Integration of green and turquoise hydrogen for blast furnace injection and power-to-X fuel production under EU renewable fuel regulation

Hard–to–abate industrial sectors such as fuel production and the iron and steel industry rely heavily on fossil carbon feedstocks and are major contributors to global greenhouse-gas (GHG) emissions. Although hydrogen–based direct reduced iron routes offer deep long–term abatement for iron and steel, their high capital intensity creates a need for transitional options that enable earlier hydrogen deployment at lower risk. This study assesses direct hydrogen injection into existing blast furnaces (BF) and assesses whether combining renewable electrolytic (“green”) hydrogen with low–carbon methane–derived (“turquoise”) hydrogen within an integrated Hydrogen Valley can reduce system costs and renewable overcapacity while preserving substantial emission reductions. To assess this, a dynamic techno–economic Power–to–X optimisation model is applied to a 6,600 t hot metal day−1 BF steel mill integrated into a gigawatt–scale industrial Hydrogen Valley in Northern Finland, explicitly representing electricity markets, hydrogen production, storage and transport, and regulatory constraints for Renewable Fuels of Non–Biological Origin (RFNBO). Supplying a constant BF hydrogen demand of 7.65 tH2 h−1 using only green hydrogen requires 380–430 MW of electrolyser capacity and 1,000–1,500 MW of wind power, resulting in hydrogen costs of €3.6–3.7 kgH2−1, whereas integrating turquoise hydrogen improves system flexibility and reduces renewable overcapacity, and lowers hydrogen costs to €2.6–3.4 kgH2−1; however, future RFNBO quota requirements lower asset utilisation and increase costs to €2.9–3.7 kgH2−1. Across all scenarios, GHG emissions decrease by approximately 20–21% per tonne of hot metal. Overall, hydrogen injection into existing BFs appears to be a cost–effective transitional pathway that supports early hydrogen infrastructure build–up while enabling meaningful near-term emission reductions and long–term progress toward fossil–free steel production.