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ROLE OF SULFUR IN REDUCING PCDD AND PCDF FORMATION
Citation:
Raghunathan, K. AND B K. Gullett*. ROLE OF SULFUR IN REDUCING PCDD AND PCDF FORMATION. ENVIRONMENTAL SCIENCE & TECHNOLOGY 30(6):1827-1834, (1996).
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Past research has suggested that the presence of sulfur (S) in municipal waste combustors (MWCs) can decrease downstream formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Thus, co-firing a MWC with coal may reduce PCDD and PCDF emissions because of the S species from the coal. Experiments were carried out to test this hypothesis and 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), 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 in 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.
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