Temperature dependence of PCDD/F-formation in boiler ash

In a municipal waste incinerator boiler ash has been sampled from the horizontal superheater pass. Samples were taken at six different sites at flue gas temperatures ranging from 630 °C to 220 °C. Moreover, three samples were taken when the mechanical knocking system was working. A strong increase in concentration is observed, especially at 300-220 °C, which shows that PCDD/F are formed in the boiler outlet. The isomer pattern is consistent with that of typical combustion samples. As predicted by theoretical investigations, the isomer pattern is dominated by only a few isomers at high temperatures, while the isomer distribution at low temperatures is more even.