Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from electric arc furnaces for steelmaking

摘要

The proportion of steel produced using electric arc furnaces (EAFs) is increasing. In this study, polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) concentrations and patterns in stack gas samples from three typical EAFs in steelmaking plants were determined to allow the contributions of EAFs in steelmaking plants to PCDD/Fs emissions in China to be assessed. Samples collection was accomplished by adopting the automatic isokinetic sampling technique, then the PCDD/Fs congeners concentrations were analyzed qualitatively and quantitatively by isotope dilution high-resolution gas chromatography high-resolution mass spectrometry (HRGC-HRMS). The mean PCDD/Fs mass concentrations in stack gases emitted during the scrap preheating phase of plants E1, E2, and E3 were 0.48, 385.55, and 0.34?ng Nmsup?3/sup, respectively, and the total toxic equivalent (WHOsub2005/sub-TEQ) concentrations were 0.05, 33.16, and 0.03?ng Nmsup?3/sup, respectively. The PCDD/Fs mass concentration in stack gases emitted during the melting phase at plant E3 was 0.12?ng Nmsup?3/sup (0.02?ng WHOsub2005/sub-TEQ Nmsup?3/sup). The operational temperature of the bag filter of the preheating in the E2 EAF was as high as 230?°C, which is conducive to the generation of PCDD/Fs, whether the temperature in the bag filter of E1 (150?°C) and E3 (120?°C) are not. Moreover, the bag filter temperature is suggested to be best controlled to below 150 °C. The emission factors (EF) for PCDD/Fs released into the air during the scrap preheating phase for plants E1, E2, and E3 were 0.13, 52, and 0.10?μg WHOsub2005/sub-TEQ tsup?1/sup, respectively, and the EF for the smelting phase from plant E3 was 0.14?μg WHOsub2005/sub-TEQ tsup?1/sup. The emission factor in E2 is 5 times higher than the highest current UNEP toolkit factor for EAFs (10?μg TEQ/tonne steel). Therefore, an update for the UNEP toolkit emission factor for a few case plants is suggested. Several congeners, including 2,3,7,8-TeCDF, 1,2,3,4,6,7,8-HpCDF, and 1,2,3,4,6,7,8-HpCDD, were dominant during the preheating phase, while 2,3,7,8-TeCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF were dominant during the smelting phase. The monitoring data from the case plants helps to better understand the PCDD/Fs emissions of EAFs using preheating process stages. However, a more complete emission inventory requires more case investigations on the PCDD/Fs emissions from representative EAFs steelmaking plants.