Concentrations and patterns of polychlorinated biphenyls at different process stages of cement kilns co-processing waste incinerator fly ash

Abstract

a b s t r a c tCement kilns can be used to co-process fly ash from municipal solid waste incinerators. However, this might increase emission of organic pollutants like polychlorinated biphenyls (PCBs). Knowledge of PCB concentrations and homolog and congener patterns at different stages in this process could be used to assess the possibility of simultaneously controlling emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and ''dioxin-like" compounds. To date, emissions from cement kilns coprocessing fly ash from municipal solid waste incinerators have not been analyzed for PCBs. In this study, stack gas and particulate samples from two cement kilns co-processing waste incinerator fly ash were analyzed for PCBs. The average total tri-to deca-chlorinated biphenyl ( P 3-10 PCB) concentration in the stack gas samples was 10.15 ng m À3. The P 3-10 PCB concentration ranges in particulate samples from different stages were 0.83-41.79 ng g À1 for cement kiln 1 and 0.13-1.69 ng g À1 for cement kiln 2. The P 3-10 PCB concentrations were much higher in particulate samples from the suspension pre-heater boiler, humidifier tower, and kiln back-end bag filters than in particulate samples from other stages. For these three stages, PCBs contributed to 15-18% of the total PCB, PCDD/F, and polychlorinated naphthalene toxic equivalents in stack gases and particulate matter. The PCB distributions were similar to those found in other studies for PCDD/Fs and polychlorinated naphthalenes, which suggest that it may be possible to simultaneously control emissions of multiple organic pollutants from cement kilns. Homolog patterns in the particulate samples were dominated by the pentachlorobiphenyls. CB-105, CB-118, and CB-123 were the dominant dioxin-like PCB congeners that formed at the back-end of the cement kiln. A mass balance of PCBs in the cement kilns indicated that the total mass of PCBs in the stack gases and clinker was about half the mass of PCBs in the raw materials.

Inhibition Effect and Mechanism of Thiourea on Electrophilic Chlorination of Aromatics in Combustion Flue Gas

“…Many industrial combustion processes, such as solid waste incineration, metal smelting, and cement production, could produce and release a series of highly toxic chlorinated aromatics, represented by polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs). − In the postcombustion zone, the formation of these highly toxic chlorinated aromatic compounds necessarily undergo the chlorination of aromatics, which is involved in the main formation pathways, de novo synthesis and precursor route. , Chlorination of aromatics can take place via free radical reaction mainly at above 600 °C and electrophilic substitution mainly at 150–400 °C. − Most PCDD/Fs, PCBs, and PCNs are formed at 200–450 °C in combustion flue gas, , which implies that electrophilic chlorination plays a more important role in the formation of these highly toxic chlorinated aromatics. , …”

Used Tires as Fuel in Clinker Production: Economic and Environmental Implications

“…In the case of cement factories, the substitution of traditional fossil fuels not only reduces emissions, particularly CO 2 , but also provides a use for wastes such as sludge, municipal solid waste, and tires, yielding energy savings and environmental benefits [5][6][7][8], with several particular case studies analyzed in this regard [9].…”

Used Tires as Fuel in Clinker Production: Economic and Environmental Implications

“…In the case of cement factories, substituting traditional fossil fuels not only reduces emissions, particularly CO2, but also provides a use for wastes such as sludge, municipal solid waste and tires, yielding energy savings and environmental benefits [5][6][7][8], with some particular case studies analysed in this regard [9].…”