System and method for load control with diffusion combustion in a stoichiometric exhaust gas recirculation gas turbine system

Abstract

A system is provided with a turbine combustor having a first diffusion fuel nozzle, wherein the first diffusion fuel nozzle is configured to produce a diffusion flame. The system includes a turbine driven by combustion products from the diffusion flame in the turbine combustor. The system also includes an exhaust gas compressor, wherein the exhaust gas compressor is configured to compress and route an exhaust gas from the turbine to the turbine combustor along an exhaust recirculation path. In addition, the system includes a control system configured to control flow rates of at least one oxidant and at least one fuel to the turbine combustor in a stoichiometric control mode and a non-stoichiometric control mode, wherein the stoichiometric control mode is configured to change the flow rates and provide a substantially stoichiometric ratio of the at least one fuel with the at least one oxidant, and the non-stoichiometric control mode is configured to change the flow rates and provide a non-stoichiometric ratio of the at least one fuel with the at least one oxidant.

1 . A system, comprising:
 an oxidant compressor configured to produce a compressed stream of an oxidant;   a turbine combustor receiving the compressed stream of the oxidant from the oxidant compressor and comprising a diffusion fuel nozzle configured to inject separate streams of a portion of the oxidant, a diluent, and a fuel into the turbine combustor to produce a diffusion flame;   a turbine driven by combustion products from the diffusion flame in the turbine combustor;   an exhaust gas compressor configured to compress and route an exhaust gas from the turbine to the turbine combustor along an exhaust recirculation path, and wherein at least a portion of the exhaust gas is directed to the diffusion fuel nozzle as the diluent; and   a tangible, machine-readable medium comprising one or more instructions configured to be executed by a processor, wherein the one or more instructions are configured to:
 adjust flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in a stoichiometric control mode to drive a first target load of the turbine; and 
 adjust the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in the stoichiometric control mode to drive a second target load of the turbine, wherein the second target load of the turbine is less than the first target load, wherein an equivalence ratio of the turbine combustor to drive the first target load and the second target load is between 0.95 and 1.05, and wherein an amount of carbon monoxide in the combustion products produced in the stoichiometric control mode is less than 5000 parts per million by volume. 
   
     
     
         2 . The system of  claim 1 , wherein the one or more instructions are configured to adjust the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor to transition from the stoichiometric control mode to a non-stoichiometric control mode to drive a third target load of the turbine, and wherein the equivalence ratio in the non-stoichiometric control mode is above 1.05 or below 0.95. 
     
     
         3 . The system of  claim 2 , wherein the amount of carbon monoxide in the combustion products produced in the non-stoichiometric control mode is less than 5000 parts per million by volume. 
     
     
         4 . The system of  claim 1 , wherein an amount of carbon monoxide in the combustion products produced in the stoichiometric control mode is less than 1000 parts per million by volume. 
     
     
         5 . The system of  claim 1 , wherein the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in the stoichiometric control mode to drive the first target load are greater than the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in the stoichiometric control mode to drive the second target load. 
     
     
         6 . The system of  claim 1 , wherein the equivalence ratio of the turbine combustor to drive the first target load and the second target load is 1.0, and wherein the first target load comprises a rated load for the turbine. 
     
     
         7 . The system of  claim 1 , wherein the turbine combustor comprises a first set of fuel nozzles coupled to a first fluid supply circuit and a second set of fuel nozzles coupled to a second fluid supply circuit, the diffusion fuel nozzle is part of either the first or second set of fuel nozzles, and the one or more instructions are configured to independently control fluid flows through the first and second fluid supply circuits. 
     
     
         8 . The system of  claim 1 , wherein the diffusion fuel nozzle comprises a first fuel passage and a first oxidant passage that are isolated from one another along the diffusion fuel nozzle. 
     
     
         9 . The system of  claim 1 , wherein the turbine combustor comprises a second diffusion fuel nozzle configured to inject separate streams of a second portion of the oxidant, a second diluent, and a second fuel into the turbine combustor to produce a second diffusion flame. 
     
     
         10 . The system of  claim 9 , wherein the one or more instructions are configured to adjust second flow rates of the second portion of the oxidant, the second diluent, and the second fuel in the stoichiometric control mode to drive a third target load, and wherein a first ratio of the flow rates and a second ratio of the second flow rates generates a combined stoichiometric ratio of the turbine combustor that is approximately 1.0. 
     
     
         11 . The system of  claim 1 , wherein the turbine combustor is without premix fuel nozzles. 
     
