Multi-shell turbine casing system   

Abstract: A multi-shell turbine casing system comprises at least one supporting cell joined to at least one retaining cell. The at least one supporting cell has at least one supporting cell wall and at least one truss section. The at least one retaining cell has at least one retaining cell wall. According to the invention, the at least one supporting cell wall and the at least one retaining cell wall form an outer shell and an inner shell. In an exemplary embodiment, the at least one truss section is oriented to provide support for the inner shell and is a triangular truss comprising cylindrical members joined by plate-type or box-type connectors. An exemplary truss section includes a plurality of horizontally oriented stabilizers joining the vertically oriented member to the outer shell. A multi-shell casing system may include additional truss sections, which may be joined to one another and to adjacent structure.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates generally to casing systems for gas turbines and more specifically to a lightweight, reinforced casing system for a low-pressure section of a power generating gas turbine.

Gas turbines used for power generating applications, such as steam turbines, have steadily increased in size over the years. Due to their increasing size, those skilled in the art have sought effective means for reducing the weight of power generating gas turbines. Therefore, while gas turbines once typically employed casing systems constructed entirely of cast iron, today\'s turbines frequently employ casing systems of welded, multi-shell construction. For example, an example of a casing system comprises an outer exhaust hood that is structurally coupled to an inner shroud.

The casing system of a gas turbine typically serves the purposes of supporting the engine\'s rotating turbo-machinery and the static structure that surrounds that machinery as well as containing the flow of working fluid, e.g., steam, passing through the gas turbine. In order to improve thermal efficiency, it is important that the static structure be dimensionally stable so as to reduce clearances between the turbo-machinery and the static structure. It is also important that the casing system that supports the rotating turbo-machinery and withstands differential pressures associated with expansion of the working fluid be sufficiently strong to bear loads associated with the turbo-machinery. As a result, while those skilled in the art have sought to reduce weight in turbine casing systems, it is also recognized that strength and rigidity are important design criteria.

In power generating (i.e., low-pressure or LP) turbine sections of gas turbines, the size and weight of the rotating turbo-machinery is typically greater than that of other engine sections. In addition, as the size of power generating turbines continues to grow, the weight of LP casing systems has also continued to increase. To provide the necessary strength with acceptable weight, designers have implemented structural reinforcements. Unfortunately, these reinforcements can cause obstructions to airflow, resulting in undesirable aerodynamic blockages.

Accordingly, those skilled in the art seek LP turbine casing systems with decreased weight and aerodynamic blockage.

According to the invention, a multi-shell turbine casing system comprises at least one supporting cell joined to at least one retaining cell. The at least one supporting cell has at least one supporting cell wall and at least one truss section. The at least one retaining cell has at least one retaining cell wall. According to the invention, the at least one supporting cell wall and the at least one retaining cell wall form an outer shell and an inner shell. Accordingly, a multi-shell casing system is provided with improved stiffness for withstanding differential pressures, sealing against leakages, and resisting compression under weight of turbo-machinery and with reduced axial aerodynamic blockage.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cut-away drawing of a reinforced casing system for a LP turbine;

FIG. 2 is a cut-away drawing of another exemplary truss-reinforced casing system for a LP turbine;

FIG. 3 is an isometric drawing of an exemplary plate-type reinforcement truss connector for a LP turbine casing system as described herein;

FIG. 4 is a cut-away drawing of another reinforced casing system for a LP turbine as is described herein;

FIG. 5 is a cut-away drawing of another exemplary truss-reinforced casing system for a LP turbine; and

FIG. 6 is an isometric drawing of an exemplary box-type reinforcement truss connector for a casing system as described herein.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals refer to like elements throughout the several views, FIG. 1 depicts a reinforced casing system 100 for a power generating (i.e., low-pressure, LP) turbine. Casing system 100 comprises first supporting cell 110, second supporting cell 120, first retaining cell 130, and second retaining cell 140. First supporting cell 110 is joined to first retaining cell 130 by flange 150. First retaining cell 130 is joined to second retaining cell 140 by flange 160. Second retaining cell 140 is joined to second supporting cell 120 by flange 170, and second supporting cell 120 is joined to first supporting cell 110 by flange 180. Once first supporting cell 110, second supporting cell 120, first retaining cell 130, and second retaining cell 140 are joined, walls of the cells combine to form a multi-shell casing system comprising outer shell 101 and inner shell 102.

