Patent Publication Number: US-2009218421-A1

Title: Combustor fuel nozzle construction

Description:
BACKGROUND 
     The subject invention relates to combustors. More particularly, the subject invention relates to oil tubes and water tubes of combustor fuel nozzles. 
     A combustor of a gas turbine typically includes one or more fuel nozzles to which fuel is delivered and from which fuel is injected into a combustion area of the combustor. Water and fuel are often injected into the combustion zone from a water tube and an oil tube, respectively. In many configurations of nozzles, the oil tube is located inside the water tube, and both the water tube and oil tube are connected to a tip. Combustion dynamics and differential thermal loading between the oil tube and water tube results in eccentricity between the oil tube and water tube during combustor operation. Further, the oil tube is often affected by vibratory frequencies during combustor operation, resulting in high vibratory stresses on the oil tube which increases wear of the oil tube and reduces its useful life. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A fuel nozzle for a combustor includes a tip section and a tube section. The tube section, in which a first end is connected to the tip section includes an outer tube having a tube axis and connected to the tip section and an inner tube disposed at least partially inside of the outer tube and connected to the tip section. The inner tube includes at least one flexible portion capable of reducing stresses in the fuel nozzle. 
     A second embodiment of a fuel nozzle includes a tip section, a base section, and a tube section disposed between the tip section and the base section and connected to the tip section at a first end and connected to the base section at a second end. The tube section includes an outer tube having a tube axis and an inner tube disposed at least partially inside of the outer tube and connected to the tip section. At least one rib is disposed on the outer tube and extends radially outwardly from an outer surface of the outer tube. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side view of an embodiment of a fuel nozzle for a combustor; 
         FIG. 2  is a cross-sectional view of the fuel nozzle of  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional view of the fuel nozzle of  FIG. 1  including a bellows; 
         FIG. 4  is a partial cross-sectional view of a tip section of the fuel nozzle of  FIG. 1 ; and 
         FIG. 5  is a partial cross-sectional view of the fuel nozzle of  FIG. 1  including a plurality of ribs. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIG. 1  is an embodiment of an improved fuel nozzle  10 . The fuel nozzle  10  includes a base  12  and a tube section  14  extending from the base  12  to a tip  16 . As shown in  FIG. 2 , in some embodiments, the base  12  includes a bore  18  through which the tube section  14  is inserted and connected to a fuel source (not shown) to provide fuel to the tube section  14 . The tube section  14  comprises an oil tube  20  disposed in a water tube  22 . In the embodiment shown in  FIG. 2 , the oil tube  20  and the water tube  22  each have circular cross sections, but other cross sections, including oval, which may be utilized depending on operational requirements of the combustor are contemplated within the scope of the current disclosure. In some embodiments, the oil tube  20  is concentric with the water tube  22  around a tube axis  24 . The tube section may further include one or more spacers  26  to maintain the oil tube  20  in a desired radial position, concentric or not, relative to the water tube  22 . The spacers  26  may be fully annular in cross section as in the embodiment of  FIG. 2 , or alternatively may constructed of segments placed between the oil tube  20  and water tube  22  and may be configured with through holes (not shown) or other means to allow a flow of water in the water tube  22  to flow from a first side of the spacer  26  to a second side of the spacer  26 . The spacers  26  may be connected to either or both of the oil tube  20  and water tube  22  by, for example, brazing. 
     As shown in  FIG. 3 , the oil tube  20  includes at least a first oil tube portion  30  and a second oil tube portion  32  connected by a least one flexible portion, in this embodiment a bellows  34 . The bellows  34  comprises one or more convolutions  36  having an outer diameter  38  and an inner diameter  40  and is connected to the first oil tube portion  30  at a first end  42  and to the second oil tube portion  32  at a second end  44 . The bellows  34  may be connected to the first oil tube portion  30  and the second oil tube portion  32  by, for example, brazing, or in some embodiments may be integrally formed with either or both of the first oil tube portion  30  and the second oil tube portion  32 . Though the embodiment shown in  FIG. 3  includes an oil tube  20  having a single bellows  34 , other quantities of bellows  34 , for example two or three bellows  34 , are contemplated within the scope of the present disclosure. 
     As shown in  FIG. 4 , the tip  16  is connected to one end of the tube section  14  and may include an annular tube adapter  46  which is concentric with the oil tube  20  and connects the oil tube  20  to a liquid fuel swirler  48 . The connections between the oil tube  20  and tube adapter  46  and the tube adapter  46  and liquid fuel swirler  48  may be accomplished by brazing. Concentric with the liquid fuel swirler  48  is an air-fuel swirler  50  which is connected to the water tube  22  at one end and connected to the liquid fuel swirler  48  at a swirler land  52 . Finally, a shroud  54  may be included which is disposed radially outboard from the air-fuel swirler  48  and attached thereto at a nozzle land  56  by, for example, brazing. The bellows  34  allow the oil tube  20  to thermally expand and contract relative to the water tube  22  and the tip  16  during operation of the combustor, thereby reducing stresses between the oil tube  20 , water tube  22  and tip  16  and extending the useful life of the nozzle  10 . 
     As shown in  FIG. 5 , in some embodiments, the water tube  22  includes a plurality of ribs  58  extending outwardly from an outer surface  60  of the water tube  22 . The ribs  58  are configured and located to shift a natural frequency of the water tube  22  away from a vibratory frequency of the combustor, which in some embodiments is about 350 Hz. The ribs  58  shown In  FIG. 5  are located at a base end  62  of the water tube  22 . The ribs  58  of this embodiment are aligned substantially along the tube axis  24  and extend substantially radially from the outer surface  60  of the water tube  22 . Further, the ribs  58  shown in  FIG. 5  are tapered such that an axial length  64  of the ribs  58  is greater at a rib base  66  than an axial length  64  at a rib tip  68 . The rib  58  location, arrangement, and configuration shown in  FIG. 5  is merely exemplary and other locations, arrangements, and configurations of ribs  58  to shift the natural frequency of the water tube  22  are contemplated within the scope of the current disclosure. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.