Quantitative Analysis of Coal by Laser-Induced Breakdown Spectroscopy Using TEA CO<inf>2</inf> Laser as the Excitation Source

Abstract

This work presents a study of the applicability of laser-induced breakdown spectroscopy based on infrared transversally excited atmospheric CO2 pulsed laser for quantitative analysis of main inorganic elements in lignite coals. Calibration standards were prepared by mixing and pelleting an appropriate amount of rock reference material and graphite. Time-integrated spatially resolved measurements of analyte spectra of standard samples were used to construct univariate calibration curves of Al, Si, Ca, Fe and Mg. The spectral intensities of analytical lines were normalized by the carbon spectral line to compensate for the shot-to-shot fluctuation of plasma parameters. The obtained curves of growth have good linearity in a wide range of concentrations (up to 1% for Al and 3% for Si). Correlation coefficients were in the range of 0.955–0.993, depending on the element. Measured limits of detection (from 2.4 to 25 ppm for analyzed metals and 61 ppm for Si) are low enough to control the coal combustion process in power plants. The Stark-broadening and the Boltzmann plot method were used to determine apparent values of excitation temperatures and electron number densities. A relatively small but measurable influence of the concentration of metal elements on the plasma parameters was observed, which should be considered in quantitative analysis of coal samples with higher inorganic elements content.