Patent Publication Number: US-8978384-B2

Title: Swirler assembly with compressor discharge injection to vane surface

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to gas turbines and, more particularly, to a swirler assembly in a gas turbine combustor including an air circuit in the swirler vanes that directs compressor discharge air to a low pressure side of the swirler vanes. 
     In a gas turbine combustor, compressed air from the compressor and fuel are mixed upstream of a combustion zone. A swirler assembly includes circumferentially spaced apart vanes for swirling and mixing the compressed air flow and the fuel passing therethrough. 
     The swirler assemblies, also described as swozzle assemblies, may have flame holding margins limited by flow deficits on a suction side of the vane turning region. This reduced flame holding margin and locally enriched air/fuel regions reduce the performance of the combustor. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an exemplary embodiment, a swirler assembly in a gas turbine combustor includes a hub, a shroud, and a plurality of vanes connected between the hub and the shroud. The vanes include a high pressure side on which air and fuel impinge the vanes and a low pressure side. An air circuit is provided in each of the plurality of vanes receiving discharge air from a compressor. Each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes. 
     In another exemplary embodiment, a gas turbine includes a compressor that progressively compresses a working fluid such as air, a combustor injecting fuel into the compressed air and igniting the air and fuel to produce combustion gases, and a turbine using the combustion gases to produce work. The combustor includes a swirler assembly that imparts swirl to the air and the fuel. The swirler assembly comprises a hub, a shroud, a plurality of vanes connected between the hub and the shroud, and an air circuit in each of the plurality of vanes. The air and fuel impinge the vanes on a high pressure side. The air circuit in each of the plurality of vanes receives discharge air from the compressor, where each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes. 
     In yet another exemplary embodiment, a method of mixing fuel and air in a swirler assembly includes the steps of providing an air circuit in each of the plurality of vanes, each of the air circuits including an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes; and directing airflow from a compressor to the air entry passage into the vanes and through the air exit passage on the low pressure side of the vanes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic of a gas turbine; 
         FIG. 2  is a cross-section through a fuel nozzle in a gas turbine; 
         FIG. 3  shows a swirler assembly with the shroud removed; and 
         FIG. 4  is a perspective view of the swirler assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a typical gas turbine  10 . As shown, the gas turbine  10  generally includes a compressor at the front, one or more combustors  14  around the middle, and a turbine  16  at the rear. The compressor  12  and the turbine  16  typically share a common rotor. The compressor  12  progressively compresses a working fluid, such as air, and discharges the compressed working fluid to the combustors  14 . The combustors  14  inject fuel into the flow of compressed working fluid and ignite the mixture to produce combustion gases having a high temperature, pressure and velocity. The combustion gases exit the combustors  14  and flow to the turbine  16  where they expand to produce work. 
     A casing surrounds each combustor  14  to contain the compressed working fluid from the compressor  12 . Nozzles are arranged in an end cover, for example, with outer nozzles radially arranged around a center nozzle. The compressed working fluid from the compressor  12  flows between the casing and a liner to the outer and center nozzles, which mix fuel with the compressed working fluid, and the mixture flows from the outer and center nozzles into upstream and downstream chambers where combustion occurs. 
       FIG. 2  is a cross-section through a fuel nozzle in a gas turbine. The nozzle assembly is divided into four regions by function including an inlet flow conditioner  1 , an air swirler assembly (referred to as a swozzle assembly)  2 , an annular fuel air mixing passage  3 , and a central diffusion flame fuel nozzle assembly  4 . 
     Air enters the burner from a high pressure plenum  6 , which surrounds the entire assembly except the discharge end, which enters the combustor reaction zone  5 . Most of the air for combustion enters the premixer via the inlet flow conditioner (IFC)  1 . The IFC includes an annular flow passage  15  that is bounded by a solid cylindrical inner wall  13  at the inside diameter, a perforated cylindrical outer wall  12  at the outside diameter, and a perforated end cap  11  at the upstream end. In the center of the flow passage  15  is one or more annular turning vanes  14 . Premixer air enters the IFC  1  via the perforations in the end cap and cylindrical outer wall. 
