Hydrogen impact on gas turbine operating flexibility in simple and combined cycle mode

This study addresses two topical issues: carbon-free power production, on the one hand, and secure and reliable energy supply on the other hand. Undeniably, to integrate increasing shares of renewables into sustainable and competitive electricity systems, “capacity mechanisms”, i.e., a range of solutions aimed at ensuring adequate power capacity, are needed. Clean, dispatchable power generation is one such solution. Specifically, gas turbines fed by green fuels such as hydrogen can be scheduled to provide power when the contribution from solar and wind sources is not enough to meet the demand or in challenging situations, even for a few hours per year. With the idea of retrofitting existing gas turbine (GT) plants to hydrogen combustion, a thermodynamic model was developed by means of Thermoflex® software in a dual context: peaking, with a small, simple-cycle (SC) GT or “load-following”, with a large size combined cycle (CC) with 1 × 1 configuration. In both cases, ad hoc control strategies were implemented to increase thermal efficiency (η) at partial load. Simulations were run on an hourly basis to meet the prescribed load profiles at representative locations, for two typical hot and cold days: computations were carried out assuming 100% hydrogen as fuel, for comparison against conventional natural gas (NG), given the same GT output requirement and environmental condition. This study's novelty stems from these constraints. The results show that replacing NG with hydrogen combines obvious decarbonization with increases in net power (Pn) and net efficiency (ηn), the magnitude of which depends on the off-design control strategy, which in turn is a function of the GT operating environment. Overall, the largest increase in ηn was quantified at about 0.6 percentage points (pp). Furthermore, the combustor shifted towards leaner conditions so that the maximum cycle temperature does not exceed that with the conventional fuel.