CO2氛围下煤及碳氢燃料燃烧碳烟颗粒物（Soot）的形成机制研究

The soot formation of oxyfuel combustion is quite different compared with air combustion in pulverized coal and hydrocarbon fuel flames due to the difference of thermal radiation and chemical reaction. This project uses a combined theoretical modeling simulation and experimental investigation to explore the soot formation in O2/CO2 atmosphere. The chemical reaction model in CO2 atmosphere is established for the main hydrocarbon mixture of pulverized coal volatile. Based on this full updating mechanism mechanism, the reduced mechanism of semi-empirical model of soot is developed. The dynamics evolution of soot particles size distribution, surface area, fractal dimension, morphology characteristics, species concentration and other characteristic quantities in-depth study is conducted in CO2 atmosphere for diffusion flame. The optical measurement, advanced thermophoretic sampling and electron microscopy scanning methods are used to explore the key parameters such as flame temperature, radiation heat flux distribution, carbon black concentration distribution, microscopic structure and dwell time of soot, and clarify the root causes of influence of chemical reaction, the flame structure and thermal radiation on the soot generating. Further, the simplified model and the simple two-equation soot model are coupled to simulate the nucleation, growth and oxidation of soot, and solving the coal tar, soot volume fraction and particle number density transport equation. The study has important scientific significance and application value for reducing pollutant emissions of combustion.

煤粉及碳氢燃料火焰富氧与空气燃烧相比，化学反应和热辐射有较大区别，因此影响火焰结构及温度分布，从而影响碳黑（Soot）的生成转化行为。本项目拟采用数值模拟与实验室试验揭示O2/CO2气氛下碳烟颗粒物的形成机制。对煤粉挥发份中含量较大的碳氢混合物详细化学反应机理，建立适用于CO2 气氛的模型并发展简化模型，基于简化模型模拟研究扩散火焰中碳烟颗粒群尺度分布、表面积、分形维数、形貌特性、组分浓度等多个特征量的动力学演变过程，并采用光学检测结合先进的热泳取样与电镜扫描法探寻火焰温度、热流及碳黑浓度分布、微观结构及驻留时间等关键参数，阐明化学反应、火焰结构及热辐射对碳黑生成产生影响的根本原因；进一步，基于简化模型，耦合简单双方程烟黑模型，模拟煤粉火焰中与挥发份反应耦合的碳黑成核、生长和氧化，并求解煤焦油、烟黑质量分数和颗粒数密度输运方程。本研究对降低燃烧污染物排放具有重要科学意义和应用价值。

本研究采用数值模拟与试验检测揭示O2/CO2气氛下碳烟颗粒物（Soot）的形成机制，并模拟计算了O2/CO2燃烧烟气及CO2液化与输送问题。首先，建立了CO2气氛下混合气的详细化学反应动力学模型，研究了CO2气氛下乙烯火焰Soot的转化机制及其生成影响因素；采用敏感性和反应路径分析及准稳态假设耦合CARM机理简化该新建模型，获得了模拟O2/CO2燃烧的简化化学动力学模型；利用该简化模型及光学测量与电镜扫描的方法对扩散火焰分别进行了模拟计算和实验探测，验证该模型的合理性，并对O2/CO2燃烧Soot的生成机制和影响进行了定量研究，得出氛围的改变对Soot的成核、生长和氧化的影响趋势各不相同，但是O2/CO2燃烧可减少Soot生成总量；分析计算了富氧燃烧烟气热物性参数，进而对烟气及CO2液化、输送问题进行了工艺流程及多相流动的分析及优化，得出了一种对温度和压力要求相对较低的液化流程，并得到了一种改进后的密相输送流程相比运用较广泛的超临界输送具有一定的优越性。上述结果丰富了燃烧污染物及CO2减排相关研究的内容。