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Electric furnace upgrade and renovation

The electric furnace upgrade and renovation represents another significant project aimed at comprehensively enhancing production capacity, following the earlier completion of the continuous casting machine’s upgrade and renovation. After the continuous casting machine was upgraded in 2006, the length of thin slab billets increased from 6.5 meters to 9.7 meters, and the casting speed rose from 200 inches per minute to 230 inches per minute. To further boost the casting machine’s production capacity, the thickness of the thin slab billets was increased from 58 millimeters to 60 millimeters. The increase in slab thickness inevitably necessitated a corresponding rise in rolling torque; therefore, the drive system of the first stand of the rolling mill underwent an electric furnace upgrade and renovation.

The SDI steel plant plans to open the furnace top cover at one go after upgrading and retrofitting the electric furnace, and continuously feed all charge materials into the furnace to achieve the following objectives:

① Reduce the power outage delay caused by adding the second batch of charge by 3.5 minutes, or shorten the smelting time by 3.7%.

② More effectively input power to achieve single-pass penetration and eliminate the occurrence of unstable penetration caused by materials in the second basket.

③ Ensure a tight seal on the furnace top to conserve energy (estimated energy savings up to 20 kWh per ton of steel) and enable preheating of the next batch of scrap steel.

In addition, it is hoped that after the electric furnace is upgraded and renovated, the amount of residual steel remaining in the furnace will be more reasonable. This will facilitate the smelting process in the next furnace and reduce the amount of slag carried into the ladle during tapping. However, after the furnace is reorganized, there may be some negative impacts: the increase in water-cooled panels and the longer length of graphite electrodes could lead to greater heat loss and a higher frequency of electrode breakage.

Since the furnace is equipped with dual furnace shells and the scrap basket has not been modified, the implementation of two scrap baskets can be achieved by using the existing pair of grab-type scrap baskets and ladles. This is because while the first furnace shell is being loaded, tapped, or maintained, the other furnace shell can be used for arc initiation/melting. Therefore, this solution will not cause any delays in the production process.

New furnace design

Considering the space constraints in the furnace workshop—such as the location of pipelines and the turnover platform—it was decided that the new furnace would not increase in diameter but would instead only extend the height of the furnace shell, allowing the steel plant to reuse the existing furnace top. To accommodate the increased volume of scrap steel in the second basket and the residual steel remaining in the furnace, it was determined that the furnace shell’s volume should be expanded to 2,260–6,000 cubic feet.