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

Chen, Xihua (2007) IMPACTS OF FLY ASH COMPOSITION AND FLUE GAS COPONENTS ON MERCURY SPECIATION. Master's Thesis, University of Pittsburgh.

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    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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    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmailORCID
    Committee ChairVidic, Radisav Dvidic@engr.pitt.edu
    Committee MemberVeser, Götzgveser@pitt.edu
    Committee MemberMonnell, Jason Djmonnell@engr.pitt.edu
    Title: IMPACTS OF FLY ASH COMPOSITION AND FLUE GAS COPONENTS ON MERCURY SPECIATION
    Status: Unpublished
    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.
    Date: 25 September 2007
    Date Type: Completion
    Defense Date: 09 July 2007
    Approval Date: 25 September 2007
    Submission Date: 25 July 2007
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Master's Thesis
    Refereed: Yes
    Degree: MSCE - Master of Science in Civil Engineering
    URN: etd-07252007-095639
    Uncontrolled Keywords: Adsorption; Flue Gas; Fly Ash; Mercury (Hg); Oxidation; Speciation
    Schools and Programs: Swanson School of Engineering > Civil and Environmental Engineering
    Date Deposited: 10 Nov 2011 14:53
    Last Modified: 04 Jun 2012 12:52
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-07252007-095639/, etd-07252007-095639

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