Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Resilient – flexible – or resiliently biased
Utility Patent
1999-01-27
2001-01-02
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Resilient, flexible, or resiliently biased
C415S231000, C415S174500
Utility Patent
active
06168377
ABSTRACT:
TECHNICAL FIELD
The present invention relates to apparatus and methods for eliminating thermal bowing of the rotor of a steam turbine resulting from non-uniform distribution of heat about the rotor due to frictional contact between a brush seal and a proud portion of the rotor.
BACKGROUND OF THE INVENTION
Steam turbines for the generation of power typically include a continuous solid elongated shaft carrying the turbine wheels and buckets. Steam turbines of impulse design typically operate above the rotor's first bending critical frequency and often near the second bending critical frequency. Steam turbine rotors, however, often have proud or high spots on the rotor, resulting from operations or run-outs caused by machining operations. Brush seals can be used for sealing between the rotors and stationary components in steam turbines. Brush seals typically comprise a plurality of metal bristles projecting from the stationary component toward the rotating component, i.e., the rotor, with the tips of the bristles engaging with and bearing against the rotor surface. Sustained rubbing between the rotor and the brush seals can lead to thermal bowing of the rotor or exacerbate an existing bowed condition of the rotor. That is, the friction generated by contact between the rotor and the stationary brush seals leads to an uneven, i.e., non-uniform, temperature distribution about the circumference of the rotor. The proud portion of the rotor therefore becomes increasingly hotter than circumferentially adjacent portions of the rotor, resulting in non-uniform axial expansion of the rotor and hence a bow in the rotor. This non-uniform temperature distribution can be particularly pronounced during start-up when there is no cooling flow about the rotor.
Thermal bowing of the rotor in steam turbines becomes an issue because bowing will cause an imbalance which can adversely affect the rotor dynamic behavior of the rotor system.
Brush seals have previously been installed in steam turbines with an initial clearance sized to ensure that the bristles do not contact the rotor during start-up. This approach eliminates or minimizes rotor dynamics concerns with brush seals. However, sealing performance is significantly compromised.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, the rotor is modified to accommodate brush seals without compromising their sealing performance, yet enabling operation of the turbine. The present invention generally prevents the non-uniform circumferential distribution of heat generated by frictional contact between the rotor and the brush seal, which would otherwise cause a differential temperature about the rotor at the location of the seal tending to bow the rotor, and provides a substantially uniform distribution of heat about the rotor at the axial location of the brush seal which permits axial expansion of the rotor without bowing.
In a preferred embodiment of the present invention, the preferential heating of the proud portion of a rotor due to frictional contact with the brush seal is eliminated and, to the extent heat generated by such frictional contact is applied to the rotor, it is substantially uniformly distributed about the rotor. To accomplish the foregoing, the rotor is provided with a groove and an insert in the form of a circumferential ring is disposed in the groove. The outer surface of the ring lies in contact with the bristles of the brush seal. The contact between the insert ring and the rotor inhibits circumferential non-uniform heat transfer to the rotor. That is, when the insert is heated locally by frictional contact with the brush seal bristles, the heat will spread circumferentially about the insert faster than it will spread axially or radially into the rotor shaft. As a result, the interface between the insert and rotor tends toward a circumferentially uniform temperature distribution and, consequently, the heat generated by the frictional contact between the brush seal and the insert is substantially evenly distributed by the insert into the rotor. The increased heat applied to the rotor at the axial location of the brush seal may expand the rotor axially but will not bow the rotor because of the uniform distribution of the heat into the rotor. The insert may be thermally insulated from the rotor by providing thermal coatings on the rotor insert interface. Alternatively, the insert may be connected to the rotor by ribs which reduce the effective heat transfer to the rotor, i.e., insulates the rotor from the insert, by creating small dead air spaces therebetween.
In another aspect of the present invention, a circumferentially extending groove is formed in the rotor at a location axially spaced from but adjacent to the frictional contact between the rotor and the brush seal. As indicated previously, the proud portion of the rotor will generate an uneven temperature distribution circumferentially about the rotor at the axial location of the contact between the brush seal and the rotor's surface. However, this uneven heat distribution will travel axially along the rotor only to a limited extent which does not cause a bow. That is, the non-uniformly generated heat about the rotor is localized, i.e., stopped by the groove, and consequently, a thermal bow does not appear in the rotor. Preferably, a pair of rotor grooves are disposed on opposite sides of the contact between the brush bristles and the rotor.
A further aspect of the present invention resides in the provision of a protrusion about the rotor at the axial location of the rotor's contact with the brush seal. Thus, a radially outwardly directed land on the rotor may be provided, the land preferably having axially extending flanges. The land and the flanges enable substantially uniform distribution of heat circumferentially about the land and flanges before the heat penetrates the rotor. At the time of heat penetration into the rotor, the land and flanges are substantially uniformly heated whereby the rotor likewise is substantially uniformly heated, thereby avoiding the formation of a bow in the rotor due to uneven heating about the rotor at the axial location of the brush seal.
In a further aspect of the present invention, the location of the frictional contact between the stationary and rotary components can be moved radially outwardly away from the rotor so as not to become part of a continuous surface of the rotor, which would otherwise bow the rotor resulting from uneven heat distribution. For example, the contact surface between the rotor and the stationary component can be provided by a protrusion on a bucket dovetail located radially outwardly of the surface of the rotor. The heat generated by the frictional contact between the brush seal and the bucket dovetail protrusion will essentially become uniformly distributed about the wheel prior to passing within the rotor. Similarly, the protrusion may be provided on the wheel rather than on the dovetail.
In a preferred embodiment according to the present invention, there is provided in a steam turbine having a rotor and a non-rotating component about the rotor carrying a brush seal for sealing engagement with the rotor, a method of substantially eliminating bowing of the rotor resulting from circumferentially non-uniform distribution of heat about the rotor due to frictional contact between the brush seal and a proud portion of the rotor, comprising the step of inhibiting circumferential non-uniform heat transfer to the rotor generated by frictional contact between the proud portion of the rotor and the brush seal.
In a further preferred embodiment according to the present invention, there is provided a steam turbine comprising a rotor and a non-rotating component about the rotor, a brush seal carried by the non-rotating component for sealing engagement with the rotor including a proud portion of the rotor and means for inhibiting circumferential non-uniform heat transfer to the rotor generated by frictional contact between the proud portion of the rotor and the brush seal whereby bowing of the
Baily Frederick George
Carr Roger Jordan
Marks Paul Thomas
Morson Alexander
Rentz Lawrence Edward
General Electric Co.
Look Edward K.
Nguyen Ninh
Nixon & Vanderhye
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