Experimentelle Untersuchung des Niedertemperatur-Reoxidationsverhaltens von DRI C

As the steel industry transitions to CO¿-neutral production, the focus is on gradually replacing the traditional blast furnace process, which is highly energy- and CO¿-intensive. These blast furnaces have traditionally relied on coke as a reducing agent, resulting in emissions of 1.85 tons of CO¿ per ton of pig iron produced. A central element of the desired decarbonization is therefore the introduction of direct reduction plants, where iron ore is reduced using hydrogen instead of coke. Hydrogen-based direct reduction is thus considered a key technology for reducing emissions from iron and steel production in the long term while ensuring the competitiveness of the industry in an increasingly climate-neutral energy system. However, directly reduced iron (DRI) can pose safety challenges during transport and handling. These arise from the possibility of reoxidation and the formation of hydrogen under certain environmental conditions. The objective of this study is to examine the low-temperature reoxidation behaviour of DRI C (HBI fines). The experiment involved the consideration of two distinct particle size fractions, in addition to a range of temperatures and ambient humidity. The oxidation kinetics were determined through experimental means, with oxygen uptake in a differential loop reactor being measured under isothermal conditions at 40, 60, and 80 °C. The results of the study demonstrate that oxide scale growth is controlled by the diffusion of electrons and/or ions. Furthermore, the investigation revealed that temperature exerts a significant influence on the oxygen saturation capacity. It was demonstrated that larger particles exhibited a higher rate of oxygen uptake in comparison to smaller particles. Microscopic surface analyses revealed that this effect can be attributed to pronounced crack formation in the larger particles. In order to capture this behaviour in the kinetic evaluation, a crack factor was introduced into the modelling approach.