Method and apparatus for optimizing the operation of a turbine system under flexible loads

A method for changing power output in a gas turbine system having a compressor, a combustor, and a turbine, comprising:

• determining an existing power output;
• determining a desired power output;
• measuring existing compressor parameters and combustor parameters;
• calculating a compressor flow rate coefficient for the desired power output;
• calculating an emission rate for the desired power output;
• if the compressor flow rate coefficient for the desired power output is less than a predetermined turndown limit, then calculating new compressor parameters that result in a new compressor flow rate coefficient above the predetermined turndown limit;
• if the calculated emission rate is greater than a predetermined emissions limit, then calculating new combustor parameters that result in an emission rate lower than the predetermined emissions limit;
• changing the power output to the desired power output;
• changing the compressor parameters to the new compressor parameters;
• and
• changing the combustor parameters to the new combustor parameters,
• wherein the compressor has an inlet and an outlet and the method element of changing the combustor parameters comprises changing an air fuel ratio by bleeding compressed air from the compressor outlet to the compressor inlet.