PCDD/PCDF formation in fluidized bed incineration

PCDF isomer distribution patterns found in samples of flue gas and fly ash from fluidized bed incinerators are distinctly different from those of grate fired incinerators or other thermal processes. The pathways for PCDD and PCDF formation are elucidated. The PCDD isomer distribution patterns found correspond to an extreme 2,6-pattern. Comparing the isomer distribution of the PCDD congeners with the chlorophenol concentrations one finds a better correlation with the chlorophenol congeners in fly ash than with those in the gas phase. The PCDF could be correlated isomer specific to the condensation of chlorophenols and chlorobenzenes. The characteristic PCDF isomer distribution patterns in the samples from fluidized bed incinerators are explained by a difference in the mechanism of formation due to a difference in fly ash composition. Due to the injection of either Ca(OH)2 or CaCO3 into the raw gas of the fluidized bed incinerators the fly ash samples show a comparatively high content in calcium (16–25%) resulting in a high pH of 11–12.7.