Ammonia Decarbonisation Pathways and Their Effects on Life Cycle Assessments

Abstract

Using the IEA Ammonia Roadmap aligned with the IMAGE electricity scenarios, an extensive database was produced allowing for prospective LCAs across three storylines from 2020 to 2050 (SSP2-Base, SSP2-RCP26, SSP2-RCP19). The scenarios correspond respectively to 3.9, 2.0, and 1.5°C of global warming in 2100 (vs. pre-industrial levels). Regionally, China produces the largest volume of ammonia as well as the ammonia with the largest climate change impact, due to the dominance of coal gasification technology. To meet 1.5°C of warming (the most sustainable scenario) a global decrease of fossil-based ammonia is needed. For many regions, electrolysis (yellow) ammonia becomes the technology with the lowest global warming potential by around 2045 in the RCP26 storyline and 2035 in RCP19. Until the regional electricity mixes are cleaner, steam reforming, steam reforming with carbon capture and storage, or methane pyrolysis offer lower emission options. However, electrolysis using on-site or designated renewable energy can create emission-free green ammonia, without waiting years for a cleaner regional grid. This means that electrolysis is the best choice for new plants if a producer is not making urea on-site (or has an alternative source of carbon dioxide if they are). Reduction in urea demand will be important for reducing reliance on steam reforming and coal gasification, and a swift uptake of electrolysis with designated renewables must be the focus. However, burden shifting associated with the dominance of renewable electricity systems and bioenergy carbon capture and storage in the RCP19 scenario must be taken into account.