焼却炉におけるダイオキシン対策の考え方

Abstract

Wastes are treated mainly by incineration in Japan. Therefore dioxins emission from incinerator shall be reduced quickly. Dioxins mean normally a summation of PCDDs and PCDFs, as their chemical structures oxygen bonds two benzene rings which are substituted by a few Cln. They consist of 75 and 135 isomers respectively, in which 17 isomers are toxic substances.In dioxins emission source, a MSW incinerator is the most, and a industrial waste incinerator is followed. A dioxin quantity from a combustion procedure is the biggest amount in industrial procedures. As dioxin formation mechanisms two processes are proposed, one is a formation from carbon residue in fly-ash which is called de novo synthesis and observed in a relatively low temperature of 300500°C, the other is from precursors. A theory of restraint of forming dioxins in combustion is maintaining of 3 T (Temperature, Time and Turbulence) in that field. As a dioxins reduction in commercial plants combustion air mixing improvements, for example, installations of nose wall and 2ndary air nozzles are mostly reported. A temperature reduction of gas treatment facility is a easy and effective improvement. Flue gas treatments for dioxins are a low-temperature bag house which removes with high efficiency, carbon adsorption bed and catalytic tower.For a Japanese government's plan that is 98% reduction of dioxin emission from MSW incinerators in 10 years later, we shall do the best.