Dioxin/furan reduction

Most known end-of-pipe technologies used for PAHs and dioxin/furan reduction are DeNOx/DeDiox systems " involving the addition of Ugnite coke, activated carbon or an activated carbon/lime mixture (Fig. 5.3). ... 

To avoid the pore blocking effect of the catalysts with coarse fly ash particles and ammonium sulphate, the destruction of dioxins/furans is usually performed after the cleaning stages or at the boiler exhaust (350 00°C). The POPs reduction rate depends mainly on the volume capacity of the installed catalyst, the reaction temperature and the contact time in the selective catal5dic reduction (SCR) reactor, as well as the presence of poisoning elements (As, Pb, P, K, etc...). 

Hartenstein, H. (2003). Dioxin and Furan Reduction Technologies for Combustion and Industrial Thermal Process Facilities, The Handbook of Environ. Chem., Vol. 3, Part O, pp. 389 23. 

Official Journal of the European Union 14.2.2006, L 42/26 Commission Recommendation of 6 February 2006 on the reduction ofthe presence of dioxins, furans and PCBs in feedingstuffs and foodstuffs. 

The results reported by Carrasco et al. (1998) revealed that nearly all studied metal emissions, measured at the exit of a cement kiln stack, were significantly higher when a blend of 80 wt% coal + 20 wt% TDF was combusted instead of pure coal. Especially notable are increased emissions in Cr, Mn, Cu, Zn, and Pb (Table 9). The exception to this trend is Hg, which exhibited a 30% reduction in its emission rate when the coal + TDF mixture was burned. The data further document reductions in NO and organic compound emissions, including PAHs, where the most drastic decrease was observed for dioxins and furans. On the other hand, emissions of CO, S02, and HC1 increased considerably with the addition of TDF (Table 9). The total particulate emissions from combustion of the blend were only slightly greater than those from pure coal. Carrasco et al. (1998) used their data to model atmospheric dispersion of the emitted contaminants in the vicinity of the... 

Dihydro-1,2-dioxines (195) (available from dienes and 02) can be transformed into furans (197) by reduction and rearrangement (into 196) and subsequent elimination of water, usually by treatment with base. In some cases Co(II) and Fe(II) catalysts have been used (76TL4363, 77JOC1900, 77SCH9, 82ACS(B)31, 89JOC3475). 

Figure 8.17 reveals that the decomposition of dioxins and furans undergoes reduction because the best fit is for the correlation between kinetic rate constants and ELUMO therefore, the compounds act as electrophilic agents. Figure 8.17 presents the correlation between the kinetic rate constants and log P for chlorinated dioxins and furans. It indicates that the higher the hydrophobicity of a given chlorinated dioxin or furan, the less reactive it will be. Table 8.11 summarizes the QSAR models for the dioxins and furans studied. 

The Stockholm Convention (UNEP 2009a) entered into force in 2004, restricting 12 persistent and bio-accumulating toxic chemicals. An additional 9 substances were included in 2009. In coming decades, the major issue under the convention will be the reduction of emissions of dioxins and furans from combustion. 

The application of oxygen results in a reduced coke consumption and a better process control. Additionally, a reduction in the emission of dioxins and furans from cold blast cupolas have been reported (see Section 4.5.1.4). 

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