Comparative life cycle assessment of natural gas and coal-based directly reduced iron (DRI) production: A case study for India

The energy-intensive steel industry is responsible for >7% of global greenhouse gas (GHG) emissions, of which the process of ironmaking contributes a large majority. Direct Reduced Iron (DRI) manufacturing, a growing technology in ironmaking, offers the potential to reduce emissions. India, as the largest manufacturer of DRI, is characterized by technological diversity, while simultaneously dominated by coal-based DRI processes. This study develops a comprehensive cradle-to-gate (raw material to iron product) life cycle assessment of three distinct technological pathways for producing DRI: direct coal reduction in a rotary kiln (rotary kiln DRI process), coal gasifier and shaft furnace (coal gasifier DRI process), and reformed natural gas and shaft furnace (NG reformer DRI process). A hybrid life cycle inventory approach is employed, involving process modeling, literature data, and industry consultation to establish baseline process metrics, followed by a sensitivity analysis to address the impact of variabilities and uncertainties. Depending on the supply chain and process assumptions, emissions attribution approach to multi-product systems, and the specific choice of inputs and outputs, the life cycle GHG emissions associated with DRI production range from 1391.1 to 1880.0 kgCO2e/t-DRI for the rotary kiln DRI process, 1565.5 to 1969.1 kgCO2e/t-DRI for the coal gasifier DRI process, and 815.3 to 1160.1 kgCO2e/t-DRI for the NG reformer DRI process. While the research considers India as a case study, the methodology and results can be directionally and broadly applicable to other geographies and process conditions.