Inlet/outlet design and equivalence ratio adjustment of an industrial MILD steel furnace

This study explores the application of Moderate or Intense Low-Oxygen Dilution (MILD) combustion regime in industrial steel reheating furnaces to enhance heating performance, minimize pollutant emissions, and prevent oxidation. The transition from conventional flame-mode to MILD combustion is achieved by optimizing furnace configurations, reducing outlet diameters, and adjusting the equivalence ratio. The novelty of this work lies in its systematic analysis and demonstration that MILD combustion ensures a higher steel ingot heating performance with minimal oxidation. Results show that MILD combustion significantly improves temperature uniformity and ingot heating performance. MILD furnaces reduced peak gas temperatures to below 1450 °C, compared to 1800 °C in flame-mode furnaces, preventing localized overheating. The MILD furnace achieved a maximum ingot target temperature of 1254.3 °C at ϕ=1.00, outperforming the flame-mode furnace (1169 °C) with extreme localized variations. Oxidation risks were minimized by reducing oxygen levels near ingot surfaces from 6.9 % to below 3 %. Emissions were significantly lowered, with NO and CO emissions dropping to 6.34 mg/kJ and below 0.6 ppm, respectively, well below EPA limits. The study confirms that MILD combustion in steel reheating furnaces meets key industrial requirements, ensuring its industrial applicability, providing a promising path toward more sustainable, improving heating performance, reducing emissions, and enhancing steel quality.