Partial-load operation of a gas turbine with an adjustable bypass flow channel

A gas turbine, comprising:

• a compressor for providing compressor air,
• a combustion chamber comprising, a burner,
• cooling channels to cool hot gas parts in the combustion chamber,
• an expansion turbine,
• a bypass flow channel, which is configured in order to variably bypass the burner and the cooling channels to deliver compressor air into a hot gas flow generated in the combustion chamber during gas turbine operation during partial load operation,
• wherein the partial load comprises a power range below a guide vane adjustment range in which primary zone temperature (TPZ) is managed, hereinafter referred to as TPZ power range, and a power range below the TPZ power range in which a thermal characteristic (TK2) is managed, hereinafter referred to as TK2 power range,
• wherein an opening cross section of the bypass flow channel is adjustable to change an amount of compressor air flowing, past the burner and the cooling channels into the hot gas flow generated in the combustion chamber, thus affecting a cooling power to cool the hot gas parts in the combustion chamber,
• and a control unit, which is configured during operation of the gas turbine in the TK2 power range to:
• (a) receive the thermal characteristic (TK2) which comprises a relative combustion chamber pressure loss (ΔBDV) or a material temperature (MT) of the combustion chamber, and
• (b) automatically adjust the opening cross section of the bypass flow channel during part load operation in the TK2 power range such that a variation rate of the opening cross section keeps the thermal characteristic (TK2) from varying by more than 10% out of a range between predetermined lower and upper limit values (GW2, GW3) by reducing and increasing the opening cross section, thereby resulting in an essentially constant cooling power in the combustion chamber,
• wherein the relative combustion chamber pressure loss (ΔBDV) is a ratio of a combustion chamber differential pressure and a compressor final pressure, and wherein the combustion chamber differential pressure is a difference between a pressure before or in a region of the burner and a downstream pressure inside the combustion chamber.