Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University
College of Chemical Engineering, Fuzhou University

开发清洁高效的煤粉燃烧技术是应对我国乃至世界范围内日益严峻的环境污染问题的重要途径，煤粉低氧稀释(MILD)燃烧技术凭借其降低NOx排放、提高热流密度均匀性等优势而被视为颇具潜力的新型燃烧方式。同时，煤粉MILD技术结合富氧燃烧技术将是未来煤炭利用过程中减少碳排放的重要方向。综述了国内外煤粉MILD燃烧的发展历程、技术特点、研究现状等，并重点针对低温预热条件下的高速射流煤粉MILD燃烧技术探讨了研究中的关键问题和研究挑战等。煤粉MILD燃烧起源于气体燃料MILD燃烧，通过增强流场对高温烟气的卷吸并稀释反应物，使高温的火焰锋面模糊甚至消失，降低燃烧峰值温度并提升温度分布的均匀性，进而显著抑制了热力型NOx和燃料型NOx的生成。煤粉MILD燃烧可通过高温预热空气或提高射流速度实现，其中后者以其在经济性和可行性上的优势而更具发展前景，然而在速度达到100 m/s左右的高速射流的强烈剪切、湍流混合条件下的煤粉MILD燃烧机理及特性研究仍有待深入开展。在高速射流强烈剪切及卷吸作用下，煤粉弥散行为与常规射流燃烧相比有明显差异，而煤粉的弥散程度又直接关系到能否实现MILD燃烧。此外，强湍流混合会改变煤粉的升温、脱挥发分、焦炭燃烧等过程，进而影响着火延迟、火焰结构和污染物生成等煤粉燃烧过程中的关键问题。基于对上述关键问题的深入了解并结合气体燃料MILD燃烧的相关研究基础，可进一步发展针对煤粉MILD燃烧的系统、准确的定义，以更好地指导煤粉MILD燃烧技术的研究与应用。

Developing a cleaner and more efficient combustion technology of pulverized coal is an important way to deal with the increasingly serious environmental pollution. Moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal is regarded as a new combustion technology with great potential due to its advantages of reducing NOx emission and improving the uniformity of heat flux in the furnace. More importantly, the pulverized coal MILD technology combined with the oxy-fuel combustion technology will be an important path to reduce carbon emission in the process of coal utilization in the future. The history, characteristics and current research status of the MILD combustion of pulverized coal worldwide are summarized, and the key issues and research challenges of the MILD combustion technology of pulverized coal with a low preheating temperature are put forward. The MILD combustion technology of pulverized coal originates from that of gaseous fuels, which strengthen the entrainment of high-temperature flue gas and then dilute the reactants to make the flame become blurred or even invisible. Under the MILD conditions, the peak temperature in the combustion region is reduced and the uniformity of temperature distribution is improved, therefore significantly inhibiting the generation of thermal NOx and fuel NOx. The MILD combustion of pulverized coal can be realized by preheating air to high temperatures or increasing the jet velocity greatly, and the second way is more economical and feasible. However, the mechanisms and characteristics of the MILD combustion of pulverized coal under the condition of strong shear and turbulent mixing, when the jet velocity is as high as around 100 m/s, still need to be further investigated. Under the strong shear and entrainment of high-speed jets, the dispersion of coal particles, which is directly related to the achievement of the MILD combustion mode, is quite different from that in the conventional coal combustion. In addition, a strong turbulent mixing will affect the heating, devolatilization and char combustion of pulverized coal, therefore changing the ignition delay, the flame structure and the generation of pollutants. Based on the in-depth understanding of the above key issues and combined with the research on the MILD combustion of gaseous fuels, a systematic and accurate criterion for the MILD combustion of pulverized coal can be further developed, so as to better guide the application of the MILD combustion technology of pulverized coal.

国家自然科学基金重点国际(地区)合作研究资助项目(51761125011)

黄文仕，吴玉新，张海，等. 高速射流煤粉MILD燃烧的研究进展[J]. 煤炭学报，2023，48(8)：3240−3251.

HUANG Wenshi，WU Yuxin，ZHANG Hai，et al. Research progress of moderate or intense low-oxygen dilution (mild) combustion of pulverized coal in high-speed jet[J]. Journal of China Coal Society，2023，48(8)：3240−3251.