As one skilled in the art will appreciate, outer shell 101 (also known as an exhaust hood) supports inner shell 102 (also known as an inner casing or inner shroud) for supporting static structure and sealing arrangements of a gas turbine and for constraining a flow of gas as it expands through the stages of the gas turbine. Thus, inner shell 102 forms a substantially enclosed envelope for containing the working fluid within the inner shell 102 despite differential pressure forces that arise as a result of expansion of the gas through the turbine stages. In addition, the elements forming inner shell 102 are configured to cooperate with one another so as to form a sealed surface suitable for substantially resisting gas leakages into or out of the envelope created by inner shell 102. Outer shell 101 provides support for inner shell 102 so as to improve its rigidity and reduce flexing and movement of inner shell 102, which could adversely affect turbine clearances and thereby impact performance and/or durability of an installed engine.

To improve strength of the casing system while reducing weight, casing system 100 includes stiffening plates that are oriented vertically to add stiffness and to resist compression under weight of static elements that are to be supported by the inner shell 102 of casing system 100 and to withstand gas pressures exerted on the inner shell. It should be appreciated that where design considerations call for strength in supporting weight, vertical orientations of the truss sections may be favored. However, where structural integrity is intended for resisting strain arising from differential pressure loads, other supporting orientations, such as horizontal and other intermediate angles, will be appropriate. The stiffening plates are also arranged and configured so as to improve structural integrity at locations of supporting pads that are positioned and configured to provide structural support for rotating turbo-machinery. This use of stiffening plates helps to facilitate the segmentation of casing system 100. Inner shell 102 is supported on outer shell 101 through the plate arrangement formed in casing system 100, particularly in first supporting cell 110, and second supporting cell 120. This arrangement is configured to provide sufficient stiffness to fortify inner shell 102 against differential pressure loads and other loads, e.g., the weight of the turbo-machinery, that inner shell 102 will support, i.e., vertically and/or in other orientations as discussed above.

As shown in FIG. 1, first supporting cell 110 includes five plates 111, 112, 113, 114, and 115. Second supporting cell 120 similarly includes five plates 121, 122, 123, 124, and 125. First retaining cell 130 is supported by first supporting cell 110 and plates 111-115. Second retaining cell 140 is supported by second supporting cell 120 and plates 121-125.

FIG. 2 is a cut-away drawing depicting another exemplary LP turbine casing system. As shown in FIG. 2, casing system 200 includes a truss arrangement configured to withstand differential pressures acting on its surfaces while also supporting its casing elements. Casing system 200 comprises first supporting cell 210, second supporting cell 220, first retaining cell 230, and second retaining cell 240. First supporting cell 210 is attached to first retaining cell 230 by flange 250. First retaining cell 230 is attached to second retaining cell 240 by flange 251. Second retaining cell 240 is attached to second supporting cell 220 by flange 252, and second supporting cell 220 is attached to first supporting cell 210 by flange 253. First retaining cell 230 and second retaining cell 240 are configured so as to maintain (e.g., by sealing) and withstand (e.g., through structural integrity) differential pressures resulting from expansion of the working fluid in the turbine. Flanges 250-253 may provide for sealing attachments by including a gasket, feather seals, or other sealant means between or adjacent to the flanges, thereby resisting, reducing or eliminating leakage through the flanges.

As shown in FIG. 2, first supporting cell 210 includes plates 211, 212, 213, and 214. Second supporting cell 220 similarly includes plates 221, 222, and 224, with another plate being hidden from view in this figure. In addition to plates 211-214, first supporting cell 210 includes first truss 260. Similarly, second supporting cell includes second truss 280. First retaining cell 230 is supported by first supporting cell 210, plates 211-214, first truss 260. Second retaining cell 240 is supported by second supporting cell 220, plates 221-224, and second truss 280.

