STUDY ON PLASMA VITRIFICATION OF ASH RESIDUES FROM MUNICIPAL SOLID WASTE INCINERATORS

摘要

Fly ashes from municipal solid waste (MSW) incinerators containing harmful constituents such as heavy metals and dioxins are classified as hazardous wastes. Twenty-seven MSW incinerators with a total design capacity of 25,400 tons/day when all installed in Taiwan shall generate fly ashes and bottom ashes daily with a quantity at about 1,000 tons/day and 4,000 tons/day respectively. Due to its space limitation and high population density, the treatment and disposal of MSW fly ash has become an issue of the public concerns in Taiwan. Currently, MSW fly ashes are treated by cement solidification method and then sent to disposal sites. In order to provide a better solution, Taiwan EPA and the Institute of Nuclear Energy Research (INER) joined together to study the plasma melting process for recycling the ash residues. Plasma vitrification of bottom ashes and fly ashes from five operating MSW incinerators in Taiwan was studied. Experimental results from lab-scale testing show that all the bottom ashes (BA) and fly ashes from boilers and economizers (FA) can be converted into high-quality slag at 1,450°C, but fly ashes from semi-dry air pollution control device (I.e. reaction ashes, RA) can not be melt even at 1,650°C due to high basicity (CaO/SiO2) and high chloride contents. To effectively vitrify the reaction ashes, bottom ashes or boiler ashes were added with proper weight ratios to control the basicity of the ash mixtures in between one and three. Pilot-scale plasma furnace with drum feeder was used to process the pre-compressed ash residues into high-quality slag having great potential to be reused as construction materials. Successful plasma vitrification testing has encouraged Taiwan EPA and INER to build a demonstrative plasma melting plant to vitrify the ash residues into water-quenched slag for further recycling study.