     The perforated walls  11 ,  12  perform the function of backpressuring the system and evenly distributing the flow circumferentially around the IFC annulus  15 , whereas the turning vane(s)  14 , work in conjunction with the perforated walls to produce proper radial distribution of incoming air in the IFC annulus  15 . 
     To eliminate low velocity regions near the shroud wall  202  at the inlet to the swozzle  2 , a bell-mouth shaped transition  26  may be used between the IFC and the swozzle. 
     After combustion air exits the IFC  1 , it enters the swozzle assembly  2 . The swozzle assembly includes a hub  201  and a shroud  202  connected by a series of air foil shaped turning vanes  23 , which impart swirl to the combustion air passing through the premixer (see  FIGS. 3 and 4 ). After exiting the annular passage  3 , the fuel/air mixture enters the combustor reaction zone  5  where combustion takes place. 
       FIGS. 3 and 4  show the swirler assembly  2  according to preferred embodiments. As shown, the swirler assembly  2  includes the hub  201 , the shroud  202 , and a plurality of vanes  23  connected between the hub and the shroud. The side  231  of the vanes  23  on which air and fuel impinge the vanes is a high pressure side. The opposite side  232  is a low pressure side. 
     In some existing swirler assembly designs, the vanes  23  include a cap feed channel  233  and a corresponding opening  234  in the shroud  202 . Compressor discharge air is fed to the cap feed channel  233  through the vane  23  and hub  201  of the swirler assembly then out through the nozzle tip to provide for nozzle tip cooling. 
     An air circuit is provided in each of the plurality of vanes  23 . The air circuit receives discharge air from the compressor. Each of the air circuits includes an air entry passage into the vanes and an air exit passage on the low pressure side of the vanes. In one embodiment, the air entry passage of the air circuit is defined by the cap feed  233 . The exit passage comprises holes  235  in the low pressure side  232  of the vane that extend into the cap feed  233 . In this embodiment, a portion of the compressor discharge air in the cap feed  233  is diverted through the exit passage  235  to the low pressure side of the vanes  23 . 
     In an alternative embodiment, a dedicated passage  236  through the vane  23  is provided for the air circuit, which passage  236  is separate from the cap feed passage  233 . In this embodiment, the air exit passage includes the holes  235  on the low pressure side of the vanes  23 . The holes  235  in this embodiment extend into the dedicated passage  236  through which compressor discharge air is directed. In this embodiment, a corresponding hole  237  is provided in the shroud  202 . 
     Preferably, the compressor discharge air is received directly from the compressor. Swirler vane low pressure injection air can be provided from either the compressor discharge or from an alternate pressure feed source. The compressor discharge feed can be taken at any point along the compressor discharge path up to the annular section feeding the combustor head end. Compressor discharge air taken directly from the exit of the compressor will be at a higher pressure (as compared to the combustor head end pressure) which may benefit swirler vane low pressure injection by creating a greater pressure differential on the suction flow deficit region of the vane. An alternate pressure feed may also be utilized to further enhance the flow/pressure differential on the vane suction side injection. 
     The swirler assembly  2  enables higher pressure clean compressor discharge air to be injected along either the pressure or suction side of the swozzle vane to improve fuel mixing locally. Injecting compressor discharge air along the vane edge can add needed air to low flow regions of the swozzle vane thus increasing flame holding margin, improving fuel mixing, and improving operability and flame stability by reducing local rich fuel pockets. Injection air can be supplied from the compressor discharge either adjacent the compressor exit (highest pressure available) or along the compressor feed circuit up to the annular feed leading to the combustor head end (lowest pressure differential). An alternate air pressure feed could also be utilized from an auxiliary compressor at a further elevated pressure and/or lower temperature. The air injection can occur on the vane suction side and/or vane pressure side and include an upstream air curtain to shroud the vane surface with higher pressure and/or lower temperature air to further facilitate fuel mixing and pressure deficit elimination. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.