Design of a guide ring / beam transition for a steam turbine

Abstract

Turbine which features: a turbine guide vane assembly with at least one blade (212, 312) having an inner side wall (214, 314) at a radially inner end of the blade (212, 312) and an outer side wall (216, 316) at the radially outer end of the blade (212, 312); and an outer support (234, 334) with a radially inwardly opening groove (246, 346); wherein the outer side wall (216, 316) is designed to engage in the groove (246, 346) in a radial direction, while being prevented from moving in an axial direction with respect to the groove (246, 346); A front contact area between the outer side wall (216, 316) and the outer support (234, 334) has a front circumferential contact surface (244, 344) formed on an upstream, rearward-facing surface of the groove (246, 346), wherein the front circumferential contact surface (244, 344) is formed by forming a circumferentially extending recess (252, 352) in the upstream, rearward-facing surface of the groove (246, 346) radially inside the front circumferential contact surface (244, 344), such that the upstream, rearward-facing surface of the groove (246, 346) contacts an opposing upstream axial surface of the outer side wall (216, 316) only at the front circumferential contact surface (244, 344), wherein the front The circumferential contact surface (244, 344) has a radial dimension that is smaller than the radial dimension of the groove (246, 346); and A rear contact area between the outer side wall (216, 316) and the outer support (234, 334) has a rear circumferential contact surface (250, 350) formed on a downstream axial surface of the outer side wall (216, 316), wherein the rear circumferential contact surface (250, 350) is designed to abut a radially inner region of the groove (246, 346), away from the radially outer end wall (248) of the groove (246, 346), such that the front circumferential contact surface (244, 344) is formed closer to a radially outer end wall (248) of the groove (246, 346) than the rear circumferential contact surface (250, 350), wherein the rear circumferential contact surface (250, 350) is formed by forming a circumferentially extending recess (254, 354) is formed in the downstream axial surface of the outer side wall (216, 316) radially outside the rear circumferential contact surface (250, 350), so that the downstream axial surface of the outer side wall (216,316) an opposing axial surface of the outer support (234, 334) only contacts the rear circumferential contact surface (250, 350), wherein the rear circumferential contact surface (250, 350) has a radial dimension that is smaller than the radial dimension of the groove (246, 346).

Description

Background of the invention

[0001] Steam turbine designs consist of static nozzle segments that direct steam flow into rotating blades connected to a rotor. In steam turbines, the nozzle assembly is typically called a diaphragm or diffuser stage. Typical diffuser stages are manufactured using one of two processes. The first is a "band / ring" process, which uses an assembly consisting of multiple airfoils contained within an inner and outer band, after which the banded airfoil assembly is welded into inner and outer rings. The second process involves directly welding airfoils to an inner and outer ring using a fillet weld at the interface. The second process is typically used for larger airfoils where access to make the weld is available.

[0002] However, the application of these methods has disadvantages. One disadvantage is the inherent weld distortion of both the flowpath and steampath sidewalls. In view of this, current steam turbine nozzle manufacturing processes consist of high-heat welds using significant amounts of metal filler material or electron beam deep penetration welds. This material and heat input causes flowpath distortion, and the blades require frequent adjustment after welding and stress relief. The consequence of this distortion is turbine efficiency losses in the steam turbine flowpath.

[0003] Other methods of inserting a single vane structure into rings still contain welds and mechanical transitions that are difficult to model and analyze. They are also not as robust to stress levels due to the welded joint and interfaces between the vanes. Another method involves attaching "hooks" to the vanes and inserting each vane into a circumferential groove in the support. This method is also difficult and time-consuming to analyze for stresses using finite element methods. Furthermore, frequency analysis is not as robust due to uncertain and changing boundary conditions between the vanes and the support.

[0004] Accordingly, current methods for manufacturing vane rings are expensive and time-consuming in both design and manufacture, and all current methods involve some type of welded joint or mechanical transition between the vane row and the rings.

[0005] Bling nozzles are currently used very little in steam turbine designs. A bling nozzle is essentially a complete nozzle flowpath machined from two half-rings without welding or fasteners. Bling nozzles offer numerous useful design properties. First, bling nozzles exhibit much lower stress levels because there are no welds or mechanical interruptions in the load path. Second, blade tolerances can be significantly improved compared to welding techniques. Third, they are easier to fabricate and exhibit better defined frequency characteristics. In this respect, 3D modeling and finite element analysis of stresses and frequencies are easier, faster, and more robust due to the simplicity of the design.

