Combined-cycle power plant with exhaust gas recycling and CO2 separation, and method for operating a combined cycle power plant

A combined cycle power plant comprising:

• a gas turbine comprising an air inlet and a compressor configured and arranged to compress air introduced through the air inlet, and an exhaust;
• a steam turbine;
• a heat recovery steam generator connected downstream to the gas turbine and configured and arranged to deliver steam to the steam turbine;
• an exhaust gas recycling line configured and arranged to return a portion of the exhaust gases, which flow from the gas turbine exhaust through the heat recovery steam generator, to the gas turbine inlet;
• an exhaust gas control device in the gas recycling line, configured and arranged to adjust said portion of the exhaust gases;
• a CO2 separating plant having a CO2 outlet and having an inlet in fluid communication with the gas turbine exhaust, the CO2 separating plant configured and arranged to separate CO2 from a non-returned part of the gas turbine exhaust gases and deliver said CO2 to the CO2 outlet;
• a supplementary firing device integrated in the heat recovery steam generator, the supplementary firing device configured and arranged to combust a carbonaceous fuel to produce additional exhaust gases with CO2 content, and to transmit the additional exhaust gases through the heat recovery steam generator;
• a fuel line leading to the supplementary firing device;
• a fuel control device in the fuel line to the supplementary firing device;
• and
• a controller in communication with both the fuel control device and the exhaust gas control device, the controller being configured and arranged to control the fuel control device to control the fuel flow to the supplementary firing device, and to control the exhaust gas control device to control said portion of the exhaust gases, such that the CO2 content in gas admitted to the gas turbine inlet is maintained constant upon an increase in firing of the supplementary firing device.