Study on polychlorinated dibenzo-p-dioxin/furan formation in iron ore sintering process
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. INTRODUCTION
POLYCHLORINATED dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are a group of chlorinated tricyclic aromatic compounds that are structurally similar. PCDDs are comprised of two benzene rings joined at their para carbons by two oxygen atoms. The PCDFs contain two benzene rings fused to a central furan ring. Different degrees and positions of chlorination on the aromatic ring structures can occur leading to 75 PCDDs and 135 PCDFs congeners in total. There are eight homologues of PCDD/Fs, monochlorinated through octachlorinated. Each homologous group contains one or more isomers. Some isomers of dioxin are known to be among the most toxic chemicals and may have carcinogenic and mutagenic effects. Emissions of dioxins and furans from production processes in the metallurgical industries have largely been underestimated in the past.[1] The smelting and refining of iron, aluminum, copper, nickel, lead, and magnesium can release dioxins into the air. Untreated waste gases from sinter plants may contain appreciable amounts of dioxins and furans, the emission of which has to be reduced to comply with the more and more stringent environmental regulations. The existing end-of-pipe dioxin and furan removal techniques[2] are relatively expensive in the case of sintering because of the large amounts of waste gases to be treated. Primary solutions that prevent the formation
PENGFU TAN, formerly Research Fellow with Materials Chemistry, Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Germany, now Principal Scientist, is with Mount Isa Mines Limited, Mount Isa, Queensland 4825, Australia. Contact e-mail: [email protected] and [email protected] DIETER NEUSCHĂTZ, Professor, is with the Materials Chemistry Department, Rheinisch-Westfalische Technische Hochschule (RWTH) Aachen, D-52056 Aachen, Germany. Manuscript submitted May 2, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS B
of dioxins and furans within the sintering process would be preferable if they were found to be feasible and reliable. Since the mechanism of dioxin formation in the iron ore sintering process is not yet very clear, it is important to acquire more knowledge about the formation of PCDD/Fs during iron ore sintering. This investigation was based on thermodynamic and kinetic calculations and computational fluid dynamics (CFD) modeling. II. THERMODYNAMIC DATABASES FOR PCDD/Fs Three thermodynamic databases of PCDD/Fs derived using the Group Additivity approach[3] and two computational molecular modeling methods, Modified Neglect of Diatomic Overlap (MNDO) and Parametrized Model 3 (PM3), respectively,[4,5] combined with the Scientific Group Thermodata Europe (SGTE) database, have been used by the authors[6] to model the formation of PCDD/Fs in thermal processes, such as the iron ore sintering process. The predictions using the three different databases have been compared, and similar thermodynamic conditions of PCDD/F formation have been found.[6] The isomer distributions of toxic PCDD/Fs have also been predicted by the authors[7] an
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