Formation pathways, gas-solid partitioning, and reaction kinetics of PCDD/Fs associated with baghouse filters operated at high temperatures: A case study

The application of the 3T method during combustion (i.e., a Temperature > 850 degrees C, a residence Time > 2 s, and sufficient Turbulence) can lead to elevated operating temperature in the baghouse filter for the municipal solid waste incineration (MSWI) systems without sufficient heat exchange capacity, which is potentially detrimental to the emission control of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). herein, a field study focusing on the distribution and variation of PCDD/Fs in gaseous and solid phases in a baghouse filter with high operating temperature (225-230 degrees C) was carried out. The concentration of PCDD/Fs in gases at the outlet of the baghouse filter was around 1 order of magnitude higher than that in inlet gases (i.e., noticeable memory effect of PCDD/Fs), because of the significant PCDD/Fs formation in filter fly ash (primarily contributed by the precursor pathway) followed by PCDD/Fs desorption. In addition, the mechanisms and factors resulting in the memory effect of PCDD/Fs were identified based on a laboratory study that carefully investigated the formation and desorption of PCDD/Fs at potential operating temperatures of baghouse filters (i.e., 180,200, and 225 degrees C). Tthe temperature was identified as the key factor inducing the memory effect of PCDD/Fs, because i) PCDD/Fs memory effect was not observed for baghouse filters with low operating temperatures of similar to 150 degrees C in previous studies; ii) both the formation and desorption of PCDD/Fs were noticeably favored by rising temperature from 180 to 225 degrees C; iii) increasing temperature appeared to facilitate the transformation from inorganic CI to organic CI and the conversion from aliphatic carbon to aromatic carbon or unsaturated hydrocarbons, both of which were favorable to PCDD/Fs formation; and iv) the release rate of PCDD/Fs from fly ash was exponentially dependent on temperature based on the modeling results of reaction kinetics.

Automated summary

The use of the 3T method in combustion can lead to elevated operating temperature in baghouse filters for MSWI systems, which is potentially detrimental to the emission control of PCDD/Fs. This study conducted a field study and laboratory investigation to analyze the distribution, variation, and memory effect of PCDD/Fs at high operating temperatures. The key factor inducing the memory effect was identified as temperature, which facilitated the formation and desorption of PCDD/Fs.