洁净煤技术

2019, (03) 9-18

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煤焦燃烧过程中细模态颗粒物的生成机理及研究进展
Formation mechanism and research progress of fine mode particle matter during coal char combustion

刘思琪;牛艳青;温丽萍;闫博康;王登辉;惠世恩;
LIU Siqi,NIU Yanqing,WEN Liping,YAN Bokang,WANG Denghui,HUI Shien

摘要(Abstract):

实现燃煤颗粒物(PM)污染排放控制必须深入了解颗粒物排放规律及生成机理。煤粉燃烧过程中产生飞灰颗粒粒径分布为粗模态,细模态和超细模态3种。与粗模态PM相比,细模态PM占比较大,其小粒径与富集性特点影响人体健康及大气环境。同时,相对于形成过程与机理相对成熟的超细模态PM,细模态PM形成机理及研究进展尚缺乏系统总结,抑制细模态PM排放存在困难。笔者分析了细模态PM的形成机理(焦炭颗粒的破碎、矿物质熔融聚合、外在矿物质破碎、表面灰粒的脱落)及主要影响因素,探讨了模拟研究进展并指出未来研究重点。煤灰PM粒径分布主要是焦炭颗粒破碎与矿物质聚合行为这2个因素相互竞争的结果。破碎行为使得细模态PM数量增多粒径减小,而矿物质聚合使得PM数量减小,有利于粗模态PM形成。影响PM形成的主要因素有孔隙结构、燃烧模式与焦炭粒径。孔隙率较高的煤胞型焦炭相较于其他结构焦炭更易发生破碎,产生更多细模态PM。增加温度与氧含量,降低粒径均有助于PM生成,但较高温度下灰粒的聚合可能导致粒径分布倾向于粗模态PM。破碎行为对焦炭燃烧特性模拟大致分为群体平衡模型和逾渗模型2类。基于细模态PM形成机理与影响因素,认为逾渗模型考虑了焦炭本身孔隙结构,更适于模拟焦炭破碎行为。本征动力学燃烧模型与逾渗模型的结合是准确预测灰颗粒粒径分布的关键,是下一步的研究重点。
Abstract:In order to control the emission of particulate matter(PM) from coal combustion,it is necessary to have a thorough understanding of the emission rule and formation mechanism of PM.During pulverized coal combustion,PM can be divided into three formation modes:coarse mode,fine mode,and ultrafine mode.Compared to the coarse mode,the fine mode particles account for a larger proportion,and affect human health and atmospheric environment due to their small sizes and enrichment characteristics.Besides,the systemic summary of formation mechanism and research progress on fine mode PM are relatively lacking,compared with that of ultrafine mode,and it is difficult to suppress the emission of the fine mode PM.In this paper,the formation mechanisms of fine mode PM(char fragmentation,mineral melt coalescence,exterior mineral fragmentation and ash shedding) as well as the main influencefactors were analyzed.The research progress of simulationwere discussed and the research emphasis in future was pointed out.The particle size distribution of PM in coal ash turns out to be the result of competition between the char fragmentation and mineral aggregation.The fragmentations results in the increase of amount and the decrease of particle size of fine mode PM,while mineral aggregation leads to the amount decrease of PM,which is conducive to the formation of coarse mode PM.The main factors affecting the formation of PM arepore structure,combustion mode and char particle size.With relatively higher porosity,char cenospheres are more likely to broken up into more fine mode PM than other chars.Both increasing temperature,oxygen content and decreasing particle size are helpful to the formation of PM,but the aggregation of ash particles at higher temperature may lead to the particle size distribution towards coarse mode PM.The simulation of coke combustion characteristics by fragmentation behavior is mainly divided as population balance model and percolative fragmentation model.On the basis of the formation mechanism and influencing factors of fine mode PM,the percolative model is more suitable for simulating the char fragmentation,which takes the porous char structure into account.Therefore,the combination of kinetics combustion model and percolative fragmentation model is the key for the accurate prediction on the ash particle size distribution,which is the next research focus.

关键词(KeyWords): 煤焦燃烧;细模态颗粒物;形成机理;逾渗模型
coal char combustion;fine mode particle matter;formation mechanism;percolative model

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作者(Author): 刘思琪;牛艳青;温丽萍;闫博康;王登辉;惠世恩;
LIU Siqi,NIU Yanqing,WEN Liping,YAN Bokang,WANG Denghui,HUI Shien

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