OCR Text |
Show of the Gordon-McBride model, or by other models shown in the literature (see, for example, Brittain et. al., 1988). The most compelling example of a product not generated by combustion modeling was lead phosphate, P~(P04)2. The results show lead to exist as lead, lead oxide, various lead chlorides, and lead sulfide. These are far more likely outcomes than the lead phosphate cited by WDOE and by Knudsen (1987). DISCUSSION The analysis of the sources and fates of trace metals during combustion of hogged wood waste, coal, and RDF in the Tacoma Steam Plant #2 fluidized beds highlights many of the difficulties associated with metals management during incineration. The regulations are very stringent and increasingly difficult to meet. The requirements for analysis exceed the capabilities of current laboratory practice; however, the problems associated with high metals content include treating the flyash as a dangerous (hazardous) waste. Tacoma Public Utilities and Ebasco Environmental personnel developed the analysis of the sources and fates of trace metals during combustion in the fluidized bed system at the Tacoma Steam Plant #2 (Tillman et. al., 1990). Much of this analysis has been summarized above. This analysis led to an extensive fuel management program including the following: o carefully sourcing the waste wood fuel to ensure that unusual levels of trace metals or other problematical compounds would not exist in the feed to the fluidized bed reactors; and o careful attention to the RDF production process, including attention to the issue of favoring the increase of the proportions of paper compounds in the RDF, and eliminating the "grits" or "middlings" from the feed to the Tacoma Steam Plant #2. This fuel management issue will extend to any future fuel-sourcing activities as well. Beyond the fuel management issue, Tacoma Public Utilities and Ebasco Environmental worked with the Pierce County Public Health Department and the WDOE to examine the speciation assumptions in the current regulations as they apply to Tacoma Steam Plant #2. An alternative set of assumptions was developed, which has been operationally accepted by WDOE for the Tacoma Steam Plant #2. This alternative set of assumptions includes the following: o Twenty percent of the chromium in the flyash is considered to be Cr+6, and that chromium is distributed among the available Ba, Sr, and Zn based upon the molar proportions of those three metals. o Fifty percent of the nickel in the flyash is considered to be NiO, depending upon the Cr/Ni molar ratio. -9- |