Process integration of turquoise hydrogen via natural gas pyrolysis for blast furnace ironmaking: techno-economic viability and CO2 mitigation

• A process integrating turquoise hydrogen with a blast furnace was proposed. • Four cases were proposed based on the heat supply method and hydrogen purity. • An increase in injection temperature is correlated with a higher replacement ratio. • All proposed cases achieved negative CO 2 emissions. • Supplying high-purity hydrogen was the best strategy for environment and economy. Efforts to decarbonize the steel sector primarily follow two pathways: the use of alternative low-carbon fuels (e.g., hydrogen, ammonia) for blast furnace (BF)-based ironmaking, and the adoption of electrified processes utilizing direct reduced iron in electric arc furnace-based ironmaking. In this study, synergistic process integration is proposed for hydrogen-based BF ironmaking, and its techno-economic and environmental impacts are assessed. Turquoise hydrogen, produced via natural gas pyrolysis, is designed across four cases to examine how variations in injection temperature and hydrogen purity affect the balance among process design, economic performance, and CO 2 mitigation potential. Heat supply strategies, including hydrogen purification units, are also considered. Each case is evaluated in terms of energy consumption, BF injection performance, economic feasibility, and environmental impact. The findings reveal that Case A achieved the highest energy efficiency of 60.4%, while Case D showed the lowest at 47.6%. Regarding BF performance, increasing the injection temperature of high-purity H 2 improved the H 2 -to-coke replacement ratio from 1.10 to 1.46 kg_coke/Nm 3 -gas, enabling a significantly higher H 2 injection rate of up to 41 kg H2 /tHM. Economically, the integration proved highly competitive due to the solid carbon byproduct; Case D achieved the most favorable unit production cost (UPC) of − 0.29 US$/kg-gas, compared to 0.016 US$/kg-gas for Case A. Environmentally, Case D also demonstrated the superior sustainability profile with a net-negative CO 2 emission of − 7.43 kg CO 2 -eq./kg-gas. Overall, the proposed integration of turquoise H 2 with BF ironmaking demonstrates strong economic and environmental performance. A remaining challenge is determining the optimal degree of hydrogen purification for alternative applications within the ironmaking process.