Abstract:
A support structure for a burner tube in a combustor cap assembly for a gas turbine combustor includes an outer annular ring; an inner annular hub; and a plurality of struts extending radially between said outer annular ring and the inner hub. The inner hub is provided with a piston ring groove and a piston ring adapted to receive and seal an inner end of the burner tube.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to gas turbine combustion technology and, more specifically, to a simplified design for combustor cap assembly. 
         [0002]    In certain, can-annular combustor arrangements in land-based electrical power generation gas turbines, combustor cap assemblies are provided at the forward or upstream end of the combustor and serve to support fuel nozzles projecting into the combustion chamber. Typically, the combustor cap assemblies support plural fuel nozzles at two locations including the forward ends at the nozzles and the aft ends of the nozzles and/or burner tubes that surround the nozzles. In some configurations, only a center fuel nozzle is surrounded by a burner tube whereas in other configurations, all of the combustor nozzles are surrounded by respective burner tubes. 
         [0003]    In certain known arrangements, the combustor cap assembly at the aft end where the cap assembly (i.e., the end closest to the combustion chamber) interfaces with the aft ends of the fuel nozzles and/or burner tubes, there is an effusion plate provided with plural apertures, each surrounded by piston ring sleeve that telescopically receives the aft end of the burner tube. Typically, the piston ring sleeve is butt-welded to the effusion plate as part of the cap assembly, and the burner tube is received over the piston sleeve, with a hula seal radially therebetween. A support structure which has inner and outer rings connected by plural spokes or struts, is positioned around the end piston ring sleeve adjacent the effusion plate and welded into place. The burner tube sleeve is fillet-welded to a backing plate at the opposite or upstream end of the cap assembly. 
         [0004]    The current design is complex and requires multiple parts which can result in inefficiencies in assembly, repairs, etc. There remains a need, therefore, for a simplified combustor cap assembly design that reduces the number of parts and facilitates assembly/disassembly but without any degradation of structural integrity. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In accordance with an exemplary but nonlimiting embodiment, there is provided a support structure for a burner tube in a combustor cap assembly for a gas turbine combustor comprising an outer annular ring; an inner annular hub; and a plurality of struts extending radially between the outer annular ring and the inner hub; wherein the inner hub is provided with a piston ring groove and a piston ring adapted to receive and seal an inner end of the burner tube. 
         [0006]    In another aspect, there is provided combustor cap assembly comprising a support structure cap assembly at forward and aft ends thereof for supporting a plurality of fuel nozzles and surrounding burner tubes, including a center nozzle and a center burner tube; the support structure at the aft end including a diffuser plate having a center opening defined in part by a sleeve facing the forward end and a wagon-wheel structure having an outer annular ring; and a plurality of struts extending radially between the outer annular ring and the inner hub; wherein the inner hub is provided with a piston ring groove and a piston ring adapted to receive and seal an inner end of the burner tube. 
         [0007]    In still another aspect, there is provided a combustor cap assembly comprising support structure cap assembly at forward and aft ends thereof for supporting a plurality of fuel nozzles and surrounding burner tubes, including a center nozzle and a center burner tube; the support structure at the aft end including a diffuser plate having a center opening defined in part by a sleeve facing the forward end and a wagon-wheel structure having an outer annular ring; a plurality of struts extending radially between the outer annular ring and the inner hub; wherein the inner hub is provided with a piston ring groove and a piston ring adapted to receive and seal an inner end of the center burner tube; and an effusion plate having a circular center opening defined by an upstanding edge, and wherein said aft end of said inner hub is attached to said upstanding edge. 
         [0008]    The invention will now be described in detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cross-section through a combustor cap assembly in accordance with a known configuration; 
           [0010]      FIG. 2  is a nozzle burner tube support structure taking from the cap assembly of  FIG. 1 ; 
           [0011]      FIG. 3  is a partial cut-away of the support structure shown in  FIG. 2 ; 
           [0012]      FIG. 4  is a nozzle burner support structure in accordance with an exemplary but nonlimiting embodiment of the invention; 
           [0013]      FIG. 5  is a partial section of a nozzle burner tube support structure in accordance with the invention, and showing additional supports for surrounding nozzles; 
           [0014]      FIG. 6  is a partial cross-section through a combustor cap assembly incorporating the nozzle burner tube support structure of  FIG. 4 ; and 
           [0015]      FIG. 7  is a view similar to  FIG. 6  but also illustrating a center nozzle installed within the nozzle burner tube. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  illustrates a known combustor cap assembly  10  for supporting a plurality of fuel nozzles (not shown) in an arrangement where five outer nozzles surround a center nozzle. In this particular example, all of the nozzles are provided with surrounding or outer burner tubes that are supported on an aft end of the combustor cap assembly. In  FIG. 1 , two outer nozzle burner tubes  12  and  14  are shown along with a center burner tube  16 . The invention here relates particularly to the support for the center burner tube  16  at the inner or aft end  18  of the cap assembly  10 . Accordingly, in describing the known arrangement shown in  FIG. 1 , the focus will be on the center burner tube  16  and its interaction with the inner or aft end  18  of the combustor cap assembly. 
