Experimental And Homogeneous Kinetics Study On Mercury Oxidation In Coal-fired Flue Gas By Bromine Compounds

The emission of mercury by coal-fired power plants is the main part from anthropogenic activities. The oxidized mercury(Hg2+) and particulate bound mercury(Hgp) are usually trapped by existing air pollution control devices. Conversely, elemental mercury (HgO) is difficult to capture. The removal of mercury will be enhanced when HgO is converted to its oxidized form. This research mainly focused on experimental and kineticas simulation study on mercury oxidation by bromine in coal-fired flue gas.The experiments were carried on laboratory horizontal tube furnace to study the effects of NH4Br affecting mercury oxidation and NO release during coal combustion, considering factors such as coal type, temperature, the addition ratio of NH4Br.The experimental results show that NH4Br additive can enhance mercury oxidation during coal combustion. Under lower temperatures, the more NH4Br additive, the more mercury oxidation; Under higher temperatures, the mercury oxidation become less slightly. The oxidation effect is strongest on1000℃to Liupanshui coal, on900℃to Gaoping coal. On the other side, NH4Br additive can enhance NO reduction and restrain NO production. During800-1100℃, the NO production in two flue gas reduce sharply. The reduction effect is strongest on900℃to Liupanshui coal, on1000℃to Gaoping coal.With the theory of chemical kinetics, we develop a comprehensive model of homogeneous mercury oxidation using bromine which relates to element Hg、C、H、O、 Br、Cl、N、S and includes90species、362reactions to predict transformation behavior of trace element Hg in coal combustion flue gas in contrast to the available experimental data using CHENKIN software, to describe transformation behavior more properly and comprehensively.With sensibility analysis of the model, we learn that the key reaction channel for mercury oxidation in flue gas:Hg changes into HgBr2via reaction Hg+Br2=HgBr2. From the study of the oxidation of Hg with various components in the flue gas, we also found that:HBr shows stronger oxidation ability than HCl; NO has almost no effect on mercury oxidation; SO2inhibits the oxidation of mercury. During oxy-fuel combustion, the combustion atmosphere and oxygen concentration have little effect on mercury oxidation; H2O inhibits the oxidation of mercury.