Assessment of Physicochemical Properties of Electrical Arc Furnace Slag and Their Effects on Foamability
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SLAG foaming can be performed in an electric arc furnace (EAF). This has several advantages including protection of the metal bath, enhanced post combustion ratio, shielding of the electrical arc, reduced arc flares, and reduced erosion of the refractory in the furnace. Slag foaming can decrease electric power consumption by 3 to 10 pct in EAF operation because foamy slag contributes to post combustion and heat transfer, which are key parameters to an energy efficient process, as well as decreased refractory consumption by 25 to 63 pct.[1] Fedina et al.[2] reported an energy saving effect of 10 to 30 kW/ton due to well-controlled slag foaming in 150 ton EAF process. Fruehan[3] reported an increase in efficiency in the range of 60 to 90 pct with slag foaming compared to 40 pct without slag foaming. However, slopping and physical entrapment of steel droplets from excessive gas generation in a highly foamy slag can
JUNG HO HEO is with the Research & Development Center, LSNikko Copper, Ulsan, 44997 Korea and also with Department of Materials Engineering, Hanyang University, Ansan 15588, Korea. JOO HYUN PARK is with the Department of Materials Engineering, Hanyang University. Contact e-mail: [email protected] Manuscript submitted March 24, 2019.
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adversely affect EAF process performance. Thus, control of slag foaming is very important for effective EAF operation. Early studies on foaming behavior were performed in aqueous solutions at room temperature by Bikerman.[4,5] Subsequent to these studies, Fruehan’s group has contributed significantly to our understanding of the foaming behavior of metallurgical slags at high temperatures.[6–12] Foaming behavior in terms of the foaming index (R), which is equal to the retention or traveling time of gas in the slag, was investigated in basic oxygen furnace (BOF) and EAF slags, viz. CaO-SiO2-FetO-MO (MO = MgO, Al2O3, P2O5, CaF2, MnO, etc.). The effects of slag composition, temperature, solid particles, and bubble size on foaming index were evaluated. Foaming index (or foam stability) was reported to be strongly affected by slag physical properties such as viscosity, surface tension, and density via dimensional analysis based on the Buckingham p theorem.[13] Specifically, an increase in viscosity enhanced foam height and foam stability by suppressing the rate of liquid drainage in the foam. A decrease in surface tension decreased the internal energy of the foam, leading to an increase in foam stability and large amounts of small spherical bubbles. Other researchers have discussed foaming behavior from the perspective of surface chemistry, such as surface elasticity and Marangoni elasticity.[14–16]
It has been argued that slag foaming should be considered under dynamic conditions rather than static (or steady state) conditions because the actual operation is performed under complicated conditions such as the presence of surface active elements, refractory corrosion, imbalances in temperature and slag composition, various rate of gas generation
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