Operation method for improving partial load efficiency in a gas turbine and gas turbine with improved partial load efficiency

1. A method for improving partial load efficiency in a gas turbine engine comprising a compressor, operating burners, a high pressure turbine and a low pressure turbine, the method comprising:

operating the gas turbine engine by regulating at least:

an air mass flow rate, and

a flame temperature,

controlling at least:

the air mass flow rate supplied to a combustion chamber from the compressor;

a number of the operating burners; and

a change in an enthalpy drop between the high and low pressure turbine to control the air mass flow rate;

wherein

the air mass flow rate supplied to the combustion chamber from the compressor comprises a bleed that extracts a fraction of the air mass flow rate of the compressor at a compressor stage more upstream of a discharge, to limit a loss of work, in which a bleed flow rate supplied to the combustion chamber is modified, and

the number of the operating burners comprises an annular combustor staging, in which the number of operating burners is modified, and

the change in the enthalpy drop between the high and low pressure turbine to control the air mass flow rate comprises a nozzle guide vane control, in which the change in the enthalpy drop between the high and low pressure turbine is modified, allowing for regulation of the air mass flow rate, and

at a lower load range, less than a first separating load value, operating the gas turbine engine by only controlling the bleed flow rate so as to limit the loss of work,

at an intermediate load range, more than the first separating load value and less than a second separating load value, operating the gas turbine engine by only controlling the annular combustor staging so as to limit a thermal distortion of hot gas path components,

at an upper load range, more than the second separating load value and less than a full operating load value, operating the gas turbine engine by only controlling a plurality of nozzle guide vanes, so as to regulate the air mass flow rate.

2. The method of claim 1 , wherein

the first separating load value is tunable, in a range comprised between 15% and 25% of a maximum turbine engine load, and/or

the second separating load value is tunable, preferably in a range comprised between 35% and 45% of the maximum turbine engine load, and/or

the upper load range is tunable, substantially equal to 98%, of the maximum turbine engine load.

3. The method of claim 1 , wherein a control of the bleed flow rate of the compressor decreases between 0% (idle) and the first separating load value.

4. The method of claim 1 , wherein the annular combustor staging provides at least for augmenting the number of the operating burners from a minimum number of the operating burners at the first separating load value to a maximum number of the operating burners at the second separating load value, the maximum number of the operating burners being equal to the maximum number of the operating burners in the turbine engine.

5. The method of claim 1 , wherein controlling the plurality of nozzle guide vanes provides at least for augmenting the enthalpy drop in the high pressure turbine from a minimum value at the second separating load value to a maximum value at the upper load range, the enthalpy drop being regulated by regulating a throat area of nozzles located upstream the low pressure turbine, by rotating airfoils.

6. The method of claim 1 , wherein the bleed flow rate comes from an intermediate stage of the compressor, different from the discharge of the compressor.