The invention relates generally to an arrangement for mounting gas turbine nozzles and more specifically to an outer sidewall retention scheme for a singlet first stage nozzle.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer sidewall portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer sidewalls. A nozzle retaining ring coupled to the outer sidewall of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner sidewall and may support the first-stage nozzles against axial movement.
Side seals may seal the annular array of segments one to the other along adjoining circumferential edges. The side seals seal between a high pressure region radially inwardly of the inner sidewall and radially outward of the outer sidewall, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure. Chordal hinge seals are used to seal between the inner sidewall of the first-stage nozzles and an axially facing surface of the nozzle support ring and between the outer sidewall and a shroud for the first stage bucket.
Referring now to
Referring to the first stage of the turbine, the stator vanes 20 forming the first-stage nozzles are disposed between inner and outer sidewalls 38 and 40, respectively, supported from the turbine casing. As noted above, the nozzles of the first stage are formed of a plurality of nozzle segments each mounting one, or two, stator vanes extending between inner and outer sidewall portions and arranged in an annular array of segments. A nozzle retaining ring 42 connected to the turbine casing is coupled to the outer sidewall and secures the first-stage nozzle. A nozzle support ring 44 radially inwardly of the inner sidewall 38 of the first-stage nozzles engages the inner sidewall 38. Particularly, the interface between the inner sidewall 38 and the nozzle support ring 44 includes an inner rail 52. The inner rail 52 includes a chord-wise, linearly extending axial projection, generally and collectively hereinafter referred to as a chordal hinge seal. It will be appreciated that high pressure compressor discharge air lies in the region 37 and lower pressure hot gases flowing in the hot gas path 14 lay on the opposite side of the chordal hinge seal. The chordal hinge seal is thus intended to seal against leakage from the high pressure region 37 into the lower pressure region of the hot gas path 14.
A nozzle comprises a plurality of radially extending airfoils arranged circumferentially about an engine axis, the airfoils being supported by radially inner and outer circumferential sidewalls. Either the inner or outer sidewalls may include some form of flange for coupling the nozzle to a stationary engine mounting structure. In general, a plurality of turbine nozzles is interleaved with a plurality of turbine rotor stages. The directing process performed by the nozzles also accelerates gas flow resulting in a static pressure reduction between inlet and outlet planes and high pressure loading of the nozzles. Additionally, the nozzles experience high thermal gradients from the hot combustion gases and the coolant air at the radial mounting surfaces.
The use of bolts and clamps at circumferential locations about a nozzle sidewall act as a restriction to the sidewall, which sidewall is hotter than the structure to which it is attached, causing radial bowing of the outer sidewall of the nozzle and stressing of the airfoils attached to the sidewall. Such stressing of the airfoils may lead to formation of cracks in the airfoil trailing edge.
The chordal hinge rail 150 on the outer sidewall 115 of the nozzle 110 projects outward radially from the outer sidewall 115. The chordal hinge rail 150 incorporates a forward-facing annular retaining land 175 at its outermost radial projection. The retaining land 175 mates with an aft-facing annular groove 180 established by an aft-facing retaining hook 185 on the retaining ring. The retaining land 175 of the chordal hinge rail 150 acting on the retaining hook 185 of the retaining ring 130 provides radial support for the nozzle 110. The annular retaining hook 185 may be divided into segments (not shown). Circumferential support is provided by an anti-rotation pin (not shown) that passes through the retaining ring 130 and the retaining land 175.
Power generation gas turbines traditionally use some type of hook retention scheme. Improvements have been made on the traditional hook retention scheme by changing from a continuous hook arrangement, typical in FA class machines by GE to a segmented hook arrangement, typical in FB class machines by GE. This change resulted in more determinate nozzle loading and better nozzle sealing but also resulted in less than optimal thermal isolation of the retaining ring and thereby a substantial cost increase to the nozzle arrangement. Some of the field issues related to hook retention designs include incomplete chordal hinge sealing, retaining ring out of roundness, and high trailing edge stresses.
Accordingly, there is a need to provide determinate nozzle loading and improved sealing while also improving thermal isolation of the retaining ring, reducing cost, and improving assembly flexibility of the nozzle arrangement.
The present invention relates to an apparatus and method for retaining the outer sidewall of a singlet first stage nozzle in a gas turbine.
