Optimizing Sustainable Fertilizer Production: Techno-Economic and Environmental Assessment of Flexible Electrolytic Ammonia Production

Abstract

Ammonia production contributes about 1% of global carbon emissions due to fossil-based hydrogen production, and renewable-powered water electrolysis is a promising mitigation option. Yet, aligning the continuous Haber-Bosch (HB) process for ammonia production with variable renewable resources remains challenging. Increasing the HB process flexibility is a solution already adopted by the industry, but the conditions under which flexible plants can reduce costs remain unclear. Here, we address this issue by modeling and optimizing two plant configurations - continuous and flexible, both featuring on-site, semi-islanded, electrolytic hydrogen production with life-cycle carbon emission caps. Our results show that fully-flexible ammonia plants in wind-rich regions can be cost-competitive with current Steam Methane Reforming (SMR) derived ammonia while reducing life-cycle CO2e emissions by over 90%. High flexibility minimizes grid import and storage costs, leading to lower Levelized Cost of Ammonia (LCOA) and decreased emissions. The renewable potential of a location, particularly the availability of abundant wind energy, is crucial for achieving a low LCOA and maximizing the emission reduction potential of flexible plants. Solar resources alone, however, cannot offset sub-optimal wind resources. In solar-dominated regions, plants with limited operational flexibility show a 7% increase in costs and emissions compared to continuous operation, primarily due to the higher reliance on battery storage and grid electricity import. Incorporating high flexibility in off-grid plants can halve costs, but semi-islanded facilities with grid connections remain more economical. Our findings offer valuable insights for plant operators, industry stakeholders, and policymakers, guiding effective strategies to decarbonize ammonia production.