Date on Master's Thesis/Doctoral Dissertation

5-2020

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Committee Chair

Willing, Gerold

Committee Co-Chair (if applicable)

Ghorbanian, Mahyar

Committee Member

Ghorbanian, Mahyar

Committee Member

Rockaway, Thomas

Author's Keywords

Selenium Speciation; IC-ICP-MS; HG-ICP-AES; WFGD Process Water; Selenite; Selenate

Abstract

During coal-fired electric power production, coal bound elemental selenium is released into the gas phase and oxidized to selenite and selenate in the wet flue gas desulfurization (WFGD) unit. Selenite and selenate solubilize in the WFGD process water. A process water system at a coal fired power plant contributes to environmental regulation compliance by removing the selenium species from WFGD process water. A selenium speciation method was developed for the purpose of better monitoring the selenium species present in the “treated” process water and to aid the process water system in meeting compliance with the Environmental Protection Agency’s Effluent Limitation Guidelines (ELG). The two species, selenite and selenate are removed from the process water through different mechanisms.

Two methods for determining the concentration of the selenium species, selenite and selenate, in coal-fired power plant WFGD process water were developed utilizing Ion Chromatography Inductively Coupled Plasma Mass Spectroscopy (IC-ICP-MS) and Hydride Generation Inductively Coupled Plasma Atomic Emission Spectroscopy (HG-ICP-AES) equipment. WFGD process water from three coal fired plants with wet limestone, forced oxidation WFGD units were separated and quantified.

The IC-ICP-MS selenium speciation method separated the selenite and selenate in the IC and quantified each species in the ICP-MS. For WFGD process water effluent samples with a 10x dilution, the average percent selenite was 48.9%, the average percent selenate was 55.8%, and the average percent total inorganic selenium recovery was 104.7%.

The HG-ICP-AES fractionation method quantified selenium by forming a volatile hydride in the HG and quantified the result in the ICP-AES. The samples required the reduction of selenate to selenite in 10 M HCl with one hour of reduction time. The mock samples and WFGD process water sample overreported the amount of total inorganic selenium present in the sample by approximately 30%.

Going forward the IC-ICP-MS method can be improved to separate and quantify other selenium species that might be present in WFGD process water. The HG-ICP-AES method is limited to determining the concentration of selenite and selenate, however, can still be useful for process water systems that only deal with selenite and selenate removal.

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