A comprehensive multiscale review of shaft furnace and reformer in direct reduction of iron oxide

Abstract

The direct reduction of iron (DRI) process plays a pivotal role in the ironmaking and steelmaking industry and has emerged as a promising solution for reducing CO₂ emissions. This intricate process spans metallurgy and chemical engineering, encompassing multiple scales (macroscale, mesoscale, microscale, nanoscale) and various reaction systems, including catalytic gas–solid (reformer) and non-catalytic gas–solid (shaft furnace) processes. The shaft furnace operated as a multiscale moving bed reactor including iron oxide pellets where a complex interplay of 17 non-catalytic gas–solid reactions and several gas reactions is observed. This review covers all relevant fields of gaseous-based DRI and introduces essential mathematical models for shaft furnaces and reformers. Key non-catalytic gas–solid and shaft furnace models developed over the last century are compared and analyzed. The effects of crucial parameters such as solid structure, gas phase conditions, clustering, carbon formation, and lattice defects are discussed. In addition, the reformer in the DRI unit functions as a bottom-fired furnace, comprising a combustion chamber and tubes that carry three types of heterogeneous catalysts, operating as a fixed bed reactor. Diverse radiative and kinetic models have been discussed to characterize the combustion chamber and reactions in detail. Finally, the review discusses potential artificial intelligence (AI) applications in this context and identifies research gaps for future investigations.