Achieving high efficiency and low NOx emission in walking beam reheating furnaces via MILD-Oxyfuel combustion: Optimization of oxygen concentration and burner configuration

The synergistic optimization of energy efficiency and pollutant reduction in steel rolling reheating furnaces is crucial for advancing energy conservation and environmental sustainability in the steel industry. This study proposes the integration of oxygen-enriched combustion with Moderate or Intense Low-oxygen Dilution (MILD) combustion, forming a novel MILD-Oxyfuel technology applied to an industrial walking-beam reheating furnace. A three-dimensional coupled combustion and heat transfer model was developed to simulate the effects of oxygen concentration and burner structural parameter on thermal efficiency and NO x emissions. Numerical investigations were conducted to identify the optimal operational and structural parameters that achieve simultaneous energy savings and emission reduction. Case study results demonstrate that: (1) An optimal oxygen concentration range of 21 %–35 % leads to a 0.42 % increase in thermal efficiency and a 1.17 % reduction in fuel consumption intensity per 1 % increase in O 2 ; (2) An optimum oxygen lance-to-burner distance of 800 mm yields the most uniform temperature distribution, improving thermal efficiency by 0.29 % compared to the benchmark condition and achieving an energy saving rate of 0.44 %, though NO x emission concentration and intensity rise by 7.95 % and 5.40 %, respectively; (3) An oxygen lance angle of 95° enhances thermal efficiency by 0.22 % and achieving an energy saving rate of 0.47 %, while reducing NO x emission concentration and intensity by 2.57 % and 3.07 %. This work elucidates the multi-parameter synergy of MILD-Oxyfuel combustion in industrial heating furnaces, offering valuable theoretical and practical insights for developing high-efficiency, low-emission thermal equipment.