Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from electric arc furnaces for steelmaking
Qiuting Yang, Lili Yang, Jia Shen, Yuanping Yang, Minxiang Wang, Xiaoyun Liu, Xuejing Shen, Changliang Li, Jia Xu, Fengfeng Li, Da Li, Guorui Liu, Minghui Zheng
Abstract
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 Nm−3, respectively, and the total toxic equivalent (WHO2005-TEQ) concentrations were 0.05, 33.16, and 0.03 ng Nm−3, respectively. The PCDD/Fs mass concentration in stack gases emitted during the melting phase at plant E3 was 0.12 ng Nm−3 (0.02 ng WHO2005-TEQ Nm−3). 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 WHO2005-TEQ t−1, respectively, and the EF for the smelting phase from plant E3 was 0.14 μg WHO2005-TEQ t−1. 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.