         [0017]    At their inner or forward ends (the ends facing or adjacent the combustion chamber), the various burner tubes are supported by sleeves  20  welded to a diffuser plate  22 . The center sleeve (also referred to herein as a “piston sleeve”)  20  is also laterally supported by a “wagon-wheel” structure  24  (best seen in  FIGS. 2 and 3 ) formed by an outer ring  26  and an inner ring or hub  28  connected by a plurality (five in the example illustrated) of radially-extending spokes or struts  30 . With this arrangement, it will be appreciated that the five surrounding nozzles/burner tubes are each located within the space defined by a pair of adjacent struts  30 . 
         [0018]    With continued reference to  FIGS. 2 and 3 , the inner hub  28  fits over the piston sleeve  20 , and the center burner tube  16  is telescoped over the piston sleeve, such that the inner end  32  of the burner tube  16  is located in close proximity to the outer edge  34  of the inner hub  28 , with an axial gap therebetween. Note also that there is a similar axial gap between the inner edge  36  of the inner hub  28  and the flanged base  38  of the piston sleeve  20 . These gaps allow for thermal growth during operation. In this known arrangement, an annular, conventional spring or “hula seal”  40  is located radially between the inner end of the burner tube  16  and the piston sleeve  20  to minimize air leakage across the diffusion plate. 
         [0019]      FIGS. 4 and 5  illustrate a simplified arrangement for supporting the inner end of a center burner tube  66  on the fuel nozzle assembly (see  FIG. 7 ) in accordance with an exemplary but nonlimiting embodiment of the invention. A center burner, inner wagon-wheel structure  42  is formed by an outer annular ring  44  and an inner ring or hub  46  with a plurality of radially-extending spokes or struts  48  therebetween. In this case, however, the inner hub  46  is constructed so as to eliminate the need for a separate piston sleeve and hula seal. In addition, the center burner tube  66  is supported at the forward end of the nozzle assembly ( FIG. 7 ) and merely sealed at the wagon-wheel structure  42 . Specifically, the inner hub  46  has tapered forward and aft ends  50 ,  52  respectively, and an inner diameter formed with an annular piston ring groove  54  axially between the ends  50 ,  52 . As best seen in  FIGS. 5 and 6 , a depending annular skirt portion  53  of the aft tapered end  52  may be butt-welded to a complimentary edge  56  in the diffusion plate  58 . The forward-tapered end  50  facilitates the telescoping of the center fuel nozzle burner tube  66  into the inner hub  46  and a piston ring  60 , seated in the groove  54 , seals the interface between the fuel nozzle burner tube  66  and the inner hub  46 . 
         [0020]      FIG. 5  also shows surrounding burner tube support sleeves  61  of a different configuration than shown in  FIG. 1  but is not intended to in any way limit the burner tube support structure described above. 
         [0021]      FIGS. 6 and 7  show the wagon-wheel support structure  42  incorporated into a combustor cap assembly  62 , and  FIG. 7  shows the same cap assembly  62  with a center nozzle  64  installed and extending into the center fuel nozzle burner tube  66 . 
         [0022]    The aft end of the fuel nozzle burner tube is sealed at the piston ring  60  but is otherwise unsecured where the burner tube is engaged by the effusion plate  58 . This arrangement allows the fuel nozzle burner tube to grow thermally in at least an axial direction relative to the inner hub  46  and the effusion plate while the seal at the piston ring  60  is maintained. 
         [0023]    This arrangement provides effective support for the inner end of the center burner tube with fewer parts and with simplicity of design at no sacrifice to structural integrity. While described herein in connection with a center nozzle burner tube, the invention has applicability in any nozzle burner tube, even without the “wagon-wheel” support structure. In other words, a support similar to the inner ring or hub  46 , could be welded to the diffusion plate at any location where a nozzle burner tube is to be supported. 
         [0024]    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.