Analysis and validation of high-grade coals using spectroscopic, proximate, and multivariate techniques

Coal is still the main primary energy source worldwide despite being a major source of carbon dioxide and other emissions. In order to improve combustion efficiency, to reduce pollutant emission and for pricing purposes, a rapid tool for coal analysis is desirable. In this work, we demonstrate that laser-induced breakdown spectroscopy (LIBS) can provide a comprehensive analysis of high-grade coals using anthracite and bituminous as examples. LIBS is capable of detecting elements such as C, Fe, Na, Mg, Mn, Ti, Si, and Al, but also of some toxic elements such as Ba and Sr. The result of the LIBS elemental analysis is confirmed by X-ray fluorescence spectroscopy. In addition, we show the determination of the coal rank, which is a measure of the state of coalification, from the H/C line intensity ratio in the LIBS spectra. Proximate analysis has been performed to specify the quality of the different coal samples and has been correlated with the results obtained by the LIBS technique. Multivariate techniques for data analysis such as Principal Component Analysis and Hierarchy Clustering Analysis were employed to differentiate the coal samples. The results obtained from LIBS show good agreement with the state-of-the-art proximate analysis.