In-Situ Suppression of Dioxin Formation in Waste Incinerators by SO2 and NH3/Urea

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The issue of dioxins (PCDD- polychlorinated dibenzodioxins) and furans (PCDF- polychlorinated dibenzofurans) in the environment are of considerable public concern. Their association with emissions from municipal solid waste incineration contributing significantly to the negativity of the debate surrounding the public acceptability of the technology. This research proposal has been developed following two recent EPSRC funded research grants investigating the reactions of PCDD/PCDF under conditions simulating the post combustion zone of municipal solid waste incinerators. Our research involves detailed, analyses of PCDD/PCDF congeners and isomers in relation to the process conditions influencing PCDD/PCDF formation, reactions and destruction. The work has developed mechanisms to describe the formation of PCDD/PCDF on flyash and their subsequent desorption into flue gases. Although there has been extensive and intense investigation of PCDD/PCDF formation in waste incinerator flyash and air pollution control residues, the exact mechanisms still remain unclear. The aim of this present research proposal is to investigate the influence of particular flue gases (SO2) and NOx control gases (NH3/urea) on the formation of PCDD/PCDF in flyash and air pollution control residues. This data is important in understanding the formation mechanisms of PCDD/PCDF and the suppressive effect of SO2 and NH3/urea. It could provide a key advance for a step change control strategy for the elimination or reduction of PCDD/PCDF formation in flyash and air pollution control residues from waste incinerators by using inherent, in-situ gases to control PCDD/PCDF. It would also result in a significant cost reduction due to savings in the use of activated carbon, which is currently used for control. In addition, the detailed understanding of the suppressive effect of SO2 and ammonium compounds on PCDD/PCDF formation could have wider implications for reducing PCDD/PCDF emissions from other combustion sources, such as coal-fired power plant and metal sinter plant at low cost. This is an ambitious proposal involving difficult experimentation with toxic materials and difficult analysis at extremely low levels of PCDD/PCDF concentration to fundamentally understand the important role of SO2 and NH3/urea in PCDD/PCDF formation reaction mechanisms.