Investigations on the removal of elemental mercury from coal fired power plants gaseous emissions by catalytic oxidation

摘要

Toxic elemental mercury (Hg0) is regularly released into the environment from coal-fired power plants. A promising technology for removing Hg0 from gas streams (such as those generated in coal fired power plants) involves catalytic oxidation of Hg0, where Hg0 is converted to an oxidised form, Hg2+, that is able to be captured using existing technologies used to capture SO2. The aim of this research project was to investigate catalytic oxidation of Hg0 using a range of transition metal oxides (α-Fe2O3, Fe3O4, CoO, Co3O4, MnO, MnO2, Mn2O3, Mn3O4, NiO, Ni2O3, and Ni3O4). Transition metal oxides were selected for study due to previous promising results that have been obtained, and their reasonable cost. Transition metal oxides that exhibited the most catalytic activity were that of Mn2O3, Mn3O4 and NiO where thereafter, more detailed tests were performed. The influence of temperature showed significant increases in mercury oxidation with increased temperature. Tests conducted investigating the influence of flue gases such as HCl, O2/CO2 and NH3 showed that in the presence of HCl, the catalytic oxidation of mercury increased. Additionally, the increase in HCl concentration also resulted in higher oxidation. In the presence of O2/CO2, mercury oxidation showed similar trends to that of streams containing only Hg0. The addition of NH3 in the gas stream significantly hindered mercury oxidation for the Mn2O3, Mn3O4 and NiO catalysts. Post characterisation studies done on all catalysts did not have any significant change to morphology, surface chemistry, and surface area.