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8093632 
Book/Book Chapter 
Formation of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and naphthalenes (PCN) in a laboratory-scale waste combustion reactor 
Jansson, S 
2011 
Nova Science Publishers, Inc. 
Heterogeneous Combustion 
77-110 
English 
The research presented in this chapter contributes to knowledge about the combustion-based formation of dioxins and dioxin-like compounds. Dioxins are among the most toxic substances known to man, and are formed as by-products of industrial processes, including waste incineration. Although the emissions of dioxins from waste incineration facilities have been greatly reduced by the improved efficiency of pollution abatement technologies, the materials that remain (ashes and filters) are highly contaminated and are thus classified as hazardous waste. The principal objective of this research was to elucidate the pathways by which dioxins and dioxin-like compounds are formed in flue gas in the post-combustion zone of a laboratory-scale reactor during well-controlled combustion of waste. The potential benefits of this improved understanding include the detoxification of waste incineration residues and further reduction of harmful emissions to air, which could reduce or even eliminate the need for costly and potentially hazardous treatment.Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) were formed rapidly in the post-combustion zone of the laboratory-scale reactor, mainly as the temperature declined from 650°C to 400°C, with a high dependency on sufficient residence time within a specific temperature interval. Prolonged residence at temperatures above 450°C led to a reduction in the concentrations of PCDDs formed. The isomer distribution patterns of the PCDDs, PCDFs and polychlorinated naphthalenes (PCNs) in the flue gas indicated that the formation of PCDDs was largely influenced by condensation of chlorophenols and, to a lower extent, by chlorination reactions. The abundance of 1,9-substituted PCDFs was low, suggesting that chlorine substitution reactions were not favoured at positions adjacent to the oxygen bridges.The effects of injection of aromatic compounds into the flue gas were compound-dependent. Injection of naphthalene caused an increase in the formation of monochlorinated naphthalene but not in other chloronaphthalene homologues, probably because of insufficient residence time at temperatures conducive to further chlorination. Injection of dibenzo-p-dioxin appeared to result in its decomposition, chlorination and re-condensation to form PCDDs and PCDFs, whereas the introduction of dibenzofuran and fluorene led to a reduction in the concentrations of PCDDs in the flue gas. © 2011 Nova Science Publishers, Inc. All rights reserved.