Abstract:
A fuel nozzle for a turbine combustor includes a nozzle head configured to supply a fuel/air mixture to a burner tube attached to said nozzle head and extending downstream of the nozzle head. The burner tube is provided with plural holes for introducing a fluid into the burner tube to thereby treat (e.g., cool) an interior wall of the burner tube by effusion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to turbine combustor nozzles and specifically, in one exemplary embodiment, to an effusion-cooled burner tube. 
         [0002]    In certain known combustor designs, a burner tube is connected to the outlet or downstream end of a nozzle head and forms a fuel preparation chamber for a fuel/air mixture introduced into the burner tube from the nozzle head. Typically, the burner tube is surrounded by an impingement cup formed with a plurality of cooling holes or apertures by which compressor discharge air may be introduced into an annular space between the impingement cup and the burner tube, to thereby impingement cool the tube. The impingement cooling air may be routed to mix with fuel at the fuel nozzle head, or to mix with the fuel/air mixture downstream of the burner tube as the mixture enters the combustion chamber. 
         [0003]    There remains a need, however, for better utilization of the cooling air used to cool the burner tube. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In accordance with a first exemplary but nonlimiting aspect, the invention provides a fuel nozzle for a combustor comprising a nozzle head configured to supply a fuel/air mixture to a burner tube attached to the nozzle head and extending downstream of the nozzle head; the burner tube provided with cooling holes for introducing a fluid into the burner tube to thereby treat (e.g. cool) an interior wall of the burner tube by effusion. 
         [0005]    In accordance with another exemplary but nonlimiting aspect, there is provided a nozzle for a gas turbine comprising a nozzle head formed with plural fuel orifices at an aft end; a burner tube attached to the aft end of the nozzle head and extending downstream of the plural fuel orifices; a swirler arranged about the aft end of the nozzle head, adapted to introduce air for mixing with fuel exiting the plural fuel orifices; the burner tube provided with plural cooling holes downstream of the swirler for introducing cooling air into the burner tube, wherein the plural cooling holes are arranged in axially-spaced, circumferentially extending rows about the burner tube, and slanted in a downstream direction. 
         [0006]    In accordance with still another exemplary embodiment, there is provided a method of effusion treating a burner tube in a turbine combustor comprising a locating a burner tube at an outlet end of a fuel nozzle, adapted to receive a fuel/air mixture; providing plural holes about the burner tube and introducing a fluid into the burner tube through the plural holes; and slanting the plural holes in a downstream direction at an angle sufficient to direct the fluid along an interior surface of the burner tube. 
         [0007]    The invention will now be described in detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross section of a known turbine fuel nozzle head and burner tube; 
           [0009]      FIG. 2  is a cross section of a turbine fuel nozzle head and burner tube in accordance with an exemplary but nonlimiting embodiment of the invention; and 
           [0010]      FIG. 3  is a schematic diagram of a gas turbine plant illustrating the location of the fuel nozzle shown in  FIGS. 1 and 2  in one exemplary but nonlimiting embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]      FIG. 1  illustrates the aft end of a turbomachine fuel nozzle  10  including the nozzle head  12  and an attached burner tube  14 . The nozzle head  12  has a conical outlet end that supplies fuel via apertures  16  to be mixed with air entering a swirler or other mixing device  18  and exiting via circumferential slots  20 . The fuel exiting the apertures  16  of the nozzle head mixes with the swirling air exiting slots  20  in the larger-diameter in the burner tube  14  before entering the combustion chamber  22 , downstream of an impingement plate  24  and splash plate  25 . In the conventional arrangement illustrated, the burner tube is surrounded by an impingement sleeve  26  radially spaced from the burner tube. The impingement sleeve is provided with circumferentially-arrayed apertures  28  by which compressor discharge air is allowed to flow through the apertures to thereby impingement cool the exterior surface of the burner tube  14 . The air then flows along the burner tube and may be routed to exit at the aft end of the burner tube to join with air being supplied to the combustion chamber  22  via apertures  30  impinging on the splash plate  25 . 
         [0012]      FIG. 2  illustrates a fuel nozzle  32  including a nozzle head  34  and burner tube  44  in accordance with an exemplary but nonlimiting embodiment of the invention. The nozzle head  34 , fuel apertures  36 , and swirler  38  and swirler holes or apertures  40  are similar to the corresponding components as described in connection with  FIG. 1 . Here, however, the impingement sleeve  26  utilized to cool the burner tube  14  is omitted. 
         [0013]    Instead, plural holes, e.g., effusion cooling holes are formed directly in the burner tube  44  such that cooling air flows directly into the burner tube to mix with the fuel/air mixture from the nozzle head  34  and swirler  38 . At the downstream end of the burner tube  44 , both the impingement plate  46  and splash plate  48  are now fixed to the aft end of the burner tube  44 . 
         [0014]    The effusion cooling holes  42  are preferably slanted in an axial direction, e.g., at an angle of between 30-60°, so that the effusion cooling air tends to flow along the inside of the burner tube  44  to thereby cool the hot side of the burner tube and, at the same time, keep the fuel away from the burner tube wall. The effusion cooling air thus enters directly into the burner tube but in part-axial direction so that air remains close to the burner tube surface as it travels at higher velocity axially along the length of the tube. 
         [0015]    The cooling holes  42  may also be slanted in one or the other of counterclockwise and clockwise, circumferential directions to cause the cooling air to swirl as it enters the burner tube  44 , either swirling with or counter to, the swirling air/fuel mixture. 
         [0016]    Two circumferential, axially-spaced rows of apertures or holes  42  are shown, but it will be appreciated that the number, diameter and pattern of the holes may vary. In one example, the cooling holes may have diameters in the range of from about 0.020 to about 0.060 in. In addition, the burner tube itself is formed with a slight conical shape, via tapered interior surface  50  with the narrower end located at the aft end of the burner tube, thereby increasing velocity and improving mixing as the mixture moves from left to right and into the combustion chamber  52 . 
         [0017]    Now that an aft row of cooling holes  52  adjacent the splash plate  48  are slanted at a more acute angle (15°-30°) relative to cooling holes  42 , thereby directing some portion of the effusion cooling air in a more axial direction at the aft end of the burner tube, thus also providing some cooling to the splash plate  48 . 
         [0018]    Other benefits not already mentioned include increased durability of the burner tube and nozzle head or tip; reduced soot formation on startup; better flame holding margin and reduced emissions. 
         [0019]    The cooling arrangement as described herein may be beneficially employed with various nozzle types including standard combustor nozzles, diffusion nozzles, DLN, combustor nozzles, primary nozzles, syngas nozzles and the like. 
         [0020]    It will be appreciated that in the event the cooling air maintains the burner tube temperature constant, i.e., prevents overheating, it may be more appropriate to state that the burner tube is “treated” with air or other fluid rather than “cooled”. 
         [0021]      FIG. 3  illustrates a gas turbine  54  incorporating a fuel nozzle  56  as described hereinabove in connection with  FIG. 2 . The fuel nozzle  56  is supplied with fuel (indicated at  58 ) for combustion within a combustor  60 . Air is supplied to the combustor  60  via air intake  62  and compressor  64 . The gaseous products of combustion are directed to the turbine section  66  and subsequently to the turbine exhaust  68 . In the illustrated embodiment, the turbine rotor  70  driven by the combustion gases also drives the compressor  64 . It will be understood that the illustrated gas turbine configuration is merely exemplary of various turbine configurations in which one or more fuel nozzles  56  may be incorporated. 
         [0022]    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.