Patent ID: 8365537

Claim:
A method for operating a combined cycle power plant comprising at least one gas turbine ( 6 ), having a compressor ( 1 ), a combustor ( 4 ) and a turbine ( 7 ), a heat recovery steam generator (HSRG) ( 9 ), a steam turbine ( 13 ), a CO 2 capture system ( 18 ), a supplementary firing ( 10 ), which is integrated into the heat recovery steam generator (HSRG) ( 9 ) or installed as a duct firing ( 10 ) in the flue duct from the gas turbine to the heat recovery steam generator (HSRG) ( 9 ), and a flue gas recirculation line, the method comprising: mixing ambient air ( 2 ) and the first partial ( 21 ) flow of the flue gases ( 19 ); compressing the mixture of ambient air ( 2 ) and first partial flow ( 21 ); combusting fuel ( 5 ) in the combustor 4 ; expanding the pressurized hot combustion gasses in a turbine ( 7 ); passing the turbine's hot flue gases through a heat recovery steam generator (HSRG) ( 9 ), which generates steam ( 30 ); splitting the flue gas of the gas turbine into at least three partial flows downstream of the heat recovery steam generator (HSRG) ( 9 ); recirculating a first partial flow ( 21 ) of flue gases ( 19 ) from the HRSG ( 9 ) via the recirculation line to the compressor inlet; directing a second partial flow ( 20 ) of the flue gases ( 19 ) from the heat recovery steam generator (HSRG) ( 9 ) to the CO 2 capture system ( 18 ) and directing a third partial flow of flue gases from the HRSG to an exhaust stack; capturing CO 2 from a second partial flow ( 20 ) of flue gases ( 19 ) from the HRSG ( 9 ) and then exhausting a remaining second partial flow of flue gases from the exhaust stack; operating the supplementary firing ( 10 ) to increase the net power output of the plant and to at least partly compensate the power consumption of the CO 2 capture system ( 18 ); and wherein the first partial flow ( 21 ) is recirculated at a recirculation rate, which is controlled at a highest possible recirculation rate under the conditions at which stable complete combustion in the gas turbine ( 6 ) can be maintained and at which a residual oxygen concentration after the gas turbine (GT O2 ) is sufficient to maintain stable complete combustion of the supplementary firing ( 10 ).