Combined cycle plant, control device thereof, and steam turbine startup method

1. A method of starting up a combined cycle plant, the combined cycle plant comprising:

a gas turbine having a compressor, a combustor, and a turbine;

a supplementary firing burner configured to raise a temperature of an exhaust gas of the gas turbine;

a heat recovery steam generator configured to generate a steam using an exhaust heat of the exhaust gas of the gas turbine; and

a steam turbine configured to be driven by the steam generated by the heat recovery steam generator,

the method comprising:

starting up the gas turbine and the steam turbine;

increasing an output of the combustor while the supplementary firing burner is not started up until after completion of a warming up of the steam turbine;

starting up the supplementary firing burner when the warming up of the steam turbine is completed;

increasing the output of the combustor and an output of the supplementary firing burner after starting up the supplementary firing burner; and

after a target output of the combined cycle plant is reached by increasing the output of the combustor and the output of the supplementary firing burner,

increasing the output of the combustor upon an increase in the target output of the combined cycle plant and upon the output of the combustor not reaching a maximum;

increasing the output of the supplementary firing burner upon the increase in the target output of the combined cycle plant and upon the output of the combustor reaching the maximum; and

making the output of the combustor constant and decreasing the output of the supplementary firing burner upon a decrease in the target output of the combined cycle plant after the target output of the combined cycle plant is reached by increasing the output of the combustor and the output of the supplementary firing burner.