Lowly Chlorinated Dibenzodioxins as TEQ Indicators. A Combined Approach Using Spectroscopic Measurements with DLR Jet-REMPI and Statistical Correlations with Waste Combustor Emissions

Abstract

Continuous monitoring of trace gas species in incineration processes can serve two purposes: (i) monitoring precursors of polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/F) or other indicator species in the raw gas will enable use of their on-line signals for process optimization, and (ii) monitoring stack gas emissions for regulated species will establish compliance records. The sensitivities required fOT the first application are in the order of to parts per trillion by volume (10 x 10-12 or 10pptv) and are now accessible with advanced methods such as jet-based, resonance enhanced multi-photon ionization (REMPI). The compliance application requires the ability to measure PCDD/F toxicity equivalents (TEQ) and would necessitate detection limits in the order of 0.00J pptv. These limits have not yet been achieved, and so REMPl-based compliance monitoring can only be indirectly approached by either pre-analysis concentration techniques or use of relatively abundant indicator substances that obey a known relationship to TEQ values. This paper describes an approach toward the second application through use of lowly chlorinated (one to three chlorines) dioxins as indicator substances. The method of jet-REMPI is briefly described, and measurements of unchlorinated dioxin, 2-monochlorodibenzodioxin, and 2,7-dichlorodibenzodioxin are presented. For the third compound, a very favourable detection limit on the order of 10pptv was projected. The indicator approach is further substantiated by measuring actual PCDDjF concentrations in the raw flue gas of a pilot scale, waste burning incinerator and by analyzing these data for correlations between the lowly chlorinated PCDD/F and the TEQ values. The extent to which these correlations are site and industry independent remains to be determined.