中国在经济高速发展的过程中，对电力的需求持续增加，其中60%以上由燃煤锅炉电站提供。为了扩大锅炉适用煤种范围和平衡煤种供求，混煤燃烧技术已被广泛采用。已有的研究结果表明，对于典型的炉外预混掺烧方式，即将不同种煤粉在炉外均匀混合再送入炉中燃烧，混煤的着火点、燃尽特性、积灰和结渣等特性不同于单煤的线性加和，而混煤在空气分级燃烧中的特性仍有待进一步探究。

        在锅炉的空气分级燃烧中，NO在还原区被大量还原，而H₂S也在还原性气氛中产生，会对锅炉的水冷壁造成严重的腐蚀。在锅炉运行过程中，电站需要通过合理控制过量空气系数、温度和预混比等，促进煤粉的充分燃烧，并在保证NO达标排放的前提下尽量减少H₂S的产生以延长锅炉寿命。而指导这一工作的前提，正是准确地把握煤粉燃尽特性和还原型气氛与给定工况的关系。   

图1   沉降炉 

图2 焦炭气化转化率-CO 

图3 CO浓度-NO浓度

图4 CO浓度-H₂S浓度

Low NOₓ combustion of blended coals is widely used in coal-fired boilers in China to control NOₓ emission; thus, it is necessary to understand the formation mechanism of NOₓ and H₂S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NOₓ and H₂S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H₂S, and NOₓ in the fuel-rich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H₂S as NO reduction accelerated. Both the CO and H₂S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H₂S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion. Thus, CO, NOₓ, and H₂S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.

Keywords blended coal combustion, NOₓ formation, H₂S formation, air staged combustion 

李振山，工学博士，清华大学副教授、博士生导师。主要研究方向有：气固表面反应与传递、化学链循环过程、污染物超低排放技术。入选2012年教育部新世纪优秀人才支持计划。

蔻享学术平台，国内领先的一站式科学资源共享平台，依托国内外一流科研院所、高等院校和企业的科研力量，聚焦前沿科学，以优化科研创新环境、传播和服务科学、促进学科交叉融合为宗旨，打造优质学术资源的共享数据平台。