Study On Reaction And Correlation Mechanism From Indicators To PCDD/Fs And Its On-line Monitoring

Energy production and enviroment protection are two of major challenges which human are facing in nowdays. Incineration of wastes as an energy resource could lead to secondary pollution such as persistent organic pollutants, of which dioxin is most toxic, can cause extremely harm to environment and humanbeing. Along with the continuous study on the reaction mechanism and emission control technology, to seek for a fast and accurate detection method of dioxin becomes a new hotspot.Basic reasearch on dioxin on-line monitoring has been carried out in this thesis. The main work focused on the assessment with the feasibility of using PAHs as the dioxin surrogate compounds. The main content of the researches involved are as follows:1)The PCDD/Fs generated from mixed reactants of acenaphthene with both diffenent modeling fly ash and atmosphere have been studied. The experiment was carried out on a fixed bed apparatus under the post-combustion condition, combined with the thermogravimetry analysis and X-ray diffraction analysis on the reaction residues. It was found that the sequence of total amounts of dioxins product was as CuCl₂/Cl₂>CuCl₂/FeCl₃>CuCl₂>CuO/CuCl₂, the capacity for chlorine supply as Cl₂>FeCl₃>CuCl₂. Chlorine was transferred from the metal chloride ligands during the reaction.2)The dioxin distribution characters produced from six different PAHs catalysed by model fly ash have been studied to reval the reation pathway, which were treated under the post-combustion condition. The results showed that de novo synthesis was the main mechanism and PCDFs accounted for extremely majority of PCDD/Fs, of which fluorene, phenanthrene, biphenyl accounted for more than 95%. Anthracene and naphthalene reached 81% even though relatively low. PAHs with biphenyl-like structures could be easily converted to PCDFs, including fluorene, phenanthrene and biphenyl. Anthracene and naphthalene, which had no biphenyl structures in the skeleton, produced a small amount of PCDFs. Pyrene was the exception probably because its higher aromatic structure was resistant to oxidation and likely to form soot via molecular growth reactions. It was also shown that phenanthrene and biphenyl structures were the intermediates during the reaction process of high-ring PAHs cracking.3)The PCDD/Fs and PAHs emission characteristics from grate waste incinerators and fluidized bed waste incinerators were studied. The correlations between PAHs and PCDD/Fs were analyzed by using mathematic statistics methods. The results showed that there were good correlations between naphthalene, flurene and PCDD/Fs. E.g., naphthalene correlated well with total PCDD/Fs (r²=0.7326) and PCDD/Fs I-TEQ (r²=0.7443). It gave better results when analyzed by multiple linear regression using naphthalene, flurene and benzo(a)pyrene as the independent variables(r²=0.8120, correlated with total PCDD/Fs).4)The Time of Flight Mass Spectrometry(TOFMS) apparatus was used for testing organic compounds in both modelling and real smoke on-line. It was shown that TOFMS gave a high response to PAHs, PCBzs and PCPhs, and was satisfied for dioxin indicators on-line monitoring.