Hydrogen–Natural-Gas Blends in a Continuous Annealing Line Under a Process-Equivalent Strip-Temperature Criterion

Hydrogen-enriched natural gas can reduce direct carbon emissions from industrial heat-treatment furnaces, but its effect should be evaluated at the required process temperature rather than only at constant burner input. This study investigates 0–100 vol.% H2 firing in the radiant-tube preheating chamber of a 108-burner industrial continuous annealing line using a zone-based mathematical model coupling combustion stoichiometry, heat transfer, and furnace energy balances. Archived natural-gas production data were additionally used as a plant-scale consistency check; a separate 2022 campaign was reproduced with a fuel-demand MAPE of 7.41% and NRMSE of 7.92%. At constant burner input, increasing H2 from 0 to 100 vol.% increased the predicted combustion-gas inlet temperature from 1986 to 2239 °C and the strip outlet temperature from 615.1 to 636.5 °C, while the effective heat-transfer coefficients decreased overall. Under the process-equivalent condition, burner input was adjusted to maintain the 615.13 °C reference strip outlet temperature. At 100 vol.% H2, the required burner input decreased from 44.84 to 42.44 kW per burner, corresponding to 5.35% and 2.05 GWh y−1 for the full chamber. Sensitivity analysis gave a 4.97–5.79% reduction range, supporting an approximately 5–6% furnace-specific burner-load reduction.