Premixing dry low NOx emissions combustor with lean direct injection of gas fuel

Abstract

Lean premixed combustion of a hydrocarbon fuel and air is combined with lean direct injection of hydrocarbon fuel and carrier fluid such as air or inert gas or a mixture of air and inert gas into a combustor downstream of the premixed reaction zone in order to achieve extremely low levels of emissions of oxides of nitrogen at the high combustor exit temperatures required by advanced heavy duty industrial gas turbines. One or more premixing fuel nozzles are used to supply a lean mixture of hydrocarbon fuel and air to the main or primary reaction zone of a gas turbine combustor. This lean fuel/air mixture has an adiabatic flame temperature below the temperature that would result in substantial thermal NOx formation. After this low temperature reaction has been completed. Additional fuel and carrier fluid are injected into the products of combustion downstream of the main reaction zone in order to raise the temperature of the mixture to the level required to operate an advanced, high efficiency, heavy duty industrial gas turbine at high load. Formation of nitrogen oxides in the region after this secondary fuel and carrier fluid injection is minimized by partial premixing of fuel and carrier fluid prior to ignition and by minimizing the residence time between the secondary fuel injection and the turbine first stage inlet.

1 . A combustor for a gas turbine comprising: 
 a primary combustion system for combusting a mixture of fuel and air in a primary reaction zone, and operable in a plurality of gas turbine modes, said gas turbine modes being determined based on a load range of the gas turbine; and    a secondary combustion system selectively operable in a high load range mode of the plurality of gas turbine modes, said secondary combustion system combusting a mixture of fuel and carrier fluid in a secondary reaction zone.    
     
     
         2 . A combustor according to    claim 1   , further comprising: 
 a combustor casing having an open end and an end cover assembly secured to another end thereof;    a flow sleeve mounted within said casing; and    a combustion liner within said flow sleeve and defining at least said primary reaction zone;    wherein said primary combustion system comprises a sleeve cap assembly secured to said casing and located axially downstream of said end cover assembly, and at least one start-up fuel nozzle and a plurality of premixing fuel nozzles communicating with said primary reaction zone.    
     
     
         3 . A combustor according to    claim 2   , wherein each premixing fuel nozzle comprises: 
 a swirler including a plurality of swirl vanes that impart rotation to entering air; and    a plurality of fuel spokes that distribute fuel in the rotating air stream.    
     
     
         4 . A combustor according to    claim 2   , wherein said combustion liner defines said secondary reaction zone downstream of said primary reaction zone, said secondary combustion system comprising a lean direct injection (LDI) fuel injector assembly communicating with said secondary reaction zone.  
     
     
         5 . A combustor according to    claim 4   , wherein said LDI fuel injector assembly comprises an air manifold, a fuel manifold, and a plurality of fuel/air injection spokes communicating with said air manifold and said fuel manifold, said plurality of fuel/air injection spokes penetrating the combustion liner for introducing fuel and carrier fluid into said secondary reaction zone.  
     
     
         6 . A combustor according to    claim 5   , wherein said carrier fluid is air.  
     
     
         7 . A combustor according to    claim 5   , wherein said carrier fluid is one of inert gas or a mixture of air and inert gas.  
     
     
         8 . A combustor according to    claim 7   , wherein said inert gas is one of steam or nitrogen.  
     
     
         9 . A combustor according to    claim 1   , wherein said secondary combustion system comprises a lean direct injection (LDI) fuel injector assembly.  
     
     
         10 . A combustor according to    claim 9   , wherein said LDI fuel injector assembly comprises an air manifold, a fuel manifold, and a plurality of fuel/air injection spokes communicating with said air manifold and said fuel manifold.  
     
     
         11 . A combustor according to    claim 1   , further comprising a transition piece disposed downstream of said primary combustion system and said secondary combustion system for flowing hot gases of combustion to turbine nozzles of the gas turbine.  
     
     
         12 . A combustor according to    claim 1   , wherein said carrier fluid is air.  
     
     
         13 . A combustor according to    claim 1   , wherein said carrier fluid is one of inert gas or a mixture of air and inert gas.  
     
     
         14 . A combustor according to    claim 13   , wherein said inert gas is one of steam or nitrogen.  
     
     
         15 . A gas turbine comprising: 
 a compressor section for pressurizing inlet air;    a combustion section disposed downstream of the compressor section for receiving the pressurized inlet air; and    a turbine section disposed downstream of the combustion section for receiving hot products of combustion from the combustion section, wherein the combustion section comprises: 
 a primary combustion system for combusting a mixture of fuel and air in a primary reaction zone, and operable in a plurality of gas turbine modes, said gas turbine modes being determined based on a load range of the gas turbine, and  
 a secondary combustion system selectively operable in a high load range mode of the plurality of gas turbine modes, said secondary combustion system combusting a mixture of fuel and carrier fluid in a secondary reaction zone.  
   
