Persistent Organic Pollutants Emission From Electric Arc Furnaces Steelmaking

Environmental pollution caused by persistent organic pollutants(POPs)has become a major global environmental problem,and reducing POPs emissions from the source is the fundamental point of controlling POPs environmental pollution.Metallurgical processes such as electric arc furnace(EAF)steelmaking are important emission sources of POPs.In recent years,scrap preheating device has been used in EAF steelmaking industry to preheat scrap steel before it is put into furnace,so as to reduce the heating time after it is put into furnace,thus reducing energy consumption and improving production efficiency.The reaction conditions such as temperature and raw materials in the preheating stage are suitable for the generation of POPs.Therefore,the preheating stage of EAF steelmaking may be an important process section for POPs emission in the EAF steelmaking.The emission levels and characteristics of polychlorinated biphenyls(PCBs),polychlorinated naphthalenes(PCNs),chlorinated and brominated polycyclic aromatic hydrocarbons(Cl/Br-PAHs)were analyzed by collecting flue gas and fly ash samples from three typical EAF smelters during the preheating and smelting stages.The key influencing factors of POPs formation during the preheating process of EAF steelmaking are put forward.It provides a theoretical basis for the reduction of POPs in the EAF steelmaking.The main results are as follows:1.The concentration level and characteristics of typical POPs-PCBs during preheating and smelting process of typical EAF steelmaking industry are expounded.The concentration range of dioxin-like PCBs(dl-PCBs)in the flue gas during the preheating phase from EAF steelmaking plant is 0.67?81.66 ng Nm^-3,and the concentration range of indicative PCBs is2.08?107.7 ng Nm^-3.The concentrations of dl-PCBs in fly ash during preheating and smelting stages are 18.4?1588 and 46.1?650.4 pg g^-1,respectively.The concentrations of indicative PCBs are 36.6?1475 and 212.8?636.9 pg g^-1.The results show that the preheating stage of EAF steelmaking is an important stage for PCBs generation.The distribution characteristics of PCBs congeners in different EAF steelmaking plants are similar,and the low-chlorinated congeners are the main ones.It is concluded that chlorination is an important way to form PCBs in EAF steelmaking.2.The concentration level and characteristics of new POP-PCNs emitted during the preheating and smelting process of EAF steelmaking are expounded.The concentration of PCNs in flue gas during the preheating stage from EAF steelmaking is 92.44?3473 ng Nm^-3.The emission levels of PCNs in fly ash during preheating and smelting are 1.05?15.18 ng g^-1 and3.44?6.32 ng g^-1,respectively,indicating that the preheating stage is an important stage of PCNs formation.Among the 57 congeners of PCNs,2-MOCN and 1-MOCN had higher concentrations.The concentration of PCNs homologues decreased with the increase of the number of chlorine substitutions.Moreover,there is a good correlation between the concentrations of PCNs and PCBs in fly ash(R=0.93),It is inferred that PCNs and PCBs have similar generation mechanisms in the EAF steelmaking.3.EAF steelmaking was identified as a potential source of Cl/Br-PAHs,and the emission level and characteristics of new POPs-Cl/Br-PAHs during the preheating and smelting process from typical EAF steelmaking were clarified.The concentration of Cl-PAHs and Br-PAHs in flue gas during the preheating stage from EAF steelmaking is 48.65?3164 and 2.93?258 ng Nm^-3,respectively.The highest concentrations of Cl-PAHs and Br-PAHs in fly ash reached 69.1 and10.05 ng g^-1.The characteristics of Cl/Br-PAHs in EAF steelmaking are not consistent with those in other thermal processes.9-Cl Phe/2-Cl Phe contributes the highest among the Cl-PAHs congeners from the flue gas,while the 1-Cl Pyr from the waste incineration process accounts for the highest proportion,reaching 50%.1-Cl Pyr is the highest proportion of Cl-PAHs in fly ash,while 9-Cl Phe/2-Cl Phe is the main congener in fly ash from secondary copper smelters.