煤粉群燃火焰中碳黑生成机理的研究

Haze is one of most urgent and important livelihood issues need to be resolved in China today, and the soot emitted from the coal-fired boilers is a major source of fine particles from which haze is formed. Although the studies on soot have being carried out decades, they are still mostly confined to simplified combustion environment, while the understanding of the soot formation mechanisms in practical combustion system is still a challenge for the international combustion society. In a pulverized coal boiler, combustion of coal occurs in a flame burning in cloud style, and the soot formation mechanisms in such a pulverized coal cloud flame remains to be revealed. In this proposed study, the soot formation in the pulverized coal cloud flame will be conducted. The experiments will be carried out to flames those are close to the practical flames in the pulverized coal boiler, under adjustable combustion conditions. Several advanced laser diagnostic methods as well as the traditional sampling methods will be applied to quantitatively measure the soot volumetric density, the temperature and major species distribution in the flame under different combustion conditions for different types of coal, using the latest reported tuning techniques to minimize the influence of coarse particles of char and ash. By correlating the flame characteristics with the soot distribution characteristics, it is expected the soot formation mechanism will be assessed and the major influencing factors on soot formation will be identified. The model to describe the soot formation process will be developed and the effective methods used for the soot formation reduction in the pulverized coal cloud flames will be summarized. In the meantime, the counter-influence of soot formation on the pulverized coal flame will be detected, and the correction for the calculation of coal combustion and the thermal radiation in the furnace will be proposed to improve the simulation accuracy.

雾霾是我国当前迫切需要解决的重大民生问题，而形成雾霾的微细颗粒的一个重要来源是燃煤锅炉排放的碳烟。尽管碳烟的研究开展了数十年，但基本仍局限于简化的燃烧环境，实际燃烧系统中碳烟的生成机理仍是燃烧界的一个挑战，煤粉锅炉中煤粉燃烧以群燃火焰的形式进行，其中碳烟的生成机理和影响机制还有待揭示。本项目以煤粉群燃火焰为对象，在与实际锅炉接近的、可控的燃烧环境进行开展实验研究，使用多种光学测量方法和传统采样方法相结合，采用最新研究报道的有效消除煤粉、飞灰等大颗粒对测量结果的干扰方法，定量地测定不同煤种和燃烧参数条件下碳烟在群燃火焰中的浓度分布、火焰内温度分布、煤焦颗粒分布和主要自由基分布，关联火焰特性与碳烟浓度分布特性，揭示群燃火焰中碳烟的生成机理和影响因素，建立生成模型，总结减少碳烟生成的措施，同时获得碳烟生成对煤粉火焰特征的反向影响规律，提出提高炉内燃烧和辐射传热计算精度的修正方法。

煤粉燃烧过程中生成大量的碳烟颗粒，了解生成特性和浓度分布特性对控制污染排放和提高炉内燃烧和辐射传热计算精度有重要意义。但煤粉火焰中碳烟的生成浓度分布的测量和模型预算具有挑战性，在测量中需有效消除煤粉、飞灰等大颗粒对测量结果的干扰，而模拟中设计多过程多维度，研究缺乏。.本项目确认了使用快速取样和多种光学方法，包括Mie 散射、LII、PLIF测定典型工况下湍流煤粉射流火焰中碳烟颗粒形貌、浓度，以及煤粉群燃火焰温度分布以及OH、CH 等重要基元的分布的可行性；研究了煤粉群燃火焰中碳烟生成机理，以及群燃火焰特性与碳烟生成特性的耦合作用，建立煤粉群燃火焰中碳烟的生成模型；实验研究了煤粉群燃火焰变化参数，包括煤种、煤粉浓度、一二次风浓度、一二次风温度以及环境气体组分和氧气浓度对群燃火焰及其碳烟生成特性的影响，校核改进煤粉群燃火焰的碳烟生成模型，总结减少碳烟生成的有效措施；模拟研究碳黑的辐射传热特性，定量评估煤粉燃烧系统中考虑碳烟生成对煤粉火焰特征、传热量的影响，建立更为可靠的煤粉燃烧模型，提出提高炉内辐射传热计算精度的修正方法。通过研究，掌握了煤粉群燃火焰中碳烟生成及其浓度分布的定量测量方法，确认了激光方法测量煤粉火焰结构及其碳烟浓度时有效消除煤粉、飞灰等大颗粒对测量结果的干扰的必要措施和关键参数；关联了火焰特性和碳烟浓度分布特性，探讨煤粉群燃火焰中碳烟生成机理， 建立煤粉群燃火焰中碳烟生成机理模型，并揭示煤粉群燃火焰的结构变化对其中碳烟生成特性的影响规律；（3）揭示碳烟存在对煤粉火焰热辐射的作用规律，并开发更为准确的煤粉燃烧与传热模型或者计算方法。本项目年度计划进展顺利，圆满地完成了任务书的各项任务，取得了一系列成果，达到了预期的结果。在本项目的支持下，发表国内外期刊、会议文章25篇，其中SCI检索收录论文7篇，EI收录8篇。