燃煤热值是煤质分析的一个重要指标,采用纳秒和飞秒以及双脉冲激光诱导击穿光谱技术对18个含有不同热值的标准煤样进行热值定量分析。对比分析了纳秒和飞秒等离子体光谱的差异,结果表明飞秒等离子体光谱较纳秒等离子体光谱具有更小的连续背景噪声,信噪比更低,谱线强度的相对标准偏差更小,稳定性更高,无需对光谱进行基线校正即可获得较高的元素含量线性拟合度,但存在光谱强度较弱的缺点。搭建了一套以飞秒激光器作为光谱激发源,以纳秒激光作为加热源的双脉冲激光诱导击穿光谱系统,通过实验证明了双脉冲激光诱导击穿光谱技术可以大幅增强谱线强度。最后分别将纳秒、飞秒以及双脉冲激光诱导击穿光谱技术与偏最小二乘法结合,对煤样的热值进行定量分析,定标曲线拟合度(R2)分别为0.9553、0.9897、0.9964,说明双脉冲激光诱导击穿光谱技术可以有效提高燃煤热值的定量分析精度。

Calorific value is a major indicator of the quality of coal. In this study, we use nanosecond, femtosecond, and dual-pulse laser-induced breakdown spectroscopy (LIBS) to quantitatively analyze the calorific values of 18 standard coal samples exhibiting different calorific values. The comparison of nanosecond and femtosecond plasma spectra denotes that the femtosecond plasma spectra exhibit less continuous noise and better signal-to-noise ratio when compared with those exhibited by the nanosecond plasma spectra; further, the relative standard deviation of the spectral line intensity is smaller, whereas the stability is higher. Femtosecond laser-induced breakdown spectroscopy (fs-LIBS) can obtain high linear fitness of the element content without any baseline correction but it has the disadvantage of weak spectral intensity. We construct a dual-pulse LIBS system using a femtosecond laser as the spectral excitation source and a nanosecond laser for plasma heating. Experiments denote that the dual-pulse LIBS can considerably enhance the emission lines. Finally, we combine nanosecond, femtosecond, and dual-pulse LIBS with the partial least squares (PLS) method to quantitatively determine the calorific values of coal samples. The fitting degrees of the calibration curves (R²) are 0.9553, 0.9897, and 0.9964 for the three aforementioned methods, respectively. The use of dual-pulse LIBS can effectively improve the accuracy of the quantitative analysis of the calorific value of coal.