Energy storage using direct iron oxide reduction and energy utilization with high temperature metal combustion

• An installation for energy storage based on iron as a metallic energy carrier is simulated. • Achieving 85.2 % energy efficiency in the reduction of iron oxides containing 30 % Fe 2 O 3 and 70 % Fe 3 O 4 . • The oxidation process at 1200 °C achieves an efficiency of 91.4 % with λ = 1.30. • The overall energy storage and utilization achieve a round-trip efficiency of 78.0 %. In response to the growing demand for renewable energy storage solutions, metal fuels have emerged as a promising alternative as recyclable energy carriers. These metals release energy through combustion, forming metal oxides, which can subsequently be regenerated into their metallic state using renewable hydrogen. Recent experimental studies have demonstrated the feasibility of self-sustaining combustion-oxidation of various finely ground metals. For the reduction step, established direct reduction iron (DRI) technology has been successfully used to convert solid iron ore into metallic iron without transitioning to the liquid phase. Through thermodynamic calculations conducted using Aspen, ensuring precise process modelling and efficiency evaluation, this study examines the technical feasibility and preliminary design of an energy storage system that employs iron as a metallic energy carrier. Iron undergoes oxidation and serves as a fuel in high-temperature reactors operating above 1200 °C, thereby releasing its stored energy and forming iron oxide. When hydrogen is available, the iron oxide can be reduced back to metallic iron through the well-established Direct Reduced Iron (DRI) process or a comparable method at approximately 750 °C. A round-trip thermal efficiency of 77.9 % has been calculated for the overall energy storage and utilization process. To further enhance global efficiency, key recommendations include hydrogen recirculation during the reduction process to ensure complete conversion and mitigating the impact of excess air in the oxidation stage.