Inhibitory Effect and Mechanism of an N-S-Based Inhibitor (CH₄N₂S) on PCDD/Fs in Flue Gas and Fly Ash in a Full-Scale Municipal Solid Waste Incinerator

Abstract

Traditional strategies for controlling polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) emission in municipal solid waste (MSW) incineration merely involve the transfer of PCDD/Fs from flue gas to fly ash and ignore the reduction in PCDD/F generation, which might enhance the difficulty associated with the disposal of fly ash and pose potential environmental risks. In this study, we conducted a PCDD/F inhibition experiment in a full-scale MSW incinerator (400 t/day) to determine the inhibition effect and action mechanism of an N-S-based inhibitor (thiourea). The results demonstrated that thiourea achieved the remarkable PCDD/F inhibition efficiencies of 44.3% (54.5% for I-TEQ) in flue gas and 91.4% (71.7% for I-TEQ) in fly ash. The variation in the ∑PCDF:∑PCDD ratio implied that the inhibitor demonstrated higher efficacy in inhibiting the de novo synthesis in flue gas and blocking the precursor reaction in fly ash. Thiourea would gradually decompose to continuously release SO2 and NH3 at the temperatures between 240 and 400 °C, which could poison the metal catalysts and weaken the chlorination capability. Additionally, the reduction of reaction and catalytic sites caused by particle aggregation in fly ash contributed to PCDD/F generation inhibition. This study revealed the inhibition effect and the underlying mechanism of an N-S-based inhibitor on PCDD/F toxicity along the post-combustion area and will pave the way for further industrial applications.