Life Cycle Assessment and Energy Efficiency Analysis of Steel Production Processes in Nigerian Iron and Steel Manufacturing Facilities Toward Net-Zero Emissions

Primary steel production is among the most energy- and carbon-intensive industrial processes globally, responsible for approximately 7–9% of anthropogenic CO₂ emissions. In sub-Saharan Africa, and Nigeria in particular, the structural and operational deficiencies of major steelmaking facilities—most acutely illustrated by the persistently underperforming Ajaokuta Steel Complex—have received limited rigorous quantitative analysis through the lens of life cycle assessment (LCA) and energy efficiency benchmarking. This study presents a gate-to-gate LCA and exergy analysis of the integrated blast furnace–basic oxygen furnace (BF-BOF) route at Ajaokuta, supplemented by techno-economic evaluation of three decarbonization interventions: top-gas heat recovery, blast furnace gas (BFG) cogeneration, and partial substitution of coal by solar thermal pre-heating of hot blast air. Process data were collected from facility operational records (2019–2023), published audit reports, and validated against the World Steel Association benchmark database. The baseline carbon intensity of Ajaokuta's simulated full-capacity operation was determined to be 2.41 tCO₂e per tonne of crude steel (tCS), compared to the global BF-BOF average of 1.89 tCO₂e/tCS—a 27.5% excess attributable primarily to aging refractory heat losses, incomplete BFG utilization (recovery rate 34.1% vs. industry norm of 85–90%), and grid electricity sourced from fossil-dominated generation. The proposed top-gas waste heat recovery system alone reduced simulated carbon intensity by 0.31 tCO₂e/tCS (12.9%), and the integrated decarbonization package—combining all three interventions—achieved a projected reduction of 0.76 tCO₂e/tCS (31.5%), bringing the facility to 1.65 tCO₂e/tCS. Annual energy savings were estimated at 4.31 GJ/tCS, equivalent to 2.14 TWh/year at the design throughput of 1.3 Mt/year. These results provide, to the authors' knowledge, the first published quantitative LCA benchmarking of Nigerian integrated steelmaking and establish a technically grounded decarbonization trajectory aligned with the International Energy Agency's net-zero steel pathway for emerging economies.