Characterization of Process Conditions in Industrial Stainless Steelmaking Electric Arc Furnace Using Optical Emission Spectrum Measurements

Emission spectroscopy is a potential method for gaining information on electric arc furnace (EAF) process conditions. Previous studies published in literature on industrial EAF emission spectra have focused on a smaller scales and DC arc furnaces. In this study emission spectrum measurements were conducted for 140t AC stainless steelmaking EAF at Outokumpu Stainless Oy, Tornio Works, Finland. Four basic types of emission spectra were obtained during the EAF process cycle. The first one is obscured by scrap steel, the second is dominated by thermal radiation of the slag, the third is dominated by alkali peaks and sodium D-lines and the fourth is characterized by multiple atomic emission peaks. The atomic emission peaks were identified by comparing them to the NIST database for atomic emission lines and previous laboratory measurements on EAF slag emission spectra. The comparison shows that the optic emission of an arc is dominated by slag components. Plasma conditions were analyzed by deriving plasma temperature from optical emissions of Ca I lines. The analysis suggests that accurate information on plasma conditions can be gained from outer plasma having a plasma temperature below 7000 K (6727 °C).