Abstract:
A unitary fuel injection manifold for a secondary fuel nozzle improves fuel-air mixing and offers flexibility to alter the mixing profile through adaptability to a variety of number, types, and orientation of discharge outlets to the combustion air mixing space around the secondary fuel nozzle. An aerodynamic surface with reduced extension into the mixing space reduces pressures drop and interference with design airflow. Manifold integrity is enhanced by elimination of fillet welds to mount external pegs.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to gas turbines and more specifically to gas turbine combustors with secondary fuel nozzles. 
     Gas turbine manufacturers continue research and engineering programs to produce new gas turbines that will operate at high efficiency without producing undesirable air polluting emissions. The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide, and unburned hydrocarbons. It is well known in the art that oxidation of molecular nitrogen in air breathing engines is highly dependent upon the maximum hot gas temperature in the combustion system reaction zone. The rate of chemical reactions forming oxides of nitrogen (NOx) is an exponential function of temperature. If the temperature of the combustion chamber hot gas is controlled to a sufficiently low level, thermal NOx will not be produced. 
     One preferred method of controlling the temperature of the reaction zone of a heat engine combustor below the level at which thermal NOx is formed is to premix fuel and air to a lean mixture prior to combustion. The thermal mass of the excess air present in the reaction zone of a lean premixed combustor absorbs heat and reduces the temperature rise of the products of combustion to a level where thermal NOx is not formed. 
     Lean, premixing fuel injectors for emissions abatement are in common use throughout the industry, having been reduced to practice in heavy duty industrial gas turbines for more than two decades. Such devices have achieved great progress in the area of gas turbine exhaust emissions abatement. Reduction of oxides of nitrogen, NOx, emissions by an order of magnitude or more relative to the diffusion flame burners of prior art have been achieved without the use of diluent injection such as steam or water. 
     A common configuration for combustors in gas turbines provides an annular array of primary nozzles each of which discharges fuel into the primary combustion chamber, and a central secondary nozzle which discharges fuel into the secondary combustion chamber. The secondary nozzle has an axial fuel delivery pipe surrounded at its discharge end by an air swirler which provides combustion air to the fuel nozzle discharge. Often the secondary nozzle is operated as a two-stage (diffusion and premixing) gas only secondary fuel nozzle with two fuel circuits. This allows the nozzle to operate in a premixed mode or diffusion mode. The secondary nozzle of each combustor is located within a center body and extends through a liner provided with a swirler through which combustion air is introduced for mixing with fuel from the secondary nozzle. The secondary nozzle is arranged to discharge fuel into a throat region between an upstream primary combustion chamber and a downstream secondary combustion chamber. Fuel is supplied to the secondary nozzle through concentrically arranged diffusion and premix pipes. 
       FIG. 1  illustrates a premixing section of a prior art secondary fuel nozzle assembly  5 . The premixing section  10  includes multiple pegs  15  fixed to an outer surface  16  of outer wall  17  of the fuel nozzle body  20 , each with a fillet weld  18 . The multiple pegs  15  extend radially outward from the fuel nozzle body and around the circumference at discrete locations. Radially internal to the fuel nozzle wall  17  are multiple secondary manifolds  25 , each manifold disposed between an inner surface  19  of the fuel nozzle wall  17  and a support structure  22  radially inward. Also radially inward from the secondary manifolds  25  are fuel chambers  30 , which may be supplied with fuel from a rear portion (not shown) of the secondary fuel nozzle assembly. The secondary manifold  25  may include radial passages  26  from the fuel chamber  30  below, communicating through the fuel nozzle wall  17  and through the peg  15 . The radial passages communicate with discharge passages  27  and through fuel injection holes  28  into the premixing space  40  around the fuel nozzle body  20 . The pegs  15  interrupt the distribution of airflow  45  and result in uneven radial and circumferential mixing of fuel and air. Further, due to the size and their far reach into the premixing space  40 , the pegs  15  cause an undesired pressure drop. 
     Accordingly, there is a need to provide a premixing arrangement for the secondary fuel nozzle that is simple and exercises improved control over fuel-air mixing. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A first aspect of the present invention provides a secondary fuel nozzle for a combustor of a gas turbine where the combustor provides a downstream combustion airflow within a fuel-air premixing space around the secondary fuel nozzle. The secondary fuel nozzle includes an elongated tube body with a fuel source end and a tip end. The nozzle also includes a unitary fuel injection manifold for premixing fuel with downstream combustion airflow. The fuel injection manifold is formed in a generally annual shape body shape within the elongated tube body and disposed between the fuel source end and the tip end. The fuel injection manifold extends radially from internal to the elongated tube body to radially above and external to the elongated tube body. The manifold extends circumferentially fully around the elongated nozzle body in a fuel-air premixing space external to the elongated tube body. The secondary fuel nozzle also includes a fuel passage from a fuel source end of the elongated tube body to the fuel injection manifold, supplying premixing fuel to the unitary fuel injection manifold. Multiple fuel channels provide for fluid communication for the premixing fuel between the premixing fuel passage within the elongated tube body and multiple fuel discharge outlets on the outer surface of the unitary fuel injection manifold. The fuel channels for the premixing fuel are circumferentially organized around the annular body of the fuel injection manifold. 
