Islanded ammonia power systems: Technology review & conceptual process design

Highlights: • Critical review of recent technological advances for decentralized, islanded ammonia power systems (1–10 MW scale). • Conceptual process design with absorbent-enhanced Haber-Bosch process (operating at mild conditions) and SOFC. • System proposal for 100% renewable energy system with round-trip efficiency of 61%. -- Abstract: Recent advances in technologies for the decentralized, islanded ammonia economy are reviewed, with an emphasis on feasibility for long-term practical implementation. The emphasis in this review is on storage systems in the size range of 1–10 MW. Alternatives for hydrogen production, nitrogen production, ammonia synthesis, ammonia separation, ammonia storage, and ammonia combustion are compared and evaluated. A conceptual process design, based on the optimization of temperature and pressure levels of existing and recently proposed technologies, is presented for an islanded ammonia energy system. This process design consists of wind turbines and solar panels for electricity generation, a battery for short-term energy storage, an electrolyzer for hydrogen production, a pressure swing adsorption unit for nitrogen production, a novel ruthenium-based catalyst for ammonia synthesis, a supported metal halide for ammonia separation and storage, and an ammonia fueled, proton-conducting solid oxide fuel cell for electricity generation. In a generic location in northern Europe, it is possible to operate the islanded energy system at a round-trip efficiency of 61% and at a cost of about 0.30–0.35 € kWh⁻¹.