Flexible heat and power generation in retrofitted oxy-fuel CCGTs with electrolysis-derived O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"> <mml:msub> <mml:mspace width="0.1em"/> <mml:mtext>2</mml:mtext> </mml:msub> </mml:

Combined-cycle gas turbines (CCGT) traditionally provide electrical power and heat for district heating, playing a key role in ensuring operational resilience and security of energy supply, but they are associated with significant CO 2 emissions. This paper investigates a retrofit concept based on oxy-fuel combustion and water electrolysis that enables decoupling of heat, electricity, H 2 , and CO 2 production within an existing CCGT. A detailed AspenPlus model of a real Finnish 1010 MW th CCGT is developed for both air-fired and oxy-fuel configurations. At the same turbine inlet temperature, oxy-fuel combustion decreased the power output from 164 to 141 MW e per gas turbine due to the change in working-fluid properties while increasing the heat for district heating (22 to 95 MW th ). Dry steam injection at the turbine inlet improved performance by lowering turbine inlet temperature, reducing CO 2 recirculation need, and increasing turbine power while decreasing compressor power demand. Subcooled water injection shifted the system toward enhanced heat recovery. The electricity required to produce O 2 for oxy-fuel combustion exceeded the CCGT output but could be supplied from the grid. The electrolysis system produced 10.2 kg/s of H 2 , and the non-recirculated flue gas contained 98.0 mol % CO 2 . Hydrogen co-firing increased the heat and power generation, the electrical efficiency of the oxy-fuel cycle, and the district heating supply temperature without requiring live steam from the steam cycle as in the air-fired configuration. Beyond emission reduction, the proposed oxy-fuel CCGT enables flexible operation through hydrogen co-firing, sustaining district heating while interacting with the electricity grid, thereby enhancing system flexibility and resilience under high renewable penetration. • Detailed AspenPlus model evaluates dry, steam, and water-injected oxy-fuel cycles. • Dry steam injection effectively increases the efficiency of the oxy-fuel cycle. • Oxy-fuel combustion in gas turbines enables flexible operation between heat and power. • H 2 co-firing enables district heating supply temperatures up to 125 ∘ C. • Turbomachinery geometry redesign is required for oxy-fuel retrofitting.