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Title: A theoretical study of properties and reactions involving arsenic and selenium compounds present in coal combustion flue gases

Abstract

Species of arsenic and selenium thought to be present in coal combustion flue gases were studied using density functional theory and a broad range of ab initio methods. At each level of theory, the calculated geometries and vibrational frequencies of each species as well as the reaction enthalpies of anticipated reactions were compared with experimental data where available. Comparisons between each calculation are given along with a discussion of the better performance of some theoretical calculations for a given species/reaction.

Authors:
;  [1]
  1. Worcester Polytechic Institute, Worcester, MA (United States)
Publication Date:
OSTI Identifier:
20762251
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory; Journal Volume: 110; Journal Issue: 17
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; ARSENIC COMPOUNDS; SELENIUM COMPOUNDS; FLUE GAS; COMBUSTION; COAL; CHEMICAL REACTIONS; REACTION INTERMEDIATES; CALCULATION METHODS

Citation Formats

Urban, D.R., and Wilcox, J. A theoretical study of properties and reactions involving arsenic and selenium compounds present in coal combustion flue gases. United States: N. p., 2006. Web. doi:10.1021/jp055564+.
Urban, D.R., & Wilcox, J. A theoretical study of properties and reactions involving arsenic and selenium compounds present in coal combustion flue gases. United States. doi:10.1021/jp055564+.
Urban, D.R., and Wilcox, J. Thu . "A theoretical study of properties and reactions involving arsenic and selenium compounds present in coal combustion flue gases". United States. doi:10.1021/jp055564+.
@article{osti_20762251,
title = {A theoretical study of properties and reactions involving arsenic and selenium compounds present in coal combustion flue gases},
author = {Urban, D.R. and Wilcox, J.},
abstractNote = {Species of arsenic and selenium thought to be present in coal combustion flue gases were studied using density functional theory and a broad range of ab initio methods. At each level of theory, the calculated geometries and vibrational frequencies of each species as well as the reaction enthalpies of anticipated reactions were compared with experimental data where available. Comparisons between each calculation are given along with a discussion of the better performance of some theoretical calculations for a given species/reaction.},
doi = {10.1021/jp055564+},
journal = {Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory},
number = 17,
volume = 110,
place = {United States},
year = {Thu May 04 00:00:00 EDT 2006},
month = {Thu May 04 00:00:00 EDT 2006}
}
  • A full-scale field study was carried out at a 795 MWe coal-fired power plant equipped with selective catalytic reduction (SCR), an electrostatic precipitator (ESP), and wet flue gas desulfurization (FGD) systems to investigate the distribution of selected trace elements (i.e., mercury, arsenic, selenium, boron, and chloride) from coal, FGD reagent slurry, makeup water to flue gas, solid byproduct, and wastewater streams. Flue gases were collected from the SCR outlet, ESP inlet, FGD inlet, and stack. Concurrent with flue gas sampling, coal, bottom ash, economizer ash, and samples from the FGD process were also collected for elemental analysis. By combining plantmore » operation parameters, the overall material balances of selected elements were established. The removal efficiencies of As, Se, Hg, and B by the ESP unit were 88, 56, 17, and 8%, respectively. Only about 2.5% of Cl was condensed and removed from flue gas by fly ash. The FGD process removed over 90% of Cl, 77% of B, 76% of Hg, 30% of Se, and 5% of As. About 90% and 99% of the FGD-removed Hg and Se were associated with gypsum. For B and Cl, over 99% were discharged from the coal combustion process with the wastewater. Mineral trona (trisodium hydrogendicarbonate dehydrate, Na{sub 3}H(CO{sub 3}){sub 2}.2H{sub 2}O) was injected before the ESP unit to control the emission of sulfur trioxide (SO{sub 3}). By comparing the trace elements compositions in the fly ash samples collected from the locations before and after the trona injection, the injection of trona did not show an observable effect on the partitioning behaviors of selenium and arsenic, but it significantly increased the adsorption of mercury onto fly ash. The stack emissions of mercury, boron, selenium, and chloride were for the most part in the gas phase. 47 refs., 3 figs., 11 tabs.« less
  • A study was conducted to investigate the effect of selective catalytic reduction (SCR) catalyst on mercury (Hg) speciation in bituminous and subbituminous coal combustion flue gases. Three different Illinois Basin bituminous coals (from high to low sulfur (S) and chlorine (Cl)) and one Powder River Basin (PRB) subbituminous coal with very low S and very low Cl were tested in a pilot-scale combustor equipped with an SCR reactor for controlling nitrogen oxides (NO{sub x}) emissions. The SCR catalyst induced high oxidation of elemental Hg (Hg{sup 0}), decreasing the percentage of Hg{sup 0} at the outlet of the SCR to valuesmore » <12% for the three Illinois coal tests. The PRB coal test indicated a low oxidation of Hg{sup 0} by the SCR catalyst, with the percentage of Hg{sup 0} decreasing from {approximately} 96% at the inlet of the reactor to {approximately} 80% at the outlet. The low Cl content of the PRB coal and corresponding low level of available flue gas Cl species were believed to be responsible for low SCR Hg oxidation for this coal type. The test results indicated a strong effect of coal type on the extent of Hg oxidation. 16 refs., 4 figs., 3 tabs.« less
  • A suite of six coals, of widely differing As, Se, Ca, Fe, and sulfur contents, was burned under self-sustaining conditions in a 17 kW downflow laboratory combustor. Size segregated ash-laden aerosol samples were isokinetically withdrawn and collected on a Berner low pressure impactor. Correlations between trace element concentration (As or Se) and that of major elements (as functions of particle size) were then used to infer chemical associations between trace metals and Ca and/or Fe, and how these depended on sulfur. These baseline data led to formation of the following hypotheses, namely: (1) dominant As and Se partitioning mechanisms dependmore » on the availability of Ca and/or Fe active sites for surface reaction; (2) increasing combustion temperature increases the availability of active cation sites, and increases partitioning of As and Se to fly ash by surface reaction; (3) sulfur competes with these surface reactions, decreasing As and Se partitioning to fly ash surfaces. These hypotheses were tested by manipulating the As, Se, Ca, Fe, and S contents for various coals by doping. Temperature was adjusted in order to achieve comparisons of different coals and different coal constituents at similar thermal conditions, through O{sub 2} and CO{sub 2} addition, as required. These results confirmed the hypotheses above, and allowed an association regime map to be constructed. This map shows that both As and Se associate with Fe and Ca, provided active sites are available. Se reacts preferentially with Fe over Ca when both are available while As reactions with both Fe and Ca are comparable. Sulfur can prevent association of both As and Se, by preferentially reacting with active sites, especially those on Fe. When sufficient sites are not available, the release of vapor-phase As and Se species is promoted. 23 refs., 4 figs., 4 tabs.« less