Patent Publication Number: US-6910336-B2

Title: Combustion liner cap assembly attachment and sealing system

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to gas turbine combustors, and more specifically to the interface between a cap assembly and combustion chamber. 
   2. Description of Related Art 
   Gas turbine combustors typically contain at least one combustion chamber with the products of combustion directed through the aft end of the combustion chamber and into a turbine. Typically, the combustion chamber is enclosed at its forward end by a cap assembly. The cap assembly is used to deliver fuel and air from the fuel nozzles to the combustion chamber. The current cap assembly that is used in many multi-nozzle combustion chambers, which is shown in cross section in  FIG. 1 , has a single region for sealing the cap assembly to the combustion chamber. Cap assembly  10  contains an outer band  11  having a sealing region  12  for sealing cap assembly  10  to combustion chamber wall  13  while also fixed to wall  13  by pins  19 . Depending on manufacturing tolerances and operating conditions this seal can become ineffective, resulting in an undesirable leakage of compressed air into combustion chamber  16 . This leakage can alter the fuel/air ratio within combustion chamber  16 , thereby affecting flame stability, and the introduction of unmixed air can adversely affect combustor emissions. Furthermore, cap assembly  10  includes an impingement plate  14  that is fixed to outer band  11  at cap assembly aft end  17  resulting in a thick and rigid joint region  15  that is directly exposed to radiation from combustion chamber  16 . Although a cooling medium is permitted to flow through mixing holes  22  of impingement plate  14  and cooling holes  18 , there are no holes directing a cooling medium towards joint region  15 . As a result, joint region  15  can be exposed to elevated temperatures for extended periods of time, leading to premature degradation of cap assembly aft end  17 . 
   SUMMARY AND OBJECTS OF THE INVENTION 
   The present invention seeks to overcome the shortfalls of the prior art by providing a cap assembly for a combustion chamber with an improved sealing system and improved cooling effectiveness proximate the combustor cap assembly aft end. In accordance with the preferred embodiment of the present invention, a cap assembly is provided that contains a generally annular seal having a plurality of raised ridges that extend radially outward and are in sealing contact with a surrounding combustion chamber wall. Utilizing a plurality of raised ridges as seals, as opposed to a single seal of the prior art, creates a more effective seal against undesirable cooling medium entering the combustion chamber. Multiple seals provide resiliency should a single seal leak due to manufacturing tolerances, damage during installation, or operating conditions. Also, having multiple seals creates a more difficult path for a cooling medium to overcome in order to enter the combustion chamber. Furthermore, having a plurality of raised ridges provides increased surface area for positioning the cap assembly within a combustion chamber. Fixed to and radially within the generally annular seal is a generally annular wall that serves as a structural support member for the cap assembly. Fixed to the generally annular wall and located radially within the generally annular seal is a generally annular dome plate that contains a plurality of openings as well as a plurality of cooling holes. Each of the plurality of openings contains a nozzle tube for receiving a fuel nozzle. 
   The cap assembly is installed within a combustion chamber wall such that the raised ridges are in sealing contact with the combustion chamber wall. A plurality of pins are utilized to position the cap assembly in place within the combustion chamber. In order to provide adequate cooling at the combustor cap assembly aft end, where the dome plate and generally annular wall are joined together, proximate the generally annular seal, the combustion chamber wall contains a plurality of cooling holes that direct a cooling medium to this joint region. With regards to combustor flame stability and emissions, it is advantageous to have a resilient sealing system in combination with controlled amounts of cooling medium injected at a desired location, as opposed to a poor sealing system that could allow an unknown amount of air dedicated for combustion mixing to leak into the system. 
   It is an object of the present invention to provide an improved sealing system between a cap assembly and a combustion chamber. 
   It is a further object of the present invention to provide improved cooling to the combustor cap assembly aft end through a plurality of strategically placed cooling holes in the combustion chamber wall. 
   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 
       FIG. 1  is a partial cross section of a cap assembly of the prior art. 
       FIG. 2  is a cross section of the cap assembly that utilizes the present invention. 
       FIG. 3  is a partial cross section of a cap assembly installed in a combustion chamber in accordance with the present invention. 
       FIG. 4  is a partial cross section of a cap assembly installed in a combustion chamber in accordance with an alternate embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention, an attachment and sealing system for securing a combustor cap assembly to a combustion chamber, is shown in detail in the accompanying  FIGS. 2-4 . Referring to  FIG. 2 , a combustor cap assembly  30  incorporating an embodiment of the present invention is shown in cross section. Combustor cap assembly  30  has a forward end  31 , an aft end  32 , and a center axis A—A. Depending on the type of combustor in which cap assembly  30  is utilized, an optional centerbody  34  may extend from aft end  32  for directing additional air and fuel into the combustor. The preferred embodiment of the attachment and sealing system between combustor cap assembly  30  and a combustion chamber is shown in greater detail in FIG.  3 . 
