Date of Award

2009

Degree Name

M.S. in Materials Engineering

Department

Department of Chemical and Materials Engineering

Abstract

Mercury (Hg) transformation under homogeneous (gas-phase oxidation reactions primarily involving chlorine species in flue gases) and heterogeneous (gas-surface oxidation reactions involving surface enhanced Hg oxidation in the presence of flue gases) environments were investigated. Gas phase experiments were performed in the presence of chlorine sources such as Cl2 and HCl. A large body of literature studies indicates that during combustion in coal-fired power plants coal mineral matter components play a major role in Hg transformation. Surface activity of these components with respect to Hg adsorption and overall Hg removal were evaluated using a laboratory-scale, fixed bed flow reactor where initial Hg concentration, temperature, residence time, gas composition, and the metal oxide surface were carefully controlled. The metal oxides of interest were γ-Fe2O3, TiO2, Al2O3, and CaO. These catalytic materials were immobilized between quartz wool in a quartz flow reactor. Homogeneous experiments with different gas compositions, different chlorine sources (HCl or Cl2), and gas-phase residence times of 1 and 2 sec showed no measurable difference in Hg oxidation except at 100°C. Hg removal (oxidation) efficiencies ranged from 2 to 15%. Heterogeneous studies in the presence of metal oxides (with Cl2 and HCl as the chlorine source) indicated that γ-iron oxide showed the highest Hg removal efficiency at 1 sec residence time, compared to other metal oxides under the same experimental conditions. However, the data were highly scattered and occasionally showed inconsistency. A reduction in the surface activity of γ-iron oxide due to aging may have been responsible for the inconsistency in some of the results. TiO2, used in the presence of Cl2 at 100°C, resulted in a 60% Hg removal efficiency which decreased with increasing temperature. TiO2 used in the presence of HCl resulted in a 55% Hg removal efficiency at 400°C. Al2O3 and CaO were ineffective with regard to Hg oxidation in the presence of Cl2 or HCl compared to γ-iron oxide and TiO2. Adsorption and overall Hg removal efficiencies showed the following trend (in descending order of effectiveness): γ- Fe2O3 > TiO2 > Al2O3 > CaO.

Keywords

Mercury Testing, Mercury wastes Environmental aspects, Coal-fired power plants Waste disposal

Rights Statement

Copyright 2009, author

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