Hydrogen–methane fuel blending for MILD combustion in CRT-scaled steel reheating furnaces: implications for temperature uniformity, pollutant mitigation, and surface oxidation

Steel reheating furnaces face critical challenges in reducing emissions, minimizing steel oxidation, and achieving the target steel ingot temperature. Hydrogen, as a low-carbon and renewable fuel, its application in MILD combustion for steel furnaces remains underexplored. This study employs a detailed analysis of CH 4 –H 2 blends in a 7 MW MILD steel reheating furnace (scaled down to 10 kW by the constant residence time method). Results reveal that hydrogen enrichment up to 60 vol% increases average furnace gas temperature to 1223 °C, enhances thermal uniformity, and enables uniform ingot heating at 1201 °C. H 2 above 60% intensifies localized combustion, reducing averaged ingot temperatures to 1091 °C and compromising uniformity due to shortened residence time and intensified local combustion. Oxidation risk increases as local oxygen levels exceed the critical 3% threshold. CO 2 emissions decrease by 55% at 80 vol% H 2 , while CO and NO remain below the EPA 130 ppm and 86 μ g / k J limit across all blends, respectively. MILD regime quality is confirmed up to 60% H 2 . Multiple regime criteria, including K v and Borghi diagrams, confirm sustained distributed MILD combustion up to 60% H 2 , with slight transition toward flamelet regime at 80% enrichment. Blending 30–60% H 2 with methane achieves an appropriate balance of performance, emissions control, and combustion stability for cleaner industrial furnace design.