Title page for ETD etd-07252007-095639 ( Browse

Type of Document

Master's Thesis

Author

Chen, Xihua

Author's Email Address

xic16@pitt.edu

URN

etd-07252007-095639

Title

IMPACTS OF FLY ASH COMPOSITION AND FLUE GAS COPONENTS ON MERCURY SPECIATION

Degree

Master of Science in Civil Engineering

Program

Civil and Environmental Engineering

School

School of Engineering

Advisory Committee

Advisor Name	Title
Radisav D. Vidic	Committee Chair
Götz Veser	Committee Member
Jason D. Monnell	Committee Member

Keywords

Flue Gas
Adsorption
Speciation
Mercury (Hg)
Fly Ash
Oxidation

Date of Defense

2007-07-09

Availability

unrestricted

Abstract

The impact of six fly ash samples on mercury speciation in simulated flue gas was evaluated in this study. A fixed bed reactor system was used to study the catalytic effect of fly ash on mercury oxidation at temperature of 140 °C in simulated flue gas consisting of N2, CO2, O2, NO, NO2, SO2, HCl, and H2O. Mercury was introduced to the reactor using a temperature controlled permeation tube. Elemental and total mercury in the effluent were measured using a semi-continuous atomic fluorescence mercury monitor. Fly ash samples were characterized using SEM-EDAX, XRD, TGA, BET analyzer and particle size analyzer. Mercury uptake tests with different fly ash samples revealed that LOI (Loss On Ignition), surface area, and particle size all had positive effects on mercury oxidation and adsorption.
Experiments with pure components showed that alumina (Al2O3), silica (SiO2), calcium oxide (CaO), magnesium oxide (MgO), and titania (TiO2) did not promote mercury oxidation or capture. Ferric oxide (Fe2O3), and unburned carbon were found to have profound effects on mercury oxidation and capture. Unburned carbon is considered the most important fly ash component for mercury oxidation due to much larger presence in fly ash than Fe2O3.
Experiments with carbon black and different flue gas composition revealed the importance of the interaction between flue gas and surface on mercury uptake. Oxygen containing surface functionalities did not enhance adsorption or oxidation of mercury by themselves. NO2 and HCl promoted mercury oxidation and adsorption on carbon black. Addition of O2 to HCl containing gas stream significantly improved mercury adsorption and oxidation. SO2 seems to inhibit both mercury oxidation and adsorption. NO and H2O had little impact on mercury oxidation or adsorption in inert gas flow. H2O may inhibit mercury adsorption in early stages of the experiment, but the inhibitory effect diminished over time.

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