The Effect of Cofiring High-Sulfur Coal with Municipal Waste on Formation of Polychlorinated Dibenzodioxin and Polychlorinated Dibenzofuran

Abstract

The effect of cofiring minor amounts (5–10 wt %) of high-sulfur coal with municipal refuse–derived fuel (RDF) on emissions of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) was studied under a range of operating conditions. Through use of a 2x factorial test matrix the program examined the effect of sulfur dioxide (SO2) concentration on preventing PCDD/F formation while accounting for differences in hydrogen chloride concentration, sorbent slurry injection, and various furnace operating conditions such as quench rate, residence time, and RDF feed rate. An understanding of the effect of coal- and operating-related parameters on the postcombustion formation of PCDD/F is expected to assist in developing strategies aimed at preventing PCDD/F formation. The test facility was a 0.6-MWt (2 × 106 Btu/h) pilot scale, grate-fired combustor, designed to mimic the solid fuel handling and combustion rates of field units. Results were analyzed by examining comparative-run-averaged yields and through development of a model based on regression methods with stepwise parameter selection. The run-averaged yields and model show that higher SO2 concentrations due to cofiring with coal result in significant suppression of PCDD/F formation, even when controlling for changes in other operating parameters. Key words: Polychlorinated dibenzodioxin; polychlorinated dibenzofuran; PCDD; PCDF; waste combustion; refuse-derived fuel; coal; cofiring; sulfur dioxide; emissions