Characterization of dioxin emissions from two municipal solid waste incinerators in Taiwan

Characterization of the dioxin removal efficiencies of the air pollution control devices (APCDs) at two existing municipal solid waste incinerators (MWIs) in Taiwan is conducted via stack sampling and analysis in this study. MWI-A (capacity: 300 ton/day-incinerator) is equipped with electrostatic precipitators (ESP) followed by wet scrubbers (WS) while MWI-B (capacity: 450 ton/day-incinerator) is equipped with cyclones, dry lime sorbent injection systems (DSI) and fabric filters (FF) as APCDs. Results indicate that the patterns of dioxin isomers at APCD inlet and stack are similar for both MWIs. The dioxin concentration at APCD inlet of MWI-B is 2.75 times higher than that of MWI-A, but the readings are quite close at stacks. This indicates that the concentration of dioxins generated as the gas stream flows through APCD at MWI-A is higher than that of MWI-B. Dioxin removal efficiency at MWI-A is negative because the operating temperature of the APCD falls in the de novo reaction window (200°C-350°C). The concentration of emitted dioxin decreases significantly at MWI-B after the injection of powdered activated carbon has been started in 1999. The dioxin removal efficiencies based on I-TEQ were significantly increased from 5.9 to 87.6% and 91.3%, respectively, compared to the condition without activated carbon injection. The dioxin removal efficiency reached 98.6% in 2000 after continuous injection of activated carbon (43.4 mg/Nm³) for one year. The lower efficiency achieved with activated carbon injection (ACI) in 1999 can be attributed to the memory effect, i.e. the dioxin or precursor desorbs slowly the flue gas and increases the dioxin concentration at stack, resulting in a lower dioxin removal efficiency than expected.