Chlorinated aromatics from combustion - the influence of chlorine,
combustion conditions and catalytic activity
Öberg, T., Öhrström, T.
Presentation at the 8th International Congress on Toxic Combustion By-Products,
Umeå, June 17-19, 2003.
Abstract
De novo formation of chlorinated aromatics in combustion processes was suggested
more than 30 years ago, and later the quantitative dependence on the HCl
concentration was shown both in the laboratory and in a full-scale study. The
role of chlorine in the thermal formation of chlorinated aromatics has however
remained a controversial issue, and it has also been difficult to establish the
relative importance of high-temperature reactions compared to catalysed
low-temperature formation. We now report results from a series of multifactor
experiments in a full-scale combustion process, where we have investigated the
influence of variations in chlorine input, combustion temperature and catalytic
activity. The results show that all three factors have a statistically
significant impact on the formation and release of these toxic by-products.
Furthermore, chlorinated benzenes (CBz), dibenzo-p-dioxins (PCDD) and
dibenzofurans (PCDF) were formed both thermally at high temperatures and
catalytically at temperatures below 400 °C. The relative importance of each of
these factors is dependent upon the constraints in the specific situation. It
was therefore not possible to assign one as generally more or less important
than the other. In this study, a main objective was to ensure that the
installation of a boiler for energy recovery would not also cause elevated
emissions of chlorinated aromatics. A possible future application for the
described experimental procedure is to assess the environmental implications of
planned boiler installations.
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