DC Electric Arc Furnace

Overview of DC Arc Furnaces

Double electrodes DC electric arc furnace offer superior stability and unidirectionality compared to AC ones, significantly benefiting heat transfer in metallurgical processes. Theoretical analysis indicates that replacing alternating current with direct current represents a major technological innovation. Since direct current avoids the zero-crossing issue, arc stability improves and grid interference is consequently reduced. The method of smelting metals using direct current in DC arc furnaces is fundamentally the same as in AC arc furnaces. However, due to the high heat generated by the anode on the charge side, the electrothermal conversion efficiency of the DC arc is higher.

Operating Principle of the Equipment

AC power from the grid is supplied to the DC flexible excitation source via a rectifier transformer. Through the flexible and variable characteristics of the DC flexible excitation source, controllable DC power is output externally. This controlled DC power enters a high-power DC plasma generator, which produces ultra-high-temperature plasma—a fourth-state matter—utilizing its extreme temperatures up to 4000°C to instantly heat and melt materials within the furnace. The furnace chamber maintains a semi-sealed negative pressure environment, allowing continuous inflow of external cold air. Fumes generated during melting are drawn upward with the incoming air, collecting at the furnace top. They then pass through the flue into a multi-tube cooler, cyclone dust collector, baghouse filter, activated carbon adsorption unit, and spray tower. This sequence achieves smoke-free, non-toxic, odorless, and acid-gas-free operation. Dust particles filtered by the collection system can be returned to the furnace for remelting, while the filtered clean gas is vented.

Advavtages of DC Electric Arc Furnace

1. DC furnaces achieve higher heat transfer efficiency than AC furnaces, reducing power consumption by 10–15% compared to traditional AC models.
2. Graphite electrode consumption is reduced by 35% relative to AC furnaces.

3. Eliminates investment in reactive power compensation devices required by AC furnaces.
4. Delivers 20% higher production capacity than AC furnaces at equivalent power ratings.
5. Causes no interference or pollution to the power grid.
6. The integrated rectifier power supply employs a three-phase full-bridge rectifier to convert AC into stable, reliable DC. The rectifier unit utilizes independent closed-loop cooling equipment for safe and reliable operation.
7. PLC control enables high automation, rapid heating rates, and stable, reliable production rhythms.
8. During smelting, voltage levels can be freely adjusted without stopping the furnace or altering power output, enabling arbitrary modification of arc length to achieve both open-arc and submerged-arc functions. Alternatively, power output can be freely adjusted while maintaining constant voltage.
9. To address differing temperatures at the positive and negative electrodes, we developed a polarity reversal system. Electrode polarity can be freely switched during smelting, ensuring uniform melt pool temperature and significantly reducing smelting time.
10. DC Power Supply Main Control Board (proprietary intellectual property) features opto-isolation to effectively shield control circuit stability from strong magnetic field interference at production sites. This board incorporates overvoltage, overcurrent, phase loss, and high-temperature protection to prevent equipment damage from short circuits. Upon fault detection, these safeguards block rectifier trigger pulses, limiting fault surge currents within preset limits.
11. This equipment incorporates electrolytic functionality. During smelting, metal ions in the molten bath are drawn toward the negative electrode through electrolysis, enhancing product yield and purity. This process significantly facilitates the enrichment of high-value metals such as rare and precious metals.

Enrichment of trace ions

12. This equipment features electromagnetic stirring functionality. The direct current furnace maintains stable current direction and constant electromagnetic field orientation. Under magnetic field propulsion, the molten material continuously circulates in a single direction, creating electromagnetic stirring that ensures thorough melting without dead zones. This results in high product quality and high yield rates.

AC Furnace

13. DC furnaces exhibit low flicker effects and noise levels, offering significant advantages for power grids and operators. Their flicker effect is only 50%–70% that of AC furnaces, while noise during submerged arc operation is over 20 dB lower than AC furnaces.
14. Heat concentration keeps the molten pool near the crucible zone close to the furnace bottom, minimizing thermal radiation in the slag line area. This provides excellent protection for refractories, extending furnace wall refractory lifespan. In AC equipment, the arc forms a 45° angle with the graphite electrode, easily striking furnace walls and damaging refractories. In contrast, the arc angle in DC equipment is 30°, preventing contact with the furnace wall and eliminating hot spots on the wall surface, thereby extending the service life of refractories.
15. Single-electrode equipment suffers from a bottom anode effect, leading to frequent burn-through of the bottom anode. Dual-electrode equipment eliminates this bottom anode effect, completely resolving the issue of bottom anode damage common in single-electrode systems.

16. During smelting, unexpected power outages may cause an insulating crust to form on the molten surface. Single-electrode DC furnaces cannot restart arcing under such conditions and require furnace disassembly. In contrast, double-electrode DC furnaces can resume arcing by adding coke or other arc-initiating materials beneath the electrodes.
17. The equipment employs thyristor rectification. During operation, the thyristors remain fully conductive, converting AC to DC without power regulation. They rapidly switch off during overcurrent or overvoltage events, providing immediate protection.