Patent Application
20070071600
This invention relates generally to rotary machines and, more particularly, to a method and an assembly for aligning an inner shell of the rotary machine with an outer shell of the rotary machine.
Steam and gas turbines are used, among other purposes, to generate power for electric generators. Known steam turbines have a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. Known gas turbines have a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). The compressor sections and the turbine sections each includes at least one row of circumferentially spaced rotating blades or buckets.
Turbine efficiency depends at least in part on controlling a radial clearance or gap between the rotor shaft and the surrounding casing. If the clearance is too large, steam or gas flow may leak through the radial clearance, thus decreasing turbine efficiency. Alternatively, if the clearance is too small, the rotating rotor shaft may undesirably contact the stationary packing ring during certain turbine operating conditions, thus adversely affecting turbine efficiency. Gas or steam leakage through the packing assembly represents a loss of efficiency and is generally undesirable.
To minimize leakage and prevent undesirable contact between rotating components and stationary components, the inner shell of the turbine is keyed axially and transversely to the outer shell of the turbine along the respective axial centerline and transverse centerline. Gib keys are generally positioned between the inner shell and the outer shell to properly align the inner shell with the outer shell during turbine assembly. Conventional gib keys typically have a generally circular disc shape and are fastened to the inner shell with a bolt. The dimensions of the packing head positioned within the inner shell, particularly a length of the packing head along the axial centerline, are limited by the circular disc shape of the conventional gib key. As a result of the dimensional limitations on the packing head, a sufficient number of packing rings are not positionable within the packing head to prevent or limit undesirable leakage, which negatively impacts turbine performance and efficiency.
In one aspect, the present invention provides a method for aligning an inner shell with an outer shell of a turbine assembly along a transverse centerline perpendicular to an axial centerline of the turbine assembly. The method includes positioning a first gib key assembly with respect to the transverse centerline. The first gib key assembly is connected to a first end surface of the inner shell to form a first groove within the first gib key assembly. A projection formed on a first end of the outer shell is mateably engaged with the first groove formed within the first gib key assembly to align the inner shell with the outer shell along the transverse centerline.
In another aspect, the present invention provides a gib key assembly for a turbine assembly including an inner shell and an outer shell. The gib key assembly includes a first set of opposing gib keys connected to the inner shell. Each gib key includes a first plate forming at least one aperture therethrough. The first plate is connected to an end surface of the inner shell. The first plate transitions into a second plate, which extends substantially perpendicular with respect to the first plate. The second plate has a contact face that is positioned with respect to a transverse centerline of the turbine assembly.
In a further aspect, the present invention provides a steam turbine. The steam turbine includes a rotor shaft, which extends along an axial centerline of the steam turbine. A stationary inner shell is positioned about the rotor shaft and forms a chamber. A packing head is connected to the inner shell and positioned within the chamber. The packing head is circumferentially positioned about the rotor shaft and forms a plurality of channels. A packing ring is retained within each channel. A gib key assembly is connected at a first end surface of the inner shell and defines a groove. An outer shell is positioned about the inner shell and forms a projection positioned within the groove to align the inner shell with the outer shell along a transverse centerline of the turbine substantially perpendicular to an axial centerline of the turbine.
The present invention provides a method and assembly for aligning an inner shell of a rotary machine, such as a steam turbine, with an outer shell of the rotary machine, wherein a packing head having an increased number of packing rings circumferentially positioned about a rotor shaft of the steam turbine is positionable within a chamber formed in the inner shell. The increased number of packing rings provides a tortuous path through which steam or fluid must flow to escape the steam turbine, thereby increasing the steam turbine efficiency.
The present invention is described below in reference to its application in connection with and operation of a steam turbine assembly. However, it will be obvious to those skilled in the art and guided by the teachings herein provided that the invention is likewise applicable to any combustion device or assembly including, without limitation, boilers, heaters and gas turbine engines, and may be applied to systems consuming natural gas, fuel, coal, oil or any solid, liquid or gaseous fuel.
