基于煤粉预热的高温煤基燃料O2/CO2无焰燃烧实验研究

Stable ignition of char is a main technology obstacle to restrict the application of O2/CO2 flameless combustion in different coal type. As pulverized coal preheating can break through ignition stabilities and have the potential of ultra-low NOx emission, the reaction characteristics of high temperature char and the transformation mechanism of (ultra-) low NOx are some key scientific problems not to be solved in the O2/CO2-flameless combustion. In this project, combined with experimental study and theoretical analysis with macro and micro level, the realization mechanism of O2/CO2-flameless combustion of high temperature coal-based fuel will be revealed, and the relationship between flue gas recirculation and flameless combustion will be explored. The distribution characteristics of temperature field and components field, especially the char combustion process and influence mechanisms, will be illustrated. The transformation mechanism and control principle of HCN, NH3 and high temperature char-N to NOx will be analyzed. In addition, the influence of preheating on flameless combustion will be illustrated, including build the transformation route of coal-N to NOx. The aim of this project is to realize high efficient combustion and (ultra-) low NOx emission, and the results will provide experimental data and theoretical support for understanding O2/CO2-flameless combustion of high temperature coal-based fuel, provide a new technology route for ultra-low NOx emission, and support the development of high efficient and clean coal combustion technology.

焦炭稳定着火是制约O2/CO2无焰燃烧煤阶适应性的技术瓶颈，煤粉预热可突破着火问题且具备超低NOx排放优势，O2/CO2无焰燃烧下煤粉预热的高温焦炭反应特性和（超）低NOx转化机制是尚待解决的关键科学问题。本申请项目采用实验研究和理论分析相结合的方法，从宏观和微观层面阐释高温煤基燃料O2/CO2无焰燃烧的实现机制，分析烟气卷吸率与无焰燃烧的基本关系，探索高温煤基燃料O2/CO2无焰燃烧的温度场和组分场分布规律，分析高温焦炭的反应特性及影响机制，揭示HCN、NH3和高温焦炭N向NOx的转化途径及控制机理，阐释预热对高温煤基燃料O2/CO2无焰燃烧的影响规律，建立煤N转化路径，实现煤粉的高效燃烧和（超）低NOx排放。研究结果为理解高温煤基燃料O2/CO2无焰燃烧机理提供实验数据和理论支撑，为煤粉O2/CO2无焰燃烧超低NOx排放提供新的技术路线，支撑煤粉的高效清洁燃烧技术发展。

O2/CO2无焰燃烧是实现碳捕集和封存，减少煤燃烧CO2排放的富有前景技术。与常规煤粉入炉燃烧不同，煤粉首先进行预热改性后再入炉燃烧具有煤种适应性广和NOx排放低的技术优势。本项目在此背景下，开展基于煤粉预热的高温煤基燃料O2/CO2无焰燃烧实验研究，主要研究内容包括揭示预热改性机制、阐释无焰燃烧实现方式、剖析无焰燃烧基本特性和构建煤氮迁移转化路径等多个方面。. 研究表明，O2/CO2气氛下，煤粉可在循环流化床内稳定、持续、均质预热，预热温度在800-1000℃之间，超过燃料着火点。与预热前原煤相比，烟煤预热燃料比表面积从24.67m2/g增加到72.10m2/g，半焦比表面积从20m2/g增加到160m2/g，预热燃料反应活性提升1到10倍以上，预热改性明显。强还原性气氛下预热中煤氮析出后转化为HCN、NH3和N2，煤N向N2的转化比超过50%，这是预热燃烧实现低NOx排放的理论基础和重要条件。. 因预热温度高于800℃，预热彻底克服了煤种适应性问题，预热燃烧对煤种没有限制。通过射流组织将预热燃料分散到全炉膛空间内，实现了高温煤基燃料的无焰燃烧，燃烧室温度为800-1200℃之间、温升低于400℃、无火焰峰面。增加一次风和二次风氧气风压、降低三次风氧气分压，保持适当的还原区停留时间，均可降低煤粉预热燃烧的NOx排放水平。测试烟煤和半焦的NO排放最低值为30.2 mg/MJ和26.8mg/MJ，煤N向NO的转化比均低于10%。其NOx排放较常规燃烧低50%以上，同时燃烧效率高于98%，尾部烟气中的CO2浓度在92-95%之间。O2/CO2环境下实现了煤、半焦等不同挥发分燃料的高效燃烧和低NOx排放。. 本项目的研究成果发表SCI论文9篇，中文核心论文3篇，会议论文5篇，申请专利9项，研究结果为煤富氧无焰燃烧技术的发展提供理论支撑和数据支持，为中国尽早实现碳达峰和碳中和提供解决思路。