Dr Nathan Barrett

Abstract: With the movement toward hydrogen-enriched blast furnace operation to lower greenhouse gas emissions, ferrous burden design must be reconsidered to optimize furnace permeability. Increasing the ratio of direct charge lump ore in the ferrous burden also presents an opportunity to lessen the emissions associated with the production of sinter and pellets. Under traditional blast furnace conditions, lump ore usage is improved by mixing it with the sinter in the burden to promote their favorable high-temperature interactions (both chemical and physical). As such, mechanistic changes to the interaction must be understood to optimize burden design, including for future operations with hydrogen addition. In this study, liquid formation in both the metallic and oxide components of ferrous burdens is microscopically investigated. Oxide liquid and solid phase stability at the interfaces of dissimilar burdens are visualized using a novel mapping technique, and metallic iron is etched to reveal microstructures indicative of carbon. Results indicate that the inclusion of hydrogen promotes the gas carburization of metallic iron in sinter, but not lump. It was concluded that mixed burden softening and melting performance with hydrogen addition were improved through the addition of lump in two ways: the highly metallic lump particles provide structural support for the collapsing sinter bed and also suppress the formation of early liquid slag from the sinter. Graphical Abstract: (Figure presented.)

Hydrogen-enriched blast furnace (BF) operation is currently being assessed to mitigate greenhouse gas emissions while the steelmaking industry transitions to low carbon emission technologies. Increasing the usage of lump ore in the BF also presents opportunity to decrease carbon emissions, as it can be directly charged to the furnace without agglomeration. Use of lump ore in modern blast furnace operations is facilitated by high temperature interactions with sinter. With more emphasis on hydrogen enrichment in BF operations, the behaviour of lump and sinter mixed burdens must be characterised under new conditions. In this study, 15% hydrogen is added to the standard gas conditions of a Softening and Melting (S&M) apparatus (replacing nitrogen). Analysis of auxiliary reactions such as the Boudouard Reaction and the Water-Gas Shift Reaction is presented and their impact on burden reduction and performance assessed. Results indicate that with the inclusion of hydrogen, the performance of sinter burden deteriorates, while lump burden shows significant improvement. Interaction between sinter and lump still occurred with the inclusion of hydrogen in the gas, and the mixed burden behaviour of 20% lump and 80% sinter fell between that of the individual burdens. From interrupted experiments, it is noted at high degrees of reduction, the lump burden forms a solid metallic layer which maintains its interparticle voidage at high temperatures, supressing exudation of liquid slag.