Experimental study on mercury content in flue gas of coal-fired units based on laser- induced breakdown spectroscopy

Accurate measurement of trace heavy metal mercury (Hg) in flue gas of coal-fired units is great significance for ecological and environmental protection. Mixed gas was used to simulate the actual flue gas of a power plant in this study. A laser-induced breakdown spectroscopy (LIBS) system for Hg measurement in mixed gas was built to study the effect of mixed gas pressure, Hg concentration in mixed gas and delay time on Hg measurement. The experimental results show that the appropriate low mixed gas pressure can obtain high Hg signal intensity and signal to noise ratio. The Hg signal intensity and signal to noise ratio increased with the increase of Hg concentration in mixed gas. The Hg signal intensity and signal to noise ratio decreased with the increase in delay time. According to the above results, the optimized measurement conditions can be determined. Different Hg concentrations in mixed gas were quantitatively analyzed by the internal standard method and traditional calibration method respectively. The relative error of prediction of the test sample obtained by the internal standard method was within 11.11%. The relative error of prediction of the traditional calibration method was less than 14.54%. This proved that the internal standard method can improve the accuracy of quantitative analysis of Hg concentration in flue gas using LIBS.