Dioxin Formation on Ash from Gasification Melting System

Abstract

Ash samples were experimentally heated in order to investigate the formation potential of dioxins by using a quartz glass tube reactor. The samples were collected from gas cooling processes such as boilers and gas cooling towers in gasification melting systems. Emphasis was placed on finding a parameter that could be used to estimate the formation potential of dioxins, and on examining the influence factors. The effects of pretreating the ash sample were tested using thermal treatment at 500 or 600°C, Soxhlet extraction by dichloromethane, or rinsing by water. The results showed that the formation potential was decreased by the pretreatments, except for Soxhlet extraction. Hence, carbon content in ash and water-soluble constituents including metal chlorides were found to be important factors for the formation of dioxins. The total amount of dioxins per gram of ash, which was defined as the sum of dioxins emitted with flue gas during the gas sampling time, and dioxins contained in ash after heating generated from ashes of gasification melting systems were 1.3-330 ng/g. A linear relationship in logarithmic scale was found between carbon content and the total amount of dioxins. Metal compounds generally did not show water solubility based on the analysis of extracted water. However, suspected compounds containing lead were shown to be soluble, which might explain the change of formation potential by water rinsing.