Inner turbine shell axial movement

A clearance control system for a turbine having a stator assembly and a rotor assembly includes a hydraulic or pneumatic controller that axially drives, through a shaft, one or more actuators connected to the stator assembly casing. The controller causes relative movement between the stator and rotor assemblies to adjust the clearances between portions of the stator and rotor in accordance with the varying operating conditions of the turbine. More particularly, the controller moves the stator relative to the rotor in first and second axial directions to compensate for thermal expansion and contraction during the operating conditions of the turbine.

TECHNICAL FIELD

The invention is directed to steam or gas turbines and especially to gas turbines having hydraulic or pneumatic actuator systems for movement of the inner turbine shell axially to achieve better clearance between the stator and rotor during operating conditions.

BACKGROUND OF THE INVENTION

Steam and gas turbines are used, among other purposes, to power electric generators. Gas turbines are also used, among other purposes, to propel aircraft and ships. A steam turbine has a steam path which typically includes in serial-flow relation, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relation, an air intake or inlet, a compressor, a combustor, a turbine, and a gas outlet or exhaust diffuser. Compressor and turbine sections include at least one circumferential row of rotating buckets. The free ends or tips of the rotating buckets are surrounded by a stator casing. The base or shank portion of the rotating buckets are flanked on upstream and downstream ends by the inner shrouds of stationary blades disposed respectively upstream and downstream of the moving blades.

The efficiency of the turbine depends in part on the axial clearance or gap between the rotor bucket shank portion angel wing tip(s) (seal plate fins), and a sealing structure of the adjacent stationary assembly, as well as the radial size of the gap between the tip of the rotating buckets and the opposite stationary assembly. If the clearances are too large, excessive valuable cooling air will leak through the gaps between the bucket shank and the inner shroud of the stationary blade and between the tips of the rotating buckets and the stationary assembly, decreasing the turbine's efficiency. If the clearances are too small, the rotating blades will strike the sealing structure of the adjacent or opposite stator portions during certain turbine operating conditions.

In this regard, it is known that there are clearance changes during periods of acceleration or deceleration due to changing centrifugal forces on the buckets, turbine rotor vibration, and/or relative thermal growth between the rotating rotor and the stationary assembly. During periods of differential centrifugal force, rotor vibration, and thermal growth, the clearance changes can result in severe rubbing of, e.g., the moving bucket tips against the stationary seal structures or against the stationary assembly. Increasing the tip to seal clearance gap reduces the damage due to metal-to-metal rubbing, but the increase in clearance results in efficiency loss.

More particularly, during turbine operating conditions the components of the turbine can thermally expand (or contract) at varying rates due to high operating temperatures in excess of 2,000 degrees Fahrenheit. The stator and rotor must be maintained apart from each other across all operating conditions to prevent damage from contact with each other. However, if a single fixed positional relationship between the stator and rotor is maintained across all operating conditions then for at least some operating conditions, i.e., startup, there will be compressed fluid leakage between the stator and rotor assemblies leading to operating inefficiencies.

It is known in the art to facilitate compressor casing movement by using pressure difference in plenums purged with extracted air. It is also known in the art to use a thermally expandable linkage to facilitate compressor casing movement and to use an air driven or stream driven piston to facilitate compressor casing movement.

SUMMARY

It is now proposed that a hydraulic or pneumatic system be used for axially moving the turbine inner casing to enable lower operating clearances. The proposed system results in better clearance between the stator and rotor. The proposed system also enables use of performance enhancers such as dual overlap on angel wing configuration, and tapered rotors.

In one exemplary implementation, the proposed system advantageously uses a hydraulic or pneumatic controller to directly drive a shaft connected to two actuators disposed at horizontal joints on the inner turbine casing. More particularly, in this first exemplary implementation, the two actuators are jointly driven by the controller and shaft in a first direction and jointly driven in a second direction opposite to the first direction.

In another exemplary implementation, the proposed system uses a hydraulic or pneumatic controller to drive a shaft to alternatively drive one of two actuators disposed at horizontal joints on the inner turbine casing. More particularly, in this second exemplary implementation, the controller drives one of the actuators in a first direction or alternatively drives the second one of the actuators in a second direction opposite to the first direction.

DETAILED DESCRIPTION

FIG. 1is a cross section of turbine10that shows where improved clearance control can be obtained by the exemplary implementations of the proposed system described herein. At location12a tapered design for the tips of rotating buckets14, also shown at16, can facilitate improved clearance control. At location18, angel wing clearance control between the shank of rotating bucket14, which forms part of rotor assembly24, and stationary stator assembly20can be varied through use of the exemplary implementations of the proposed system. Likewise at location22, reducing the axial gap between teeth on the rotor assembly24and stationary stator assembly20through use of the exemplary implementations of the proposed system provides variable clearance control. More particularly, clearance control at locations12,18and22can be varied in accordance with thermal operating conditions by relative axial movement of the inner turbine casing and stationary stator assembly20in relation to the rotor assembly24.

FIG. 2shows in schematic form the system for variable clearance control in a turbine to include hydraulic controller26or pneumatic controller28for moving the turbine inner casing30relative to the turbine outer casing32. Since stator assembly20, shown inFIG. 1, is fixedly connected to turbine inner casing30, it follows that the movement of turbine inner casing30results in the movement of stationary stator assembly20. Accordingly, the movement of turbine inner casing30and stationary stator assembly20is also relative to rotor assembly24.

FIG. 3shows schematically the arrangement of hydraulic controller26or pneumatic controller28to axially move turbine inner casing30relative to rotor assembly24(shown inFIG. 1) and turbine outer casing32. Controller26,28drives a shaft34connected to actuators36,38to effect the relative movement.

FIG. 4shows another exemplary implementation of the proposed system to include actuators40and42fixedly connected to turbine outer casing32and driven by hydraulic controller44through actuator shaft46to move stationary stator assembly20and turbine inner casing30relative to turbine outer casing32and rotor assembly24(shown inFIG. 1) in first and second directions shown by directions arrow A. AlthoughFIG. 4has been shown with hydraulic controller44, those ordinarily skilled in the art will readily recognize that the controller could be pneumatic.

FIG. 5shows yet another exemplary implementation of the proposed system to include actuators56and58which are alternatively driven by hydraulic controller44through actuator shaft50and abutting surfaces52and54to move turbine inner casing30and stationary stator assembly20(shown inFIG. 1) relative to the turbine outer casing and rotor assembly24in a first direction when abutting surface52of shaft50contacts actuator56, and in a second, opposite, direction, when abutting surface54of shaft50contacts actuator58, as shown by directions arrow A. AlthoughFIG. 5has been shown with hydraulic controller44, those ordinarily skilled in the art will readily recognize that the controller could be pneumatic.

FIGS. 6A and 6Bshow still yet another exemplary embodiment wherein actuators such as those described in the previous exemplary embodiments can be used for adjusting and maintaining crucial clearances between the dual overlaps on angel wing configurations of rotating buckets and the stationary stator assembly. More particularly,FIG. 6Ashows the casing in the aft/running position with a dual overlap at the angel wing location60, maintaining a necessary axial gap clearance at location62, while maintaining an overlap at location64.FIG. 6Bshows that the casing has been moved forward thus lessening the dual overlaps at location60, increasing the axial gap at location62, and increasing the dual overlaps at location64.