MILD富氧煤粉燃烧新模式下NOx生成机理与调控方法研究

MILD富氧煤粉燃烧是结合先进MILD燃烧和第一代富氧燃烧优势的新一代燃烧技术。与传统空气和富氧煤粉燃烧相比，其NOx生成与还原机理明显不同，且更为复杂，存在热力型NOx明显降低、高浓度CO2/H2O强化NO的均相和异相还原，特别是再循环烟气中NO浓度对燃料氮的转化有重要的影响。本项目采用独特设计的CO平面扩散火焰煤粉燃烧实验装置研究不同温度和氧气浓度O2/Ar、O2/CO2和O2/N2燃烧气氛下煤粉燃烧NOx生成演变过程，重点研究高温低氧、高浓度CO2/H2O和再循环NO对燃料氮的释放、分配、生成与还原的影响机制，定量分离不同NOx生成机理（热力型NOx、燃料型NOx、NOx还原和再循环NO再燃）对总NOx排放的重要性。建立MILD富氧煤粉燃烧模型及NOx生成与还原详细化学反应机理模型，确定MILD富氧煤粉燃烧的NOx生成机理、反应路径及调控方法，为超低NOx排放提供理论依据。

MILD Oxy-coal combustion is the novel generation Oxy-coal combustion technology with the combination of advanced MILD combustion and the first generation Oxy-coal combustion. Its essential is that coal particles burn under the conditions of mild temperatures, low oxygen concentrations, high concentrations of carbon dioxide and vapor and recycled NO. Compared with the conventional air coal combustion and Oxy-coal combustion, the NOx formation and reduction mechanisms for MILD Oxy-coal combustion is distinctly different and more complicated, which include the decreasing thermal NOx, the enhanced homogenous and heterogeneous NOx reduction with high concentrations of CO2, H2O and CO and the recycled NO reburning with the exception of NOx formation and reduction under the fuel rich conditions. In this proposal, the coal particle combustion experimental setup with the CO flat diffusion flame is specially designed to investigate the coal nitrogen evolution under the O2/Ar、O2/CO2和O2/N2 combustion environments with different ambient temperatures, oxygen concentrations, CO2 and H2O concentrations and recycled NO concentrations. The influencing mechanisms of low oxygen dilution, high concentrations of CO2 and vapor and the recycled NO concentrations on the release, partition and conversion of coal nitrogen species are elucidated during the MILD Oxy-coal combustion process. The relative importances of different NOx formation mechanisms including thermal NOx, fuel NOx, NOx reduction and recycled NO reburning are quantitatively isolated to identify the contributions of each NOx mechanism on the overall NOx emission. The detailed chemical reaction models of NOx formation and reduction coupled with the MILD Oxy-coal combustion model with the char gasification reaction with CO2 and H2O are built to simulate and determine the NOx formation mechanisms and reaction pathways by switching on or off the special reaction routes. Then the NOx control strategies are proposed by adjusting the optimum reaction pathways through controlling coal nitrogen release rate, partition ratio of volatile nitrogen and char nitrogen under fuel rich zone and inhibiting the NOx reformation under the burnout zone. The achievements will provide the solid fundamentals to realize the ultra low NOx emissions for MILD Oxy-coal combustion.