In the steelmaking process using electric arc furnaces (EAF), heat transfer within the furnace chamber is a highly complex phenomenon dominated by radiation, accompanied by conduction and convection. The efficiency of heat transfer directly affects the melting rate of scrap, the lifespan of furnace lining, and overall energy consumption—making it a critical aspect of EAF operation.
1. Main Heat Transfer Paths in EAF Steelmaking
During steel production in an EAF, heat is transferred through several key routes:
- Direct radiation from the electric arc to the molten bath surface;
- Radiation from the arc to the furnace lining surface;
- Secondary radiation from the furnace lining to the molten bath;
- Mutual radiation between furnace walls and roof;
- Radiation from the molten pool surface to the furnace lining;
- Conduction and convection from the molten surface to the interior of the steel bath;
- Heat dissipation through furnace walls, doors, water-cooled components, and flue gas systems.
2. Characteristics at Different Melting Stages
In the early melting stage, solid scrap surrounds the arc, and most of the arc energy is absorbed directly by the scrap. The furnace lining receives relatively little radiation, reducing its thermal load. A higher input power leads to a faster melting rate at this phase.
As the melting process progresses, a molten bath of steel and slag forms. The arc radiates heat toward both the molten bath and the refractory lining. Specifically:
About 10% to 30% of the arc power is radiated directly to the bath surface;
The remaining 70% to 90% is radiated to the furnace lining and molten bath from the arc column, roughly split equally.
Radiation absorption depends on the blackness (emissivity) of materials:
- Slag: 0.5–0.6
- Molten steel: 0.65
- Furnace lining: 0.8–0.9
This makes the lining the most efficient absorber, heating to higher temperatures than the molten bath. Although the lining is not a heat source, it acts as a thermal medium, absorbing arc radiation and re-emitting it to the slag and steel. This explains the need for gradual heating during the initial furnace drying stage, to avoid lining damage.
3. Optimized Operation: Foam Slag and Thermal Efficiency
Operational strategies such as foam slag submerged arc operation can optimize thermal transfer:
- Increase slag emissivity;
- Reduce arc radiation to the lining;
This lowers the thermal load on the refractory, thereby extending lining service life and improving energy efficiency.
4. Heat Transfer Limitations in the Molten Bath
Since there is no significant vertical natural convection in the steel bath, and the arc’s electromagnetic stirring effect is localized, the entire molten pool remains nearly static. As a result, heat from the arc must transfer downward through conduction, which is relatively inefficient.
