Patent ID: 8408006

Claim:
A method for operating a combined cycle power plant comprising at least one gas turbine and a heat recovery steam generator with a CO 2 capture system and flue gas recirculation system comprising a flue gas duct, which directs a first partial flow of flue gases from the heat recovery steam generator to an inlet gas flow of the at least one gas turbine, at least one control body to control a recirculation ratio, a re-cooler with temperature control to cool recirculation flue gases, at least one CO2 and/or oxygen concentration measurement device, wherein the first partial flow, which is recirculated, is cooled by a recirculation flue gas re-cooler before mixing with ambient air for reintroduction into a compressor of the gas turbine, and a second partial flow is directed via the CO2 capture system to a stack for release to the environment, the method comprising: controlling a flue gas recirculation rate and a re-cooling temperature of the recirculated flue gases, depending on load, to optimize the overall plant efficiency including the CO 2 capture system wherein flue gas recirculation rate at base load equals a recirculation rate for best CO2 capture efficiency of the CO2 capture system and is reduced below a recirculation rate for best CO2 capture efficiency of the CO2 capture system at a load below base load, and wherein at part load the re-cooling temperature is increased over a base load re-cooling temperature.