Abstract:
A crossfire tube assembly with telescoping inner and outer crossfire tubes with an enhanced cooling mechanism for connecting adjacent combustors in a gas turbine is disclosed. The enhanced cooling configuration includes a plurality of channels formed in the telescoping region of the inner and outer crossfire tubes of the assembly to improve heat transfer and reduce local operating temperatures such that component life is extended.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to gas turbine combustors and more specifically to an improved cooling scheme for a crossfire tube assembly, which interconnects adjacent can-annular combustors.  
           [0003]    2. Description of Related Art  
           [0004]    A combustion system for a gas turbine engine, especially those used to generate electricity, are comprised of a number of cylindrical combustors disposed in an annular array about the turbine, commonly referred to as a can-annular combustor. It is a common practice to join these individual combustors by a conduit referred to as a crossfire tube assembly, comprised of a plurality of tubes, to aid in cross ignition between combustors. In operation a combustor with an ignition source, typically a spark plug, ignites the fuel/air mixture and the sudden increase in pressure causes the reaction to pass through the crossfire tube assembly into the adjacent combustor, there by igniting the fuel/air mixture in the adjacent combustor. This process eliminates the need for ignition sources in each combustor.  
           [0005]    The crossfire tube assembly engages the adjacent combustors and is held in place at each end by a fastening means such as a retaining clip. Each of the tubes, which together in a typical crossfire tube assembly, mate to each other at their respective free ends to allow combustion gases to pass between adjacent combustors. This intersection is typically a telescoping arrangement and due to assembly tolerances and operating issues this intersection is not adequately cooled and becomes the point of maximum operating temperature. The high temperatures cause premature deterioration of the tubes and in some cases burning of the free ends of the crossfire tubes within the assembly. Premature deterioration and burning of the crossfire tubes can cause damage to the surrounding combustion hardware as well as  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0006]    It is an object of the present invention to provide a crossfire tube assembly for connecting adjacent combustors in a gas turbine engine.  
           [0007]    It is yet another object of the present invention to provide a crossfire tube assembly having an improved cooling configuration to reduce component deterioration due to long-term exposure to elevated temperatures.  
           [0008]    In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross section view of the crossfire tube assembly of the prior art.  
         [0010]    [0010]FIG. 2 is a perspective view of the hollow inner crossfire tube in accordance with the preferred embodiment of the present invention.  
         [0011]    [0011]FIG. 3 is a partial cross section view of the crossfire tube assembly shown installed in the combustor in accordance with the preferred embodiment of the present invention.  
         [0012]    [0012]FIG. 4 is a detail view in cross section of the telescoping arrangement of the inner and outer tubes in accordance with the preferred embodiment of the present invention.  
         [0013]    [0013]FIG. 5 is an end view, taken from FIG. 2, of the inner crossfire tube in accordance with the preferred embodiment of the present invention.  
         [0014]    [0014]FIG. 6 is a perspective view of the hollow inner crossfire tube in accordance with an alternate embodiment of the present invention.  
         [0015]    [0015]FIG. 7 is a detail view in cross section of the telescoping arrangement of the inner and outer tubes in accordance with an alternate embodiment of the present invention.  
         [0016]    [0016]FIG. 8 is a perspective view in cross section of the outer tube in accordance with an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to FIG. 1, a crossfire tubes assembly  10  in accordance with conventional design is shown. The assembly consists of an inner tube  11  and an outer tube  12 . Inner tube  11  is telescopically received within outer tube  12 . Combustion gases pass through passage  13 , which is formed by the inner and outer tubes, and exit into adjacent combustors (not shown) at tube ends  14  and  15 . Crossfire tube assembly  10  is contained within a generally annular plenum (not shown), which contains compressor discharge air for cooling. Ideally, cooling air passes along the outer wall  16  of inner tube  11  and into the telescoping region  17  of crossfire tube assembly  10 , where the air continues to cool the outer wall  16  of inner tube  11 . It has been determined through engine operations that this telescoping region  17  of crossfire tube assembly  10  is in fact not adequately cooled and excessive damage, including melting of inner tube  11  at this location, has been seen. Premature failure of these components requires earlier replacement and additional maintenance costs of the engines. The present invention, as described below, seeks to overcome these issues by providing an improved cooling configuration that directs cooling air along the inner tube outer wall, especially within the telescoping area between the inner and outer crossfire tubes.  
         [0018]    Referring now to FIGS. 2 and 3, the crossfire tube assembly  30  of the present invention is shown. Crossfire tube assembly  30  includes an inner hollow tube  31  having a first inner end  32 , a second inner end  33 , a first inner wall  34  having a first axis A-A therethrough. Inner tube  31  further includes a first outer wall  35  coaxial with and radially outward from first inner wall  34 , where the first outer wall  35  has a first diameter D1 at the second inner end  33 . First inner wall  34  and first outer wall  35  thereby form a first thickness  38 , typically at least 0.050 inches. The inner tube  31  also contains a plurality of first air purge holes  36 , which are preferably proximate the first inner end  32 .  
         [0019]    Additionally, inner tube  31  contains a plurality of channels  37  and  38  that extend along the first outer wall  35  proximate the second inner end  33  of inner tube  31 .  