     
         12 . A method, comprising:
 introducing an oxidant to at least one oxidant compressor to produce a compressed oxidant stream;   introducing a portion of the compressed oxidant stream and a fuel stream to a diffusion fuel nozzle of a turbine combustor, wherein the diffusion fuel nozzle is configured to inject separate streams of the portion of the compressed oxidant stream and the fuel stream to produce a diffusion flame;   mixing the portion of the compressed oxidant stream and the fuel stream at a point of combustion to produce the diffusion flame;   driving a turbine with combustion products generated by the diffusion flame in the turbine combustor;   adjusting flow rates of the portion of the compressed oxidant stream and the fuel stream to the turbine combustor in a stoichiometric control mode to drive a first target load of the turbine; and   adjusting the flow rates of the portion of the compressed oxidant stream and the fuel stream to the turbine combustor in the stoichiometric control mode to drive a second target load of the turbine, wherein the second target load of the turbine is less than the first target load, wherein an equivalence ratio of turbine combustor to drive the first target load and the second target load is between 0.95 and 1.05, and wherein an amount of carbon monoxide in the combustion products produced in the stoichiometric control mode is less than 5000 parts per million by volume.   
     
     
         13 . The method of  claim 12 , comprising receiving feedback from a sensor indicative of the amount of carbon monoxide in the combustion products and adjusting the flow rates based on the feedback. 
     
     
         14 . The method of  claim 12 , comprising introducing a second portion of the compressed oxidant stream and a second fuel stream to a second diffusion fuel nozzle of the turbine combustor to produce a second diffusion flame. 
     
     
         15 . The method of  claim 14 , comprising adjusting second flow rates of the second portion of the compressed oxidant stream and the second fuel stream in the stoichiometric control mode to drive a third target load of the turbine, and wherein a first ratio of the flow rates and a second ratio of the second flow rates generates a combined stoichiometric ratio of the turbine combustor that is approximately 1.0. 
     
     
         16 . The method of  claim 12 , comprising adjusting the flow rates of the portion of the compressed oxidant stream and the fuel stream to the turbine combustor to transition from the stoichiometric control mode to a non-stoichiometric control mode to drive a third target load of the turbine, and wherein the equivalence ratio in the non-stoichiometric control mode is above 1.05 or below 0.95. 
     
     
         17 . The method of  claim 12 , wherein the equivalence ratio of the turbine combustor to drive the first target load and the second target load is 1.0, and wherein the first target load comprises a rated load for the turbine. 
     
     
         18 . A system, comprising:
 an oxidant compressor configured to produce a compressed stream of an oxidant;   a turbine combustor receiving the compressed stream of the oxidant from the oxidant compressor and comprising a diffusion fuel nozzle configured to inject separate streams of a portion of the oxidant, a diluent, and a fuel into the turbine combustor to produce a diffusion flame, and wherein the diffusion fuel nozzle comprises a first passage, a second passage, a third passage, and a fourth passage configured to inject separate streams of the portion of the oxidant, the diluent, and the fuel into the turbine combustor to produce the diffusion flame;   a turbine driven by combustion products from the diffusion flame in the turbine combustor; and   a tangible, machine-readable medium comprising one or more instructions configured to be executed by a processor, wherein the one or more instructions are configured to:
 adjust flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in a stoichiometric control mode to drive a first target load of the turbine; and 
 adjust the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor in the stoichiometric control mode to drive a second target load of the turbine, wherein the second target load of the turbine is less than the first target load, wherein an equivalence ratio of the turbine combustor to drive the first target load and the second target load is between 0.95 and 1.05, and wherein an amount of carbon monoxide in the combustion products produced in the stoichiometric control mode is less than 5000 parts per million by volume. 
   
     
     
         19 . The system of  claim 18 , comprising an exhaust gas compressor, wherein the exhaust gas compressor is configured to compress and route only an exhaust gas from the turbine to the turbine combustor along an exhaust recirculation path, and wherein at least a portion of the exhaust gas is directed to the diffusion fuel nozzle as the diluent. 
     
     
         20 . The system of  claim 18 , wherein the one or more instructions are configured to adjust the flow rates of the portion of the oxidant, the diluent, and the fuel to the turbine combustor to transition from the stoichiometric control mode to a non-stoichiometric control mode to drive a third target load of the turbine, and wherein the equivalence ratio in the non-stoichiometric control mode is above 1.05 or below 0.95.