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

Field studies were conducted to study the emission and distribution characteristics of dioxins by elevating the chlorine concentration in feedstock in a circular fluidized bed boiler. The concentration and total equivalent quantity of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in all flue gas, electrostatic ash, bag filter ash, and bottom ash samples under blank condition (i.e., feedstock was normal coal) and chlorine labeling condition (i.e., feedstock mixed with coal and chlorine-containing labeling 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 flue gas. PCDDs were the predominate congeners in flue gas, accounted for 50.1-60.4% of the total PCDD/F concentration under chlorine labeling and blank conditions, while PCDD/F distribution changed from PCDD- to PCDF-predominate by increasing chlorine content in feedstock under all field test conditions: 46.6-92.9%, 34.0-76.1%, and 47.0-53.1% of PCDFs were distributed in electrostatic ash, bag filter ash, and bottom ash, respectively. Highly chlorinated PCDD/F congeners such as O8CDD/F and 1,2,3,4,6,7,8-H7CDD/F were the primary contributors to dioxin concentration in flue gas and bottom ash samples, whereas low-chlorinated 2,3,7,8-T4CDF and 1,2,3,7,8-P5CDF congeners became critically dominating in electrostatic and bag filter ash.

Automated summary

Field studies were conducted to investigate the emission and distribution characteristics of dioxins in a circular fluidized bed boiler by increasing the chlorine concentration in the feedstock. The results showed that the addition of chlorine increased the concentration of PCDD/Fs in all gaseous and ash samples, with the largest increment observed in electrostatic ash and flue gas. PCDDs were the dominant congeners in the flue gas, while the distribution of PCDD/F changed from PCDD-predominant to PCDF-predominant as the chlorine content in the feedstock increased. Highly chlorinated PCDD/F congeners were the primary contributors to dioxin concentration in flue gas and bottom ash samples, while low-chlorinated congeners became critically dominating in electrostatic and bag filter ash.