         [0020]    [0020]FIG. 3 shows, in detail, the hollow outer tube  41  of crossfire tube assembly  30 . Outer tube  41  has a first outer end  42 , a second outer end  43 , a second inner wall  44  and a second outer wall  45  coaxial with a radially outward from second inner wall  44 . Second inner wall  44  has a second diameter D2 at first outer end  42 . Second inner wall  44  and second outer wall  45  thereby form a second thickness  48 , typically at least 0.050 inches. Outer tube  41  further includes a plurality of second air purge holes  46  which are preferably proximate the second outer end  43 .  
         [0021]    Inner tube  31  is telescopically received in outer tube  41  to form crossfire tube assembly  30  due to the fact that the first diameter D1 of inner tube  31  is slightly less than the second diameter D2 of outer tube  41 , such that the second inner end  33  of inner tube  31  is located radially inward from second inner wall  44  of outer tube  41 . Therefore, the first inner wall  34  communicates with the second outer wall  45  via channels  37  and  38 .  
         [0022]    Cooling the ends of the crossfire tubes is an important aspect to maintaining their integrity given the harsh operating conditions. The air purge holes,  36  and  46 , of inner tube  31  and outer tube  41 , respectively, consist of at least two holes which are preferably equally spaced about first end  32  of inner tube  31  and second end  43  of outer tube  41 . Preferably, the air purge holes,  36  and  46 , are at least 0.050 inches in diameter.  
         [0023]    In order to adequately cool the telescoping connection of inner tube  31  to outer tube  41 , channels  37  and  38  are formed along first outer wall  35  of inner tube  31 , such that cooling air can pass along the telescoping walls. This configuration is detailed further in FIG. 4. In the preferred embodiment, channels  37  and  38  extend along first outer wall  35  in a direction such that they are parallel to axis A-A of inner tube  31 . Channels  37  and  38  are separated into two distinct rows R1 and R2, respectively, separated by a section of first outer wall  35  of inner tube  31  (see FIG. 2), where Row R2 is proximate the second inner end  33 . The second inner end  33  of inner tube  31  is cooled by compressor discharge air, shown by arrows  50  in FIG. 4. Compressor discharge air  50  passes along second outer wall  45  of outer tube  41  and along the first outer wall  35  of inner tube  31 , where it then enters channels  37  and  38  of rows R1 and R2, thereby further cooling first outer wall  35 . Cooling air  50  then flows along second inner wall  44  to further cool that wall before dissipating into the combustor.  
         [0024]    In order to provide the most efficient cooling, channels  37  and  38  should have an axial length CL, in a direction parallel to axis A-A of at least 0.0.50 inches, a circumferential width CW of at least 0.010 inches and a radial depth RD of at least 0.010 inches (see FIG. 5). Although not shown in the figures, it is to be understood that each of the channels  37  and  38  may have a circumferential length in addition to the axial length CL, resulting in channels that “spiral” about the tubes  31  and  41  on which they are located. Such spiral channels may be used in those situations where increased heat transfer to the cooling air is desired. In order to provide additional heat transfer and increase the effectiveness of the compressor discharge cooling air  50 , the channels  37  and  38  are offset circumferentially relative to each other by an angle ∝, such that the cooling air from channels  37  does directly enter a channel  38 . This offset relationship of the channels  37  and  38  in Rows R1 and R2 is shown in detail in FIG. 5. The preferred amount of angular offset is at least 5 degrees, but is dependent upon the amount of cooling required along inner tube  31 .  
         [0025]    An alternate embodiment of the present invention is shown in FIG. 6. Inner tube  61 , as with the preferred embodiment, has a first inner end  62 , a second inner end  63 , a first inner wall  64  having a first axis B-B therethrough. Inner tube  61  further includes a first outer wall  65  coaxial with and radially outward from first inner wall  64 , where the first outer wall  65  has a first diameter D3 at the second inner end  63 . First inner wall  64  and first outer wall  65  thereby form a first thickness  68 , typically at least 0.050 inches. The inner tube  61  also contains a plurality of first air purge holes  66  which are preferably proximate the first inner end  62 . Additionally, inner tube  61  contains a plurality of channels  69  that extend along the first outer wall  65  proximate the second inner end  63  of inner tube  61 . Unlike the preferred embodiment, there is only one row, R3, of cooling channels  39 . The amount of cooling channel rows and their positions depends upon the amount of cooling required along the inner tube.  
         [0026]    In yet another embodiment of the present invention, the cooling channels, which on the preferred embodiment were located on the outer wall of the inner tube, are now located along the inner wall of the outer tube, as shown in FIGS. 7 and 8. FIG. 7 shows a detail view similar to that of FIG. 4, including inner tube  71  and outer tube  81 . Inner tube  71  has first inner end  72 , not shown, and second inner end  73 . Outer tube  81  has a first outer end  82  and second outer end  83 . All other features of the inner and outer tubes of this embodiment are identical to those described in FIGS.  2 - 5 , with the exception of the cooling channels  87 . Cooling channels  87  formed in Row R4 are located along the second inner wall  84  of outer tube  81  such that the compressor discharge cooling air  90  passes along the first outer wall  75  and second outer wall  85  of inner tube  71  and outer tube  81  where it then enters channels  87  of rows R4, thereby further cooling first outer wall  75 . Cooling air  90  then flows along second inner wall  84  to further cool that wall before dissipating into the combustor.  
         [0027]    While the invention has been described in what is known as presently the 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 within the scope of the following claims.