   In the preferred embodiment of the present invention, combustor cap assembly  30  is located radially within a first generally annular wall  35  of combustion chamber  36 . A plurality of first cooling holes  37  are located about first generally annular wall  35  and inject a cooling medium from outside of combustion chamber  36 . Combustor cap assembly  30  also includes a generally annular seal  38  having a plurality of raised ridges  39  that are continuous about generally annular seal  38  and extend radially outward and are in sealing contact with first generally annular wall  35 . In order to increase the sealing effectiveness of this type of seal, it has been determined that a plurality of raised ridges, preferably two, are optimal. Therefore, should one of the ridges not seal completely due to manufacturing tolerances or excessive wear, an additional seal is present. Fixed to and radially within generally annular seal  38  is a second generally annular wall  40  which primarily serves as structural support for cap assembly  30 . A generally annular dome plate  41  is fixed to second generally annular wall  40  at joint region  47  and is also located radially within generally annular seal  38 . Joint region  47  is separated from combustion chamber  36  by dome plate thickness  48  in order to protect it from radiation effects from combustion chamber  36 . Generally annular dome plate  41  has a plurality of openings  42  located about center axis A—A as well as a plurality of second cooling holes  43 . Second cooling holes  43  provide a large amount of the air to combustor  36  as well as serve to cool dome plate  41  from the heat generated by combustion immediately adjacent in combustor  36 . As a result of the amount of cooling required for the entire dome plate  41 , versus the cap assembly aft end  32 , the plurality of second cooling holes  43  outnumber the plurality of first cooling holes  37  about first generally annular wall  35 . Fixed to openings  42  in dome plate  41  is a plurality of nozzle tubes  44  each of which receive a fuel nozzle for injecting fuel and air into combustor  36 . In the preferred embodiment, nozzle tubes  44  are telescopically received within openings  42  of dome plate  41 . Typically, due to the operating temperature of cap assembly  30 , it is also necessary to cool at least one of nozzle tubes  44  through a plurality of third cooling holes  46 . Once combustor cap assembly  30  is installed in first generally annular wall  35  of combustion chamber  36 , a plurality of pins  45  are installed to secure cap assembly  30  in place. Pins  45  extend from radially outward of combustion chamber  36 , through first generally annular wall  35 , through generally annular seal  38 , and through second generally annular wall  40 . It is preferred that pins  45  are placed axially between raised ridges  39 , such that they do not adversely affect the seal that is created when raised ridges  39  are in contact with first generally annular wall  35 . In order to provide sufficient support of combustor cap assembly  30  against the mechanical and aerodynamic loads of combustion chamber  36 , plurality of pins  45  comprises at least five pins. 
   Referring back to first cooling holes  37 , they are positioned relative to combustor cap assembly  30  such that they inject a cooling medium proximate cap assembly aft end  32 , generally towards combustion chamber  36 . The addition of cooling holes at this location is critical for cap assembly cooling. Due to manufacturing and assembly requirements, it is not feasible to add additional second cooling holes  43  immediately adjacent joint region  47 . If this region were directly exposed to elevated temperatures, with minimal cooling, degredation of cap assembly aft end  32  would occur, as with the prior art. Therefore, it is desirable, in the preferred embodiment, to position first cooling holes  37  such that they direct a cooling medium towards joint region  47 , such that not only is aft end  32  cooled by impingement cooling, but the cooling medium then creates a film layer along first generally annular wall  35  as it enters combustion chamber  36 . Although a variety of cooling mediums could be used to cool cap assembly  30  and inject into combustion chamber  36 , it is preferred that the cooling medium is either compressed air or steam. 
   An alternate embodiment of the present invention is shown in partial cross section in FIG.  4 . The alternate embodiment of the present invention is nearly identical to the preferred embodiment with the exception of the length of the generally annular seal and orientation of the plurality of first cooling holes, therefore only the components affected by these changes will be described in detail. In this alternate configuration, combustor cap assembly  50  has a generally annular seal  51  with a plurality of raised ridges  52  that are in scaling contact with first generally annular wall  53  of combustion chamber  54 . Unlike the preferred embodiment, generally annular seal  51  extends beyond dome plate  55 . The longer length of generally annular seal  51  allows the cooling medium injected through first cooling holes  56  to impinge on generally annular seal  51  at joint region  58 . As with the preferred embodiment, joint region  58  is separated from combustion chamber  54  by dome plate thickness  59  to protect joint region  58  from the radiation effects of combustion chamber  54 . Furthermore, the plurality of first cooling holes  56  can be oriented perpendicular to first generally annular wall  53  to provide a more effective impingement cooling and film layer along first generally annular wall  53  after cooling joint region  58 . 
   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.