Briefly in accordance with one aspect of the present invention, an outer sidewall retention scheme for a first stage singlet nozzle of a gas turbine is provided. The retention scheme includes a circumferential retaining ring. The retaining ring incorporates a main body and a pair of circumferential retaining lands projecting inward radially from the main body of the retaining ring. The pair of circumferential retaining lands may be separated from each other by a predetermined distance. A circumferential annular retaining groove is formed between the pair of circumferential retaining lands with the groove having a width of the predetermined distance between the pair of circumferential retaining lands.
A first stage nozzle including an inner sidewall and an outer sidewall may be assembled on the retaining ring. A first lug and a second lug may be mounted on an outer face of the outer sidewall of each nozzle. The first lug and the second lug are adapted to fit within the circumferential annular retaining groove of the retaining ring. A first retaining pin is provided for attaching the first lug within the circumferential annular retaining groove to the pair of circumferential retaining lands and a second retaining pin is provided for attaching the second lug within the circumferential annular retaining groove to the circumferential retaining lands. Two chordal hinges rails may be provided for the nozzle. One chordal hinge rail is mounted on the outer sidewall for each nozzle. A chordal hinge rail is also provided on the inner sidewall for each nozzle.
In accordance with a second aspect of the present invention, a method is provided for retaining a first stage singlet nozzle in a first stage of a gas turbine. The gas turbine will include a first stage retaining ring with a pair of parallel circumferential retaining lands and a groove in-between, a nozzle including an outer sidewall with a first lug, a second lug and a chordal hinge rail, and an inner sidewall with a chordal hinge rail.
The method includes providing radial and circumferential support for the nozzle with an outer sidewall retention scheme by pinning the first lug to the pair of circumferential retaining lands and pinning the second lug to the pair of circumferential retaining lands. Axial support for the nozzle is provided by a chordal hinge rail on the outer sidewall and a chordal hinge rail on the inner sidewall.
According to a third aspect of the present invention, a gas turbine employing a sidewall retention scheme for a first stage singlet nozzle is provided. The retention scheme includes a circumferential retaining ring. The retaining ring incorporates a main body and a pair of circumferential retaining lands projecting inward radially from the main body of the retaining ring. The pair of circumferential retaining lands may be separated from each other by a predetermined distance. A circumferential annular retaining groove is formed between the pair of circumferential retaining lands with the groove having a width of the predetermined distance between the pair of circumferential lands.
A first stage nozzle including an inner sidewall and an outer sidewall are provided. The outer sidewall may be skewed off an axial direction of the retaining ring. A first lug and a second lug mounted on an outer face of the outer sidewall of each nozzle are adapted to fit within the circumferential annular retaining groove of the retaining ring. A plurality of retaining pins, including a first retaining pin and a second retaining pin for each of the plurality of first stage nozzles is included. A first retaining pin is adapted for attaching the first lug within the circumferential annular retaining groove to the pair of circumferential retaining lands. A second retaining pin is adapted for attaching the second lug within the circumferential annular retaining groove to the circumferential retaining lands. Each nozzle further includes a chordal hinge rail on the outer sidewall and a chordal hinge rail on the inner sidewall.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The following embodiments of the present invention have many advantages, including improved nozzle stability, determinate nozzle loading, airfoil trailing edge stress reduction, improved retaining ring thermal isolation, improved nozzle arrangement assembly flexibility, improved chordal hinge sealing, and improved nozzle castibility.
Power generation gas turbines traditionally use a hook retention scheme. Hook retention schemes inherently have several design drawbacks that cannot be overcome. The present invention overcomes the drawbacks of the hook design. An embodiment of the inventive design retains the first stage nozzle with two axially oriented pins. The benefits of this retention scheme include improved nozzle stability, determinate nozzle loading, airfoil trailing edge stress reduction, improved retaining ring thermal isolation, improved nozzle arrangement assembly flexibility, improved chordal hinge sealing, and improved nozzle castibility.
