Patent Publication Number: US-7712302-B2

Title: Crossfire tube assembly for gas turbines

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a crossfire tube assembly for gas turbines and particularly relates to a crossfire tube assembly having a gasket/bellows combination for air tight sealing of the crossfire tube assembly. 
   As well known, combustors in stationary land based gas turbines are interconnected by crossfire tubes. These crossfire tubes enable initial ignition of a combustor adjacent to an ignited combustor thereby eliminating the need for separate ignition, and corresponding elements for enabling separate ignition, from each combustor. Crossfire tubes are well known in the gas turbine environment. See for example U.S. Pat. Nos. 4,249,372 and 6,606,865. In the system disclosed in the latter patent, a bellows with annular rings at opposite ends is arranged between combustor flanges. While those bellows assemblies have performed and have demonstrated significant improvement over prior crossfire tube assemblies, the sealing capability of prior crossfire tube assemblies of this type has been brought into question. Absent an air tight seal, hot gases escaping from the crossfire tubes may damage adjacent parts of the turbine. Accordingly there has been demonstrated a need for an improved sealing system for a crossfire tube assembly whereby the crossfire tube assembly is completely airtight with effective thermal disassociation between the hot gases flowing through the crossfire tube assembly and adjacent components of the turbine. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In a preferred embodiment of the present invention, there is provided a crossfire tube connection between casing bosses of adjacent combustors in a gas turbine comprising a pair of annular metallic inserts engaged with respective casing bosses, each annular metallic insert formed with an annular recess; a bellows assembly including a bellows having a plurality of axially-spaced convolutions about an axis; and flanges sealed to respective opposite ends of the bellows; gaskets located in respective ones of the annular recesses in sealing engagement with the flanges and the annular metallic inserts at respective opposite ends of the bellows assembly; and means securing the flanges to the casing bosses at opposite ends of the bellows assembly whereby the crossfire tube is sealed between adjacent combustors. 
   In another preferred embodiment, there is provided a combustor and crossfire tube assembly comprising a pair of combustor bosses spaced from one another; each of the bosses including an annular seat; a bellows assembly between the bosses and including a bellows and annular flanges sealed to the bellows at respective opposite ends of the bellows; gaskets between the seats and the flanges at respective opposite ends of the bellows assembly for sealing between the flanges and the seats; the flanges and the bosses having annular bolt rings and bolts securing the flanges and bosses to one another. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a bellows type outer crossfire tube assembly in accordance with a preferred embodiment of the present invention with parts in full and partially assembled positions; and 
       FIG. 2  is a fragmentary perspective view with parts broken out in cross-section of the assembly of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings particularly to  FIG. 1 , there is illustrated an outer crossfire tube assembly generally designated  10  arranged between a pair of casing bosses  12  of adjacent combustors in a gas turbine. The bosses  12  are annular in nature and have facing bolt circle holes for securement of the crossfire tube assembly between the casing bosses. Arranged between the casing bosses  12  is an outer crossfire bellows assembly generally designated  16 . Bellows assembly  16  includes a bellows  18  having inner and outer diameters defined by axially spaced convolutions  20 . The bellows assembly  18  lies generally co-axial with and between the casing bosses  12  and terminates at opposite ends in cylindrical sections  22 . A pair of annular flanges  24  are provided, each having an internal cylindrical opening  26  for receiving an end  22  of the bellows  18 . The ends  22  of bellows  18  are sealed to the flanges  24 , for example, by fillet type welds between the bellow&#39;s ends and the flanges forming an airtight seal. 
   Also illustrated in the drawing figures is a pair of annular inserts  28  received in recessed annular shoulders  30  of the casing bosses  12 . The inserts  28  have an interior cylindrical opening  32  in excess of the diameter of the ends of the bellows. The inserts  32  also include an annular recess  34  facing the bellows assembly  16 . A spiral gasket  36  is provided in a recess  34  between the annular face of the flange  24  and the insert  28 , the recess  34  being preferably located on the inserts  28 . The gasket  36  is formed of a thermicullite material commercially available. 
   Additionally, the annular surfaces of the flanges  24  which axially face and align with one another also mount a sleeve  37 . Particularly, the sleeve is formed of a pair of telescoping concentric cylinders  38  and  40 , each secured at one end particularly by welding to the flange  24 . As illustrated in  FIG. 1 , the cylindrical sleeve  38  is larger in diameter than the cylindrical sleeve  40  such that the sleeves may telescope relative to one another on movement of the combustor bosses  12  relative to one another. Also, there is an inner crossfire tube, not shown, which passes between the combustor bosses and axially along the bellows assembly  16  and through which the actual ignition gases flow for igniting the adjacent combustor from a previously ignited combustor. It will also be appreciated that in final assembly, the bellows assembly is secured to the casing bosses by bolt circles and bolts  50  passing through the bolt openings through the flanges  24  for reception in bolt sockets in the casing bosses. Consequently, when the opposite ends of the bellows assembly is secured to the combustion bosses, the flanges bear against and compress the gaskets  36  into sealing engagement with the inserts  28 . 
   It will appreciated that the inserts  28  may be formed integral with the casing bosses  12 . Thus for original equipment manufacture, the inserts may comprise part of the casing bosses and form a seat for the gaskets  36 . For retrofit applications, the inserts  28  are welded to the interior of the casing bosses. 
   With the foregoing described arrangement, it will be appreciated that the bellows assembly can be readily and easily installed between the combustor casing bosses and removed to replace the seals as needed. Thus, by unbolting the flanges  24  from the casing bosses, the bellows assembly  16  can be removed from between the bosses. While the advantages of ready and easy installation and removal of the bellows assembly are obtained, it will also be appreciated that an airtight seal is provided between the casing bosses. The seal in the retrofit configuration illustrated with discrete inserts  28  is provided by the welding of the seats  28  to the casing bosses, the welding of the opposite ends of the bellows  18  to the flanges  24  and the compression of the gaskets  36  between the flanges  24  and the inserts  28 . Thus only the spirally wound gasket  36  is required for sealing the bellows assembly to either the insert  28  or the seat in the bosses when the bosses and the inserts are formed integrally as in an original equipment manufacturer. 
   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 understood that the invention is not to be 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.