| dc.description.abstract | Based on the Taiwan EPA statistics, the amount of fly ash generated by municipal solid waste incinerators (MSWIs) has increased year after year. Therefore, how to properly treat dioxin in fly ash has become an emerging issue. Batch pyrolysis tests for removing PCDD/Fs in fly ash had been conducted. Based on the experiences and results of batch pyrolysis tests, a continuous pyrolysis system is designed and constructed. Preliminary tests indicate that temperature in reactor can be stably controlled at 350oC as working temperature of electric furnace is set at 500oC, and the retention time can be controlled at 20, 25 and 40 minutes, respectively, with the corresponding inclination angle of 5o, 3o and 1o. Results indicate that total TEQ removal efficiencies of PCDD/Fs are 99.84%, 99.76% and 99.44% with 40, 25 and 20 minutes of retention time, respectively. The PCB destruction efficiencies are 99.43%, 98.25% and 97.26%, respectively. Total TEQ removal efficiencies increase with increasing retention time. Furthermore, removal efficiencies of lowly Cl-substituted congeners (4-5Cl) are lower than that of highly Cl-sbustituted congeners (6-8Cl). It may be attributed to the significant dechlorination of PCDD/Fs taking place in the system. Besides, the PCDD/F concentrations of fly ash after treatment with this continuous system are lower than 1.0 ng I-TEQ/g of dioxin-containing standard for hazardous waste and the PCDD/F concentrations of flue gas are lower than 0.1 ng I-TEQ/Nm3. Regarding the distribution of gas- and solid- phase PCDD/Fs, the results indicate the PCDD/F congeners remain in the fly ash are significantly higher than that vaporize into the gas phase after pyrolysis. However, the trend of PCB distribution is opposite. Based on the same operating condition, TEQ removal efficiencies of PCDD/Fs increase as 5% Ca(OH)2 is added into the fly ash for pyrolysis.
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