洁净煤技术

2019, v.25;No.124(06) 51-60

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气体燃料再燃脱硝机理及工程应用进展
Denitration mechanism and engineering application progress of gas fuel reburning

王鹏涛;王乃继;梁兴;牛芳;
WANG Pengtao;WANG Naiji;LIANG Xing;NIU Fang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;

摘要(Abstract):

气体燃料再燃脱硝技术能有效降低锅炉初始NO_x排放,针对气体燃料再燃脱硝机理及工程应用现状,分析了5个因素对再燃脱硝效果的影响规律,总结了国内外将气体燃料再燃技术用于锅炉改造中的典型示范工程及运行效果。气体燃料再燃脱硝的本质是烃类物质受热分解产生相关基团,这些基团与NO_x碰撞生成相应的含氮中间体,含氮中间体与还原性基团发生还原反应,最终将部分NO_x转化为N_2。具体表现为,甲烷再燃过程中主要生成CH_3中间体,其与NO的消减反应是脱硝反应的关键,而多碳烃类燃料再燃过程中生成HCCO中间体的过程,及其与NO的还原反应是再燃的核心。结果表明,再燃脱硝过程中再燃区停留时间、过量空气系数、温度均存在适宜的范围,再燃燃料组成和再燃燃料与NO_x的混合特性对脱硝效果有显著影响。增加再燃燃料和NO_x在再燃区的停留时间不仅有利于NO_x还原,也有利于再燃燃料的燃尽,但过长的再燃区停留时间不但不能增加NO_x还原率,反而会降低燃料的燃烧效率。最佳的再燃区停留时间为0.6~1.1 s,且进一步增加停留时间并不会增加脱硝效率。再燃区过量空气系数对再燃还原效率和燃尽特性有显著影响。再燃区最佳过量空气系数保持在0.85~0.90较为合适。提高再燃区的温度有利于提高再燃燃料的脱硝效率,再燃区最佳脱硝温度在1 000~1 100℃。再燃燃料的组成不同,对NO_x的还原效果不同,烃类物质再燃脱硝与其受热分解密切相关,在相同的再燃条件下,再燃脱硝性能与其受热分级速率完全相关,研究表明多碳烃类物质的存在可以显著增强再燃气体混合物的还原效果,且焦油和煤焦等物质的存在对NO还原反应有明显的催化作用。另外,气体燃料再燃脱硝过程不仅受到化学反应难易程度的影响,还与再燃燃料在高NO_x浓度区的扩散过程相关,强化再燃燃料在再燃区与NO_x的混合特性也有利于提高脱硝效率。美国、欧盟和日本等国家针对电站锅炉再燃脱硝的研究和工程示范工程起步较早且获得了较显著的效果,我国四川江油电厂天然气再燃技术改造示范工程同样证明了再燃脱硝的可行性及经济性。
Gaseous fuel reburning denitrificationtechnology can effectively reduce the initial nitrogen oxide emission of the boiler. In this paper,aiming at NO_x reduction mechanism of gaseous fuel reburning and its application status in Engineering,the effects of five factors on the reburning effect were analyzed. The typical demonstration projects and their operation effects of gaseous fuel reburning technology in boiler retrofit were summarized. The research at home and abroad shows that the essence of denitrification by gaseous fuel reburning is that hydrocarbons decompose by heat to produce related groups,which collide with NO_x to generate corresponding nitrogen-containing intermediates. At the last,the nitrogen-containing intermediates react with reducing groups to convert part of NO_x into N_2. Specifically,CH_3 intermediate is mainly generated in the process of methane reburning,and the reduction reaction between CH_3 and NO is the key to denitrification,while HCCO intermediate is generated in the process of multi carbon hydrocarbon fuel reburning,and the reduction reaction with NO is the core of reburning. The results show that there are proper ranges of reburning zone residence time,excess air coefficient and temperature during reburning. What′s more,the reburning fuel composition and the mixing characteristics of reburning fuel and NO_x also have a significant effect on the reburning effect. Increasing the residence time of reburning fuel in reburning zone is not only conducive to NO_x reduction,but also conducive to the burnout of reburning fuel. However,the too long residence time in reburning zone will not increase the NO_x reduction rate,but will reduce the combustion efficiency of fuel. The best residence time of reburning zone is 0.6-1.1 s,and the further increase of residence time will not increase denitrification efficiency.The excess air coefficient in the reburning zone has a significant effect on the reburning reduction efficiency and burnout characteristics. The best excess air coefficient in reburning zone is 0.85-0.90.The high temperature of reburning zone is conducive to improving the denitrification efficiency of reburning fuel,and the optimal denitrification temperature in reburning zone is 1 000-1 100 ℃.The composition of reburning fuel is different,and the reduction effect of NO_x is different.The reburning denitrification of hydrocarbon is closely related to its thermal decomposition. Under the same reburning condition,the reburning denitrification performance is completely related to its heating classification rate. The research shows that the presence of multi carbon hydrocarbon can significantly enhance the reduction effect of reburning gas mixture,and the presence of tar and coal char can have obvious catalysis effect on the NO reduction. In addition,the denitrification process of gas fuel reburning is not only affected by the difficulty of chemical reaction,but also related to the diffusion process of reburning fuel in the high NO_x concentration area. Strengthening the mixing characteristics of reburning fuel and NO_x in the reburning area is also conducive to improving the denitrification efficiency.The United States,European Union,Japan and other countries started earlier and achieved remarkable results in the research and engineering demonstration projects of power plant boiler reburning and denitrification. The demonstration projects of natural gas reburning technology transformation of Sichuan Jiangyou Power Plant also proved the feasibility and economy of reburning and denitrification.

关键词(KeyWords): 再燃;脱硝;气体燃料;氮氧化物;工程应用
reburning;NOx reduction;gaseous fuel;NOx application in engineering

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基金项目(Foundation): 煤炭科学研究总院面上资助项目(2016ZYMS007);; 天地科技股份有限公司科技创新创业资金专项资助项目(2018-TD-MS007)

作者(Author): 王鹏涛;王乃继;梁兴;牛芳;
WANG Pengtao;WANG Naiji;LIANG Xing;NIU Fang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;

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