Rigorous environmental and energy life cycle assessment of blast furnace pig iron in Brazil: The role of carbon and iron sources, and co-product utilization

Abstract

Iron and steel are valuable commodities worldwide. Pig iron is produced mainly by blast furnaces, being the primary raw material used in steel manufacturing. The ironmaking sector is intensive in energy use and greenhouse gas emission; however, detailed information on further environmental impacts concerning the blend of material sources and co-product utilization as well as a rigorous application of the life cycle assessment (LCA) method are scarce. This study aimed to assess the environmental and energy performance of the production of 1.0 t of pig iron from cradle-to-gate via LCA. Global warming potential (GWP), renewable and non-renewable cumulative energy demand (CEDR and CEDNR), fossil resource scarcity (FRS), mineral resource scarcity (MRS), blue water footprint (WF), and land use (LU) were assessed in five scenarios in the Brazilian context, being S0: the baseline scenario with coke as a carbon source; S1: partial utilization of by-/co-products (top gas and slag), representing the current industry practice; S2: carbon and iron input blends proportional to the current industry practice; S3: current industry mix (S1 and S2 combined); and S4: ex-ante (forecast) scenario with an enhanced blend of inputs and maximum utilization of co-products. Results show that, when evaluated against an unrefined but realistic fossil-based state of the technology (S0), the existing practice in co-product utilization (S1) provided more gains in terms of GWP, CEDNR, FRS, and MRS (11 % on average) than the current iron and carbon input blends (S2, 9 % on average) if compared side-by-side. The current industry mix (S3) showed further improvement in environmental and energy performance (22 % on average) compared with the baseline scenario (S0), while the forecasted scenario (S4) indicated additional gains, reducing GWP by 47 % (down to ~1 t CO2 eq), CEDNR by 69 %, FRS by 70 %, MRS by 12 %, and WF by 5 %. The GWP, CEDNR, and FRS presented the greatest improvements with a significant statistical difference, and using charcoal as a carbon source was key in that regard, despite the great increase in CEDR (3× for biomass) and LU (2×) indicators suggesting that a robust sustainable wood supply chain will be decisive for the sector strategy. The sensitivity analysis (SA) and benchmarking of the ex-ante scenario (S4) showed notable competitiveness of such pig iron in the global market, especially for carbon and energy footprints, reaching 0.69 t CO2 eq t−1 pig iron and 4.6 GJNR t−1 pig iron from 100 % sustainable charcoal and including rail logistics (SAiv), which are from 2× to 5× smaller than those of any conventional blast furnace pig iron reported in the consulted literature.