[0006] One problem with current bling designs is the transition between the carrier and the bling. Most nozzle designs have locating elements or small spacers to maintain a small axial clearance between the nozzle and the casing. The spacers act to keep the nozzle under tension in the rearward direction against the steam face. This aids assembly and also helps with removal of the nozzle after years of service. In view of this, corrosion occurs on the surfaces after years of service, and if the transition from the nozzle to the casing is tight on both axial surfaces, it would be very difficult to remove the nozzle because it would tend to stick in place due to corrosion. Blings also "roll" or flex more downstream than the push-in nozzle design.Many vanes use the contact elements only on the lower half (usually three), and the upper half has a wider gap toward the front surface. This allows the upper half of the vane to temporarily separate from the rear surface, allowing foreign matter to penetrate behind the surface and create a leakage flow path.

[0007] DE 10 2007 020 863 A1, US 2004 / 0 253 095 A1, DE 103 58 378 A1 and DE 10 2004 024 683 A1 each disclose a turbine nozzle ring arrangement with at least one stator blade with an airfoil, an inner side wall and an outer side wall, and an outer ring carrier with a radially inwardly opening groove into which the outer side wall engages while being prevented from moving in the axial direction, and with different configurations of front and rear contact areas and abutment surfaces between the outer side wall and the outer ring carrier. Brief description of the invention

[0008] The present invention relates to an improved transition between the bling and the carrier to improve the loading, sealing and disassembly of the bling while reducing flexion in the downstream direction.

[0009] For this purpose, according to the invention, a turbine is provided which has the features of independent claim 1. Particularly preferred embodiments of the invention are specified in the dependent claims. Short description of the drawings

[0010] These and other objects and advantages of the invention will be appreciated and understood by carefully studying the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings: Fig. 1 is a schematic elevation view of a conventional stage having a guide vane formed using the band / ring process; Fig. 2 is a schematic elevation view of a conventional stage having a vane formed using the bling-type construction; Fig. 3 is a schematic elevation view of a vane / carrier transition in the bling design according to a first exemplary embodiment of the invention; Fig. 4 is an enlarged schematic elevation view of the bling / carrier transition area of Fig. 3; Fig. 5 is an enlarged schematic elevational view of the bling / carrier transition area with a front seal according to another exemplary embodiment of the invention; and Fig. 6 is a schematic elevational view of a singlet construction according to yet another exemplary embodiment of the invention. Detailed description of the invention

[0011] As mentioned above, in the bling design of the nozzle ring, the airfoil shapes are cut into two 180° rings to form the bling step. This eliminates the need for mechanical fits and welded elements during manufacturing, thereby solving the problems mentioned above. More specifically, the invention relates to an improved design of the interface between the outer ring of the bling and the carrier. This design serves several purposes. It improves assembly by providing relief in appropriate areas to assist in inserting the bling into the casing. Furthermore, it facilitates future disassembly after years of corrosion occurring at the interface between the bling and the casing. It also reduces the ability of the bling to flex in the downstream direction through strategically located contact areas.Furthermore, it increases the contact pressure between the bling and the housing, which improves the vapor surface seal.

[0012] Fig. Figure 1 shows the traditional design of an action turbine stage, which uses a partition, bands, and rings welded into an assembly. More specifically, this traditional design uses a vane assembly 10 consisting of a number of vanes 12 contained within an inner and outer band 14, 16, which are welded into an inner ring 26 and an outer ring 28, as at 18, 20, 22, 24.

[0013] Fig. Figure 2 shows the traditional bling design. Specifically, the traditional bling design uses a locating element or small spacer 130 to maintain a narrow clearance between the nozzle ring 132 and the housing 134 in the axial direction, as shown at the steam surface or axial contact surface 136. As mentioned above, this aids in assembly and removal of the nozzle ring after years of service. Also shown is a horizontal connecting bolt hole 138 and the intermediate seal 140, which is located in the space between the bling 110 and the rotor 142.

[0014] As mentioned above, this invention generally relates to the features of the mechanical connection between a bling-type nozzle ring and the support (shell or housing) in which it is mounted. The key to the design is the strategic placement of the elements that make contact with the shell and the removal of the abutment elements from the structure. The first coupling element is a front (or upstream) external contact area, provided, for example, by a cutout (recess) on the housing side. This cutout on the housing side allows for a small contact area that only abuts when the bling is almost completely seated in the housing groove. This allows for easy assembly. Disassembly is also improved because the contact surface is very small and separates as soon as the bling is slightly lifted.

[0015] The rear face, or vapor contact surface, also has a very small contact area. Placing the recess on the bling in this position allows for quick separation from the housing groove when the device is disassembled. This also reduces the corrosion problem to just a small circumferential contact surface, reducing the risk of "sticking" or rust bonding when the device is disassembled several years later. Another significant benefit of this narrow circumferential rear contact surface is that it helps concentrate the axial load of the bling onto a small area. This, in turn, reduces leakage at the vapor surface.

