Methods and apparatus for starting up combined cycle power systems

A method for starting a combined cycle power generation system, the combined cycle power generation system including a gas turbine, a steam turbine, a heat recovery steam generator that generates steam, and receives exhaust heat from said gas turbine and is equipped with attemperators at discharge terminals of a high pressure superheater and a reheater and is connected to the steam turbine and supplies steam to the steam turbine, a condenser connected to the steam turbine, and bypass paths from the heat recovery steam generator to the condenser and from a high pressure steam line to a hot reheat steam piping;

• said method comprising:
• loading the gas turbine up to a rate that is approximately equal to a maximum rate of the gas turbine;
• maintaining steam temperature of steam supplied to the steam turbine at a substantially constant temperature from an initial steam admission into the steam turbine until all of the steam generated by the heat recovery steam generator with the gas turbine operating at up to a maximum load is admitted into the steam turbine;
• modulating a flow of steam through the bypass paths so as to control the high pressure steam pressure, reheat pressure and low pressure steam pressure from the heat recovery steam generator, and provide alternate paths for the steam while steam turbine admission valves are modulated during loading;
• and
• after substantially all the steam is admitted into the steam turbine, raising the steam temperature at a rate compatible with allowable steam turbine stress and differential expansion to achieve normal steam turbine output and efficiency.