| Abstract |
The Tacoma, W A Steam Plant #2 is a fluidized bed incinerator designed to bum, in combination, waste wood, coal, and refuse-derived fuel (RDF). The plant, owned by the Light Division of the City of Tacoma, operates under stringent ash management regulations of the Washington Department of Ecology (WDOE). Those regulations designate flyash from incineration as a dangerous (hazardous) waste if the solid products of combustion fail the EP-Toxicity and Toxic Characteristics Leaching Procedure (TCLP) tests, or if the flyash contains more than 100 parts per million by weight (ppmw) of any of the following IARC (International Agency for Research in Cancer) carcinogenic compounds: As2O3, BaCr04, BeO, CdO, NiO, Pb3(PO4)2, SrCr04, and ZnCr04• The state regulations further require that any incinerator operator assume that 100 percent of the metal in question (i.e. As, Ba, Ni, Pb) be treated as if it exists in the IARC compound form. Tacoma Light Division and Ebasco Environmental have developed an ash management strategy to ensure that the ash would not be designated a dangerous waste. The strategy consists of: (1) characterizing each fraction of the municipal waste stream and the consequent RDF; (2) characterizing all other feeds to the fluidized bed incinerator; and (3) evaluating speciation of trace metals, where possible, either by literature analysis and testing or by computer modeling. The characterization of the waste stream is of particular significance since trace metal slates have been developed for the following fractions: glossy papers, non-glossy papers, cardboard, plastics, wood, leather and rubber, inorganics, and "other/not identified." The ash management strategy next involves examining the blended fuel feed composition. Particular attention is paid to the RDF produced from the municipal waste by control of the RDF production process. The fuel composition data is then related to the flyash composition to ensure success. Finally, the ash management strategy addresses the issue of speciation to develop alternative assumptions regarding trace metals speciation that more closely represent current laboratory and theoretical research. The speciation analysis is of particular significance, since it uses empirical data where possible (Le. determining the percentage of chromium reporting as Cr^+6), and uses accepted thermodynamic modeling where appropriate (i.e. determining the fate of Ni). |
