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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.

Recently, a commercial version of a residential solid oxide fuel cell (SOFC) system with a flat tubular cell has been developed. However, the system cost still remains very high, which is a barrier to its widespread use. In this study, the potential for cost reductions in SOFC stack production was investigated in order to contribute to the viability of the widespread use of such residential SOFC systems in future. A cost analysis of 700 W SOFC stack production based on a process integration modeling was conducted. The present bottom–up approach enabled us to perform a sensitivity analysis with a variety of parameters in terms of cell design, the production process and cell performance. This allowed us to investigate the effects of these factors on the production cost, thereby revealing the quantitative impact of each technological improvement on the cost reduction potential. The present analysis also revealed innovation pathways which could result in technology scenarios where residential SOFC systems could reach a break-even point in comparison with the baseload electricity cost. The analysis of the cost reduction potential presented here provides a useful viewpoint for developing a research strategy for state-of-the-art SOFC technology.