Effect of gangue on CO₂ emission for different decarbonisation pathways

Abstract

At present, iron and steelmaking industry worldwide is going through the transition of decarbonisation to meet its goal of reaching net zero by 2050. In addition, Australian iron and steelmaking industry is facing its own challenge of processing lower grade ores with increasing gangue content. Two major pathways are direct reduction of iron – electric arc furnace pathway (DRI-EAF) and direct reduction of iron – electric smelter-BOF (DRI-electric smelter-BOF) pathway. In the present work, a mass and energy balance model of basic oxygen furnace (BOF) and electric arc furnace (EAF) have been developed using thermodynamic software. The EAF model showed that with 100 wt-% cold DRI, the specific electric energy requirement varied between 514 and 651 kWh/tls whereas in case of hot DRI, it varied between 399 kWh/tls and 510 kWh/tls. As the gangue content increased from 10.7 wt-% to 19.1 wt-%, yield decreased from 88 wt-% to 75.5 wt-% and slag weight increased from about 200 kg/tls to 630 kg/tls. The BOF model showed that the slag produced in a BOF varied between 63 kg/tls and 73 kg/tls for lower to higher grade ores reflecting different hot metal chemistry (P, Mn) coming from different ores. The results indicated that electric smelter-BOF is more compatible to process lower grade ores than EAF where quantity of slag and loss of yield are very high with increasing gangue content. CO2 emissions from H2DRI-EAF and H2DRI-electric smelter-BOF pathway for different types of ores increased with the increasing gangue content. For H2DRI-EAF pathway, as gangue content increases from 10.7 wt-% to 19.1 wt-%, CO2 emission rises from 0.10 t/tls to 0.19 t/tls as more limestone is needed to remove the gangue which also increases the production of CO2. In case of H2DRI-electric smelter-BOF pathway, CO2 emission increases from 0.12 t/tls to 0.19 t/tls with increasing gangue content. CO2 emissions from both pathways are significantly lower than the current BF-BOF pathway.