Process and thermodynamics of hydrogen reduction of iron ore

Abstract

The interest in hydrogen reduction of iron ore lies in the pursuit of more sustainable and efficient steel production methods, aiming at the decarbonization of the steel industry. The H-DRI technology uses green hydrogen as a reducing agent, enabling steel production with a lower environmental impact. The process involves several stages: initially, the iron ore is preheated and fed into a shaft reduction furnace, where hydrogen is injected to reduce the ore to metallic iron, generating water vapor as a byproduct. This metallic iron, known as sponge iron (DRI), is then compressed into hot briquetted iron (HBI) for easier handling and transportation. Finally, the briquettes are melted in an electric arc furnace, where carburization and adjustment of the steel composition occur. The thermodynamics of iron ore reduction by hydrogen involves endothermic reactions, requiring additional energy to maintain a constant reduction temperature. The reduction occurs through a series of stages, starting with hematite (Fe2O3) being converted into magnetite (Fe3O4) and finally into metallic iron, with wüstite (Fe(1-x)O) as an intermediate at temperatures above 570°C. The Baur-Glässner diagram is used to predict the equilibrium conditions of the reduction reactions, indicating that higher temperatures and lower degrees of gas oxidation are favorable. This technology represents a significant advancement in the production of green steel, offering a promising solution for reducing greenhouse gas emissions.