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Title	The Fate of Arsenic at the Tacoma Steam Plant #2
Publisher	Digitized by J. Willard Marriott Library, University of Utah
Date	1992
Spatial Coverage	presented at Cambridge, Massachusetts
Abstract	On three occasions, Tacoma Steam Plant #2 experienced relatively high concentrations of arsenic (e.g. > 100 ppmw) in the flyash produced by fluidized bed combustion of refuse derived fuel (RDF), coal, and hogged wood waste. These concentrations produced apparent exceedences of state regulations for As in the flyash, because Washington regulations assume that all arsenic reports as arsenic trioxide (As2O3) , and because those regulations state that flyash containing> 75 ppmw As must be handled as a dangerous (e.g. hazardous) waste. Ebasco Environmental undertook research to identify the sources of such arsenic in the fuel feed, the probable arsenic product slate in the flyash, and potential mechanisms capable of generating such products. The sources of the arsenic were probably a few loads of wood waste containing some residual slag from the abandoned Tacoma copper smelter. The sources also could have included random loads of construction wood containing measurable quantities of copperchromium-arsenate (CCA) wood preservative. Coal and RDF did not prove significant sources of As in the fuel feed. Ebasco Environmental then evaluated the oxidation state and binding energy of the arsenic in the flyash, recognizing that the bulk of recent experience and research demonstrates that arsenic does not behave in strict accordance with thermodynamic equilibrium calculations. Using the University of Utah as a subcontractor, Electron Scanning for Chemical Analysis (ESCA) techniques were used to identify arsenic species. This research led to the following conclusions: (1) the dominant species had an oxidation state of +3, and (2) the dominant species had binding energies sufficiently low to preclude their existence as As2O3. Through a detailed review of the literature, Ebasco Environmental evaluated potential mechanisms, reaction pathways, and product slates associated with the arsenic in the flyash at Tacoma Steam Plant #2. The most probable mechanisms and reaction pathways involve mobilizing or volatilizing the arsenic. The mobile or volatile As compounds then react with CaO and potentially alumina and silica, or other compounds, to form large polymers and complexes with vapor pressures which preclude evolution in the vapor phase and oxidation to arsenic trioxide. Some arsenic trioxide may evolve or form. The ASzO3 which does evolve or form will oxidize, at least partilly, to As2O5. On this basis it has been concluded that significantly less than 50 percent of the As in the Tacoma Steam Plant #2 flyash exists as As2O3.
Type	Text
Format	application/pdf
Language	eng
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ARK	ark:/87278/s6fj2kcs
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Reference URL	https://collections.lib.utah.edu/ark:/87278/s6fj2kcs

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Title	Page 6
Format	application/pdf
OCR Text	Show Because the issue involved is strictly one of IARC Metals regulations, the following analysis was perfonned: 1) identify potential sources of the arsenic, particularly In quantities and concentrations sufficient to cause the exceedences noted; 2) analyze the experience of other combustion systems as a foundation to understand the possible reactions of arsenic in the fuel,emphasizing probable arsenic product speciation associated with fluidized bed combustion; 3) analyze the flyash for probable/possible arsenic oxidation states and consequent species existing in the flyash using Electron Scanning for Chemical Analysis (ESCA); 4) evaluate the results of ESCA analysis, focusing upon explaining the results in terms of probable arsenic compounds formed and probable mechanisms available to produce such products, drawing upon experience of other researchers; and 5) develop supportable conclusions, and identify actions by Tacoma Public Utilities which might be taken to eliminate future arsenic exceedences. This paper reports on the results of that analysis. It documents why the IARC standard assuming 100% As as A~03 is no longer appropriate in the case of the bubbling fluidized bed combustion systems used at Tacoma S team Plant #2. 2.0. BACKGROUND The investigations focused upon the following issues: 1) determining the sources of arsenic at the Tacoma Steam Plant #2, including all types of fuel; 2) determining the general behavior of arsenic in combustion systems, particularly at temperatures typically experienced in fluidized beds; and 3) evaluating the chemical reactions between arsenic and calcium compounds in combustion settings. The fuels analysis involved both fuel testing and specification review. The combustion analysis relied heavily upon hazardous waste incineration research, since most investigations of the fate of arsenic currently are associated with this arena. 2.1. Sources of Arsenic at Tacoma Steam Plant #2 There are several potential sources of arsenic for the Tacoma Steam Plant #2 including: 1) the RDF, 2) the wood fuel, 3) the coal, and 4) bed media. All of these sources have been reviewed by Ebasco Environmental. 2.1.1. RDF as a Source of Arsenic While the timing of the arsenic excursions in the flyash somewhat rules out RDF as the significant source of this metal due to the high concentrations experienced in January and February, 1991, one event occurred in Oct., 1990. Consequently RDF has been evaluated. Table
Setname	uu_afrc
ID	12500
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6fj2kcs/12500