Performance evaluation of the natural gas combined cycle with various hydrogen co-firing rates

Hydrogen is a promising carbon-free fuel for reducing CO₂ emissions in power generation and is increasingly being integrated into gas turbine combined cycle (GTCC) systems. This study evaluates the thermal performance of a 600-MWe-class GTCC plant under hydrogen co-firing by analyzing two idealized operational scenarios—fixed turbine inlet temperature (TIT) and fixed gas turbine (GT) output—and additionally proposes a load-following strategy that maintains constant total GTCC output. A process simulation model was used to assess the impact of hydrogen blending on GT performance, flue gas composition, and the bottoming cycle—including the heat recovery steam generator (HRSG) and steam turbine (ST)—under three ambient conditions. Hydrogen co-firing introduced a performance trade-off: GT efficiency improved due to favorable combustion properties, while ST output decreased owing to degraded HRSG heat transfer. Under the fixed TIT scenario, GT efficiency increased with minor reductions in ST output. In contrast, under fixed GT output, TIT and turbine exit temperature (TET) declined, significantly reducing steam temperature and ST output, especially at high hydrogen blending ratios. The greatest performance degradation occurred under the lowest TIT condition. To address this trade-off, an additional scenario was developed by regulating TIT to adjust the GT/ST power split and maintain constant GTCC output. This approach resulted in thermal efficiency gains of up to 0.72 percentage points. The proposed model incorporates radiative and convective heat transfer mechanisms and captures the key thermophysical effects of hydrogen-rich combustion gas, offering practical insights for stable and efficient GTCC operation under hydrogen co-firing conditions.