Fluxing Options and Slag Operating Window for Metso's Sustainable DRI Smelting Furnace

Decarbonization of the steel industry has recently been the focus of many research and technological development tasks. Most of the developments are targeting the replacement of the highly CO2 emissive blast furnace (BF), which has been the main primary smelting furnace in the ironmaking step of steel production. However, replacement of the BF has been a challenging task because of BF's many established capabilities over the years, especially its flexibility in using low-grade iron feed. In this regard, Metso has been developing an advanced furnace technology, Metso's Outotec direct reduced iron (DRI) smelting furnace. The recently developed 6-in-line electric furnace for DRI smelting can be used for primary smelting of DRI from blast furnace grade iron ore. Compared to the electric arc furnace (EAF), the DRI smelting furnace can handle larger slag volumes that emanate from the high gangue in BF-grade DRI. Therefore, slag fluxing plays an important role in operating the DRI smelting furnace. This paper presents fluxing options and proposes operating temperature windows for the DRI smelting furnace. The optimal operating temperature range is found to be between 1300 degrees C and 1600 degrees C. For the examined slag compositions, viscosity at 1500 degrees C is < 0.35 Pa s. Additionally, the effect of slag chemistry on the corrosion resistance of the MgO-based refractory materials has been experimentally investigated, and magnesia-chromite was observed to be more compatible for the studied slag composition and temperature ranges.