Assessment of variable solar- and grid electricity-driven power-to-hydrogen integration with direct iron ore reduction for low-carbon steel making

Abstract

Power-to-gas (PtG) technologies offer a promising approach for decarbonization of energy-intensive industries, particular the iron and steel (I&S) sector, which depends on specific chemical feedstock and processes that are not currently directly electrifiable. However, PtG implementation faces challenges in the medium term related to the carbon footprint of electricity networks, decoupling process applications from variable renewable energy inputs, and economic feasibility. In this study, the design, energy, emissions, cost, and hourly operation of a power-to-hydrogen (PtH2)-based direct reduction of iron (DRI)-electric arc furnace (EAF) system, are investigated for solar energy-rich conditions in the near- to medium term (2030) with the intent to facilitate the deployment of low-carbon DRI-EAF steel making. A plant hourly operating and sizing methodology is developed based on PtH2 and use of renewable, low-cost solar photovoltaic (PV) electricity and H2 storage to counteract grid emissions and cost. The analysis approach is generically applicable to different solar-rich locations and other variable renewable electricity sources. For base-case system design/operating conditions, the emission intensity of the PtH2-I&S process is found to be abated from 890 to 567 kgCO2/tLS (∼36%), in absence of EAF scrap steel use, relative to the use of grid electricity only with no H2 storage, with a slight reduction in the levelized of cost steel (CLS) at 618 USD/tLS. Relative to conventional natural gas (NG)-DRI-EAF and blast/oxygen furnace (BF-BOF) processes, emission intensity is reduced by ∼43–60% and ∼53–74%, respectively. At off-base case PV and water electrolysis capacities, steel making emission intensity reductions of ∼40% relative to conventional NG DRI-EAF are achievable at normalized PV capacities, α = 3, relative to the plant nominal hourly electricity demand, and normalized electrolysis capacities, β ≥ 1.3, relative to the nominal hourly capacity requirement, while maintaining CLS within less than +25% of NG DRI-EAF. Based on the performance improvement and cost reduction potential for electrolysis and solar PV, the sub-space of normalized PV and electrolysis capacities yielding a ∼40% reduction in emission intensity within the above CLS limit would be significantly enlarged towards lower PV capacities (α ≥ 2) and electrolysis capacities (β ≥ 1.2).