CO2 accounting model and carbon reduction analysis of iron and steel plants based on intra- and inter-process carbon metabolism

Carbon emission accounting for iron and steel plants (ISPs) is crucial to formulate prospective low-carbon strategies. In this study, a CO2 emission accounting model for an ISP that accounts both direct and indirect emissions is proposed. Especially, the proposed model considers the effect of the by-product gases of steel production on the intra- and inter-process carbon metabolism. For a comprehensive evaluation of the carbon emission level of an ISP, direct emissions are correspondingly categorized into process direct emissions (PDE) or combustion direct emissions (CDE), and as for indirect emissions, purchased electricity indirect emissions (EIE) and purchased coke indirect emissions (CIE) were considered. Subsequently, a case study is performed with the proposed model by calculating the CO2 emissions of an ISP using both the blast furnace-basic oxygen furnace (BFBOF) and electric arc furnace (EAF) routes. The results show that the CO2 emissions of the ISP reach 1971.63 kg/ t-cs, whereas the PDE of the BF process is 496.09 kg/t-cs, which is the bottleneck of carbon reduction. Furthermore, a top gas recycling-oxygen blast furnace (TGR-OBF) process-based integrated steelmaking process is built to analyse the possible carbon reduction potential. A comparison of the proposed TGR-OBF with traditional BF route reveals that a carbon reduction of 45.39% can be achieved with the TRG-OBF route. In addition, the effects of scrap rate and proportion of electricity generated from alternative energy on the carbon emissions of EAF is discussed. To reduce the EIE in ISPs, measures to optimise the power supplying structure should be considered. Scenario analysis indicates that by improving the efficiency of power generation of on-site power plants (OPPs) and increasing the application of waste energy recovery technology (WERT), EIE can be reduced by 44.49%.