INDUCED BREAKDOWN SPECTROSCOPY; HIGH-TEMPERATURE; PARTICLES

A new route for directly measuring the fly ash unburned carbon in a gas solid flow by laser-induced breakdown spectroscopy (LIBS) was proposed. A homemade gas-solid flow generation system was developed to simulate the gas solid flow in the duct of a coal-fired plant. For improving the measurement performance, the emission characteristics of the laser induced plasma, the influence of the fly ash mass flow rate, and the correlation between the unburned carbon content and the carbon emission intensity were studied in detail. The SNR of the Si spectral line at 288.15 nm was selected as the index for false spectra identification because the distribution of Si is not related to the particle size. The results highlight the change of the plasma shape and volume with fluctuations of the gas solid flow because of the uneven distribution of the fly ash particle size and number in the laser focal spot. The mass flow rate of the fly ash affected the false hit rate, while it did not affect the intensity of the analyte lines. The regression coefficients (R-2) between the normalized intensity of C 247.86 nm and the unburned carbon content improved from 0.93 to 0.98 when the false spectra were rejected. The good agreement between the normalized intensity of C 247.86 nm and the unburned carbon content indicates that LIBS can be developed as a promising tool for directly measuring the fly ash unburned carbon in a gas-solid flow.

Laser-induced breakdown spectroscopy; Carbon emission; Plasma temperature; Fly ash; Unburned carbon;ONLINE ANALYSIS; INDUCED PLASMAS; COAL; LIBS; SPECTROMETRY; NITROGEN; BOILER; STEEL; AIR

Laser ablation chemical analysis of fly ash samples was studied by laser-induced breakdown spectroscopy (LIES). Ablation was performed using a 1064 nm Nd:YAG laser in air environment. The molecular emission CN was measured together with the atomic carbon (CI). The combination of atomic and molecular carbon emissions (CI and CN) was available to establish the calibration model for quantitative analysis of the unburned carbon content in fly ash. In order to further improve the measurement accuracy, the matrix effect of fly ash samples was presented and it is found that two lines of the same element in the same order could be used to characterize the plasma temperature. The influence of laser energy on plasmas temperature was studied to estimate the correction factor with the ratio of two Mg ionic lines (Mg II 279.5 nm and Mg II 280.2 nm). The results showed that the combination of carbon atomic and molecular emissions with plasmas temperature correction could improve the accuracy and precision for quantitative analysis of unburned carbon in fly ash samples. (C) 2017 Elsevier B.V. All rights reserved.