Mercury Monitor Method Analysis And Experiment In Flue Gas And Liquid-solid Wastes From Coal-fired Power Plant

Heavy metal pollution from coal combustion has attracted much attention around the world. The mercury pollution from coal-fired power plants has been paid much attention by China’s government due to the volatility, biological concentration and toxicity of mercury in nature. As a trace element in coal, the mercury is difficult to be analyzed precisely. Moreover, the mercury migration process to flue gas and liquid-solid wastes is complicated in coal-fired power plants. Therefore, it is of importance to establish accurate analysis method for flue gas and various liquid-solid wastes to master the mercury emission characteristics of coal combustion.A power plant of Jingneng Company is chosen as the demonstration in this thesis. The samples of coal, bottom ash, fly ash and desulfurization gypsum are collected. The accurate analysis method of mercury content of the above samples is established based on atomic absorption spectrum. The mercury content results of solid waste samples are stable and repeatable. As a result, the averaged mercury contents for coal, fly ash, and bottom ash are 210.1 ng/g,684.4 ng/g, and 1.8 ng/g, respectively. The mercury content result of gypsum seriflux has fluctuations. After separation, the mercury content is from 130 ng/g to 219 ng/g for solid gypsum, and from 37.8 ng/g to 2.3 ng/g for liquid.The flue gas at the inlet of ESP, the outlet of ESP, and the outlet of WFGD is sampled by OH Method. The mercury concentration in the flue gas at the inlet of ESP is from 25.1 μg/m3 to 34.2 μg/m3,15.6 μg/m3 to 18.3 μg/m3 at the outlet of ESP, and 3.5 μg/m3 to 4.6 μg/m3 at the outlet of WFGD. The concentration of Hg2+ and Hg0 in the flue gas is distinguished by OHM. The ratio of Hg2+/Hg0 is more than 3 for the flue gas at the inlet and outlet of ESP, and more than 8 times at the outlet of WFGD. 30B method is simple and convenient compared with OH method for the total mercury concentration sampling, but it could not distinguish the valence of mercury. The total mercury concentration value by OH method is slightly lower than that by 30B method. Complicated reactions occur for mercury in flue gas at the flue gas duct. Hg0 is oxidized in SCR, which leads to the high ratio of Hg2+/Hg0 at the inlet of ESP. ESP captures a portion of Hg0 and Hg2+, which leads to the decrease of mercury concentration at the outlet of ESP. Most Hg2+ is absorbed in the WFGD, resulting in the concentration of Hg2+ decreases after the WFGD.