Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Between axial flow runner and vane or vane diaphragm structure
Reexamination Certificate
2001-11-01
2003-05-06
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Between axial flow runner and vane or vane diaphragm structure
C415S174200, C415S231000
Reexamination Certificate
active
06558118
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a steam turbine having a brush seal between non-rotatable and rotatable components arranged and located to eliminate thermal bowing resulting from non-uniform distribution of heat about the rotatable component due to heat generated by frictional contact between the brush seal and the rotatable component and particularly relates to apparatus and methods for locating the contact between the brush seal and rotatable component radially outwardly of the rotor shaft.
In U.S. Pat. No. 6,168,377 of common assignee herewith, there is disclosed a steam turbine having a brush seal located between a non-rotatable component and a rotatable component of the rotor shaft. As explained in that patent, brush seals typically comprise a plurality of metal bristles projecting from the stationary component and engaging the surface of the rotor. Sustained rubbing between the rotor and the brush seal can lead to thermal bowing of the rotor or exacerbate an existing bowed condition of the rotor. As disclosed in that patent, it is recognized that the contact between the brush seal and the sealing surface should be located radially outwardly of the rotor shaft in order to isolate the generated heat from the outer diameter of the rotor. Otherwise, the friction-generated heat may cause a non-uniform temperature distribution about the circumference of the shaft, resulting in a bow in the rotor. While various methods and apparatus are disclosed in that patent for eliminating that problem, one such solution located the brush seal/friction-generating surface of the rotor to a bridge mounted on bucket dovetail flanges radially outboard of the shaft diameter. In that manner, the generated heat is isolated from the rotor, eliminating any tendency of the rotor to bow.
In a companion application Ser. No. 09/985,638, combined brush and labyrinth seals are mounted on the stationary component for sealing engagement with axially projecting flanges on axially adjacent bucket dovetails. As in U.S. Pat. No. 6,168,377, the frictional contact area of the brush seal bristles and the flanges of the buckets is spaced radially outwardly of the shaft, tending to minimize or eliminate rotor shaft bowing due to non-uniform distribution of heat about the shaft caused by the heat generated from such frictional contact.
Applying brush seals in the diaphragm packing area, i.e., the stationary component, is currently limited in the number of stages the brushes may be installed due to the aforementioned rotor dynamic constraints. Where brush seals cannot be used, labyrinth-type packing seals are used which result in a decrease in section efficiency due to the increased secondary losses of the labyrinth packing seals relative to the brush seal. Also, conventional labyrinth-type packing on the inside of the diaphragm web as a backup to a brush seal results in a dramatic thrust change to the rotor in the event of brush seal failure.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there are provided apparatus and methods for eliminating thermal bowing of a rotor shaft of a turbine resulting from non-uniform distribution of heat about the rotor shaft due to heat generated by frictional contact between a brush seal and the rotatable component. Particularly, there is provided a plurality of arcuate bridging members which are located and have an axial span between the wheels, particularly the bucket dovetails, of adjacent stages of the turbine. The bridging members are spaced radially outwardly of the rotor shaft surface and provide a sealing surface for engagement by the bristle tips of brush seals carried by the web of a diaphragm forming part of the non-rotatable component. The brush seal is located radially outwardly of the rotor shaft surface and at an upstream location along a leakage path between the non-rotatable and rotatable components. The contact area is also located in radial registration with a wheelspace void whereby heat transfer resulting from the frictional contact of the brush seal and sealing surface occurs axially and radially and thus dissipates before thermally affecting the rotor shaft surface.
The bridging members have axial end edges which cooperate with surfaces on the bucket dovetails to form tongue-and-groove connections with the adjacent stages. Additionally, the rotor shaft carries an annular rim projecting radially outwardly from the rotor shaft surface and substantially centrally between adjacent stages. The rim and the bridging members have cooperating dovetail connections such that the bridging member is substantially centrally supported between the adjacent stages. Further, one or more labyrinth teeth form a labyrinth seal between the diaphragm web and the bridging member. Preferably, the teeth are mounted on the bridging member and project radially outwardly toward the diaphragm web. The labyrinth seal serves as a backup seal in the event of failure of the brush seal.
The bridging members are readily applied to the turbine stages. Particularly at a radial entry location, the outer flange of a groove formed on each of the axially adjacent bucket dovetails and a portion of the adjacent bucket dovetails are removed, permitting radial entry of the bridging member. The bridging member can then be displaced in a circumferential direction about the rotor shaft to a final location. Upon installation of all bridging members, the final bridging member at the radial entry location may be staked or otherwise secured, for example, by screws, to the bucket dovetail at that location.
In a preferred embodiment according to the present invention, there is provided a steam turbine comprising a rotatable component including a rotor shaft carrying axially adjacent bucket rows and a non-rotatable component about the rotatable component, the rotor shaft having a shaft surface, a bridging member extending generally axially between the adjacent bucket rows at a location spaced radially outwardly of the shaft surface and mounted for rotation with the rotatable component and a brush seal carried by the non-rotatable component for sealing engagement with the bridging member.
In a further preferred embodiment according to the present invention, there is provided in a steam turbine having a rotatable component including a rotor shaft having a rotor shaft surface and a non-rotatable component about the rotatable component carrying a brush seal for sealing engagement with the rotatable component, a method of substantially eliminating bowing of the rotor resulting from circumferential non-uniform distribution of heat about the rotor shaft surface due to frictional contact between the brush seal and the rotatable component, comprising the step of inhibiting circumferential non-uniform heat transfer to the rotor shaft surface generated by frictional contact between the rotatable component and the brush seal by extending a bridging member between axially spaced bucket dovetails at a location radially outwardly of the rotor shaft and engaging the brush seal against the bridging member.
REFERENCES:
patent: 6168377 (2001-01-01), Wolfe et al.
patent: 6290232 (2001-09-01), Reluzco et al.
patent: 6431827 (2002-08-01), Wolfe et al.
Baily Frederick George
Brisson Bruce William
Burnett Mark Edward
Caruso David Alan
Turnquist Norman Arnold
McAleenan James M
Nixon & Vanderhye
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