Laser-Induced Breakdown Spectroscopy Combined with Temporal Plasma Analysis of C₂ Molecular Emission for Carbon...

A benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants. The spectral intensities of molecular CN and C₂ emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the laser-induced breakdown spectroscopy spectrum of coal. The emission persistence time of C₂ molecule emission is measured from the coal plasma generated by a nanosecond laser ablation with a wavelength of 266 nm in the Ar atmosphere. The emission persistence time of molecular C₂ emission along with the spectral intensities of major ash elements (Fe, Si, Al, and Ca) and carbon emissions (atomic C, molecular CN, and C₂) shows a better relationship with the carbon wt% of different coal samples. The calibration model to measure elemental carbon (wt%) is developed by combining the spectral characteristics (spectral intensity) and the temporal characteristics (emission persistence time of C₂ molecule emission). The temporal characteristic studies combined with the spectroscopic data in the partial least square regression model have resulted in an improvement in the root mean square error of validation, and the relative standard deviation is reduced from 10.8% to 4.1% and from 11.3% to 6.0%, respectively.