Scaling the production of renewable ammonia: A techno-economic optimization applied in regions with high insolation

Abstract

In light of climate change mitigation, countries aim to maximize the integration of variable renewable energy. This presents an opportunity for fossil fuel exporting desert countries to diversify and transition not only the domestic economy towards solar but also to become an exporter of solar energy through a suitable energy carrier. This paper investigates ammonia (NH3) as a promising carrier option. Essential chemical industries rely on conventionally produced ammonia as the intermediate product from which a wide variety of fertilizers and industrial products are produced. This work presents a methodology for designing, simulating and optimizing an industrial-scale facility that utilizes solely renewable electricity, applied in the context of UAE – a major ammonia exporter. Hydrogen is obtained from desalinated seawater electrolysis and nitrogen from air separation that is then processed in the Haber-Bosch process. A simulation of the integrated plant, that includes desalination, electrolysis, air separation, refrigeration and storage, is carried out in the Aspen Plus® environment. A large-scale plant continuously operated has a specific energy consumption of 10.43 kWh/kg-NH3 and an electric process efficiency of 37.4%. The optimal configuration of generation and storage to operate this plant based on hourly resolution operations and considering options of flexible sub-processes is specified with linear optimization. The fully renewable and cost-optimally configured system entails 3.5 GW of PV, 0.24 GWh of battery storage, and achieves about 37% efficiency for the UAE conditions. The levelized cost of ammonia (LCOA) for this base case is estimated at $718/ton-NH3 and further reductions are possible under the expected technical advancements at $450/ton making it directly competitive with conventionally produced ammonia.