Method for starting premixed combustion in combustor for two-shaft gas turbine

A two-shaft gas turbine comprising:

• a compressor having an inlet guide vane on a compressor air intake, an opening degree of the inlet guide vane controlling an amount of air that is to be introduced into the compressor;
• a combustor including a diffusion pilot burner for diffusion combustion and a plurality of premix burners for premixed combustion;
• a plurality of premix burner fuel systems to supply fuel to the plurality of premix burners;
• a high-pressure turbine connected to the compressor through a gas generator shaft and driven by a combustion gas formed in the combustor, the compressor being driven by the high-pressure turbine through the gas generator shaft which has a rotational rate;
• an output turbine connected to an output turbine shaft driving a load device, and driven by the combustion gas discharged from the high-pressure turbine;
• and
• a gas generator controller, wherein the gas generator controller stores a first relationship of an amount of fuel to a load of the compressor and an atmospheric temperature, a second relationship of an amount of air to the load of the compressor, the atmospheric temperature and the rotational rate of the gas generator shaft, and a third relationship between the amount of fuel and the amount of air, a first ratio of a reduction in the amount of fuel to an increase in the atmospheric temperature being greater than a second ratio of the reduction in the amount of air to the increase in the atmospheric temperature;
• the gas generator controller comprising:
• a fuel controller to calculate the amount of the fuel to be introduced into the combustor based on the load and the atmospheric temperature, and to control an opening degree of a fuel control valve in accordance with the first relationship such that the amount of the fuel is equal to the calculated amount;
• an inlet guide vane opening degree controller to calculate an amount of air to be introduced into the combustor based on the load, the atmospheric temperature of the air and the rotational rate of the gas generator shaft, and to control the opening degree of the inlet guide vane, in accordance with the second relationship, such that the amount of air is equal to the calculated amount;
• and
• a switching controller to calculate a fuel-air ratio based on the third relationship between the amount of the fuel calculated by the fuel controller and the amount of air calculated by the inlet guide vane opening degree controller, and to control the plurality of the premixed burner fuel systems based on the calculated fuel-air ratio.