Full hoop casing for midframe of industrial gas turbine engine

A can annular industrial gas turbine engine, including: a single-piece rotor shaft spanning a compressor section (82), a combustion section (84), a turbine section (86); and a combustion section casing (10) having a section (28) configured as a full hoop. When the combustion section casing is detached from the engine and moved to a maintenance position to allow access to an interior of the engine, a positioning jig (98) is used to support the compressor section casing (83) and turbine section casing (87).

FIELD OF THE INVENTION

The present invention relates to an industrial gas turbine engine outer casing. In particular, this invention relates to a full hoop outer casing for a combustion section of an industrial gas turbine engine.

BACKGROUND OF THE INVENTION

Conventional can-annular industrial gas turbine engines have a rotor shaft that spans the compressor section, the combustion section, and the turbine section, and which is constructed as a single piece. High pressures and temperatures contained by the industrial gas turbine engine outer casing provide motivation to keep the outer casing as small as possible. This leads to outer casing designs that follow the shape of the internal components of the engine. The overall shape of the industrial gas turbine engine, and the fact that the outer casing mimics the overall shape, make it impossible to create a single casing that encloses the entire engine. Consequently, the outer casing is usually an assembly of different casing sections assembled about the engine internal components.

In an industrial gas turbine engine where a single piece rotor shaft spans different engine sections, the casing sections are usually split into an upper half and a lower half to facilitate assembly and disassembly of the engine. Leaving the casing bottom halves assembled while removing the top halves also enables access to interior portions of the engine while providing a structural backbone that holds components of the engine in place during maintenance, such as when only certain internal components may be removed and replaced. As a result, conventional industrial gas turbine engines typically have an upper and lower casing that may roughly correspond to a compressor section of the engine, an upper and lower casing that may roughly correspond to a combustion section, and an upper and lower casing that may roughly correspond to a turbine section.

This configuration yields a horizontal joint where the upper and lower casings meet that runs along each side of the industrial gas turbine engine. Further, a circumferential joint is formed around the engine where axially adjacent casings abut. All joints present an opportunity for leakage leading to less efficient engine performance. Furthermore, casings are thicker where there are joints and thinner where there are no joints, leading to the potential for differential thermal expansion. To mitigate the effect of differential thermal expansion, longer startup and shut down times may be used. Further, differential thermal expansion during any transient temperature changes may cause an ovaling of the casing. This ovaling may be detrimental to internal components which count on a circular shape for the casing for proper performance, such as to maintain a desired blade clearance or for proper seal performance. Further, where the horizontal joint and a circumferential joint meet, a four way joint is formed. Four way joints are particularly challenging with respect to mechanical design considerations.

Current industrial gas turbine engine technology provides a maximum pressure ratio of about 22:1. That is, the compressor compresses air to a maximum of approximately 22 times the pressure of ambient air before the air is delivered to the combustors. The mechanical compression alone increases the temperature of the compressed air to approximately 440° C. Conventional split casings made of steel and within the combustion section, where the highest pressures and temperatures occur, may be near their maximum mechanical capacity when at 22 atmospheres and approximately 440° C. However, industrial gas turbine engines operate more efficiently with greater pressure ratios. Thus, conventional industrial gas turbine engine casing designs may inhibit the progress of industrial gas turbine engine development

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have devised an innovative improved outer casing for a can-annular industrial gas turbine engine; i.e. an engine having a single piece rotor shaft that spans a compressor section, a combustion section including a plurality of can combustors, and a turbine section. The combustion section casing includes at least a first section that is configured as a full hoop. There may be a second section that may also be configured as a full hoop, or may be configured as a split casing. A full hoop combustion section outer casing provides many advantages. A full hoop casing has no horizontal joint, reducing the opportunity for leakage and associated reduced operating efficiency of the industrial gas turbine engine. The four way joint of conventional industrial gas turbine engine casing configurations is eliminated, leaving at most a three way joint. A resulting three way joint may possess significantly greater structural resiliency than a four way joint, and thus is a mechanical improvement over the four way joint. Further, a casing configured as a single piece, full hoop, will be able to handle greater hoop (circumferential) stresses. This permits greater design flexibility in the size and shape of the combustion section outer casing, and also permits industrial gas turbine engine designs with a pressure ratio of over 22:1, which is approximately a design limitation of conventional industrial gas turbine engine outer casings. Still further, a full hoop casing avoids the problem of where to place a horizontal joint in industrial gas turbine engines utilizing certain advanced combustion system designs that may place combustors so close together that there may be little room for horizontal joints of conventional design.

With the innovative design, split compressor and turbine casings may remain, and the combustion section casing may be configured such that the compressor and turbine casing sections can be removed in the conventional manner, thereby permitting access to the compressor and turbine for maintenance operations. In an embodiment, the combustion section hoop casing may be axially positionable. For example, the entire combustion section casing or a section of the combustion section casing may be configured such that it can be moved to permit access to the combustion section. The movement may be an axial repositioning from an operating position, where the combustion section casing is attached to the turbine section casing, to a maintenance position forward (upstream with respect to an overall flow of working fluids through the industrial gas turbine engine). In the maintenance position, access to the combustion section is possible.

