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Show The work of Keating is particularly interesting because it documents dioxin and furan emissions from biomass combustion only in those cases where spiking of samples with precursors existed. Studies cited included combustion of wood treated with pentachlorophenol (PCP) and tri- and tetrachlorophenate. In such situations, dioxins and furans were formed in measurable quantities. Regarding coal combustion, the Keating study cited work by Haile el al., Harless and Lewis, Kimble and Gross, and Ahlberg et. ale - with all such studies finding no dioxin or furan emissions in the emissions from coal combustion. Keating funher cited the source tests on the Ames, Iowa spreader stoker frred with 85% coal/15% RDF (heat input basis), documenting no measurable emissions of dioxins and furans. On this basis, TRACE does not ascribe dioxin or furan emissions either to biomass or to coal. The exclusion of biomass is on the basis that, in most industrial settings, pcp contaminated wood would not be an ordinary fuel source used. Dioxin and furan emissions for MSW combustion were evaluated based upon the individual source tests and data bases. Highly useful correlations were developed for the Quebec City incinerator [3, 33]. However these correlations, while highly instructive, deal only with one combustion device. The data base developed by Beychok [5] and shown in Table 7, is more instructive, since it deals with a wide range of MSW combustion facilities. While this data base does not yield correlations on a total basis, it does offer insights if cenain adaptations are made. These adaptations include removing data points associated with RDF combustion, and data points associated with incinerators operated at less than 79 percent excess air. Given these adjustments, two regression equations can be constructed, each with r values exceeding 0.9: Dioxins u Ob/MMBtu) = [(1.74S·SR) - 3.071] • 9.75xl0·' (13) and Furans u Ob/MMBtu) = [(1.958·SR) - 3.396] • 9.75xHt' (14) The use of stoichiometric ratio as the driving variable is not unexpected. As shown previously. particulate emissions are governed to some extent by the percentage of excess air in the system. or the stoichiometric ratio. Further, combustion temperature is reduced significantly by increasing quantities of excess air. Consequently the SR term indicates the presence of more flyash to promote dioxin fonnation (see equation 11), and a decrease in the temperatures required to destroy dioxins, furans, and their precursors. 3.6. Outputs of TRACE The outputs of TRACE provide a reasonable profile of expected uncontrolled airborne emissions for such pollutants as particulates, trace metals, oxides of nitrogen, PAH's. and dioxins and furans. At the same time the outputs of TRACE provide a profile of the expected composition of the bottom ash from a low grade fuel furnace or boiler. Since these outputs are based upon the results from existing well designed and operated full scale facilities. or pilot plants capable of reproducing the results from full scale facilities. the results of TRACE fairly reproduce what can be expected from a modem 14 |