In combination, walls of first supporting cell 210, second supporting cell 220, first retaining cell 230, and second retaining cell 240 form a multi-shell casing system comprising outer shell 201, also known as an exhaust hood, and inner shell 202. Inner shell 202 is supported on outer shell 201 through the plate arrangement formed in casing system 200, primarily in first supporting cell 210, and second supporting cell 220. This support arrangement is configured to provide sufficient stiffness to fortify inner shell 202 against the weight of the turbo-machinery and differential pressures that inner shell 202 will support, i.e., vertically and in other directions.

As shown in FIG. 2, first truss 260 comprises column 261, which is cylindrical and oriented vertically, and stabilizer 262, which is cylindrical and oriented in a vertical plane, at an angle relative to column 261 (i.e., rotated at an angle, e.g., approximately 30 degrees, from column 261). It should be appreciated that other cross-sections are contemplated for column 261 such as triangular, rectangular, square, trapezoidal, and oval. At their base ends, column 261 and stabilizer 262 are joined by base member 264, which is oriented horizontally and joined at one end to a base end of column 261 via connector 265, which is a plate-type connector, and at the other end to a base end of stabilizer 262 using another connector (not shown). At their distal ends, column 261 and stabilizer 262 are joined by connector 263, which is a plate-type connector. Thus, column 261, stabilizer 262, and base member 264 form a triangular truss section joined by plate-type connectors. It should be appreciated that other cross-sections for the truss 260, such as rectangular and trapezoidal sections, are also contemplated.

To enhance the rigidity and strength of first supporting cell 210, first truss 260 also includes a plurality of stabilizers 266, 267, 268 joining connector 263 to plates 213 and 214 and to cell wall 215, which forms a portion of outer shell 201. Similarly, a base end of first truss 260 includes a plurality of stabilizers 269, 270, 271 joining connector 265 to plates 213 and 214 and to cell wall 215. Thus, first truss 260 lends stability and strength to first supporting cell 210 with decreased weight and aerodynamic blockage. The reduced blockage associated with the trusses also helps to reduce or avoid vacuum pull issues that can arise from incorporation of structure within first supporting cell 210 and second supporting cell 220.

As shown in FIG. 2, second truss 280 comprises column 281, which is cylindrical and oriented vertically, and stabilizer 282, which is cylindrical and oriented in a vertical plane, but at an angle relative to column 281 (i.e., rotated at an angle, e.g., approximately 30 degrees, from column 281). At their base ends, column 281 and stabilizer 282 are joined by member 284, which is oriented horizontally and joined at one end to a base end of column 281 via connector 285, which is a plate-type connector, and at the other end to a base end of stabilizer 282 using another plate-type connector (not shown). At their distal ends, column 281 and stabilizer 282 are joined by connector 283, which is a plate-type connector. Thus, column 281, stabilizer 282, and member 284 form a triangular truss section joined by plate-type connectors. Again, it should be appreciated that other cross-sections, such as rectangular and trapezoidal sections, are also contemplated.

To enhance the rigidity and strength of second supporting cell 220, second truss 280 also includes a plurality of stabilizers 286, 287, 288 joining connector 283 to plates 221 and 222 and to cell wall 225, which forms a portion of outer shell 201. Similarly, a base end of second truss 280 includes a plurality of stabilizers 289, 290, 291 joining connector 285 to plates 221 and 222 and to cell wall 225. Thus, second truss 280 lends stability and strength to second supporting cell 220 with decreased weight and aerodynamic blockage.

As shown in FIG. 2, plate 214 and cell wall 215 of first supporting cell 210 include stress distribution panels 216, 217, 218, and 219 to distribute stresses where stabilizers 267, 268, 270, and 271 join with plate 214 and cell wall 215. Similarly, plate 221 and cell wall 225 of second supporting cell 220 include stress distribution panels to distribute stresses where stabilizers 287, 288, 290, and 291 join with plate 221 and cell wall 225. Finally, first truss 260 and second truss 280 include blocks 272 and 292, respectively, for transmitting load carried by first retaining cell 230 and second retaining cell 240.

