Developing Suppression Techniques for Dioxin (DXN)s Released from Small-scale Incinerators for Industrial Wastes by Adding Titania Particles

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The present work is aimed at developing a method for suppressing the formation of dioxin (DXN)s emitted from small-scale incinerators for industrial wastes, which are difficult of operate under well controlled combustion, by adding a chemical (sulfur-contained titania) into incinerators. In the first year, the lab-scale experiments on incomplete combustion of me waste samples prepared by adding hydrated lime (Ca(OH)_2) with a given content into PVC powders were performed. The experiments revealed that the DXNs concentration in the burnt samples with 33.2wt%-added Ca(OH)_2 decreased by about 1/10 compared to that without the addition. However, we concluded that this technique adding chemicals into an incinerator is insufficient for the future regulation of tolal emission even if titania, which might be more reactive than Ca(OH)_2 is applied. Thus, we focused on the secondary heat treatment for fly ash in which DXNs arc most concentrated. In the conventional method, DXNs in the fly ash a … More re dechlorinated under reductive atmospheres below 500 deg. C. by adding some chemical since fly ash is subject to solidification above 500 deg. C. In the second year, we investigated the mechanism on solidification of fly ash at the high temperature and attempted to establish the technique of high-temperature treatment for fly ash preventing it from the solidification. Sodium hydroxide (NaOH) and mullile were chosen as an additive that can trap chlorine in fly ash, assuming that it might contribute the solidification, and then me chosen chemical was mixed with fly ash at a given ratio, followed by heating in an electric furnace at 700 deg.C. It was found that no solidification of fly ash with the additives took place after the heat treatment. Moreover, the X-ray diffractometer analyses indicated that the fly ash prior to the heating did not contain calcium chloride (CaCl_2) but CaClOH, which was a product of reaction between Ca(OH)_2 and HC1, and that sodium chloride (NaCl) was detected in the heated sample with NaOH and wadalite in the treated one with mullitc. The differential thermal analyses revealed that for the sample without additives there was an exothermic peak in ihe cooling step (around 800 deg.C). while this peak was not detected in that with additives. Furthermore, the DXNs in the samples before and after the heal treatment were analyzed. The results showed that DXNs concentration in the treated samples with additives decreased by less than 1/!05 compared to the untreated one without additives. These findings confirmed that the application of these additives has the advantages not only to prevent fly ash from the solidification but also to enhance the decomposition of DXNs. Less