煤粉燃烧初期钠元素与碳烟相互作用的光学诊断研究

Laser-induced Incandescence(LII)Diagnostics on Sodium-soot Interaction in Early Stage of Pulverized Coal Combustion

煤粉燃烧过程中生成的碳烟对炉内辐射换热过程有显著影响,在随烟气进入大气后,会引发温室效应,同时危害人体健康。为研究煤粉燃烧过程中易挥发矿物质元素钠对碳烟生成的影响,本实验制备了一系列不同钠含量的煤样,使用一种新型两级平焰燃烧器,将煤粉颗粒给入燃烧器,利用激光诱导白炽光测量了酸洗煤及载钠煤的沿程碳烟空间分布,同时使用扫描电迁移粒径仪测量了热解阶段生成的细颗粒物数浓度分布。结果表明:碳烟在煤粉燃烧初期出现,约31 ms后达到峰值,随后减弱消失。碳烟信号峰值对应的煤粉颗粒停留时间与按照10%最大火焰信号强度定义的煤粉着火特征时间近似相同,表明碳烟的生成氧化过程与煤粉着火过程密切相关。碳烟的光学测量结果与颗粒物采样结果均表明:随着煤样中钠含量增加(0~0.641%),生成的碳烟量明显增加,而煤粉点火几乎不受影响。这表明载入钠元素会促进燃煤初期碳烟生成。

The soot generated during the combustion of pulverized coal has a significant impact on the radiative heat transfer inside furnace.Besides,after entering the environment with the flue gas,soot can enhance the greenhouse effect and endanger human health.To investigate the effect of the volatile sodium contained in coal on soot formation,in this work,a novel two-stage flat-flame burner was used and a series of coal samples with different Na content were studied.Laser-induced incandesce was applied to detect the soot spatial distribution for different coal samples,including the demineralized coal and the coal containing specific content of Na.In addition,the scanning electromobility particle sizer was utilized to measure the number concentration distribution of fine particles generated in the pyrolysis stage.The results show that soot is mainly generated in the pyrolysis stage during the combustion of pulverized coal.The soot signal intensity reaches a peak after about 31 ms,and then decreases.The residence time of pulverized coal particles corresponding to the peak value of soot signal is approximately the same as the characteristic time of pulverized coal ignition,which is defined by 10%of the maximum flame signal intensity.It indicates that the generation and oxidation of soot is closely related to the ignition process of pulverized coal.Both the optical measurement results of soot and the sampling results of particulate matter show that with the increase of Na content in the coal samples(0-0.641%),the amount of soot increases significantly,while the ignition of pulverized coal is almost unaffected.This phenomenon indicates that the loading of Na element can promote the generation of coal-derived soot in early stage.