     According to another aspect of the present invention, a combustor for a gas turbine including a turbine and a compressor is provided. The combustor includes a secondary fuel nozzle organized along an axial centerline of the combustor and at least one primary fuel nozzle surrounding the secondary fuel nozzle. A backplate supplies one or more fuel sources to the primary nozzles and the secondary fuel nozzle. The combustor provides a combustion air supply from a compressor to the primary fuel nozzles and the secondary fuel nozzle. 
     The secondary fuel nozzle includes an elongated body tube having a fuel supply end with an opposing tip end. The elongated body tube includes multiple internal passages formed in concentric tubes delivering air and fuel to a tip nozzle and to a tip swirler. A unitary fuel injection manifold is provided for premixing fuel with downstream combustion air flow. The fuel injection manifold is formed in a generally annual body shape within the elongated tube body and disposed between the fuel source end and the tip end. The fuel injection manifold extends radially from internal to the elongated tube body to radially above and circumferentially fully around in a fuel-air premixing space external to the elongated tube body. The body of the fuel injection manifold disposed radially above the elongated tube body forms an aerodynamically streamlined outer surface for combustion air in the premixing space. The axial ends of the outer surface of the fuel injection manifold smoothly taper in radially for attachment to an outer radial surface of the elongated tube body. 
     A fuel passage from a fuel source end of the elongated tube body to a proximity of the fuel injection manifold supplies premixing fuel to the unitary fuel injection manifold. Multiple fuel channels provide fluid communication between the premixing fuel passage within the elongated tube body and multiple fuel discharge outlets on the outer surface of the unitary fuel injection manifold. The multiple fuel channels are circumferentially disposed around the body of the fuel injection manifold. 
     Briefly in accordance with a further aspect of the present invention, a fuel injection manifold for a premixing fuel of a secondary fuel nozzle of a combustor of a gas turbine is provided. The fuel injection manifold includes a unitary body forming a generally annular segment of a nozzle tube for a secondary fuel nozzle of a gas turbine. The unitary body includes an inner radial section for mounting within the nozzle tube and a radially elevated portion with an aerodynamically shaped outer surface for extending above the outer surface of the nozzle tube into a premixing space of the secondary fuel nozzle. The unitary body is supplied with a premixing fuel source from within the nozzle tube. 
     Multiple fuel injection channels in the unitary body establish a fluid communication path for the premixing fuel from the fuel source within the nozzle tube to fuel discharge opening in the premixing space radially surrounding the nozzle tube. One or more fuel discharge outlets to the premixing space surrounding the nozzle tube are provided for each of the fuel channels. The fuel discharge openings are adapted for enhancing mixing of the fuel with a combustion airflow in the premixing space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates a premixing section of a prior art secondary fuel nozzle assembly; 
         FIG. 2  illustrates an embodiment of a secondary fuel nozzle including an inventive fuel injection manifold; 
         FIG. 3  illustrates FIG. an expanded isometric cutaway view for an embodiment of the unitary fuel injection manifold of the elongated nozzle body; 
         FIG. 4  illustrates a cross-section A-A through a center of an embodiment of the fuel injection manifold section of the elongated nozzle body; 
         FIG. 5  illustrates an isometric exterior view of an embodiment of a fuel injector manifold cutoff on downstream side; 
         FIG. 6  illustrates a downstream cutaway interface for an embodiment of the fuel injector manifold  130  with support ring; 
         FIG. 7  illustrates an isometric view of an embodiment of a fuel injection arrangement where the manifold includes two holes normal to the airflow; 
         FIG. 8  illustrates an embodiment of fuel injection arrangement with a rectangular slot normal to the airflow; 
         FIG. 9  illustrates an embodiment of a fuel injection arrangement with a rectangular slot including a 30-degree backward discharge angle to the airflow; 
         FIG. 10  illustrates an embodiment of a fuel injection arrangement with a rectangular slot including 30-degree forward discharge angle to the airflow; and 
         FIG. 11  illustrates an embodiment of a combustor for a gas turbine employing the inventive fuel injection manifold for a secondary fuel nozzle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following embodiments of the present invention have many advantages including eliminating pegs that extend far into the fuel flow around the nozzle body, and exercising improved control over the over the fuel-air mixing without extending into the combustion airflow with the attendant obstruction to the airflow pattern that result with pegs. Embodiments of the present invention integrate fuel injection holes into a fuel injection manifold of the nozzle body. The fuel injection manifold is made simple and more robust by eliminating the pegs and the associated fillet weld between the nozzle body and pegs. The inventive arrangement further provides ease of manufacturability, retrofitability and low-cost. 
