Patent Application
20120292860
This invention relates to seals in the combustion section of gas turbines, and particularly to upper and lower seals between the transition duct and the turbine inlet.
A typical industrial gas turbine engine has multiple combustion chambers in a circular array about the engine shaft in a “can annular” configuration. A respective array of transition ducts, also known as transition pieces, connects the outflow of each combustor to the turbine inlet. Each transition piece is a tubular structure that channels the combustion gas flow between a combustion chamber and the turbine section.
The interface between the combustion system and the turbine section occurs between the exit end of each transition piece and the inlet of the turbine. One or more turbine vanes mounted between outer and inner curved platforms is called a nozzle. Retainer rings retain a set of nozzles in a circular array for each stage of the turbine. Upper and lower seals on an exit frame of each transition piece seal against respective outer and inner retainer rings of the first stage nozzles to reduce leakage between the combustion and turbine sections of the engine. These seals conventionally have sufficient clearance in their slots to accommodate relative dynamic motion and differential thermal expansion between the exit frame and the retainer ring. For this reason, such seals may be called “floating seals”. However, such clearance increases gas leakage across the seal, thereby reducing engine efficiency.
The invention is explained in the following description in view of the drawings that show:
The upper seal 54 may include a second strip 70 that is cantilevered from the first strip 55 along a common edge 65 of the two strips. The second strip 70 may be generally parallel to the flat intermediate portion 66 of the first strip 55. The second strip 70 and the flat intermediate portion 66 together form a spring clamp that may slide over the upper rail 68. The second strip 70 has a free or distal edge with a bend that forms a ridge or bead 72 along at least a portion of the free edge that seals along a line of contact 74 with the forward surface of the upper rail 68. The second strip 70 elastically flexes against the forward surface of the upper rail 68 thus maintaining a constant seal along the line of contact 74 while allowing relative movement between the upper span 48A of the exit frame 48 and the outer retainer ring 52. An abrasion resistant coating or pad (not shown) may be attached or applied to the bead 72 or to the upper rail 68 along this interface.
The lower seal 78 may include a second strip 88 that is cantilevered from the edge of the first strip 79 along a common edge 81 of the two strips. The second strip 88 may be generally parallel to the flat intermediate portion 84 of the first strip 79. The second strip 88 and the flat intermediate portion 84 together form a spring clamp that may slide over the lower rail 86. The second strip 88 has a free or distal edge with a bend that forms a ridge or bead 90 along at least a portion of the free edge that seals along a line of contact 92 with the forward surface of the lower rail 86. The second strip 88 elastically flexes against the forward surface of the lower rail 86 thus maintaining a constant seal along the line of contact 92 while allowing relative movement between the lower span 48B of the exit frame 48 and the inner retainer ring 76. An abrasion resistant coating or pad (not shown) may be attached or applied to the ridge or bead 90 or to the lower rail 86 along this interface.
The first strip 55, 79 of each respective seal 54, 78 may be more rigid than the second strip 70, 88 due to greater thickness of the first strip 55, 79 and/or a different material than the second strip 70, 88. For example, the first strip may be a cermet material of a first thickness and the second strip may be a metal alloy of a second thickness thinner than the first thickness. The second strips 70, 88 may be attached to the first strips 55, 79 for example by spot welding, diffusion bonding, transient liquid phase bonding or other known means. Such fabrication allows different alloys and fabrication techniques to be used for the first strips 55, 79 and second strips 70, 88 for specialization or customization of the two parts. For example, a more rigid first strip 55, 79 can maintain the shape of the seal, while a more flexible second strip 70, 88 provides an elastic preload. For economy of fabrication, the first strips 55, 79 may be formed by casting, while the second strips 70, 88 may be formed by sheet metal die-cutting and stamping.
The resulting upper and lower seals 54, 79 provide consistent sealing during extreme thermal operating conditions while preventing undesirable load transfer between the combustion system and turbine system hardware. The spring-loaded clamp design provides pre-tension to firmly seal against the exit frame 48. Thus, these seals improve combustion system efficiency by reducing leakage. In order to maximize engine efficiency and minimize maintenance costs, the present upper and lower exit frame seals allow relative motion between the transition piece and the turbine inlet while maintaining sealing and wear characteristics.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
This application claims benefit of the 20 May 2011 filing date of U.S. Application No. 61/488,209 which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61488209 | May 2011 | US |