A stationary inner shell 20 is positioned about the rotor shaft and extends along axial centerline 16. Inner shell 20 includes a generator end surface 21 and an opposing turbine end surface 22. Inner shell forms a chamber 23 within which the rotor shaft is positioned. As shown in
In one embodiment, steam turbine 10 includes a seal assembly 30, as shown in
Packing ring 28 includes a plurality of teeth 36 positioned in opposition to a plurality of rotor shaft circumferential projections 48 extending outward from rotor shaft 32. A positive force may force fluid flow between the multiple restrictions formed within radial clearance 33 defined at least partially between teeth 36 and rotor shaft 32. More specifically, radial clearance 33, the number and relative sharpness of teeth 36, the number of rotor shaft circumferential projections 48 and/or the operating conditions, including pressure and density, are factors that determine the amount of leakage flow. Alternately, other geometrical arrangements can also used to provide multiple or single leakage restrictions.
As shown in
Referring to
For example, as shown in
In one embodiment, a suitable coating material, such as a stellite coating 94 or a nitride coating, is applied to at least a portion of contact face 82, for example at an edge of contact face 82. Any suitable coating material known to those skilled in the art and guided by the teachings herein provided may be applied to at least a portion of contact face 82. Stellite coating 94, as shown in
Gib key assemblies 70 and/or 71 allow an increased number of channels 26 to be formed along the length of packing head 24 compared to conventional packing heads. Specifically, in one embodiment, the increased area within chamber 23 as a result of gib key assembly 70 and/or 71 of the present invention allows for the formation of eight channels 26 within packing head 24, whereas conventional packing heads including generally circular disc-shaped gib keys have a length suitable for formation of a maximum of five channels. With the increased number of packing rings 28 positioned within cooperating channels 26, steam leakage within steam turbine 10, which results in a decrease in steam turbine efficiency, is greatly reduced.
In one embodiment, a method for aligning inner shell 20 of steam turbine 10 with outer shell 60 of steam turbine 10 along transverse centerline 18 includes positioning or locating first gib key assembly 70 with respect to transverse centerline 18. Gib key assembly 70 is connected to generator end surface 21 of inner shell 20 to form groove 88 within gib key assembly 70 along transverse centerline 18. In one embodiment, at least a portion of second plate 80 of each gib key 72 is inserted into void 86 formed in generator end surface 21. As shown in
Alternatively, or additionally, a second gib key assembly 71 is positioned or located with respect to axial centerline 16 and transverse centerline 18. In one embodiment, second gib key assembly 71 is positioned on generator end surface 21 and radially opposes first gib key assembly 70, for example positioned along vertical centerline 17. Second gib key assembly 71 is connected to generator end surface 21 of inner shell 20 to form second groove 90 within second gib key assembly 71. In one embodiment, with gib key assembly 71 connected to inner shell 20, at least a portion of second plate 80 of each gib key 72 is positioned within a second void formed in generator end surface 21, the same or similar to void 86 shown in
The above-described method and assembly provide a steam turbine with increased energy efficiency. More specifically, the method and assembly of the present invention aligns an inner shell of the steam turbine with an outer shell of the steam turbine along a transverse centerline of the steam turbine, while providing an increased area within the chamber formed by the inner shell. A packing head having an increased number of packing rings circumferentially positioned about the rotor shaft of the steam turbine is positioned within the chamber. The increased number of packing rings positioned along a length of the packing head provides a reduction in steam leakage from within the steam turbine, resulting in an increase in steam turbine efficiency.
Exemplary embodiments of a gib key assembly are described above in detail. The methods and assemblies are not limited to the specific embodiments described herein or to the specific arrangements assembled, but rather, the methods and assemblies may be utilized independently and separately from other methods and assemblies described herein. For example, the gib key assembly described above may also be used in combination with other turbines.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
