Technical analysis of high-efficiency and flexible direct reduced iron plants integrated with high-temperature electrolysis

The iron and steel sector is one of the hardest-to-abate sectors from an emission point of view, emitting 3.74 GtCO2 annually and contributing to 10% of global energy-related greenhouse gas emissions. Hydrogen-based direct reduced iron is one of the options to achieve deep decarbonization of the sector. This study proposes an innovative hydrogen-DRI process integrating a high-temperature solid oxide electrolyzer cell. The main idea is to produce the reducing stream by means of the electrolyzer, while using natural gas only in the bottom part of the furnace to increase the carbon content and cool down the direct reduced iron. Three cases featuring different integration degrees between iron and hydrogen production units are assessed. The high integration level reduces the direct carbon dioxide emission by 96% compared to the reference natural gas fed process. Finally, an off-design analysis is performed to assess the mass and energy balances of the system operating at different loads in response to variable availability of renewable electricity. The results show that the plant can be efficiently used in several off-design configurations, maintaining good product quality while managing the electric consumption and hydrogen production rates.