Effect of the Concentrations of Different Flue Gas Components on Mercury Speciation

This paper presents and establishes a reaction kinetic model of Hg/Cl/C/H/O/N/S to investigate the reaction characteristics of mercury during coal combustion and elucidate its migration and transformation mechanisms in flue gas. Using CHEMKIN software, the influence of HCl, Cl2, and other flue gas components on the mercury oxidation reaction rate is examined. Building on this, the mechanism of Hg homogeneous oxidation under the influence of multi-component and multi-reaction interactions is revealed. The results indicated that as Hg concentration increased, the transformation rate of mercury also increased. As the reaction temperature increases, the reaction rate of HCl and elemental mercury also increases, leading to a higher transformation rate of mercury at elevated temperatures. Additionally, an increase in Cl2 concentration leads to a higher amount of HgCl2 produced. When the Cl2 concentration was 4 × 10−5 mol/L, the amount of mercury chloride produced was highest, increasing by 40% compared to the absence of Cl2. As chlorine concentration increases, more Hg2+ is converted from Hg0, enhancing its capture and removal by existing technologies, which significantly contributes to environmental sustainability and mercury emission control in coal-fired power plants. It is also shown that the rate of change of HgCl2 varies with different Cl2 concentrations, with higher Cl2 concentrations inhibiting mercury oxidation beyond a certain threshold. The reaction was most intense when the mercury concentration was 5 × 10−5 mol/L. At this concentration, the largest amount of HgCl2 is produced. The mercury conversion rate curve remained consistent after adding NO and SO2, with a HgCl2 amount increasing as NO and SO2 concentrations rose. This indicates that the addition of NO and SO2 converts Hg0 to Hg2+, thereby improving mercury removal efficiency and contributing to sustainability.