[0016] Another significant advantage or improvement of this design over typical straight walls, locating elements, and a wider leading face gap is the ability of this arrangement to limit bling deflection. When the bling is under steam path load, it will attempt to shift downstream in the inner ring region due to aerodynamic forces (pressure) on the airfoil. Designs that utilize hooks on the vanes, when the vanes are inserted into a support groove, have very limited downstream deflection due to the hook connection. When a bling is inserted into the groove, some of the advantageous load path is lost to reduce deflection. The layout of this design, in the exemplary embodiments shown, has the leading locating surface on the outside and the inner locating surface on the inside.The pair limits the element's ability to rotate or roll within the groove with a relatively narrow gap at the front interface. The separation of these two surfaces allows the force couple to compensate for some of the flexion in the downstream direction.

[0017] If the entire surface were straight with a narrow gap, then there could be a significant problem with corrosion, which would cause the parts to stick in place and make disassembly difficult, if not impossible without destroying the device. If all the surfaces were straight and the front one had a wide gap and a contact element as in the Fig. 2, there would be no way to limit the bending (rolling) of the bling.

[0018] The Fig. 3 and Fig. 4 illustrate an exemplary embodiment of the invention in which, instead of arranging an abutment element disposed between the bling 210 and the housing or shroud (carrier 234), a narrow, circumferential abutment surface (front circumferential abutment surface 244) is formed in the carrier. Specifically, the bling consists of vane(s) 212 and an inner and outer sidewall 214, 216. In the embodiment shown in the Fig. 3 and Fig. In the embodiment illustrated in Figure 4, the outer sidewall is received in a circumferentially extending groove 246 of the carrier 234 (housing or shell). A narrow forward circumferential abutment surface 244 is disposed at an axial contact surface along the upstream side of the groove 246, proximate the end wall 248 of the groove, thereby establishing limited contact with the carrier 234 (housing, shell) both to reduce downstream deflection (rolling) and for ease of assembly, because the abutment surface is created instead of a local standoff or abutment element 130.

[0019] The steam surface 236, for example, provides, compared to the bling construction made of Fig. 2 only for limited contact. More specifically, as shown, a narrow, circumferential abutment surface (rear circumferential abutment surface 250) is created on the downstream axial surface of the outer sidewall 216 for abutting the carrier 234 (housing or shell). In this exemplary embodiment, the narrow front circumferential abutment surface 244 of the housing groove 246 and the narrow rear circumferential abutment surface 250 of the vapor surface are provided by forming a circumferential recess 252 in the carrier 234 (housing or shell) and by machining the bling 210 to create a circumferential depression 254 radially outward of the rear circumferential abutment surface 250 (vapor surface abutment surface), respectively.

[0020] Fig. 5 is one of the Fig. 4, but illustrating the installation of a V- or W-seal 256 between the carrier 234 and the outer sidewall 216 of the bling. A "C" seal may also be used. In traditional designs, sealing is not possible in most cases because the front part of the vane, where it meets the housing, has a wide gap and greater clearance due to the presence of the abutment element. Because the gap is now maintained at a tighter clearance and has a continuous surface, it is possible to incorporate a pressure-activated or spring-loaded seal when using the bling design.

[0021] The in the embodiments of the Fig. The ring / beam connection proposed in Figures 3 to 5 can also be applied to a single vane or singlet design as shown in Fig. 6. This is a single vane 310 that has been machined along with the airfoil 312 on its inner and outer sidewalls 314, 316. The outer wall 316 of the single vane is then welded to a fixed outer ring 358 using a front 360 and a rear 362 narrow axial weld in the form of low-heat welds to resemble a bling construction. The single vane and outer ring assembly is then inserted into a corresponding groove 346 of the carrier 334. The vane assembly (outer ring 358 and vane welded thereto) is not welded to the carrier 334. The vane assembly can move radially in the carrier groove. As in the embodiment of the Fig. 3 and Fig. 4, a narrow front circumferential contact surface 344 on the upstream side of the guide ring arrangement has been created by forming a recess in the housing groove 346 in the circumferential direction as at 352, and a narrow rear circumferential contact surface 350 (steam surface contact surface) has been created by machining a recess 354 in the fixed outer ring 358 on the downstream side of the guide ring arrangement.

