Advantages of the Electric Bottom Tapping (EBT) Electric Arc Furnace

Advantages of the Electric Bottom Tapping (EBT) Electric Arc Furnace

Compared to the tapping through a trough, the EBT (Eccentric Bottom Tapping) technique for electric arc furnaces utilizes identical electrical equipment, and the upper part of the furnace body remains circular. However, the lower section of the furnace body features a nose-like elliptical cross-section. The tapping port is arranged at the base of the protruding nose-like section. A water-cooled block connects the protruding nose-like section of the lower part of the furnace body to the circular upper part. The furnace wall is assembled using water-cooled wall blocks to form a water-cooled furnace wall.

1. Numerous production practices have demonstrated that, compared to tapping through a taphole, the adoption of an eccentric bottom tapping electric arc furnace yields the following significant outcomes:

The system can thoroughly achieve slag-free tapping and the operation of steel and slag flow. The amount of steel flow in the furnace is generally controlled at 10% to 15%, while the slag flow rate can exceed 95%. Consequently, eccentric bottom tapping has become one of the essential technologies in the short process of "ultra-high power electric arc furnace - external refining - continuous casting" and in direct current electric arc furnaces, creating the necessary conditions for oxidizing tapping.

2. The water-cooled area of the electric arc furnace's water-cooled wall can be increased from 70% of the steel tapping slot to 87% to 90%, thereby enhancing the furnace lining's lifespan by 15% and expanding the furnace chamber diameter (the 45t furnace from the German BS company has expanded from the original 4.2m to 4.6m). The consumption of refractory materials can be reduced by 2.5 to 3.5 Kg/t, the cost of repairing and gunning the furnace lining can be reduced by 60%, and the furnace capacity can be expanded by 12.5%.

3. The inclination angle of the furnace body has been reduced from 42-45 degrees to 12-15 degrees, which can shorten the length of the furnace bus bar, thereby increasing the active power input into the furnace by 10%-33% and the power factor from 0.707 to 0.8. This adjustment shortens the smelting time by 3-7 minutes and reduces power consumption by 15%-30%.

4. Furthermore, the reduction in the inclination angle of the furnace body can simplify the furnace design (improving the stress conditions of connecting components such as non-magnetic support frames and cable connectors in the furnace bus bar, and reducing the mass of the tilting cradle), and also reduces the likelihood of electrode breakage.

5. By reducing the tapping time by 75%, the tapping temperature can be lowered by 30°C, thereby shortening the smelting time, reducing power consumption, decreasing electrode wear by 6%, and increasing productivity by 10% to 15%.

6. The steel tapping flow is short and vertical, concentrated without dispersion, which can mitigate the secondary oxidation and gas absorption of the steel flow during the tapping process. Coupled with the shortened tapping time, the content of hydrogen, oxygen, nitrogen, and inclusions in the steel is reduced. This also facilitates the adoption of ladle covering and argon protection techniques. The eccentric bottom tapping poses difficulties in mixing and stirring the molten steel near the tapping port, resulting in significant differences in composition and temperature between this area and other regions. Furthermore, maintenance of the furnace bottom is more challenging compared to tapping through a tundish.

The EBT electric furnace structure modifies the traditional electric furnace's taphole into a taphole box, with the taphole vertically positioned at the bottom of the taphole box. A taphole opening and closing mechanism is installed beneath the taphole to regulate its operation. Additionally, an operational port is centrally located on the top of the taphole box, facilitating the operation and maintenance of the taphole's packing.

The primary advantage of the EBT electric furnace lies in its realization of slag-free tapping and the increased utilization area of water-cooled furnace walls. The merits are as follows:

(1) Reduction in the angle of steel tapping.

Simplifying the tilting structure of the electric furnace: reducing the impedance of the furnace bus bar: increasing the usable area of the water-cooled furnace wall, thereby enhancing the lifespan of the furnace body. 缺

(2) Operation of retaining steel and slag.

The production of slag-free steel enhances the quality of the steel, facilitating refining operations. The retention of steel and slag is beneficial for electric furnace smelting and energy conservation.

(3) Steel tapping from the furnace bottom.

Reducing the tapping temperature conserves energy consumption; reducing secondary oxidation enhances the quality of steel; and prolongs the lifespan of the steel ladle.

Owing to the numerous advantages of the EBT electric furnace, it has rapidly gained popularity worldwide. Currently, when constructing electric furnaces, particularly those integrated with external refining processes, slag-free tapping is a prerequisite, and the EBT is the preferred choice.

The tapping operation of the EBT electric furnace. During tapping, the furnace is tilted approximately 5° towards the tapping side, and then the tapping mechanism is activated. The tapping port filler automatically falls under the static pressure of the molten steel, allowing the steel to flow into the ladle, thus achieving automatic pouring and tapping. When the molten steel reaches approximately 95% of the required amount, the furnace is quickly tilted back to prevent slagging. During the tilting process, about 5% of the molten steel and a small amount of slag also flow into the ladle. After the furnace is returned to its upright position (with 10% to 15% of steel and ≥95% of slag remaining in the furnace), the tapping port is inspected and maintained. The tapping port is then closed, the filler is added, scrap steel is loaded, and the arc is reignited for melting.