A Comprehensive Costing and Emissions Analysis of Blue, Green, and Combined Blue-Green Ammonia Production

This work presents a costing and emissions analysis of three ammonia production pathways. These include blue ammonia production via autothermal reforming, green ammonia production via low temperature electrolysis of water and a combined blue-green process. The combined blue-green process utilizes oxygen produced by electrolysis as part of the feed to the autothermal reformer. Air is also fed to the autothermal reformer to provide nitrogen for ammonia synthesis in the downstream Haber–Bosch process. This approach eliminates the need for an air separation unit. Detailed Aspen models were developed for each production pathway to determine feedstock and utility requirements. These inputs were integrated into the H2A Production Cash Flow Analysis Tool to calculate the levelized cost of ammonia (LCOA). Emissions analysis accounted for process emissions from the Aspen simulations, upstream emissions from grid electricity usage, and upstream emissions from feedstock. Validation of the model against literature values confirmed the accuracy of key performance metrics, including feedstock conversion efficiency, levelized electricity consumption, and carbon capture rate. The results indicate that the combined blue-green process reduces the LCOA by 7% compared to standalone blue and green ammonia plants while also lowering life-cycle greenhouse gas emissions by 63% relative to conventional blue ammonia production. This emissions reduction comes at a cost of approximately 112 per tonne of CO2 avoided─substantially lower than alternative decarbonization options such as direct air capture. The study also highlights the critical role of methane leak rates and renewable electricity sources. Low methane leaks are essential for ensuring the environmental viability of blue and blue-green ammonia pathways. Additionally, while the importance of renewable electricity for green ammonia is well established, this study confirms its importance for blue ammonia based pathways as well. The economic and environmental advantages of the combined blue-green process suggest it is a promising and affordable transitional technology for decarbonizing ammonia production and scaling up green hydrogen capacity for future applications.