Simultaneous suppression of PCDD/F and NOx during municipal solid waste incineration

Abstract

Thiourea was tested as a dioxins inhibitor in a full-scale municipal solid waste incinerator with high capacity (34th−1). The suppressant, featuring a high S- and N-content, was converted into liquor and then injected (35kgh−1) into the furnace (850°C) through the inlets already used for Selective Non-Catalytic Reduction (SNCR) of flue gas NOx. The first results show that thiourea reduces the dioxins in flue gas by 55.8wt.%, those in fly ash by 90.3wt.% and the total dioxins emission factor by 91.0wt.%. The concentration of PCDD/Fs was 0.08ngTEQNm−3, below the national standard of 0.1ngTEQNm−3. The weight average chlorination degree of dioxins decreases slightly after adding the inhibitor, indicating that it suppresses both the formation and the chlorination of dioxins. Analysis of fly ash by scanning electron microscope (SEM) suggests that the particle size becomes larger after adding the inhibitor. Further analysis using an energy dispersive spectrometer (EDS) reveals that the sulphur content in fly ash rises, but the chlorine content declines when adding thiourea. These results suggest that poisoning the metal catalyst and blocking the chlorination are probably responsible for suppression. NOx reduction attains 42.6wt.%. These tests are paving the way for further industrial application and assist in controlling the future emissions of dioxins and NOx from MSWI.