Ammonia-based direct reduction of iron ores: Modelling and experimental assessment

The iron and steel industry is a cornerstone of the EU economy, producing materials essential to various industrial sectors but contributing approximately 5% of the EU's total CO2 emissions. Among the most promising pathways for decarbonising the steel industry is the adoption of Direct Reduced Iron (DRI) technology, particularly hydrogen-based DRI (H2-DRI), which has the potential to eliminate CO2 emissions during the most carbon-intensive stage of steel production by using hydrogen as a reducing agent instead of fossil fuels. However, hydrogen's low volumetric energy density and the complexity of its transport and storage present practical limitations to large-scale deployment. In this context, ammonia emerges as a compelling alternative energy carrier, thanks to its higher volumetric density, established logistics infrastructure, and the ability to decouple hydrogen production from its point of use. This work investigates the feasibility of ammonia-driven DRI (A-DRI) by combining thermodynamic analysis, kinetic modelling, and experimental characterisation of porosity and phase evolution during hydrogen reduction. A reactor-scale model based on the Unreacted Shrinking Core (USC) framework is developed to quantify the coupled effects of temperature, gas composition, and mass-transfer resistances, while ex-situ measurements establish correlations between metallisation, pore structure, and diffusion behaviour. Results show that ammonia can be integrated into a shaft furnace without altering the fundamental reduction pathway: in-furnace cracking on metallic iron efficiently releases hydrogen, whereas ammonia itself does not participate directly in iron-oxide reduction. Although its use increases the thermal load, appropriate gas-recirculation strategies enable operating conditions compatible with existing H2-DRI designs. Overall, A-DRI may provide a promising route to low-carbon ironmaking while mitigating the infrastructural barriers associated with large-volume hydrogen supply.