Role of Sulfur in Reducing PCDD and PCDF Formation

• Published in: Environmental science & technology Vol. 30; no. 6; pp. 1827 - 1834
• Main Authors: Raghunathan, K, Gullett, Brian K
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.1996
• Subjects: Applied sciences; Chemistry; Dioxins; Exact sciences and technology; Pollution; Sulfur; Urban and domestic wastes; Waste materials; Wastes; Pilot plant; Chemical analysis; Combustion gas; Incineration; Medium effect; Waste treatment; Reaction mechanism; Pollutant creation; Reactor; Sulfur; Gaseous phase reaction
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es950362k

Past research has suggested that the presence of sulfur (S) in municipal waste combustors (MWCs) can decrease the downstream formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Thus, co-firing a MWC with coal, because of the S species from coal, may reduce PCDD and PCDF emissions. Experiments were carried out to test this hypothesis and to determine the role of S. A field-sampled MWC fly ash was injected into the EPA's pilot-scale reactor, doped with hydrogen chloride (HCl). The tests involved either natural gas or coal combustion. Besides the combustion environment, MWC fly ash injection temperature and sulfur-to-chlorine ratio (S/Cl) were varied. Flue gas was sampled and analyzed for PCDD and PCDF to determine in-flight formation. In the natural-gas-fired reactor, when S was added (as sulfur dioxide, SO2), the PCDD and PCDF formation decreased dramatically at S/Cl ratios as low as 0.64, and with varying furnace conditions, the inhibitory effect was consistent for S/Cl ratios of about 1. In tests with the coal-fired furnace, the S inhibitory effect was again observed at S/Cl values of 0.8 and 1.2, respectively, for the two coals tested. S inhibition mechanisms were studied in a bench-scale reactor. Results show that the depletion of molecular chlorine (Cl2), an active chlorinating agent, by SO2 through a gas-phase reaction appears to be a significant inhibition mechanism in addition to previously reported SO2 deactivation of copper catalysts.