Primary Measures for Reduction of PCDD/F in Co-Combustion of Lignite Coal and Waste:  Effect of Various Inhibitors

Abstract

Co-combustion of coal and waste in power plants poses both environmental and economic challenges, especially because of the high polychlorinated dibenzo-p-dioxin and furan (PCDD/F) emissions from solid waste. In this study, we performed a series of experiments focusing on the prevention of PCDD/F formation by the use of various inhibitors added to the fuel before combustion. A mixture of lignite coal, solid waste, and poly(vinyl chloride) (PVC) was thermally treated in a laboratory-scale furnace at 400 degrees C. Twenty different additives were investigated at a level of 10 wt% of the total fuel during the experiments. We have divided them into four general groups according to their chemical nature: metal oxides, N-containing compounds, S-containing compounds, and N- and S-containing compounds. The resulting values showed a significant reduction of PCDD/F levels when N- and S-containing compounds were used as additives to the fuel. Principle component analysis (PCA) was used to illustrate the effect of the 20 different inhibitors on the congener patterns emitted. As a result, the most effective inhibitors for PCDD/F formation in flue gases were determined to be (NH4)2SO4 and (NH4)2S2O3; they are inexpensive and nontoxic materials. Both compounds can suppress the formation of toxic compounds such as PCDD/Fs by more than 98-99%, and the most toxic PCDD/F congeners were not detectable in most of the samples. Thus, these compounds were also studied as a lower percentage of the fuel. (NH4)2SO4 resulted in a greater than 90% reduction of PCDD/F even when composing only 3% of the fuel combusted. However, less than 5% (NH4)2S2O3 resulted in far weaker inhibition. The PCDD/F homologue distribution ratio for samples with varying percentages of (NH4)2SO4 and (NH4)2S2O3 was also investigated. Higher percentages of the inhibitors produced a lower percentage of lower chlorinated PCDDs. The opposite effect was found for PCDFs.

Effects of gaseous NH3 and SO2 on the concentration profiles of PCDD/F in flyash under post-combustion zone conditions

“…This indicates that the inhibition mechanisms may be highly temperature dependent and likely different for PCDD and PCDF, respectively. It has been reported that the suppression effects of sulphur-containing compounds are higher for lower chlorinated PCDD and higher chlorinated PCDF (Pandelova et al, 2005;. In addition, Chang et al (2006) reported that PCDD/F inhibition in the particulate-phase was more than the gaseous-phase and PCDD was reduced more than PCDF.…”

Atmospheric Emission of PCDD/Fs, PCBs, Hexachlorobenzene, and Pentachlorobenzene from the Coking Industry

“…Many sources for the emission of UP-POPs have been identified and quantified (7,8), and the effects of various parameters on the formation of UPPOPs have been demonstrated in many studies (9)(10)(11)(12)(13). Sources of POPs and their relative importance have changed substantially over the past several decades.…”

The Possibilities of Reduction of Polychlorinated Dibenzo-P-Dioxins and Polychlorinated Dibenzofurans Emission

“…To the most frequently encountered inhibitors there belong nitrogen and sulphur compounds which bring about the blocking of the metallic active centers in the particles of volatile dust, on the surface of which one may notice "de novo" synthesis [50][51][52][53][54].…”