Environmental evaluation of european ammonia production considering various hydrogen supply chains

Ammonia synthesis is a topic of high interest in the industry as the market continues to expand and demand increases. The current ammonia production route is very energy and carbon-intensive, relying greatly on natural gas both as feedstock as well as for heat and power generation within the plant. In the present work, a cradle-to-gate environmental assessment of conventional and greener hydrogen production routes integrated with ammonia synthesis is carried out according to ReCIPe impact assessment method. Hydrogen production through conventional steam methane reforming coupled with gas-liquid carbon dioxide absorption by amines and chilled ammonia, electrolysis, and iron-based chemical looping are analysed and compared. Mass and energy balances from process flow modelling are used as inputs for the environmental evaluation using Life Cycle Assessment. The system boundaries considered in this work include: i) main processes: ammonia production, hydrogen production, carbon dioxide separation; ii) upstream processes: nitrogen, natural gas, ilmenite, Methyl-DiEthanol-Amine, chilled ammonia and catalysts supply chains, iii) downstream processes: carbon dioxide compression, transport and storage, degradation/disposal of solvents/oxygen carrier. The results show that natural gas-based ammonia synthesis integrated with chemical looping hydrogen production gives the highest reduction in Global Warming Potential while six out of the nine investigated impact indicators (excluding Global Warming Potential) suffer an increase between 30% and 60%. In the case of hydrogen produced from electrolysis, unless the electricity necessary for electrolysis is obtained from non-fossil sources, it results in the highest overall emissions to air, water and soil.