Influence of C-Fe Lines Interference Correction on Laser-Induced Breakdown Spectroscopy Measurement of Unburned Carbon in Fly Ash
YAO Shun-chun1, CHEN Jian-chao1, LU Ji-dong1*, SHEN Yue-liang2, PAN Gang1
1. School of Electric Power of South China University of Technology, Guangzhou 510640, China 2. Electric Power Research Institute of Guangdong Power Grid Co. Ltd., Guangzhou 510080, China
摘要： 在燃煤电厂，飞灰含碳量是直接反映锅炉燃烧效率的重要指标，控制含碳量水平和低氮燃烧之间的平衡要求实现含碳量的在线(或快速)检测。将激光诱导击穿光谱技术应用于飞灰含碳量的快速测量，针对测量中248 nm附近的C和Fe谱线干扰问题，提出了利用Fe谱线修正的方法以提取重叠峰中C谱线的积分强度，对比分析了Fe 248.33 nm, Fe 254.60 nm和 Fe 272.36 nm谱线分别作为Fe 247.98 nm的修正谱线时提取的C修正积分强度对飞灰含碳量定标曲线和未知样品重复测量精确度的影响。研究结果表明，对C和Fe谱线干扰进行强度修正可以提高含碳量定标曲线的拟合度，并且可以显著改善低含碳量样品重复测量的精确度。但同时需要注意用于修正的Fe谱线的合理选取，防止在对低含碳量样品中C谱线强度的过度修正。从定标曲线和重复测量精确度总体评价而言，Fe 254.60 nm谱线最适用于LIBS测量飞灰含碳量时的C和Fe谱线干扰的修正。
关键词：激光诱导击穿光谱;C-Fe谱线干扰;飞灰含碳量
Abstract：In coal-fired plants, Unburned carbon (UC) in fly ash is the major determinant of combustion efficiency in coal-fired boiler. The balance between unburned carbon and NOx emissions stresses the need for rapid and accurate methods for the measurement of unburned carbon. Laser-induced breakdown spectroscopy (LIBS) is employed to measure the unburned carbon content in fly ash. In this case, it is found that the C line interference with Fe line at about 248 nm. The interference leads to C could not be quantified independently from Fe. A correction approach for extracting C integrated intensity from the overlapping peak is proposed. The Fe 248.33 nm, Fe 254.60 nm and Fe 272.36 nm lines are used to correct the Fe 247.98 nm line which interference with C 247.86 nm, respectively. Then, the corrected C integrated intensity is compared with the uncorrected C integrated intensity for constructing calibration curves of unburned carbon, and also for the precision and accuracy of repeat measurements. The analysis results show that the regression coefficients of the calibration curves and the precision and accuracy of repeat measurements are improved by correcting C-Fe interference, especially for the fly ash samples with low level unburned carbon content. However, the choice of the Fe line need to avoid a over-correction for C line. Obviously, Fe 254.60 nm is the best choice for the correction of the C-Fe interference.
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