In some cases a conventional industrial gas turbine engine is supported via a compressor base that supports the compressor outer casing, and a turbine base that supports the turbine outer casing. During maintenance of conventional industrial gas turbine engines, the lower half of the combustion section casing remains in place, and thereby serves as part of a backbone of outer casing lower halves that holds components of the industrial gas turbine engine in relative position with each other. When a combustion section full hoop outer casing is moved from an operating position to a maintenance position, the combustion section casing and the turbine section casing necessarily are disconnected from each other. As a result, the compressor section lower casing, the turbine section lower casing, and associated components would not be held in place with respect to each other. The present inventors have also devised a positioning jig to provide a temporary connection between the compressor section casing and the turbine section casing. The positioning jig could connect to existing attachment points in the casing lower sections when the upper sections are removed, or could connect to dedicated attachment points in either half of the casing sections, or both, or at any other location capable of transferring the necessary mechanical loads.

In addition to a positioning jig, additional supports may be used to provide additional support. This additional support may prevent, for example, either the compressor section or the turbine section from rotation about their respective bases. These additional supports may be in any form appropriate for carrying the desired mechanical loads, including for example simple jacks.

Turning to the drawings,FIG. 1shows a schematic representation of a partial longitudinal cross section of a combustion section outer casing10and portions of an outer casing upper half12associated with a compressor section and an outer casing upper half14associated with a turbine section in an operating position. The combustion section outer casing10may be secured to the compressor section outer casing upper half12at a forward interface16. The forward interface16may include a compressor section outer casing upper half aft flange18secured to a combustion section outer casing forward flange20, however other fastening means may be employed. Likewise, the combustion section outer casing10may be secured to the turbine section outer casing upper half14at an aft interface22. The aft interface22may include a combustion section outer casing aft flange24secured to a turbine section outer casing upper half forward flange26. The embodiment shown permits the compressor section outer casing upper half12and/or the turbine section outer casing upper half14to be removed in a conventional manner while leaving the combustion section outer casing10in place.

In an embodiment, the combustion section outer casing10includes a first section28and a second section30. The first section28may be disposed adjacent combustors (not shown) and transition ducts (not shown) with respect to a longitudinal axis32of the industrial gas turbine engine which is the axis of rotation of the engine shaft (not shown). The first section28may entirely enclose the combustors and transition ducts, or the first section28may include combustor openings34through which combustors may extend once the industrial gas turbine engine is fully assembled. These combustor openings34may be angled with respect to the longitudinal axis32and/or angled with lines extending radially (not shown) from the longitudinal axis32. In an embodiment, the combustors may be secured to the combustion section outer casing10.

In an embodiment, the transition ducts may lie entirely radially inward of radial clearance line36. In embodiments where the transition ducts are positioned within the radial clearance line36, the first section28is free to move axially forward with respect to the engine from the operational position as shown, to a maintenance position. This is possible because the radially extreme portion38of the first section that includes the combustor openings34downstream to a downstream end40of the combustion section outer casing10would be able to clear the transition ducts radially.

Embodiments like this may be used in emerging can annular industrial gas turbine engine technology that employs advanced transitions39, where the advanced transitions are configured to properly orient and accelerate combustion gases received from a respective combustor and deliver them directly onto a first row of turbine blades. In these designs, the advanced transition may deliver the combustion gases tangentially to the turbine inlet annulus (not shown). As a result, the conventional first row turbine guide vanes typically used to orient and accelerate combustion gases are no longer needed. The advanced transition ducts may then be supported by the turbine vane carrier41(shown schematically) which would no longer need to support the first row of turbine vanes. Since the advanced transitions are supported by structure unrelated to the combustion section outer casing10, the combustion section outer casing10is free to move to the maintenance position without removing the advanced transitions. This represents a reduction in maintenance costs when the combustion section outer casing10must be moved to access other parts of the combustion section. However, the combustor openings34may be configured (e.g. large enough) to permit an advanced transition to be removed through the combustor openings34without having to move the first section28to the maintenance position.

In embodiments including a second section30, the second section30may be disposed between the first section28and the compressor section casing upper half12and a compressor section casing lower half (not shown). The second section30may be configured as a split ring or a full hoop. In instances where the second section30is configured as a split ring, it may be removed in a manner similar to other split rings, or it may simply remain in place. In instances when the second section30is configured as a full hoop, it cannot be removed unless the rotor shaft is also removed. In the configuration shown inFIG. 1, a combustion section outer casing10includes an integral interface42. At the integral interface42, an aft end44of the second section30interfaces with a fore end46of the first section28. In particular, in the embodiment shown, a radially oriented, annular shaped first section surface48abuts a radially oriented, annular shaped second section surface50when the first section28is in the operating position. This abutment forms an annular seal51, and together with the abutment at the aft interface22, defines the operating position for the first section28. In order for the first section28to move from the operation position (to the left in the figure) it is clear that a most radially inward surface52of the second section30must clear the most radially outward surface54of the compressor section outer casing upper half12and the compressor section outer casing lower half (not shown) by a clearance amount54, at least to the extent of axially overlapping portions of the combustion section outer casing10and the compressor section outer casing halves when in the maintenance position. Likewise, a most radially outward surface56of the aft end44must be disposed so as to clear the first section28when the first section28is moved from the maintenance position.

