Thermodynamic evaluation of an ammonia-fueled combined-cycle gas turbine process operated under fuel-rich conditions

Ammonia is a promising energy carrier and carbon-free fuel for power generation using combined-cycle gas turbines. However, its use results in the generation of relatively large amounts of NOx in the combustor. To address this issue, we propose a combined-cycle configuration including exhaust gas recirculation (EGR), in which the gas turbine is operated under fuel-rich conditions and the uncombusted hydrogen is burned in the heat-recovery steam generator (HRSG). Thus, hydrogen in the flue gas of the gas turbine increases the output power and improves the thermal efficiency of the system. Furthermore, in the combined system with EGR, the exhaust gas does not contain O2 and the combustion temperature can be reduced without altering the equivalence ratio. The proposed system is evaluated by thermodynamic modeling, and we find that low NOx emissions can be achieved while maintaining high thermal efficiency. Cold EGR is likely to be required to maintain the turbine inlet temperature below a technically feasible level, and a tradeoff between thermal efficiency and the NOx concentration at the combustor outlet is observed. The ideal operating conditions for this process thus depend on the technically feasible turbine inlet temperature, EGR ratio, and the permissible NOx concentration in the exhaust gas.