Design of a modular and heterogeneous electrolysis system to increase flexibility in the use case of direct iron reduction

2021, Germany produced 40 million tons of crude steel, making it the largest producer in the EU. The steel industry accounted for 55 million tons of CO 2 -equivalents, or 7.2% of national greenhouse gas emissions, with about 70% of production relying on conventional blast furnaces. Hydrogen offers a promising pathway to decarbonize this sector. This study investigates how electrolysis systems can be rapidly scaled while maintaining flexibility to adapt to fluctuating electricity prices. A blast furnace simulation model from the literature was extended by integrating a large-scale heterogeneous electrolysis system, and its responsiveness to dynamic electricity costs was assessed. Results show that waste heat integration is insufficient for systems based solely on HTEL. The most efficient configuration was a combination of 40% HTEL and 60% PEMEL, achieving 3.46 MWh per ton of crude steel. A price-driven control principle for electrolysis was successfully implemented and validated with literature data. While Germany remains a key steel producer, countries such as Brazil already achieve more efficient production due to higher renewable shares and lower electricity prices. • Modular heterogeneous electrolysis model for iron reduction built, tested in Simulink. • Assessed waste-heat integration for HTEL water vaporization to boost H 2 efficiency. • Presented price-controlled electrolysis using modular baseload and flexible units.