As shown in FIG. 3, connector 300 is a plate-type truss connector and comprises plate 301, which is rectangular in shape when viewed in one direction. In this embodiment, thickness 302 of plate 301 is approximately one fifth as great as width 304 and approximately one twentieth as great as length 306. As shown in FIG. 3, column 310, which is cylindrical, is joined to connector 300 using any welding procedure such as a butt joint. Other members 320, 330, 340, and 350 are joined to connector 300 by inserting plate 301 into a notch in an end of each tube followed by welding. For example, member 350 is joined to connector 300 by inserting plate 301 into notch 351 in end 352 of member 350 and welding member 350 to plate 301 where they make contact.

As shown in FIG. 4, casing system 400 comprises first supporting cell 410, second supporting cell 420, third supporting cell 430, first retaining cell 440, second retaining cell 450, and third retaining cell 460. First supporting cell 410 is joined to first retaining cell 440 by flange 470. First retaining cell 440 is joined to second retaining cell 450 by flange 471. Second retaining cell 450 is joined to third retaining cell 460 by flange 472, and third retaining cell 460 is joined to third supporting cell 430 by flange 473. Third supporting cell 430 is joined to second supporting cell 420 by flange 474, and second supporting cell 420 is joined to first supporting cell 410 by flange 475. Once first supporting cell 410, second supporting cell 420, third supporting cell 430, first retaining cell 440, second retaining cell 450, and third retaining cell 460 are joined, walls of the cells combine to form a multi-shell casing system comprising an outer shell and an inner shell. First retaining cell 440 and second retaining cell 450 and third retaining cell 460, in combination, are configured so as to maintain (e.g., by sealing) and withstand (e.g., through structural integrity) differential pressures resulting from expansion of the working fluid in the turbine.

As shown in FIG. 4, first supporting cell 410 includes plates 411 and 412, which are oriented vertically to add stiffness to first supporting cell 410 and to resist compression under weight of turbo-machinery that is to be supported by first supporting cell 410 and the inner shell of casing system 400. Second supporting cell 420 includes plates 421, 422, and 423 that are oriented vertically to add stiffness to second supporting cell 420 and to resist compression under weight of turbo-machinery that is to be supported by second supporting cell 420. Third supporting cell 430 includes plates 431 and 432 that are oriented vertically to add stiffness to third supporting cell 430 and to resist compression under weight of turbo-machinery supported by third supporting cell 430. First retaining cell 440 is supported by first supporting cell 410 and plates 411 and 412. Second retaining cell 450 is supported by second supporting cell 420 and plates 421-423. Third retaining cell 460 is supported by third supporting cell 430 and plates 431 and 432.

FIG. 5 shows is a cut-away drawing of another exemplary LP turbine casing system of modular construction. As shown in FIG. 5, casing system 500 comprises first supporting cell 510, second supporting cell 520, third supporting cell 530, first retaining cell 540, second retaining cell 550, and third retaining cell 560. First supporting cell 510 is attached to first retaining cell 540 by flange 570. First retaining cell 540 is attached to second retaining cell 550 by flange 571. Second retaining cell 550 is attached to third retaining cell 560 by flange 572, and third retaining cell 560 is attached to third supporting cell 530 by flange 573. Third supporting cell 530 is attached to second supporting cell 520 by flange 574, and second supporting cell 520 is attached to first supporting cell 510 by flange 575.

In combination, walls of first supporting cell 510, second supporting cell 520, third supporting cell 530, first retaining cell 540, second retaining cell 550, and third retaining cell 560 form a multi-shell casing system comprising outer shell 501 and inner shell 502. Inner shell 502 is supported by outer shell 501, and the plate arrangement formed in first supporting cell 510, second supporting cell 520, and third supporting cell 530 reinforces casing system 500. This arrangement is configured to provide sufficient stiffness to fortify inner shell 502 and to resist excessive deformation under loads that are to be supported by inner shell 502. For example, inner shell 502 is configured so as to maintain (e.g., by sealing) and withstand (e.g., through structural integrity) differential pressures resulting from expansion of the working fluid in the turbine. Thus leakages are to be prevented through sealing, and turbine hardware, bearings, and sealing arrangements are supported.

