In steelmaking, the melting stage of an electric arc furnace (EAF) is the period when energy input is most concentrated. It plays a decisive role in melting efficiency, power consumption, and overall furnace performance. The characteristics of heat transfer in this stage are closely related to the charge condition, arc coverage, and refractory temperature.
1. Initial Stage: Arc Covered by Scrap
When steel scrap is charged into the furnace, the electrodes strike an arc above the solid charge and near the furnace roof, radiating intense heat. If the scrap is arranged and distributed properly, the electrodes quickly penetrate into the charge, covering the arc with the scrap.
At this stage, the charge directly absorbs the arc’s radiant energy, with minimal heat exchange involving the furnace lining. This allows the furnace to operate with maximum voltage and arc power, while auxiliary burners run at full capacity to accelerate heating and melting.
2. Middle and Final Stages: Arc Exposure and Lining Involvement
As the scrap melts, the arc becomes exposed to the molten bath, and the furnace lining begins to participate in heat exchange. The lower-temperature zones of the molten bath are mainly heated by radiation from the lining.
Because the angle between the furnace wall and the bath is slightly greater than 90°, and the furnace roof is nearly parallel to the bath surface, the roof plays a dominant role in heating the bath.
Arc power distribution can be expressed as:
P_arc = P_useful + P_loss + P_storage
P_useful – Energy heating the slag and molten steel, including direct arc radiation and reflected radiation from the lining;
P_loss – Heat lost through the lining and other pathways;
P_storage – Energy absorbed by the lining, raising its temperature.
3. Influence of Temperature Changes on Heat Transfer
At the beginning of the melting stage, the large temperature difference between the molten bath and the lining enables significant radiant heat transfer. However, as bath temperature rises:
P_useful decreases;
P_loss and P_storage increase;
Power consumption rises, and lining temperature increases.
When the lining temperature approaches the refractory limit, damage occurs—especially to the furnace roof.
4. Energy-Saving and Lining Protection Strategies
To reduce heat loss, lower power consumption, and extend the service life of the furnace lining and roof, the arc power should be gradually reduced as the molten bath temperature increases.
In actual steelmaking, weak points in the lining often appear when about 70% of the scrap is melted, leading to “burn-through” conditions caused by the above heat transfer factors.
