Formation of chlorinated dioxins and furans in a hazardous-waste-firing industrial boiler

This research examined the potential for emissions of polychlorinated dibenzodioxin and dibenzofuran (PCDD/F) from industrial boilers that cofire hazardous waste. PCDD/F emissions were sampled from a 732 kW (2.5 x 10(6) Btu/ h), 3-pass, firetube boiler using #2 fuel oil cofired with 2,4-dichlorophenol or 1,2-dichlorobenzene and a copper naphthenate mixture. PCDD/F levels were significantly elevated when improved combustion conditions (reduced carbon monoxide, increased carbon dioxide) followed periods of flame wall-impingement and soot formation/deposition on the boiler tubes. Boiler tube deposits became a sink and source for PCDD/F reactants (copper and chlorine) and PCDD/F, resulting in continued formation and emissions long after waste cofiring ceased. The role of deposits in PCDD/F formation makes emissions dependent on current as well as previous firing conditions, resulting in uncertainty regarding prediction of emissions based solely on the type and rate of cofired hazardous waste.