Features of the EBT Electric Arc Furnace

Features of the EBT Electric Arc Furnace

The structural hallmark of the Eccentric Bottom Tapping (EBT) electric furnace is the replacement of the traditional tapping spout with a dedicated tapping box. The tap hole itself is positioned vertically downward at the bottom of this box.

The lower section of the tap hole is fitted with a dedicated opening and closing mechanism. The top center of the tapping box features an operational port to facilitate the maintenance and replacement of the tap hole filler material.

Advantages of the EBT Electric Arc Furnace

The primary advantage of the EBT design is its ability to achieve slag-free tapping while simultaneously increasing the usable area for water-cooled panels on the furnace wall. The specific benefits are as follows:

(1) Reduced Tapping Tilt Angle: This simplifies the furnace tilting mechanism, reduces impedance in the short network, increases the coverage area of the water-cooled sidewalls, and extends the overall furnace lining life.

(2) Slag Retention and Steel Tapping: Slag-free tapping improves final steel quality and benefits subsequent ladle refining operations. Retaining slag and a portion of molten steel in the furnace aids the next heat's smelting process and improves energy efficiency.

(3) Bottom Tapping: This method allows for a lower tapping temperature, saving electrical energy. It also reduces the secondary oxidation of the steel stream, further enhancing quality, and increases ladle lining life.

Due to these significant advantages, EBT technology has been rapidly adopted worldwide. For new electric furnace installations, especially those integrated with external ladle refining, slag-free tapping is now a standard requirement, making EBT the preferred design.

EBT Tapping Operation

During tapping, the furnace is tilted approximately 5° toward the tapping side. The tap hole mechanism is then opened. The hydraulic pressure of the molten steel causes the filler material to dislodge automatically, allowing the steel to flow into the waiting ladle in a controlled stream, enabling automatic pouring. When approximately 95% of the target steel has been tapped, the furnace is quickly tilted back to prevent slag carryover. During this return tilt, the remaining ~5% of steel and a small amount of slag flow into the ladle. After the furnace is returned to its upright position (leaving about 10-15% of the heat as liquid heel and ~95% of the slag), the tap hole is inspected, maintained, closed, and refilled with new filler material. The furnace is then charged with scrap, and arcing for the next melt begins.

The EBT Smelting Process Paradigm

The adoption of EBT has fundamentally shifted the role of the electric arc furnace. It has evolved from a unit that performed the complete set of operations—melting, oxidation, reduction refining, and final temperature/composition/quality control—into a high-efficiency "chemical reactor" focused primarily on melting, heating, and essential refining functions (notably dephosphorization and decarburization). Process operations that are more efficiently performed at lower power intensity, such as precise composition adjustment and inclusion morphology control, are transferred to the ladle refining furnace.

The ladle furnace provides optimal conditions for refining the initial molten steel, allowing for strict control of composition, temperature, inclusions, and gas content to meet increasingly stringent customer quality demands.

To maximize efficiency, dephosphorization and even partial decarburization are advanced as much as possible into the melting period. The subsequent oxidation refining and heating phase primarily focuses on carbon control. Alloying elements that are easily oxidized and required in large quantities are typically not added during this stage but are deferred to the ladle furnace. This streamlined approach is particularly beneficial for shortening the overall tap-to-tap time, reducing consumable costs, and boosting productivity.

The EBT practice of retaining a steel and slag heel at the start of melting provides an immediate molten pool. This, combined with enhanced oxygen injection and bottom stirring, creates ideal conditions for advancing metallurgical reactions early in the cycle. From the perspective of maximizing productivity and minimizing costs, the modern EBT furnace aims for the shortest possible melting time, the highest heating rate, and the minimization of all non-productive auxiliary times (such as furnace repair, charging, electrode replacement, and tapping) to achieve optimal economic performance.

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