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Show 2.1.4. Conclusion Regarding Sources of Arsenic in the Feed Based upon extensive testing of all feed streams, it is apparent that the arsenic entered the fluid bed operations from one minor supplier, and from a few random loads by demolition and construction debris chipping operations. Arsenic is not introduced in concentrations of concern from any of the major fuel sources: RDF, coal, or hogged wood waste. 2.2. Expected Fate of Arsenic in Combustion Systems Traditionally, regulations have been developed on the worst case assumption that all arsenic (As) in products of combustion is in the form of arsenic trioxide (ASz03). This assumption has been based upon the desire to protect the public from arsenic toxicity. Further, it has been based upon the absence of. any data regarding the speciation of arsenic in gaseous or solid products of combustion. This assumption is explicitly <;arried in the ash regulations of the State of Washington, based upon the Kundsen analysis [13]. In combustion assessments, the tradition is to assume that the behavior of all metals will confonn to thermodynamic equilibria calculations (see, for example, [1], [2], [4]) using Gibbs Free Energy minimization. It is therefore assumed that all arsenic will vaporize at temperatures well below 620°F (6000 K). Barton et. ale [2] place the arsenic volatilization temperature at 90°F (306°K). Once in the gas phase, combustion analysts in the past have typically made the assumption that the dominant arsenic product of combustion is ASz03 [19]. This assumption has been made in the absence of additional data. Recent data developed by several researchers have dramatically changed that view of the behavior of certain metals, including arsenic, in combustion systems. Careful metal balances developed at the EPA research rotary kiln have shown that arsenic may not be as volatile as equilibrium calculations indicate. Table VI, from Thurnau [21] documents the fate of arsenic in a rotary kiln as a function of temperature. The fate demonstrated by Thurnau is that, at temperatures in the 1500 - 1550°F region, some 49 - 77 percent of the arsenic does not go into the vapor phase but remains in the solid phase. Arsenic in the kiln ash has not been volatilized (see [2], [20], [21]). Alternatively the arsenic may be in the gas phase only very briefly and may recondense or otherwise react to become a solid within the primary combustion chamber. |