Method for operating a gas turbine in a simple cycle and in a cycle combined with a steam turbine

A method for operating a gas turbine selectively in a simple cycle and in a cycle combined with a steam turbine, comprising the steps of:

• a) introducing exhaust gases from the gas turbine into a waste-heat boiler,
• b) transferring a major proportion of thermal energy of the exhaust gases to a water/steam circuit in the waste-heat boiler to generate steam,
• c) admitting the live steam generated in the water/steam circuit into a steam turbine,
• d) releasing exhaust gases from the waste-heat boiler to the atmosphere through a chimney,
• e) extracting a part of the air compressed by a compressor for use as cooling air for the gas turbine, and
• f) cooling the extracted air before entry into the gas turbine, the improvement comprising the steps of:
• g) feeding a gaseous medium through a cooler into the waste-heat boiler,
• h) cooling the extracted air by heat exchange with the, gaseous medium in the cooler, wherein the gaseous medium is heated to a temperature near to that of the cooling air,
• i) mixing the heated gaseous medium with the exhaust gas from the gas turbine, and
• j) selectively directing the mixture of exhaust gas and heated gaseous medium to one of the water/steam circuit in the combined cycle and to the environment in the simple cycle.