As shown in FIG. 5, first supporting cell 510 includes plates 511 and 512, which are oriented vertically to add stiffness to first supporting cell 510 and to resist compression under weight of turbo-machinery supported by first supporting cell 510. Second supporting cell 520 includes plates 521 and 522 and trusses 523, 524, and 525, which are oriented vertically to add stiffness to second supporting cell 520 and to resist compression under weight of turbo-machinery supported by second supporting cell 520. Third supporting cell 530 includes plates 531 and 532, which are oriented vertically to add stiffness to third supporting cell 530 and to resist compression under weight of turbo-machinery supported by third supporting cell 530. First retaining cell 540 is supported vertically by first supporting cell 510 and plates 511 and 512. Second retaining cell 550 is supported vertically by second supporting cell 520 and plates 521 and 522 and trusses 523, 524, and 525. Third retaining cell 560 is supported vertically by third supporting cell 530 and plates 531 and 532.

As shown in FIG. 5, each truss 523, 524, and 525 comprises a triangular central truss section oriented in a vertical plane. Each central truss section comprises a vertically-oriented tubular column, an angled tubular stabilizer that is rotated at an angle, e.g., approximately 30 degrees from vertical, and a horizontal base member. For example, truss 524 comprises column 581, which is cylindrical and oriented vertically; stabilizer 582, which is cylindrical and oriented at an angle approximately 30 degrees from vertical; and base member 583, which is oriented horizontally. At their base ends, column 581 and stabilizer 582 are separated by base member 583, which is joined at one end to a base end of column 581 via connector 585, which is another box-type connector, and at the other end to a base end of stabilizer 582 using another box-type connector (not shown). At their distal ends, column 581 and stabilizer 582 are joined by connector 584, which is a box-type connector. Thus, column 581, stabilizer 582, and base member 583 form a triangular truss section joined by box-type connectors.

To enhance the rigidity and strength of second supporting cell 520, each truss 523, 524, 525 includes a plurality of stabilizers, which join each box-type connector to adjacent structure of second supporting cell 520. For example, truss 524 also includes a plurality of stabilizers 586, 587, 588 joining connector 584 to the box-type connectors of trusses 523, 525 and to cell wall 529, which forms a portion of outer shell 501. Similarly, a base end of truss 524 includes a plurality of stabilizers 589, 590, 591 joining connector 585 to adjacent box-type connectors of trusses 523, 525 and to cell wall 529. Plate 521 and cell wall 529 of second supporting cell 520 include stress distribution panels for coupling to stabilizers of trusses 523, 524, 525 and for distributing stresses and transmitting loads carried by those stabilizers. Thus, trusses 523, 524, and 525 lend stability and strength to second supporting cell 520 with decreased weight and aerodynamic blockage.

As shown in FIG. 6, connector 600 is a box-type reinforcement truss connector for a turbine casing system. Connector 600 comprises a rectangular or cubic box wherein thickness 602 and width 604 and depth 606 are approximately equal. As shown in FIG. 6, column 610 is joined to connector 600 using either a welded butt joint or by threaded insertion into a matching hole in box 620. Other members 630, 640, 650, and 660 are joined to connector 600 in a similar fashion. Thus, connector 600 provides a strong connector for joining the members of trusses such as the trusses of FIGS. 2 and 5.

Accordingly, a multi-shell casing system for low pressure stages of gas turbines is provided with improved stiffness for resisting loads imposed on the casing system such as differential pressure loads, loads imposed by supporting static structure of a gas turbine and, where desirable, loads from weight of turbo-machinery supported by the casing system. This improved system also reduces the amount of structural materials used for specific designs, resulting in weight and cost benefits. In addition, the improved system reduces axial aerodynamic blockage, resulting in improvements in cycle performance. Finally, the invention helps to reduce or avoid vacuum pull issues associated with conventional plate stiffening systems.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.