November 12, 2025
Detailed Introduction to Five Core EBT Smelting Processes
The Eccentric Bottom Tapping (EBT) electric arc furnace incorporates specific operational methodologies to optimize efficiency and quality. The following outlines five key smelting processes integral to EBT furnace operation.
1. Rapid Melting and Heating Operation
This is the primary function of the electric arc furnace, commencing immediately after the first scrap charge. The objective is to melt the scrap and raise the molten steel to tapping temperature in the shortest possible time. EBT furnaces employ intensified smelting techniques to achieve this, including:
Maximum Power Input: Supplying electrical power at the highest possible rate.
Oxy-Fuel Burner Assistance: Using burner nozzles to deliver concentrated heat, accelerating scrap melt-down.
Oxygen Injection & Stirring: Blowing oxygen to decarburize and generate exothermic heat, while also agitating the bath.
Bottom Gas Stirring: Injecting inert gas (e.g., Ar, N₂) through porous plugs to homogenize temperature and composition.
Foamy Slag Practice: Creating an insulating, foamy slag layer to improve arc stability and thermal efficiency, thereby accelerating heating.
2. Dephosphorization Operation
Phosphorus removal in the EAF is managed by controlling slag oxidation (FeO content), basicity (CaO/SiO₂ ratio), and temperature. Key operational strategies include:
Enhanced Oxygen Input: Intensive oxygen blowing and oxy-fuel burner use to increase the FeO content of the early slag, promoting phosphorus transfer from metal to slag.
Early Formation of a Highly Oxidizing, Basic Slag: Utilizing the lower initial bath temperature—which favors dephosphorization—to form an effective slag as soon as possible.
Slag Removal (Slag-Off): Removing the initial phosphorus-rich slag promptly and replacing it with a fresh slag to prevent "phosphorus reversion" (return of P to the steel) during subsequent temperature increases or tapping.
Powder Injection: Directly injecting lime (CaO) and fluorspar (CaF₂) powder into the molten pool with an oxygen carrier stream. This can achieve dephosphorization rates up to 80%, with simultaneous desulfurization rates nearing 50%.
Slag-Free Tapping (EBT Advantage): The EBT design allows for minimal slag carry-over into the ladle. Controlling slag volume to ~2 kg/t steel significantly limits phosphorus reversion. With a slag containing 1% P₂O₅, phosphorus reversion can be kept to ≤0.001%.
Target Control: The final target phosphorus content at tap is set below 0.02%, considering subsequent alloying and final product specifications.
3. Decarburization Operation
EBT operations often employ a high-carbon charge strategy for several critical purposes:
Protection of Metallic Iron: During oxygen blowing in the melt-down phase, carbon oxidizes preferentially to iron, reducing metallic yield loss (burning).
Lower Melting Point: Carbon lowers the melting point of scrap, accelerating the formation of a liquid pool.
Enhanced Bath Agitation: The carbon-oxygen (C-O) reaction produces CO gas, which vigorously stirs the molten pool. This promotes slag-metal reactions and facilitates early dephosphorization.
Refining and Purification: During the refining/heating period, a sustained, active C-O reaction (carbon boil) expands the slag-metal interface, aids in further dephosphorization, homogenizes bath temperature and composition, and promotes the flotation of gases and inclusions.
Foamy Slag Generation: The CO gas is essential for creating and maintaining an effective, insulating foamy slag layer, which dramatically improves thermal efficiency and heating rates.
4. Alloying Operation
Alloying in EBT practice is primarily conducted in the ladle during tapping ("ladle alloying"). This approach offers greater control and yield. Key principles are:
Ladle Addition Standard: Most ferroalloys are added to the steel stream as it fills the ladle.
Furnace Additions for Specific Alloys: Non-oxidizing, high-melting-point elements like Nickel (Ni), Tungsten (W), and Molybdenum (Mo) may be added directly to the furnace to ensure complete dissolution.
Consideration of Retained Steel ("Heel"): When employing a steel retention practice, the chemical influence of the previous heat's residual metal on the next heat's composition must be carefully calculated.
Temperature Management: Tapping temperature must be adjusted to compensate for the cooling effect of large alloy additions. Proper ladle pre-heating and post-tap heating (e.g., via ladle furnace) are crucial to maintain temperature and improve alloy yield.
Two-Stage Adjustment: Ladle alloying during the tap is a pre-alloying step. Final, precise composition trimming is completed in a secondary refining station (e.g., Ladle Furnace). Pre-alloying targets the middle of the specification range to allow for smooth, controlled final adjustments.
5. Temperature Control
Precise thermal management is fundamental to successfully executing all metallurgical processes. Different stages have specific temperature requirements:
Dephosphorization: Favors lower temperatures (e.g., < 1550°C). This thermodynamic advantage is why dephosphorization is emphasized early in the process, coinciding with the initial melt-down phase.
Oxidation/Refining: Requires a higher bath temperature (typically > 1550°C) to sustain an active carbon-oxygen boil for purification and efficient heating.
Tapping & Downstream Processing: The furnace must provide sufficient superheat to compensate for thermal losses during tapping, secondary refining (LF, VD), and transfer to the caster. The required initial furnace temperature is calculated based on the specific downstream process route and steel grade.
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