Novel self-pressurized ammonia-powered solid oxide fuel cell hybrid system using anode recirculation with water removal for improving high-altitude performance: Feasibility exploration

In order to solve performance degradation caused by ambient pressure drop under high-altitude, a novel self-pressurized ammonia-powered solid oxide fuel cell hybrid system using anode recirculation with water removal is proposed by introducing turbocharger subsystem. The self-pressurization of fresh air without extra electricity supply is realized by utilizing a part of anode exhaust-gas to drive turbocharger turbine after burning, while the other part is recirculated for improving system fuel utilization rate. The combined effect of key parameters on whole hybrid system electrical, exergetic efficiencies and economic performance are evaluated. Furthermore, the high-altitude performance improvement of proposed novel system is revealed based on the optimum design point, which is the trade-off between thermodynamics and economics. The results indicate that the net power ratio of turbocharger subsystem to whole hybrid system is 3.38% under preliminary design condition. It is interesting to find that as recirculation rate of anode exhaust-gas exceeds the critical value of 0.82, the decreasing stack fuel utilization rate could improve system efficiencies and decline system levelized cost of electricity. Besides, as recirculation rate goes up, the whole system levelized cost of electricity and net power ratio of turbocharger subsystem declines firstly and then goes up slightly. The decreasing stack operating temperature and increasing turbocharger compressor pressure ratio present a positive effect on the net power ratio of turbocharger subsystem. The optimal system electrical efficiency of 76.82% and levelized cost of electricity of 0.13526 $/kWh are obtained at the optimal condition. The novel system electrical and exergetic efficiencies only decline by 2.95% and 2.76% with a 6500 m increase of working altitude, respectively.