Innovative ammonia blended natural gas fueled gas turbine − spilt transcritical CO₂ cycle combined system based on dual-temperature CO₂ turbines: Energy, environmental and economic performance trade-off

In order to solve the temperature interference problem, this paper proposes a novel ammonia-blended natural gas fueled gas turbine − split transcritical CO₂ cycle (GT-STCC) combined system based on dual-temperature CO₂ turbines. One split stream of CO₂ is pumped to CO₂ heater for recovering GT waste heat, while the other stream is pumped to CO₂ regenerator for utilizing high-temperature CO₂ turbine (HCT) waste heat and driving low-temperature CO₂ turbine (LCT). The sensitivity analysis of system thermodynamic performance with respect to fuel ammonia blending ratio, compressor pressure ratio, heat exchanger effectiveness, LCT CO₂ split ratio, CO₂ evaporation pressure is performed under the same total fuel heat input. In addition, the impacts of key operation parameters on power generation cost (PGC) and pollutant emission, including CO, CO₂, NO_x, are clarified. Energy, environmental and economic performance trade-off is achieved through a tri-objective optimization based on genetic algorithm. The results show that a 50 % increase of fuel ammonia molar blending ratio results in a 1.29 % decrease of total thermal efficiency, a 24.66 % decrease of total normalized pollutant emission, and a 35.71 % increase of power generation cost (PGC) for novel GT-STCC. As compressor pressure ratio or heat exchanger effectiveness changes, the normalized CO₂ and NO_x emissions show opposite trends. The PGC and total normalized pollutant emission reach minimums under the same LCT CO₂ split ratio of 0.4, while they obtain minimums at different CO₂ evaporating pressures of 250 bar and 350 bar, respectively. The tri-objective optimization shows that the optimal total system thermal efficiency, total pollutant emission and PGC are 54 %, 0.3149 × 10^-1 t/MWh and 0.05176 $/kWh, respectively. Compared to the GT − supercritical CO₂ − transcritical CO₂ cascade system, the novel GT-STCC system is a more promising power system due to its simpler configuration, 2 % higher overall thermal efficiency and 12.8 % lower PGC.