       FIG. 2  illustrates an embodiment of a secondary fuel nozzle  100  with an inventive fuel injection manifold  130 . The secondary fuel nozzle includes a base section  105  that includes provisions for attachment to a combustor of a gas turbine and which supplies fuel and air to an elongated nozzle body  120 . The elongated nozzle body includes a base end  106  and a tip end  107 . The tip end  107  includes a nozzle tip  108  supplied by a center fuel passage  110  and an air passage  111  for cooling air for the nozzle tip  108 . The tip end  107  further includes an air swirler  115  taking air from air passage  112  outside radially from the nozzle tip  108  for establishing a swirling fuel-air mixture downstream. Along a length of the elongated nozzle body  120 , a fuel injection manifold  130  is provided for injecting fuel into air stream  160  of premixing section  150 . The fuel injection manifold  130  is unitary. An outer portion  135  of the fuel injection manifold extends aerodynamically outward radially from the outer wall  119  of the elongated nozzle body  120  and circumferentially around the elongated nozzle body. An inner portion  140  of the fuel injection manifold extends radially into the elongated nozzle body and is supported from an inner structure below. The fuel injection manifold  130  may be butt-welded to upstream and downstream sections of the outer tube wall  119  and third tube wall  118 . 
       FIG. 3  illustrates an expanded isometric cutaway view for an embodiment of the unitary fuel injection manifold  130  of the elongated nozzle body.  FIG. 4  illustrates a cross-section A-A through a center of the fuel injection manifold section of the elongated nozzle body. The center fuel passage  110  providing fuel to the nozzle tip ( FIG. 2 ) is enclosed by first tube wall  116 . The second annular passage  111  supplying air to the nozzle tip is enclosed by second tube wall  117 . The third annular passage  155  supplying premix fuel to the fuel injection manifold  130  is enclosed by third tube wall  118 . The fourth annular passage  112  supplying air to swirler ( FIG. 2 ) at tip end of nozzle is enclosed by outer wall  119 . The fuel injection manifold is formed as an annular ring. The annular ring includes a smoothed aerodynamic exterior protrusion  135 , radially elevated relative to outer surface  122  of outer wall  119 . Axial ends of the protrusion  135  smoothly taper inward radially to the outer surface  122  of the adjacent outer wall  119 . The internal body section  140  of unitary fuel injection manifold  130  extends inward radially relative to the adjacent outer wall  119 . Circumferential quadrants  165  of fuel injection manifold include axial air channels  175  allowing air to pass between upstream and downstream portions of air passages  112 . Between quadrants  165 , radial fuel channels  145  provide fuel for premixing from fuel channel  155  to fuel discharge outlets  146  into the combustion airstream  160  outside the outer surface of  147  of the manifold. 
     Annular support elements  123  may extend radially outward at circumferential sectors of the center tube section  116  providing support for and separation from the second tube wall  117 . Air channels through the fuel manifold section are disposed circumferentially between support elements  123  and radially between center wall  116  and second tube wall  117 . The air channels connect upstream and downstream portions of air passages  111 . 
     Support ring  170  may extend between second tube wall  117  and underside  124  of internal body  140  of fuel injection manifold. The support ring  170  may radially support the downstream side of internal body  140  of the manifold. The support ring  170  may further act provide endwall  127  for premix fuel passage  155 . Outer radial ring part  169  may further provide a firm seat for downstream end of internal body  140  of fuel injection manifold 
       FIG. 5  illustrates an isometric end view of an embodiment of a fuel injector manifold  130  cutoff on downstream side. The raised exterior portion  135  include may include a plurality of fuel discharge outlets  146  (shown as slots). In this example, four fuel discharge outlets  146  are illustrated. The downstream end of fuel injector manifold includes inner manifold body  140  through which fuel discharge channels (not shown) supply fuel to the fuel discharge outlets  146 . Air passages  175  are provided through the fuel injector manifold to supply air to swirler ( FIG. 2 ) at the tip end of the elongated nozzle body. 
