Effects of increasing chlorine concentration in feedstock on the emission and distribution characteristic of dioxins in circular fluidized bed boiler

Abstract

Field studies were conducted to study the emission and distribution characteristics of dioxins by elevating the chloring concentration in feedstock in a 600MW circular uidized bed (CFB) boiler. The concentration and total equivalent quantity of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in all ue gas, electrostatic ash, cloth bag ash and boiler ash samples under blank condition (i.e., feedstock was normal coal) and chlorine labelling condition (i.e., feedstock mixed with coal and chlorine-containing labelling agent) were analyzed. Results illustrated that the concentration of PCDD/Fs in all gaseous and ash samples increased with the addition of chlorine in feedstock, with the largest and least increment in dioxin concentration observed in electrostatic ash and ue gas. PCDDs were the predominate congeners in ue gas, accounted for 50.1-60.4%of the total PCDD/Fs concentration under chlorine labelling and blank conditions, while PCDD/Fs distribution changed from PCDD-to PCDF-predominate by increasing chlorine content in feedstock under all eld test conditions: 46.6-92.9%, 34.0-76.1%, and 47.0-53.1% of PCDFs were distributed in electrostatic ash, cloth bag ash, and boiler ash, respectively. Highly chlorinated PCDD/F congeners such as O 8 CDD/F and 1,2,3,4,6,7,8-H 7 CDD/F were the primary contributors to dioxins concentration in ue gas and boiler ash samples, whereas low-chlorinated 2,3,7,8-T 4 CDF and 1,2,3,7,8-P 5 CDF congeners became critically dominating in electrostatic and cloth bag ash.