Towards carbon neutrality: The ammonia approach to green steel

Abstract

The steel sector accounts for 7 % of global greenhouse gas emissions, making its decarbonization a critical challenge. The use of green hydrogen in the direct reduction process enables a significant reduction in CO2 emissions, reaching levels as low as 29 kgCO2/tSTEEL. However, one of the major challenges lies in the temporal and geographical mismatch between steel and hydrogen production. This issue is particularly pressing for the survival of steel supply chains in regions where green hydrogen production costs are expected to remain high. In such cases, transporting hydrogen from areas with more competitive production costs becomes essential. The transportation costs associated with hydrogen present an additional hurdle, driving the search for alternative solutions. Among these, ammonia has emerged as a viable option as a hydrogen carrier. This study uses an Aspen Plus process simulation model to analyze the complete steel production cycle, including ammonia cracking and the production of steel from direct reduced iron. It evaluates the impact of ammonia usage on the process and its overall efficiency. Two main scenarios are analyzed: direct injection of ammonia into the reduction furnace and external ammonia cracking. Production costs are calculated based on the transportation distances of hydrogen and ammonia. In a scenario where hydrogen is produced on-site, with an energy cost of 50 $/MWh and a hydrogen production cost of 5 $/kg, the final steel production cost amounts to 816 $/tSTEEL. However, these costs increase significantly with transportation distances. Using ammonia in these scenarios, despite its higher energy consumption, offers economic savings of up to 11 % for transportation distances of 5000 km. Looking ahead, with hydrogen production costs expected to drop to 2 $/kg, these savings could rise to 20 %.