燃煤初期碳烟生成的激光诱导白炽光LII诊断研究

Laser-Induced Incandescence(LII)Diagnostics on the Soot Formation in the Early Stage of Pulverized Coal Combustion

本文基于光学可视化Hencken平焰燃烧器系统平台,采用激光诱导白炽光(LII)方法对煤粉燃烧初期碳烟生成过程进行诊断。结果表明,高阶PH煤在燃烧初期产生的碳烟量高于低阶准东(Zhundong)煤。化学渗透热解模型计算结果证明这主要由PH煤热解过程中更高的焦油产量所致。时间尺度分析表明,在1500 K, 20%O2燃烧条件下,PH煤碳烟生成的特征时间(约20 ms)滞后于煤粉点火特征时间(约10 ms)和挥发分燃烧特征时间(约12 ms).随着环境中氧气浓度的降低,碳烟生成的特征时间增加。通过建立简化的碳烟生成/氧化模型,进一步揭示了煤粉燃烧初期煤粉点火、挥发分燃烧和碳烟生成过程的内在联系。实验中还发现与常规条件相比,富氧条件对煤粉燃烧初期碳烟生成存在抑制作用。

In this work, we diagnosed the soot formation in the early stage of coal combustion with the laser-induced incandescence(LII) technique in an optically-accessible Hencken flat flame burner system. Results indicate that the combustion of high-rank PH coal yields a higher amount of soot than that of low-rank Zhundong coal. It is mainly attributed to the higher tar production from PH coal according to the calculation results of chemical percolation devolatilization(CPD) model.Further time-scale analyses manifest that the appearance of soot particles(about 20 ms) lags behind the ignition of coal particles(about 10 ms) and combustion of released volatiles(about 12 ms) in the condition of 1500 K and 20% O2. Moreover, the characteristic time of soot formation is postponed as the increase of ambient oxygen concentration. By establishing a simple soot formation/oxidation model, the essential relations among coal ignition, volatile combustion, and soot formation are clarified. Compared with conventional condition, the negative effect of oxy-coal conditions on the soot formation in the early combustion stage is also discovered in our experiments.