Break down of cost for different routes to green ammonia

“Green” ammonia to be used as an energy storage medium and directly as a marine fuel has attracted significant attention recently. Ammonia is among the chemicals with a growing demand worldwide. From a climate perspective, this is a challenge since commercial ammonia production is very energy-intensive, responsible for about 1% of global greenhouse gas emissions, and produces 2.07 ton CO2 per ton of ammonia. Green ammonia can be produced by using conventional ammonia synthesis, however with the hydrogen produced from water electrolysis rather than using steam methane reforming. The remaining components of the conventional route are an air separation unit to supply nitrogen and a Haber-Bosch loop (HBL) to synthesise the ammonia. Although, green ammonia production from renewables is not a new technology, cost reduction in renewable electricity, and progressed technical readiness of electrolyzers have opened new opportunities. The increased cost of green ammonia compared to fossil-derived “grey” ammonia is, however, still a matter of concern for maritime transportation. In this work, the thermodynamics of green ammonia production are studied and the economic feasibility is evaluated to suggest the most cost-effective solution. The production cost is modeled using both low- and high-temperature electrolyzers (AEC and SOEC, respectively) operating with renewable electricity input only and assumed to be closely coupled with a HBL. It is shown that by applying SOEC with a HBL there is a possibility of heat integration and waste heat recovery from the HBL leading to economic advantages. On the other hand, AEC is a mature technology and has today a lower CAPEX than SOEC. Consequently, two different routes; one based on AEC and one on SOEC, are described. A techno-economic analysis is carried out to identify the most cost-effective system and show the share of each of the major components on the required CAPEX. Currently, although SOEC performs efficiently compared with AEC, employing this technology to produce green ammonia is not economically advantageous. However, it is shown that ammonia costs will likely be lower using the SOEC route as compared to the one using AEC considering the cost reductions expected from upscaling of the electrolysis production.