Mercury speciation in combustion systems: Studies with simulated flue gases and model fly ashes
Bench-scale experiments were conducted to study the effects of flue gas and fly ash parameters on the oxidation of elemental mercury (Hg0) in simulated flue gases containing hydrogen chloride (HCl), nitric oxide (NO), nitrogen dioxide (NO{sub 2}), sulfur dioxide (SO{sub 2}), and water vapor (H{sub 2}O). Gas-phase studies indicated that the oxidation of Hg0 in the presence of these gaseous species was very slow at low to moderate temperatures (25--350 C). In the presence of HCl, Hg0 oxidation proceeded at measurable rates only at high temperatures ({gt}700 C) and high HCl concentrations ({gt}200 ppm). The presence of SO{sub 2} and H{sub 2}O in the simulated flue gas significantly inhibited the gas-phase oxidation of Hg0 in the presence of HCl. The effects of fly ash composition were investigated using a fixed bed containing different model fly ashes consisting of mixtures of major components found in coal fly ashes. Work to date has focused on the potential catalytic oxidation of Hg0 within a temperature range of 150--250 C by two- and three-component model fly ashes composed of mixtures of: alumina (Al{sub 2}O{sub 3}), silica (SiO{sub 2}), ferric oxide (Fe{sub 2}O{sub 3}), cupric oxide (CuO), and calcium oxide (CaO). Al{sub 2}O{sub 3} and SiO{sub 2} were inactive in oxidation of Hg0 in the presence of HCl, but they were active in the presence of NO. CuO and Fe{sub 2}O{sub 3} exhibited significant catalytic activities in the surface-mediated oxidation of Hg0 in the presence of both HCl and NO. The reactivities of these two oxides in the presence of HCl were hypothesized to be effected through the formation of a chlorinating agent, most probably chlorine (Cl{sub 2}), from gas-phase HCl on the surface of the metal oxides. CuO was much more effective in the oxidation of Hg0 than Fe{sub 2}O{sub 3}, and its catalytic activity was less sensitive to the presence of oxidation inhibitors in the simulated flue gas.
- Research Organization:
- Geraghty and Miller, Research Triangle Park, NC (US)
- OSTI ID:
- 20002203
- Report Number(s):
- CONF-990608-; TRN: IM200002%%203
- Resource Relation:
- Conference: Air and Waste 92nd Annual Meeting and Exhibition, St. Louis, MO (US), 06/20/1999--06/24/1999; Other Information: 1 CD-ROM. Operating Systems: Windows 3.1, '95, '98 and NT; Macintosh; and UNIX; PBD: 1999; Related Information: In: Air and Waste 92nd annual meeting and exhibition proceedings, [9500] pages.
- Country of Publication:
- United States
- Language:
- English
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