     
     
         16 . A gas turbine according to    claim 15   , wherein said combustion section further comprises: 
 a combustor casing having an open end and an end cover assembly secured to another end thereof;    a flow sleeve mounted within said casing; and    a combustion liner within said flow sleeve and defining at least a primary reaction zone;    wherein said primary combustion system comprises a sleeve cap assembly secured to said casing and located axially downstream of said end cover assembly, and at least one start-up fuel nozzle and a plurality of premixing fuel nozzles communicating with said primary reaction zone.    
     
     
         17 . A gas turbine according to    claim 16   , wherein each premixing fuel nozzle comprises: 
 a swirler including a plurality of swirl vanes that impart rotation to entering air; and    a plurality of fuel spokes that distribute fuel in the rotating air stream.    
     
     
         18 . A gas turbine according to    claim 16   , wherein said combustion liner defines said secondary reaction zone downstream of said primary reaction zone, said secondary combustion system comprising a lean direct injection (LDI) fuel injector assembly communicating with said secondary reaction zone.  
     
     
         19 . A gas turbine according to    claim 18   , wherein said LDI fuel injector assembly comprises an air manifold, a fuel manifold, and a plurality of fuel/air injection spokes communicating with said air manifold and said fuel manifold, said plurality of fuel/air injection spokes penetrating the combustion liner for introducing fuel and carrier fluid into said secondary reaction zone.  
     
     
         20 . A gas turbine according to    claim 19   , wherein said carrier fluid is air.  
     
     
         21 . A gas turbine according to    claim 19   , wherein said carrier fluid is one of inert gas or a mixture of air and inert gas.  
     
     
         22 . A gas turbine according to    claim 21   , wherein said inert gas is one of steam or nitrogen.  
     
     
         23 . A gas turbine according to    claim 15   , wherein said secondary combustion system comprises a lean direct injection (LDI) fuel injector assembly.  
     
     
         24 . A gas turbine according to    claim 23   , wherein said LDI fuel injector assembly comprises an air manifold, a fuel manifold, and a plurality of fuel/air injection spokes communicating with said air manifold and said fuel manifold.  
     
     
         25 . A gas turbine according to    claim 15   , wherein said combustion system further comprises a transition piece disposed downstream of said primary combustion system and said secondary combustion system for flowing hot gases of combustion to the turbine section.  
     
     
         26 . A gas turbine according to    claim 15   , wherein said carrier fluid is air.  
     
     
         27 . A gas turbine according to    claim 15   , wherein said carrier fluid is one of inert gas or a mixture of air and inert gas.  
     
     
         28 . A gas turbine according to    claim 27   , wherein said inert gas is one of steam or nitrogen.  
     
     
         29 . A method of combustion in a gas turbine combustor including a primary combustion system operable in a plurality of gas turbine modes and including at least one start-up fuel nozzle and a plurality of premixing fuel nozzles communicating with a primary reaction zone, and a lean direct injection (LDI) combustion system communicating with a secondary reaction zone, the method comprising: 
 (a) in a low-range turbine load mode, supplying fuel to the said at least one start-up fuel nozzle and mixing the fuel with air in the primary reaction zone;    (b) in a mid-range turbine load mode, supplying fuel to the premixing fuel nozzles and premixing the fuel with air for combustion in the primary reaction zone; and    (c) in a high-range turbine load mode, carrying out step (b) and then supplying fuel and carrier fluid to the LDI combustion system for combustion in the secondary reaction zone.    
     
     
         30 . The method of    claim 29   , wherein said carrier fluid is air.  
     
     
         31 . The method of    claim 29   , wherein said carrier fluid is one of inert gas and a mixture of air and inert gas.  
     
     
         32 . The method of    claim 31   , wherein said inert gas is one of steam or nitrogen.  
     
     
         33 . A method of combustion for achieving low levels of emissions of oxides of nitrogen (NOx) at high combustor exit temperatures comprising lean direct injection of hydrocarbon fuel and carrier fluid into a combustor downstream of a premixed combustion zone of said combustor to which a lean mixture of hydrocarbon fuel and air have been supplied and combusted at an adiabatic flame temperature below the temperature that would result in substantial thermal NOx formation.  
     
     
         34 . The method of    claim 33    in which the hydrocarbon fuel and carrier fluid are partially premixed prior to lean direct injection into the products of combustion from the premixed combustion zone, thereby causing auto-ignition and raising the temperature of the resulting combustion products.  
     
     
         35 . The method of    claim 33   , wherein said carrier fluid is air.  
     
     
         36 . The method of    claim 33   , wherein said carrier fluid is one of inert gas or a mixture of air and inert gas.  
     
     
         37 . The method of    claim 36   , wherein said inert gas is one of steam or nitrogen.