Thermodynamic carbon-deposition behavior and mitigation-pathway comparison in decarbonized blast furnace gas–coke oven gas–natural gas mixtures

In low-carbon blast furnace ironmaking, heating mixtures of decarbonized blast furnace gas, coke oven gas, and natural gas provides a route for preparing hydrogen-rich reducing gas, but carbon deposition remains a critical constraint. This study combined Gibbs free energy minimization with standardized regression to quantify effects of temperature, pressure, and gas-source fractions on the equilibrium carbon-deposition amount and minimum addition amounts for H 2 O, CO 2 , and O 2 pathways. Across 600–1600 K, 1–10 atm, and the full gas-source fraction space, the mixtures exhibited a widespread thermodynamic carbon-deposition tendency. Gas-source fractions and temperature had stronger effects than pressure, and 800–950 K showed pronounced nonlinear and interaction responses. At high temperatures, increasing decarbonized blast furnace gas or coke oven gas fractions and decreasing natural gas fraction and pressure lowered the carbon-deposition amount and minimum addition amounts. Considering feasibility, addition amount, and reducing-gas quality, H 2 O provided the most balanced performance.