Comparative exergy analysis between rotary hearth furnace-electric arc furnace and blast furnace-basic oxygen furnace steelmaking routes

Resource fuel used in integrated steelmaking processes are different based on fuel availability consideration. A fuel-based comparative energy utilisation efficiency in integrated steel plants as obtained through exergy analysis for two steelmaking routes, namely, rotary hearth furnace-electric arc furnace (RHF-EAF) and blast furnace basic oxygen furnace (BF-BOF) is presented with additional consideration of electrical energy input replacing fuel energy in EAF for RHF-EAF route. Initially, exergy flow models of sub-systems (BF, BOF, RHF and EAF) are established separately. These sub-system models are coupled together to analyse the exergy flows, exergy losses and exergy efficiencies of the two integrated steelmaking systems. Gas-based exergy efficiency based on input exergy of RHF-EAF steelmaking process is always found to be better than conventional BF-BOF process as well as BF-Tenova Flexible Modular Furnace system (a modified BF-BOF process having electric arc facility in BOF to increase the scrap percentage in BOF charge). However, BF-BOF processes are found to be superior to RHF-EAF process when metal-based exergy efficiencies are compared. Combined metal plus gas-based exergy efficiencies of RHF-EAF steelmaking process are marginally better than BF-BOF route. Efficiency of scrap reycle for both steelmaking routes has also been analysed through exergy efficiency parameters. It was found that exergy utlisation efficiency of RHF-EAF steelmaking process based on both products steel and total by-product fuel gas for hot charging of direct reduced iron (DRI) above 600 degrees C is superior to BF-BOF steelmaking process for all levels of scrap charging in steel making. For hot charged DRI at 600 degrees C in RHF-EAF steelmaking process, the combined exergetic efficiency based on metal and by-product fuel gas is around 75% compared to 67% of BF-BOF and modified BF-BOF steelmaking systems, indicating more efficient input fuel utlisation than both variants of BF-BOF route.