       FIG. 6  illustrates a downstream cutaway interface of the fuel injector manifold  130  with support ring  170 . Support ring  170  may extend between second tube wall  117  and underside of internal manifold part  140 , providing support for the underside of inner manifold body  140  and providing an endwall  127  for fuel passage  155  ( FIG. 3 ) supplying manifold fuel injection passages  145  ( FIG. 4 ). 
     It should be understood that many embodiments of the inventive manifold body may be provided for fuel premixing in an elongated nozzle body with different combinations and types of internal fuel flows and air flows within the nozzle body and that such alternate arrangements are considered within the scope of the present invention. 
       FIG. 7  illustrates an isometric end view the fuel injection manifold  130  without inner secondary fuel nozzle components. Here it may be seen that the exterior body  135  of the fuel injection manifold includes a smooth exterior surface  147  for reducing interference with the combustion airflow  160  around the elongated nozzle body (not shown). Internal body sections  140  of the fuel injection manifold are interspersed with air channel  175  allowing fluid communication for air in passage  112  ( FIG. 2 ) from the upstream end of the elongated nozzle body to the tip end swirler ( FIG. 2 ). Fuel injection outlets  146  are disposed circumferentially around the manifold in locations with internal body sections  140 . 
       FIG. 8  illustrates a fuel injection arrangement with a rectangular slot  172  normal to the combustion airflow  160 .  FIG. 9  illustrates a fuel injection arrangement with a rectangular slot  173  including a 30-degree backward discharge angle  176  to the combustion airflow.  FIG. 10  illustrates a fuel injection arrangement with a rectangular slot  174  including 30-degree backward discharge angle  177  to the combustion airflow  160 . It should be understood that arrangements may be provided with openings of different shapes, number of openings and direction of discharged fuel relative to the combustion airflow. It should also be understood that the fuel nozzle body may also be provided with varying numbers of secondary manifold internal body elements  140  and air passages  175  circumferentially distributed. 
     The size, shape and orientation of fuel injection openings from the secondary manifold segments, as well as the number of circumferentially distributed secondary manifold segments will influence the radial and circumferential fuel-air mixing. Performance of the various arrangements of  FIGS. 7-10  may be compared favorably against a baseline performance of the peg arrangement as to equivalence, a radial profile of phi (1/equivalence ratio) and unmixedness. 
       FIG. 11  illustrates a combustor  200  for a gas turbine that may employ the inventive fuel injection manifold  130  for a secondary fuel nozzle  100 . Enhanced fuel premixing provided by the inventive fuel injection manifold  130  in the secondary fuel nozzle  100  for the combustion resulting in improved combustor performance and reduced emissions. Here, the combustor  200  comprises a liner  210  within combustor wall  215 . The combustor includes a primary combustion chamber  215  and a secondary combustion chamber  220  adjacent to and downstream of primary combustion chamber  215  and separated by a venturi  225 . At least one primary fuel nozzle  230  is positioned radially about a combustor centerline  245  to deliver fuel to primary combustion chamber  217 . Secondary fuel nozzle  100  may be disposed along centerline  245 , encircled by at least one primary fuel nozzle  230 , and positioned to inject fuel towards secondary combustion chamber  220 . Combustion air  240  is provided from compressor (not shown) and flows outside flow liner  210  in flow sleeve  211 , supplying air to the at least one primary nozzle  230  and secondary fuel nozzle  100 . Primary fuel nozzles  230  and secondary fuel nozzle  100  receive fuel from one or more fuel sources  231 ,  101  through backplate  250 . The secondary fuel nozzle  100  shown with cutaway fuel injection manifold section may receive a first fuel source through center fuel passage  111  to the nozzle tip  108 . As previously shown in  FIG. 3 , the nozzle tip also receives a cooling airflow from internal to the secondary fuel nozzle. Swirler  115  circumferentially outside nozzle tip  108  may swirl air passed from within secondary fuel nozzle promoting mixing of fuel and air at nozzle tip. Annular fuel injector manifold  130  receives premixing fuel internal to secondary fuel nozzle and injects premixing fuel into combustion airflow  160  of premixing space  180 . Low radial protrusion of fuel injector manifold  130  into premixing space  180  and aerodynamic outer surface minimize pressure drop in premixing space  180 . Fuel discharge openings on outer surface of fuel injector manifold  130  may be shaped, sized, oriented and numbered to promote mixing in the premixing space  180 . A downstream swirler  185  may be positioned at discharge of premixing space  180  to further mix premix fuel-air with fuel-air mixture from nozzle tip  108 . 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.