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PCDD/F FORMATION RATES FROM FLY ASH AND METHANE COMBUSTION CARBON SOURCES
Citation:
Gullett*, B K., E. Altwicker, E. Wikstrom**, AND A. Touati. PCDD/F FORMATION RATES FROM FLY ASH AND METHANE COMBUSTION CARBON SOURCES. Presented at 21st Int. Symp. on Halogenated Env. Organic Pollutants & POPs (Dioxin 2001), Kyongju, Korea, 9/9-14/01.
Description:
The abstract discusses polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD,F) from fly ash and methane combustion carbon sources. (NOTE: PCDD,Fs are formed in trace quantities in combustion processes via two primary mechanisms: de novo synthesis in which they are formed from nonextractable carbon structures that are basically dissimilar to the final product, and precursor formation/reactions via aryl structures derived from either incomplete aromatic oxidation or cyclization of hydrocarbon fragments.) Extensive laboratory efforts on the de novo synthesis and precursor mechanisms have not yielded mechanistic rates, homologue profiles, or PCDD/F ratios that satisfactorily reflect sampled concentrations of PCDD,Fs in field units. The observed de novo rates at the optimum-temperature vary from about 0.2 to 2 ng PCDD,F per g of fly ash per s of solid-phase residence time, which is still more than 2 to 3 orders of magnitude below apparent incinerator rates. Entrained flow combustor tests have obtained rates with homologue profiles and PCDD/F ratios more closely mimicking those observed in the field, but they are still insufficient to adequately discern distinctive carbon source mechanisms and, hence, provide methods of formation prevention. To more adequately simulate and control the conditions under which PCDD,F formation is expected in combustion, a flow reactor was built to test these mechanistic hypotheses in a reasonably realistic simulation.