EFFECT OF SOOT AND COPPER COMBUSTOR DEPOSITS ON DIOXIN EMISSIONS

An experimental study was conducted to investigate the effects of resi dual soot and copper combustor deposits on the formation of polychlori nated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCD Fs) during the combustion of a chlorinated waste. In a bench-scale set up, distillate fuel oil doped with copper compounds was fired under so oting conditions in a quartz reactor heated by a Linberg furnace to 90 0 degrees C. Soot- and copper-containing aerosols were carried by the hot flue gas and deposited on a separate quartz ''deposition'' tube co nnected to the exit of the quartz reactor. Selected experiments were a lso conducted to deposit either soot or copper on separate quartz depo sition tubes. In a separate setup, 1,6-dichlorohexane was injected int o a natural-gas-fired furnace reactor to produce a flue gas that conta ined 6.2% oxygen, 8.6% carbon dioxide, 10-50 ppm carbon monoxide, and 500 ppm hydrogen chloride. The deposition tubes were separately attach ed to the furnace reactor and a flue gas slip stream was passed throug h the tubes into a PCDD/F sampling train. The deposition tubes were ma intained at 320 degrees C by an electrical heating tape. Sulfur dioxid e (SO2) was injected near the flame zone of the furnace reactor in sel ected experiments. High levels of PCDD/Fs were measured at the exit of the deposition tubes containing both soot and copper deposits. No PCD D/Fs were found during experiments using a tube with only soot deposit s, and trace amounts of PCDD/Fs were found with a deposition tube cont aining only copper deposits. Repeated experiments with the same deposi tion tube containing soot and copper deposits resulted in reductions i n the amount of PCDD/Fs formed, indicating decreased formation with ti me. Significantly lower PCDD/F emissions were measured from the experi ments with SO2 injection, indicating that SO2 is effective in suppress ing PCDD/F formation reactions. It was also found that a deposition tu be previously exposed to flue gases from 1,6-dichlorohexane incinerati on exhibited residual PCDD/F formation reactions when exposed to flue gases from the combustion of natural gas. The results demonstrate that the combustor deposits containing copper and soot can cause ''memory effects'' that can play an important role in the emissions of PCDD/Fs from commercial incinerators.