Abstract:
Disclosed herein is a fuel nozzle. The fuel nozzle includes a first fuel introduction location, a second fuel introduction location, and fuel passages. The first fuel introduction location is located radially about the fuel nozzle and is connected with a fuel passage. The second fuel introduction location is located at an end of the fuel nozzle and is connected with another fuel passage such that the fuel passage connected to the first fuel introduction location is separate from the fuel passage connected to the second fuel introduction location.

Description:
TECHNICAL FIELD  
       [0001]     This application relates generally to gas turbines, and more specifically, to a secondary fuel nozzle for a gas turbine combustor with individually controlled fuel circuits intended to provide optimum combustion system emissions concentrations.  
       BACKGROUND OF THE INVENTION  
       [0002]     A gas turbine combustor is essentially a device used for mixing fuel and air, and burning the resulting mixture. Gas turbine compressors pressurize inlet air which is then turned in direction or reverse flowed to the combustor where it is used to cool the combustor and also to provide air to the combustion process. Multiple combustion chamber assemblies may be utilized to achieve reliable and efficient turbine operation. Each combustion chamber assembly comprises a cylindrical combustor liner, a fuel injection system, and a transition piece that guides the flow of the hot gas from the combustor liner to the inlet of the turbine section. Gas turbines for which the present fuel nozzle design is to be utilized may include one combustor or several combustors arranged in a circular array about the turbine rotor axis.  
         [0003]     Traditional gas turbine combustors use diffusion (i.e., non-premixed) combustion in which fuel and air enter the combustion flame zone separately and mix as they burn. The process of mixing and burning produces flame temperatures exceeding 3900° F. Because diatomic nitrogen rapidly disassociates and oxidizes at temperatures exceeding about 3000° F. (about 1650° C.), the high temperatures of diffusion combustion result in relatively high NOx emissions.  
         [0004]     The ability to control the amount of fuel flow to different regions of the combustor allows for the minimizing of CO and NOx emissions for a given set of operating conditions.  
         [0005]     Accordingly, there is a need for independent variable control of fuel flow to fuel introduction locations of the combustor as a means to further reduce emissions across full ambient ranges and gas turbine load ranges and provide an additional tuning level for enhanced operability optimization.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     Disclosed herein is a fuel nozzle. The fuel nozzle includes a first fuel introduction location, a second fuel introduction location, and fuel passages. The first fuel introduction location is located radially about the fuel nozzle and is connected with a fuel passage. The second fuel introduction location is located at an end of the fuel nozzle and is connected with another fuel passage such that the fuel passage connected to the first fuel introduction location is separate from the fuel passage connected to the second fuel introduction location.  
         [0007]     Further disclosed herein is a gas turbine combustor. The gas turbine combustor includes a primary combustion chamber, a plurality of primary nozzles, a secondary combustion chamber, and a secondary nozzle. The plurality of primary nozzles are capable of delivering fuel to the primary combustion chamber. The secondary combustion chamber is downstream of the primary combustion chamber. And, the secondary nozzle is capable of delivering fuel to the secondary combustion chamber. The secondary nozzle has a plurality of individually controlled fuel circuits.  
         [0008]     Yet further disclosed herein is a method for controlling fuel flow in a secondary fuel nozzle for a gas turbine combustor. A first fuel flow is conveyed to a reaction zone of the combustor. And a second fuel flow is conveyed to a downstream combustion chamber of the combustor such that the first fuel flow is controlled independently of the second fuel flow and the second fuel flow is controlled independently of the first fuel flow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures:  
         [0010]      FIG. 1  is a partial cross section view of a gas turbine for use in accordance with an embodiment of the invention;  
         [0011]      FIG. 2  is a side view of an exemplary secondary nozzle for use in accordance with an embodiment of the invention;  
         [0012]      FIG. 3  is an enlarged view of a secondary nozzle peg area of the secondary nozzle of  FIG. 2 ;  
         [0013]      FIG. 4  is an enlarged view of a secondary nozzle pilot tip of the secondary nozzle of  FIG. 2 ; and,  
         [0014]      FIG. 5  is an enlarged view of a lip seal region of the secondary nozzle of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Referring to  FIG. 1 , a gas turbine  10  (partially shown) includes a compressor  12  (also partially shown), a plurality of combustors  14  (one shown), and a turbine section represented here by a single blade  16 . Although not specifically shown, the turbine is drivingly connected to the compressor  12  along a common axis. The compressor  12  pressurizes inlet air which is then reverse flowed to the combustor  14  where it is used to cool the combustor and to provide air to the combustion process.  
         [0016]     As noted above, the plurality of combustors  14  are located in an annular array about the axis of the gas turbine. A transition duct  18  connects the outlet end of each combustor  14  with the inlet end of the turbine to deliver the hot products of combustion to the turbine in the form of an approved temperature profile.  
         [0017]     Each combustor  14  may comprise a primary or upstream combustion chamber  24  and a secondary or downstream combustion chamber  26  separated by a venturi throat region  28 . The combustor  14  is surrounded by combustor flow sleeve  30  which channels compressor discharge air flow to the combustor  14 . The combustor  14  is further surrounded by an outer casing  32  which is bolted to a turbine casing  34 .  
