OCR Text |
Show 2. DIOXINS CONTROL BY COMBUSTION CONTROL In response to the developments in the U.S. and Europe over dioxins and furans, studies and reviews in Japan of dioxin and furan analysis methods are nearly co.pleted and the control method has now been established. Presently information on how dioxins and furans are formed in each Waste-to-Energy Plant is being collected, and in the near future, full collection of know-hows related with dioxins and furans will be attained. At present, however, little is known of the control of dioxins and furans contained in the flue gas generated in a Waste-to-Energy Plant and data of E.P.A. of the U.S., reports from Denmark, etc. are the only reliable criteria. Against such background, here we present our ideas on the control of dioxins and furans based on our knowledge derived from studies of dioxins and furans from the viewpoint of a manufacturer of Waste-to-Energy Plants. 2-1) Relationship between furnace combustion conditions and dioxins formation mechanism The waste processed by incineration contains such org:Hlic mfltters as tar composed of benzene rings. It is considered that, depending on combustion conditions in the furnace, these organic matters are transformed into organic chlorides by free chlorine generated from vinyl chloride, salt, etc. and dioxins, containing 2, 3, 1, 8 - tetrachlorodibenzo-p-dioxin(TCDD), and polychlorinated dibenzofuran (PCDF), etc. are derived as part of these organic chlorides. Therefore, dioxins and furans are not originally contained in the waste delivered to the plant but nearly all of them are formed by reactions in high temperature conditions in the furnace. Hereafter, furans are generally referred to as dioxins. (1) Characteristics of thermal destruction Dioxins are originally stable compounds but they decompose under high temperatures. As shown in Fig.2-1, thermal destruction profiles on organic compounds ~ncluding peDD have been reported. According to this figure, dioxins begin to decompose very quickly in the neighborhood of 100t; and decompose almost completely over |