气体燃料无焰氧燃烧的氧化反应及NOx生成规律研究

Flameless combustion (also termed as Moderate or Intense Low-oxygen Dilution, MILD combustion) is an efficient and clean combustion technology. Compared with the traditional combustion, its reaction zone increases dramatically where temperature distribution is uniform and no visible high-temperature flame front exists. Extremely low NOx emission and simultaneously high thermal efficiency can be achieved in the flameless combustion. Hence it has been considered as one of the most promising combustion technologies of the 21st century. There is a misconception that flameless combustion should be established by high preheating of the air, which has limited its application. On the other hand, oxy-combustion has generated significant interest for carbon capture and storage. While successful, the technology still faces many challenges, i.e., the approach of further increasing the thermal performance of the system, and the challenge of improving the stabilization of oxy-fuel combustion. This research bridges the promising flameless and oxy-fuel combustion technology to provide the innovative efficient and clean solution of the gaseous fuels utilization. This project is aimed at investigating the foundational mechanism of the flameless oxy-combustion of gaseous fuels, i.e., (1) quantitatively examining the characteristics of the reaction regime of the flameless oxy-combustion; (2) investigating the NO formation and reduction mechanism under the flameless oxy-combustion; (3) clarifying the effect of fuel-oxidant initial conditions on the characteristics of the flameless oxy-combustion of gaseous fuels.

无焰燃烧，亦称中度或强低氧稀释燃烧，具备高效与低污染优势。与传统燃烧相比，其反应区域增加、炉温均匀、辐射换热效率高、NOx排放低、燃烧稳定性好。国际燃烧界将它视为21世纪最具前途的新型高效低污染燃烧技术之一。但受无焰燃烧需高温预热空气观点的影响，该技术的应用范围有限。另一方面，氧燃烧方式因其能大规模富集CO2，也吸引了同行的极大关注，但该技术仍面临燃烧稳定性差和效率低的问题。基于申请人发现无焰燃烧无需高温预热氧化剂的突破性进展，申请人将无焰燃烧与氧燃烧技术结合，形成无焰氧燃烧方式，提高氧燃烧炉温均匀性、增强炉内换热、提高氧燃烧热效率、降低污染物尤其是NOx的排放。本研究探索气体无焰氧燃烧的基础问题：（1）研究气体无焰氧燃烧的反应区域特征；（2）研究气体无焰氧燃烧的NOx生成及还原的规律；（3）研究燃料及氧化剂射流初始条件对气体无焰氧燃烧的影响。

无焰燃烧（即中度或强低氧稀释燃烧）已被证实具备高效与低污染优势。其与传统燃烧相比的明显优势在于：无焰反应区域增加、炉温均匀、辐射换热效率高、NOx排放低、燃烧稳定性好。另一方面，富氧燃烧因能实现CO2大规模富集而在近年吸引了同行的极大关注。本研究成功地将无焰燃烧与富氧燃烧相结合，实现了无焰氧燃烧方式，进一步提高富氧燃烧燃烧室温度均匀性、增强炉内热性能、提高富氧燃烧效率、降低污染物尤其是NOx的排放。通过2015年至2017年的三年研究，项目已完成：（1）气体无焰氧燃烧反应区域特性、（2）气体无焰氧燃烧NOx生成及还原规律、及（3）燃料及氧化剂射流初始条件对气体无焰氧燃烧影响，这三方面的既定研究内容。在气体无焰氧燃烧反应区域特性方面，研究较系统地揭示了气体燃料无焰氧燃烧反应区的氧化动力学机制，找到了控制无焰氧燃烧氧化的关键路径及自由基，根据对氧化动力学过程的理解进行了无焰氧燃烧总包反应机理的优选与优化；在气体无焰氧燃烧NOx生成及还原规律方面，较全面地研究了气体燃料无焰燃烧的NOx生成及还原路径，研究了当量比、反应温度、反应区氧浓度、燃料加氢等情况下无焰（氧）燃烧的NOx生成及还原路径，发现无焰燃烧方式下热力型路径被抑制后，无焰燃烧NOx生成主要受N2O-中间型及快速型路径主导；在燃料及氧化剂射流初始条件对气体无焰氧燃烧影响方面，总结了各类射流初始条件对气体燃料无焰氧燃烧的影响，实验获得了无焰燃烧的最优运行范围，实验实现了气体燃料无焰燃烧的NOx近零排放，并讨论了获得无焰燃烧NOx近零排放的条件和机理。