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Distribution of dioxins, their precursors and surrogates in dust laden gas streams from metallurgical industry: implication to formation and filtration mechanisms

Friday, 2 September, 2005 - 09:30
Campus: Brussels Humanities, Sciences & Engineering campus
Nadezhda Zyaykina
phd defence

Abstract

Currently metallurgy is the main European industrial source of dioxins. The thesis work deals with dioxins (polychlorinated dibenzo-para-dioxins and dibenzofurans, PCDD/F), polychlorinated benzenes and phenols, originating from several metallurgical processes: iron ore sintering, manganese ore sintering, melting of pure copper cathodes and secondary copper smelting. The general aim of this project is to investigate the dioxin problem in metallurgy, concentrating on the three aspects: adsorptivity of metallurgical filter dust, gas-to-particle (G/P) partitioning, and formation.

The filter dust samples originate from either an electrostatic precipitator or a baghouse filter. Such powders have a complex composition, including all elements necessary for dioxin formation, and are highly heterogeneous. The samples were thermally treated applying the following methods: a) gas-solid chromatography on reference materials, b) desorption of filter dust, with either time-resolved or selective analysis, c) desorption of samples with intermediate sampling of products with following selective analysis of the traps, and d) the de novo (carbon oxidation) test on pre-desorbed powders. More data is now available on identity, and relative and total amounts of compounds that are released from metallurgical filter dust when it is being re-heated.

Gas/particle partitioning of dioxins was studied on the basis of industrial sampling data from several full-scale plants and laboratory de novo test data. The industrial sampling took place before and after a baghouse filter, simultaneously of the gas phase and particulates, in the most cases when an adsorbent was injected to the stream before the filtration unit. The G/P partitioning coefficients were calculated and compared a) between the plants, when flue gas cleaning was limited to filtration only, and b) within a plant, when adsorptivity of the original process dust increased due to addition of zeolite, lignite coke or a mixture of Sorbalite and activated carbon. Finally, the cleaning efficiency of dioxins from the two phases and PCDD/F mass balance of the filtration unit were evaluated. Regarding the laboratory data, influence on the partitioning of all the experimental parameters, as well as volatility were considered.

Formation of aromatic and chloroaromatic compounds from metallurgical filter dust was studied by coupling the traditional de novo test set-up with Jet-REMPI (resonance enhanced multi-photon ionization) time-of-flight mass spectrometer. This combination allowed to obtain time-resolved data (time-temperature-concentration) for benzene, monochlorobenzene, o-dichlorobenzene, toluene and phenol, as well as for the class of polychlorinated aromatic hydrocarbons (PAH). The detected amount and the maximum concentration(s) depend greatly on the test temperature and a sample origin, while humidity has an ambiguous effect. In contradiction with previously available timeaveraged data, the rapid changes of concentration and non-linearity of increase of the yield were demonstrated for all the cases.