More specifically, the first stage nozzle is attached to the retaining ring at the outer sidewall with two axially oriented pins. Both pins are supported on each end in axially oriented pinholes in the retaining ring thereby being simply supported. One pin passes through a pinhole in a nozzle lug. A second pin passes through a slot in a nozzle lug. The slot is open to the pressure side of the nozzle. The first pin prevents the nozzle from translating in the radial and tangential directions. The second pin prevents the nozzle from rotating about the axial direction. Combined with the inner sidewall and outer sidewall chordal hinge rails, the result is a fully constrained, non-redundant retention system. The lugs are positioned in such a way as to maximize nozzle stability, minimize stress input into life limiting features, i.e. the trailing edge, and to guarantee deterministic nozzle loads. The nozzle stability is maximized by moving the lugs as far forward as possible and as far apart as possible to generate longer moment arms for reacting out gas loads. Moving the support lugs away from the trailing edge minimizes the stress input into the trailing edge. The nozzle loads are made more deterministic by designing the retention features to only be capable of supporting loads in the designated directions. The inventive retention scheme also drastically reduces thermal input from the nozzle into the retention features in comparison to the original hook design. Minimizing the contact area and preventing dead cavities between the nozzle and the retention features accomplish this reduction. The inventive retention scheme is designed for ease of assembly and manufacturing.
The improved retention scheme results in improved nozzle and retaining ring life, leakage reduction resulting in nitrogen oxide (Nox) reduction, and substantially lower nozzle arrangement cost relative to comparable technology engines.
The outer sidewall retention scheme for first stage singlet nozzles includes a circumferential retaining ring with a circumferential annular groove, a plurality of first stage nozzles each with an inner sidewall and an outer sidewall, a first lug and a second lug mounted on the outer sidewall of each nozzle, a first retaining pin and a second retaining pin, and a chordal hinge rail on the each sidewall for each nozzle.
A plurality of axial-oriented through-holes 345 are provided between the aft circumferential face 326 and the forward circumferential face 328 of the aft retaining land 325. A plurality of axial-oriented closed-end bore holes 350 are provided through the aft face 333 of forward retaining land 330. The plurality of axial-oriented through-holes 345 in the aft retaining land 325 and the plurality of axial-oriented closed-end bore holes 350 in the forward retaining land 330 are radially and circumferentially organized coaxially to accept a retaining pin (not shown) axially through the aft retaining land 325 and into the bore hole 350 of the forward retaining land 330. The coaxially oriented holes with centerline 358 are further arranged circumferentially in pairs, equally spaced around the retaining lands. The circumferential arrangement of the paired holes 360, being key to the positive capture scheme of the retaining pins, will later be described in greater detail. The diameter of the paired holes 360 are sized to accept retaining pins for the nozzle.
The first stage nozzle 400 includes an inner sidewall 410, an outer sidewall 420 and an airfoil 430 in-between. The airfoil 430 may include an internal cavity for nozzle cooling having an entrance aligned generally in axial and circumferential alignment with the air-cooling hole (
The outer face 422 of the outer sidewall 420 includes two retaining lugs. A first lug 440 and a second lug 445 are positioned forward from the aft edge 450 of the sidewall by a predetermined distance s, the lugs being in axial alignment with respect to the aft end of the sidewall. The first lug 440 is positioned on the pressure side 456 of the sidewall. The second lug 445 is positioned on the suction side 454 of the sidewall. The first lug 440 and the second lug 445 may be circumferentially positioned in proximity to the edge of their respective edge of the outer sidewall 420. The first lug 440 and the second lug 445 include a width w1. W1 is adapted to fit within the circumferential retaining groove (
The outer sidewall 420 further includes a chordal hinge rail 460 on the aft edge 450. The chordal hinge rail 460 runs from the inner face of the sidewall from the pressure side to the suction side and extends in a generally outward radial direction from the aft edge 450 of sidewall. The chordal hinge rail 460 projects sufficiently outward radially to cover at least partially or fully the radial reach of the through-holes (
Referring to
The inner sidewall 410 further includes a chordal hinge rail 470 on an inner face. The chordal hinge rail 470 runs across the inner face 415 of the inner sidewall 410 from the pressure side to the suction side and extends in a generally inward radial direction from the inner face 415 of the inner sidewall 410. The chordal hinge rail 470 includes the raised seating surface of a chordal hinge seal 475 that seats with an inner support ring to provide axial support for the inner sidewall of the nozzle. The chordal hinge seal 475 further blocks against passage of high-pressure air from the compressor between the inner sidewall and the inner support ring.
As previously described, axially oriented holes for retaining pins are arranged circumferentially in pairs, equally spaced around the aft retaining land of the retaining ring. The first stage nozzles may be assembled on the retaining ring as illustrated in
Similarly a second retaining ring half may be assembled with nozzles until full.
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.