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Although the blast furnace process is the dominant ironmaking route to supply the feedstocks for steelmaking, a number of alternative ironmaking technologies such as the direct reduction process have grown rapidly in recent decades. This development is largely in response to the increasingly stringent emission control policies, rising costs of energy, and the increasing costs and environmental effects of coke usage. In direct reduction processes, iron oxides are reduced to iron at a temperature below its melting point. More than 79% of direct reduced iron is produced by Midrex and Energiron, both of which use gas‐based shaft furnaces. A proper understanding of these processes is required to improve the performance and operation of the plants based on them. Therefore, herein, it is aimed to provide a comprehensive review of research that is carried out over the last several decades to examine the effects of the important phenomena on the performance of the gas‐based shaft furnaces. The review is divided into experimental and mathematical investigations. The main features, limitations, and shortcomings of each study are discussed. Finally, the review concludes with current knowledge gaps and suggestions for further research in this thriving sector of the steel industry. [ABSTRACT FROM AUTHOR]

The investigations on direct reduced iron (DRI) have commonly been made at two different scales: the pellet scale and the macroscopic or reactor scale. The reduction of a single pellet is typically investigated for developing kinetics of chemical reactions accompanied by heat and mass transport, whereas in the macroscopic view, the reduction process is investigated in the reactor scale. However, these two aspects are not independent of each other and usually the kinetic parameters that are used in the reactor modeling come from the single pellet study. This article reviews the most relevant models in the literature with regard to direct reduction reactions in the pellet scale together with more recently developed new approaches. This review also presents a critical assessment of the previously proposed models in terms of which models are applicable under what conditions and to what types of the solid structure. The flaws and pitfalls in some of these models are also pointed out with cautions. The present article is broadly divided into experimental and mathematical sections. [ABSTRACT FROM AUTHOR]