Study On Emission Profile Of PCDD/Fs And PBDD/Fs In The Electric Arc Furnace Steelmaking Process

Electric arc furnace(EAF)steelmaking is a steelmaking method using scrap steel as the main raw material,which can effectively realize the recycling and utilization of steel resources.However,due to lax management,the scrap steel is easily tainted by organics such as plastics and grease,and the steelmaking process will emit persistent organic pollutants(POPs)such as dioxins.To date,there are few studies on the emission levels and profile of polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs)and polybrominated dibenzo-p-dioxins and dibenzofurans(PBDD/Fs)in different stages of the EAF steelmaking process,especially the research on PBDD/Fs in this process is still blank.This study determined the PCDD/Fs and PBDD/Fs emission levels and profile of the stack gas samples and fly ash samples from three typical EAF steelmaking plants,in order to provide support for the assessment of the contribution of EAF steelmaking plants to China's dioxin-like pollution emissions.The main research results obtained in this research are as follows:1.The emission levels and congener profile of PCDD/Fs in the stack gas from different stages of the EAF steelmaking process are studied.Taking three typical EAF steelmaking enterprises(hereinafter referred to as E1,E2,E3)as the survey subjects,it was found that the average toxic equivalent concentration(TEQs)of PCDD/Fs in the flue gas emitted during the scrap preheating stage of plants E1,E2and E3 were 0.05,33.16 and 0.03 ng WHO₂₀₀₅-TEQ/Nm³,the emission factors(EF)are respectively 0.13,52 and 0.10?g WHO₂₀₀₅-TEQ/t;in the smelting stage,the TEQs of PCDD/Fs in the flue gas emitted by plant E3 is 0.02 ng WHO₂₀₀₅-TEQ/Nm³,the EF is 0.14?g WHO₂₀₀₅-TEQ/t.It is speculated that the large difference in emissions between the three plants is mainly due to the different raw materials and the different working temperatures of the bag filter.In the scrap preheating stage,2,3,7,8-Te CDF,1,2,3,4,6,7,8-Hp CDF and 1,2,3,4,6,7,8-Hp CDD are the dominant congeners,while in the smelting stage,2,3,7,8-Te CDF,1,2,3,7,8-Pe CDF and 2,3,4,7,8-Pe CDF are dominant.These data are helpful to understand the PCDD/Fs emission status of EAF steelmaking plants with scrap preheating process.2.The emission levels and congener profile of PBDD/Fs in the stack gas from different stages of the EAF steelmaking process are studied.In the preheating stage,the TEQs of PBDD/F of plants E1,E2 and E3 are 72.7,971.2,10.8 pg WHO₂₀₀₅-TEQ/Nm³,and EF are 0.17,1.51,0.0356?g WHO₂₀₀₅-TEQ/t,respectively;in the smelting stage,the TEQs of E3 are 4.5 pg WHO₂₀₀₅-TEQ/Nm³,and the EF is0.0359?g WHO₂₀₀₅-TEQ/t.PBDD/F accounts for 2.8%-57.7%of the total TEQs of chlorine and brominated dioxins.The emission of PBDD/F deserve more attention,and the proportions are fluctuant in different plants,which may be caused by the difference in the composition of the feedstock and the operating temperature of the bag filter.The congener profiles of PBDD/F from different plants are also different.These data provide data support for estimating the emission level of PBDD/F in a typical EAF steelmaking industry.3.The emission levels and profile of PCDD/Fs and PBDD/Fs in the fly ash from different stages of the EAF steelmaking process are studied.Regarding PCDD/Fs,in the scrap preheating stage,the TEQs of PCDD/Fs of plants E1,E2and E3 are 3.2,689.9,11.4 pg WHO₂₀₀₅-TEQ/g,respectively,while in the smelting stage,the corresponding value is 5.7,368.9,337.3 pg WHO₂₀₀₅-TEQ/g,respectively.In the scrap preheating stage,the TEQs of PBDD/Fs of plants E1,E2and E3 are 57.6,49.8,25.0 pg WHO₂₀₀₅-TEQ/g,respectively,while in the smelting stage,the corresponding value is 8.8,28.8,629.1 pg WHO₂₀₀₅-TEQ/g,respectively.Regarding the congener profile,there are certain differences between different plants and different stages,but they are mainly furans.The influence of the physical and chemical properties of EAF fly ash on the formation of dioxin was also discussed.It was found that Cu,Zn,Pb,Ni and other elements may promote the formation of PCDD/Fs and PBDD/Fs in the fly ash,while Ca may inhibit the formation of dioxins.TOC content is positively correlated with the formation of pollutants and the content of Cl element is positively correlated with the formation of PCDD/Fs.Discussing the levels and emission profiles of chlorine and brominated dioxins in fly ash produced during the EAF steelmaking process,and characterizing the physical and chemical properties of fly ash as a complex matrix,which is essential for proper handling of fly ash and is of great significance for understanding the formation of chlorine and brominated dioxins.