Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack flue gases of sinter plants

This study investigated four sinter plants, classified into two categories - with selective catalytic reduction (SCR) (S1, S2 and S3) and without SCR (S4) as its air pollution control device. Polychlorinated dibenzofurans (PCDFs) are dominant in the stack flue gases of sinter plants with and without SCR. The polychlorinated dibenzofurans/polychlorinated dibenzo-p-dioxins (PCDFs/PCDDs) ratio exceeds 1 extremely. The degree of chlorination of the sinter plant without SCR is towards hepta and hexa congeners while that of the sinter plant with SCR is towards penta and hexa congeners. PCDD/Fs are indeed decomposed (75.5% and 69% on ng and ng TEQ bases, respectively) and not only reduced in degree of chlorination. The overall concentration in the stack flue gas of sinter plants with SCR (7.97-14.1 ng/Nm³; 0.995-2.06 ng TEQ/N m³) is lower than that of the sinter plant without SCR (28.9 ng/Nm³; 3.10 ng TEQ/N m³). In Taiwan, based on the emission factors of 0.970 μg TEQ/ton-feedstock (sinter plants with SCR) and 3.13 μg TEQ/ton-feedstock (sinter plant without SCR), the annual PCDD/F emission of 44.7 g TEQ/year from sinter plants is 60 and 121 times higher than those from municipal solid waste incinerators (0.750 g TEQ/year) and MWIs (0.369 g TEQ/year). These results show that sinter plants have become the dominating PCDD/F emission source since tighter emission limits have been applied to incinerators.