[0022] The mechanical features of the transition area between the individual vane and the outer ring are used as an assembly and alignment device to provide improved reliability and risk reduction. In this regard, the mechanical lock between the outer ring 358 and the vanes 310 means that in the event of a vane failure, the rings and vanes cannot move downstream because a mechanical connection is present that prevents the assembly from failing due to pressure. In addition, the mechanical lock serves the purpose of a predetermined and repeatable weld lock. In this regard, the weld beam (assuming electron beam welding) would stop when it encounters the radial lock surface. A further advantage of the embodiment according to Fig. 6 is that the radially outer surface of the outer sidewall 316 of the vane is formed as a flat end instead of a more costly circumferentially cut end. The exemplary embodiment according to Fig. 6 has an inner ring 364 that is mechanically attached and brazed or welded to the inner sidewall 314 of the vane, or is simply mechanically attached to the vane.

[0023] A stator / beam connection in the bling embodiment for a steam turbine is provided with only limited contact at the front and rear circumferential abutment surfaces 244, 344, 250, 350 with the support (casing, shell) 234, 334 to facilitate assembly. There is also only limited contact at the front and rear circumferential abutment surfaces 244, 344, 250, 350 at strategic locations to both reduce downstream rolling or flexion of the inner section and facilitate disassembly due to the limited contact in areas where corrosion may occur.

[0024] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be recognized that the invention is not limited to the disclosed embodiment, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. List of reference symbols 10 Guide ring arrangement 12 blades 14 Inner Band 16 Outer band 18 Weld seam 20 Weld seam 24 Weld seam 26 Inner Ring 28 Outer Ring 110 Bling 130 contact element, small spacer 132 guide ring 134 housings 136 Steam surface, axial contact surface 138 connecting bolt hole 140 intermediate seal 142 Rotor 210 Bling 212 airfoil 214 Inner side wall 216 Outer side wall 234 carriers (housing, jacket) 236 steam area 244 front circumferential contact surface 246 groove 248 End wall 250 rear circumferential contact surface 252 recess 254 recess 256 Seal 310 single guide vane 312 airfoil 314 Inner side wall 316 Outer side wall 334 carriers 344 front circumferential contact surface 346 groove 350 rear circumferential contact surface 352 recess 354 recess 358 Outer Ring 360 Axial front weld 362 Axial rear weld 364 Inner Ring

Claims

[1] Turbine which has: a turbine nozzle assembly having at least one blade (212, 312) having an inner sidewall (214, 314) at a radially inner end of the blade (212, 312) and an outer sidewall (216, 316) at the radially outer end of the blade (212, 312); and an outer carrier (234, 334) having a radially inwardly opening groove (246, 346); wherein the outer side wall (216, 316) is adapted to slidably engage the groove (246, 346) in a radial direction while being prevented from moving in an axial direction relative to the groove (246, 346); a front contact region between the outer side wall (216, 316) and the outer support (234, 334) has a front circumferential abutment surface (244, 344) formed on an upstream, rearward-facing surface of the groove (246, 346), wherein the front circumferential abutment surface (244, 344) is formed by forming a circumferentially extending recess (252, 352) in the upstream, rearward-facing surface of the groove (246, 346) radially inward of the front circumferential abutment surface (244, 344) such that the upstream, rearward-facing surface of the groove (246, 346) contacts an opposite upstream axial surface of the outer side wall (216, 316) only at the front circumferential abutment surface (244, 344), wherein the front circumferential bearing surface (244, 344) has a radial dimension that is smaller than the radial dimension of the groove (246, 346); and a rear contact region between the outer side wall (216, 316) and the outer support (234, 334) has a rear circumferential abutment surface (250, 350) formed on a downstream axial surface of the outer side wall (216, 316), wherein the rear circumferential abutment surface (250, 350) is intended to bear against a radially inner region of the groove (246, 346), remote from the radially outer end wall (248) of the groove (246, 346), so that the front circumferential abutment surface (244, 344) is formed closer to a radially outer end wall (248) of the groove (246, 346) than the rear circumferential abutment surface (250, 350), wherein the rear circumferential abutment surface (250, 350) is formed by forming a circumferentially extending recess (254, 354) is formed in the downstream axial surface of the outer side wall (216, 316) radially outward from the rear circumferential bearing surface (250, 350), so that the downstream axial surface of the outer side wall (216,316) contacts an opposite axial surface of the outer carrier (234, 334) only at the rear circumferential contact surface (250, 350), the rear circumferential contact surface (250, 350) having a radial dimension which is smaller than the radial dimension of the groove (246, 346). [2] The turbine of claim 1, wherein the outer sidewall (316) includes an outer sidewall segment welded to an outer ring (358) received with the outer sidewall (316) in the groove (346). [3] The turbine of claim 2, wherein the outer ring (358) extends partially circumferentially and is welded to a plurality of outer sidewall segments of the outer sidewall (316). [4] The turbine of claim 1, further comprising a seal (256) between the rearward facing surface of the groove (246) and the upstream axial surface of the outer sidewall (216).

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