Abstract
Formation/decomposition mechanisms of PCDDs and PCDFs were investigated in combustion experiments of model wastes using a laboratory-scale fluidized-bed reactor with a high-temperature hold section at 600℃. The temperature-hold section was equipped after a furnace for the reduction of the PCDD/F emission. The amounts of PCDDs and PCDFs formed were reduced and their homologue profiles were shifted toward lower chlorinated species at downstream sampling points in the temperature-hold section. The ratios of the concentrations of PCDD congeners at the downstream sampling points to those at the inlet point in the temperature-hold section were more dispersed than those of PCDF congeners. This may indicate that PCDDs are decomposed through dechlorination reactions more than PCDFs in these experiments. In addition, the condensation reaction of precursors such as chlorophenol was observed in the PCDD congener distributions. The condensation reaction is not negligible in the various pathways of PCDD formation/decomposition in this temperature range. The PCDF congener formed through the dechlorination reaction after the formation from carbon/PAHs was observed in their congener proportions. These results show that the PCDD/F formation reactions occur in parallel with their decomposition reactions and the reactions have a different dependence on experimental conditions.
