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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.
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Format	application/pdf
Language	eng
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ARK	ark:/87278/s6fj2kcs
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ID	12522
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6fj2kcs

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Title	Page 3
Format	application/pdf
OCR Text	Show 1.0. INTRODUCTION Tacoma Steam Plant #2 is a two-unit 43 Megawatt electric (MW J generating station which is fueled by a combination of wood waste and coal, supplemented with refuse derived fuel (RDF). The unit employs two bubbling fluidized bed combustors which consume the fuels identified. These fluidized beds also utilize limestone as a feed material, with the limestone being used to capture sulfur dioxide and hydrogen chloride in order to control acid gas emissions. The limestone is fed to the fluidized beds at calcium/sulfur (Ca/S) molar ratios of >3.1. During most of its operating history, the Tacoma Steam Plant #2 has operated without generating flyash with unusual concentrations of trace metals. However, during the period of October, 1990 - March, 1991, arsenic concentrations in the fly ash became variable (see Table I). These flyash concentrations of arsenic did not translate into failures of the Toxic Compound Leaching Procedure (TCLP), and they did not perterb the TCLP results (see Table I). These arsenic concentrations in fly ash did, however, cause three exceedences of the state IARC Metals Standards as shown in Table II. Table ll. Limits of Metal Concentrations in Flyash Products From Incinerators in the State of Washington Without Triggering Dangerous Waste Regulations IARC Metal Arsenic Barium Beryllium Cadmium Lead Nickel Strontium Zinc IARC Metal Compound A~03 BaCr04 BeO CdO Pb3(P04h NiO SrCrO" ZnCr04 ppmw as metal required to maintain IARC compound emissions < 100 ppmw () 75 54 (or Cr limited) 36 88 770 790 43 (or Cr limited) 36 (or Cr limited) () These values take into account the prior transmittal by Ebasco Environmental to the Washington Department of Ecology on Mar. 14, 1990 [8]. ----------------------------------------------------------------------------------------------------------------------- The IARC concentration exceedences occurred on Oct 16,1990; Feb 20,1991, and Feb 22,1991. The exceedences were limited to arsenic, and did not involve any other metal. Further, these exceedences demonstrate that the issue is clearly not related to the fIring of RDF.
Setname	uu_afrc
ID	12497
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6fj2kcs/12497