Retrofittable air assisted fuel injection method to control gaseous and acoustic emissions

Abstract

In the operation of gas turbine engines, it is an ever increasing goal to reduce the amount of harmful elements contained within the emissions of the engine. It is also desirable to provide a method and system that is capable of being utilized to retrofit existing gas turbine engines. In particular, it is of primary importance to reduce the amounts of nitrogen oxides contained within the emissions. Many times, reduced emissions comes at the cost of decreased flame operability. The present invention provides airflow to the pilot fuel line of a combustor in order to reduce the total harmful emissions, yet at the same time allow improved flame stability.

We claim:  
     
         1 . A method of combusting hydrocarbon fuel, comprising: 
 injecting an air stream into an air assist valve resulting in an air assist valve air stream;    allowing said air assist valve air stream and pilot fuel to flow through a pilot fuel tube resulting in a pilot fuel stream;    allowing fuel to flow from a premix fuel line to a premixer resulting in a premix fuel stream;    combining said pilot fuel stream, premix fuel stream, and an air stream resulting in a mixture stream;    igniting said mixture stream; and    wherein a temperature and composition of said mixture stream are selected to control simultaneously the amounts of NO x  formed in a main combustor and a stability of a flame in said main combustor, thereby controlling a total amount of NO x  emitted.    
     
     
         2 . The method as in  claim 1 , wherein said pilot fuel is in liquid form.  
     
     
         3 . The method as in  claim 1 , wherein said pilot fuel is in gaseous form.  
     
     
         4 . The method as in  claim 1 , further comprising expanding the mixture stream across a turbine thereby producing power.  
     
     
         5 . The method as in  claim 1 , wherein between 0-50 percent of the total fuel is supplied through said pilot fuel line.  
     
     
         6 . The method as in  claim 1 , wherein between 50-100 percent of the total fuel is supplied through said premix fuel line.  
     
     
         7 . The method as in  claim 1 , wherein said air assist valve air stream is less than 10 times said pilot fuel stream.  
     
     
         8 . The method as in  claim 1 , wherein said NO x  emitted is below 9 parts per million.  
     
     
         9 . The method as in  claim 1 , wherein said air stream is bleed air from a gas turbines engine core compressor and injected into said air assist valve resulting in an air assist valve air stream.  
     
     
         10 . A system for combusting a hydrocarbon fuel, comprising: 
 a combustor having an upstream end and a downstream end; and    a premix area connected to the upstream end of said combustor for receiving and substantially premixing fuel and air prior to delivery of said upstream end of said combustor, said premix area comprising;    a centerbody extending longitudinally through said premix area;    at least one premix fueling pathway positioned radially around said centerbody which receives premix fuel;    at least one fueling pathway positioned radially within said centerbody, which receives air assisted pilot fuel and allows said air assisted pilot fuel to exit through a pilot fuel outlet pathway;    an igniter located within said centerbody; and    at least one pilot air pathway positioned radially within said centerbody and allows said air to exit through a pilot air outlet pathway.    
     
     
         11 . The system as in  claim 10 , further comprising an air assist line in communication with a pilot fuel.  
     
     
         12 . The system as in  claim 11 , wherein said air assist line has a check valve to prevent fuel entering a source of said air assist line.  
     
     
         13 . The system as in  claim 11 , wherein said air assist line air flow is between 0 and 60 lb/hr.  
     
     
         14 . The system as in  claim 11 , wherein said air assist line is in communication with a bleed air valve from a core compressor.  
     
     
         15 . The system as in  claim 11 , further comprising an air assist pump.  
     
     
         16 . A system for combusting a hydrocarbon fuel, comprising: 
 a combustor having an upstream end and a downstream end;    a pilot fuel line in communication with an air assist line, wherein fuel from said pilot fuel line is injected with air from said air assist line and allowed to flow through a pilot flow tube to a premix area;    a check valve controllably communicating with said air assist air stream;    a premix fuel line connected to said premix area, radially located around a centerbody;    said premix area is connected to the upstream end of said combustor for receiving and substantially premixing fuel from said pilot fuel tube and said premix fuel tube, said premix area comprising;    said centerbody extending longitudinally through said premix area;    a fueling pathway positioned radially within said centerbody, which receives air assisted pilot fuel;    a pilot air pathway positioned radially within said centerbody; and    an igniter located centrally within said centerbody.    
     
     
         17 . The system as in  claim 16 , wherein 0-50 percent of the fuel is supplied through said pilot fuel line.  
     
     
         18 . The system as in  claim 16 , wherein 50-100 percent of the fuel is supplied through said premix fuel line.  
     
     
         19 . The system as in  claim 16 , further comprising a combustor liner in communication with a heat shield, said heat shield in communication with a combustor cap, wherein said heat shield is interposed between said combustor liner and said combustor cap.  
     
     
         20 . The system as in  claim 16 , wherein said air assist line air flow is between 0 and 60 lb/hr.  
     
     
         21 . The system as in  claim 16 , wherein said air assist line is in communication with a bleed air valve from the compressor.  
     
     
         22 . The system as in  claim 16 , further comprising an air assist pump.