         [0018]     Primary nozzles  36  provide fuel delivery to the upstream combustor  24  and are arranged in an annular array around a central secondary nozzle  38 . Ignition is achieved in the various combustors  14  by means of sparkplug  20  in conjunction with crossfire tubes  22  (one shown). The secondary nozzle  38  provides fuel delivery to the downstream combustion chamber  26 .  
         [0019]      FIG. 2  illustrates an exemplary secondary nozzle  38  having two fuel introduction locations including secondary nozzle pegs  40  and a secondary nozzle pilot tip  42 . The secondary nozzle pegs  40  provide fuel to a pre-mix reaction zone of the combustor  14 , while the secondary nozzle pilot tip  42  provides fuel to the downstream combustion chamber  26  where it is immediately burned (diffusion combustion). The secondary nozzle  38  is a combustion system fuel delivery device having separate and individually controlled fuel circuits which allows for the ability to individually vary fuel flow rates delivered to the two fuel introduction locations (secondary nozzle pegs  40  and secondary nozzle pilot tip  42 ). For example, the fuel flow rate through the secondary nozzle pilot tip  42  may be varied independently from the fuel flow rate through the secondary nozzle pegs  40  and the fuel flow rate through the secondary nozzle pegs  40  may be varied independently from the fuel flow rate through the secondary nozzle pilot tip  42 . Further, the secondary nozzle pegs  40  and the secondary nozzle pilot tip  42  each have their own independent fuel piping circuit, with each having independent and exclusive fuel sources. The fuel flow rate delivered to the secondary nozzle pilot tip  42  is less than about 2% of the total gas turbine fuel flow and is capable of, in one embodiment, delivering and controlling the fuel flow rate in the range of about 0.002 pps (pounds per second) to about 0.020 pps. Independent control of the two fuel introduction locations provides an additional degree of freedom which may be exercised to optimize the combustion system and minimize the CO and NOx emissions produced by the gas turbine system. In particular, the independent control of the two fuel introduction locations may achieve sub-5 ppm (parts per million) NOx emissions across the full ambient and load range. The fuel piping circuits and passages are described in greater detail below.  
         [0020]      FIG. 3  further illustrates the secondary nozzle pegs  40  and the independent fuel circuits and passages. The secondary fuel nozzle  38  comprises a series of concentric tubes. The two radially outermost concentric tubes  44  and  48  provide a tertiary gas passage  46 . The tertiary gas passage  46  provides tertiary gas to the secondary nozzle pilot tip  42 .  
         [0021]     A secondary gas fuel passage  50 , adjacent to the tertiary gas passage  46 , is formed between concentric tubes  48  and  52 . The secondary gas fuel passage  50  communicates with the plurality of radially extending secondary nozzle pegs  40  arranged about the circumference of the secondary nozzle  38  and supplies secondary gas fuel to the secondary nozzle pegs  40 .  
         [0022]     A sub-pilot gas fuel passage  54 , adjacent to the secondary gas fuel passage  50 , is defined between concentric tubes  52  and  56 . The sub-pilot gas fuel passage  54  supplies sub-pilot gas fuel to the secondary nozzle pilot tip  42 .  
         [0023]     A water purge passage  58 , adjacent to the sub-pilot gas fuel passage  54 , is defined between concentric tubes  56  and  60 . The water purge passage  58  provides water to the secondary nozzle pilot tip  42  to effect carbon monoxide (CO) and nitrogen oxide (NOx) emission reductions.  
         [0024]     A liquid fuel passage  62 , the innermost of the series of concentric passages forming the secondary nozzle  38 , is defined by tube  60 . The liquid fuel passage  62  provides liquid fuel to the secondary nozzle pilot tip  42 .  
         [0025]     Additionally, although  FIG. 2  shows four independent fuel circuits, it should be noted that the number of fuel circuits may be varied according to operational and design considerations.  
         [0026]      FIG. 4  further illustrates the secondary nozzle pilot tip  42 . The secondary nozzle pilot tip  42 , in one embodiment, may be a three piece assembly having a sub-pilot portion  64 , which contains the sub-pilot gas fuel at the secondary nozzle pilot tip  42  and abuts tube  52 , a water purge portion  66 , which contains the water at the secondary nozzle pilot tip  42  and abuts tube  56 , and a tip portion  68 , which forms an outlet end to the secondary nozzle  38 . The three piece secondary nozzle pilot tip may be fixedly joined, for example, by an electron beam welding process.  
         [0027]      FIG. 5  illustrates a lip seal  70  between tube  56  and a secondary nozzle base  72 . The lip seal  70  prevents fuel leakage within the secondary nozzle  38  by forming a controlled interference fit between the tube  56  and the secondary nozzle base. It will be appreciated that lip seals  70  may be utilized between other fuel passage defining tubes (other than tube  56 ) and the secondary nozzle base  72  as required to prevent fuel leakage.  
         [0028]     While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.