Heat balance analysis of existing gas turbines using hydrogen, ammonia, and ammonia-cracked fuels

Achieving carbon neutrality in thermal power generation requires a transition from natural gas to carbon-free alternatives such as hydrogen and ammonia. In this study, performance changes of a large industrial gas turbine were evaluated for hydrogen, ammonia, and ammonia cracked fuel (H2/N2 = 75/25 in molar ratio) using the commercial heat-balance software THERMOFLEX. A 1350 °C-class F-type turbine (GE 9F.03) was modeled and validated against published rated specifications, and off-design calculations were performed over a wide load range. The results show that, at the same power output, hydrogen, ammonia, and ammonia cracked fuel achieve higher thermal efficiency on an LHV basis than natural gas, whereas HHV-based efficiency decreases due to increased exhaust H2O. Fuel switching also shifts compressor operation: at the same inlet air flow rate, the compressor pressure ratio increases by 1.01% (hydrogen), 7.38% (ammonia), and 6.07% (ammonia cracked fuel), suggesting reduced operability margin. To mitigate this issue, the throat area of the choked first-stage turbine nozzle was increased. By enlarging the throat area by 1.0% (hydrogen), 7.6% (ammonia), and 6.2% (ammonia cracked fuel), the compressor pressure ratio was restored to the natural-gas case while maintaining high power output and efficiency. These findings suggest that adjusting the throat area of the turbine 1st nozzle enables carbon-neutral operation in existing combined cycle power plants.