It can also be seen in the illustrated embodiment that the second section30includes an axially extending portion58. The axially extending portion58extends more or less parallel to the industrial gas turbine engine longitudinal axis32from the compressor section outer casing. This is done to minimize a longitudinal profile of a radius60of an inner surface62of the second section30and an inner surface64of the first section28, which in turn decreases an amount of area of the first section28and the second section30exposed to the pressure of the compressed air within the engine. By minimizing the amount of surface area exposed to the elevated pressure, forces exerted by the compressed air on the first section28and the second section30are minimized, and this permits minimizing a structural bulk of these sections. Portions of the first section28with a larger radius60exist for purposes of clearing the aft end44of the second section30, and thus are incorporated and are designed to accommodate the increased forces resulting from the increased radius60.

FIG. 2schematically depicts an industrial gas turbine engine80including a compressor section82incorporating a compressor section outer casing83, a combustion section84, and a turbine section86incorporating a turbine section outer casing87. The compressor section outer casing83includes the compressor section outer casing upper half12and a compressor section outer casing lower half88. The combustion section84includes a combustion section outer casing10, which is shown in a maintenance position. The turbine section outer casing87includes the turbine section outer casing upper half14and a turbine section outer casing lower half90. The embodiment ofFIG. 2shows a single piece combustion section outer casing10. In a multi piece embodiment such as inFIG. 1, the second section30would remain in place and only the first section28would be moved forward as depicted inFIG. 2.

Also shown are a compressor section base92configured to support the compressor section82and a turbine section base94configured to support the turbine section86. In a conventional industrial gas turbine engine80there may be no other supports and thus a conventional combustion section outer casing lower half (not shown) must be secured between and to the compressor section outer casing lower half88and the turbine section outer casing lower half90in order to hold the assembly in place. However, with the present invention, when the combustion section outer casing10is in the maintenance position, gap96is formed between the compressor section outer casing lower half88and the turbine section outer casing lower half90. Consequently, a positioning jig98may be implemented in order to hold the assembly in place when the combustion section outer casing10is in the maintenance position. The positioning jig98may span a length of the industrial gas turbine engine80to secure the compressor section82in position relative to the turbine section86. The positioning jig98may be connected by any means known to those of ordinary skill in the art, including by fastening into existing flange connection points etc. The positioning jig98then prevents relative movement of the compressor section82and/or the turbine section86along the industrial gas turbine engine longitudinal axis32.

In addition to positioning jigs98, additional supports may be utilized to prevent other relative movement. For example, a compressor section additional support100may provide additional support for the compressor section82, and a turbine section additional support102may likewise provide additional support for the turbine section86. Without the compressor section additional support100, gravity may urge the compressor section82to rotate about a compressor section base connection point104where the compressor section base92connects to the compressor section82, or to rotate about a compressor section base grounding point106where the compressor section base92connects to the ground, or both. Such rotation may at a minimum disturb a positioning of the compressor section82relative to the turbine section86. The supports may take any form known to those of ordinary skill in the art, including but not limited to jacks etc.

Likewise, without the turbine section additional support102, gravity may urge the turbine section86to rotate about the a turbine section base connection point108where the turbine section base94connects to the turbine section86, or to rotate about a turbine section base grounding point110where the turbine section base94connects to the ground, or both. Such rotation may at a minimum disturb a positioning of the turbine section86relative to the compressor section82. Installing the compressor section additional support100and the turbine section additional support102may prevent such tendency for a section to rotate, and thus provide rotational stability in addition to the axial stability provided by the positioning jig98. The axial stability together with the rotational stability will suffice to hold the compressor section82and the turbine section86in position relative to each other when the combustion section outer casing10not connected to either in an operating position, but is instead in a maintenance position. Maintenance operations are thus made more secure with minimal additional effort.

It has been shown that the innovative hoop structure combustion section casing10provides a stronger casing that may permit higher pressure of compressed air, which may in turn allow for more efficient industrial gas turbine engine designs. Further, the design may reduce leakage and may permit combustion section casings of lighter design due to the increased structural strength. The combustion section casing design also allows for easy maintenance of combustion section components in an operating position and may include additional positioning components that enable the combustion section casing to be moved to a maintenance position where even greater access to the combustion system components is realized, while still maintaining the compressor and turbine sections in a fixed relative position. Consequently, the design disclosed herein represents an improvement in the art.