, 16, 18) and spacers (28, 30, 32) having counterbores (54) in said openings; and a plurality of tubes (42) extending through said openings in said wheels (12, 14, 16, 18) and spacers (28, 30, 32) at circumferentially spaced locations about said rotor (R) for flowing a thermal medium; characterised by each said counterbore (54) having a radial extending groove (64) thereabout; a bushing (48) in each said counterbore (54) of said one wheel (12, 14, 16, 18) and spacer (28, 30, 32) for supporting said tube (42) therein; a retainer ring (62) in each said counterbore groove (64) and projecting radially inwardly sufficiently to prevent movement of said bushing (48) in one axial direction, each ring (62) having a circumferential extent terminating in ends spaced from one another enabling reduction of the outer diameter of said ring (62) to locate the ring in said groove; said ring (62) having radial inward tabs (69) for engaging the tube (42) when the ring (62) is subject to substantial centrifugal forces upon rotation of the rotor (R) to maintain the ring (62) within the groove (64) and prevent axial displacement of the bushing (48) in said one axial direction. A system according to Claim 1 wherein said tabs (69) have arcuate, radially inwardly directed faces (70) substantially corresponding to the curvature of the tubes (42). A system according to Claim 1 wherein each said ring (62) has an increasing inner diameter thereabout between said tabs (69) in a direction toward said ring ends. A system according to Claim 3 wherein the distances between radially inwardly directed faces (70) of said tabs (69) and an outer diameter of said ring (62) at each location of a tab (69) are substantially identical. A system according to Claim 1 wherein said tabs (69) are circumferentially spaced one from the other about said ring (62) and said ring (62) has a thickness in a radial direction between said tabs (69) decreasing toward the ends of said ring (62). A system according to Claim 5 wherein the distances between radially inwardly directed faces (70) of said tabs (69) and an outer diameter of said ring (62) at each location of a tab (69) are substantially identical. A system according to Claim 6 wherein said tabs (69) have arcuate, radially inwardly directed faces (70) substantially corresponding to the curvature of the tubes (42).

Inventors: MASHEY THOMAS CHARLES, MASHEY, THOMAS CHARLES
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 2000
Main classification: F01D5
IPC codes: F02C7, F01D5