Dioxin formation and control in a gasification-melting plant

We investigated dioxin formation and removal in a commercial thermal waste treatment plant employing a gasification and melting process that has become widespread in the last decade in Japan. The aim was to clarify the possibility of dioxin formation in a process operation at high temperatures and the applicability of catalytic decomposition of dioxins. Also, the possible use of dioxin surrogate compounds for plant monitoring was further evaluated. The main test parameter was the influence of changes in the amount and type of municipal solid waste (MSW) supplied to the thermal waste treatment plant which from day to day operation is a relevant parameter also from commercial perspective. Here especially, the plastic content on dioxin release was assessed. The following conclusions were reached: (1) disturbance of combustion by adding plastic waste above the capability of the system resulted in a considerable increase in dioxin content of the flue gas at the inlet of the bag house and (2) bag filter equipment incorporating a catalytic filter effectively reduced the gaseous dioxin content below the standard of 0.1 ng toxic equivalency (TEQ)/m(3) (N), by decomposition and partly adsorption, as was revealed by total dioxin mass balance and an increased levels in the fly ash. Also, the possible use of organohalogen compounds as dioxin surrogate compounds for plant monitoring was further evaluated. The levels of these surrogates did not exceed values corresponding to 0.1 ng TEQ/m(3) (N) dioxins established from former tests. This further substantiated that surrogate measurement therefore can well reflect dioxin levels.