Why DC Electric Arc Furnaces Better than AC

About Electric Arc Furnaces

Electric arc furnaces on the market are broadly categorized into DC arc furnaces and AC arc furnaces based on their current type. Each type is further classified by arc length into open-arc furnaces and submerged-arc furnaces.

Details of AC Electric Arc Furnace

The AC arc furnaces structure is relatively simple: three-phase AC power connects to three electrodes without complex rectifier circuits, resulting in lower costs. Price is a key advantage of AC furnaces. However, due to the inherent characteristics of alternating current, the arc light undergoes a continuous cycle of ignition, extinction, re-ignition, and re-extinction—meaning the arc is unstable. Additionally, AC furnaces exhibit a low power factor, averaging 0.85, meaning 15% of electrical energy is wasted. This necessitates reactive power compensation device to raise the factor to 0.9.

Furthermore, The AC furnace is meticulously designed based on specific raw material characteristics, prohibiting arbitrary changes to feedstock properties. For example, suppose the iron grade in your raw material was designed at 55% during the initial design phase, but you later obtain better material with an iron grade of 80%. In that case, your furnace becomes unusable and must be adjusted to process material with a grade of around 55%. The arc length in AC furnaces also cannot be arbitrarily altered. For AC furnaces, the choice between open arc and buried arc operation is fixed; only one mode can be selected.

Details of DC Electric Arc Furnace

The DC furnaces require rectifier circuits to convert AC to DC. Under DC conditions, the mineral heating process avoids repeated ignition and extinction, maintaining a stable state. The power factor of DC furnaces typically exceeds 0.9. Based on electrode configuration, DC furnaces are categorized as single-electrode or dual-electrode types.

Defect of Single-electrode furnaces

Single-electrode furnaces feature a single graphite electrode at the top (negative electrode), with the positive electrode positioned at the furnace bottom (bottom electrode). Dual-electrode furnaces have both positive and negative graphite electrodes located above the furnace. Most DC furnaces on the market are single-electrode types. However, single-electrode furnaces suffer from a significant issue: the bottom electrode is prone to damage. Since the bottom electrode must contact the bottom graphite bricks, which in turn must contact the raw materials inside the furnace, extremely high temperatures occur during smelting. Under continuous production, the temperature of the graphite bricks can exceed 1000°C, causing the bottom electrode to melt due to the intense heat.

Once melted, the bottom electrode becomes unusable, necessitating its replacement and the rebuilding of the refractory lining. For small experimental furnaces, a single replacement is manageable. However, for large industrial furnaces, replacing the furnace bottom takes at least 15 days, resulting in substantial losses.

Advantages of dual-electrode Electric Arc Furnace

To resolve the single-electrode electric arc furnace, YND dedicated itself to developing dual-electrode EAF, which completely resolves the problem of bottom electrode melting. However, due to differing temperatures beneath the positive and negative electrodes, prolonged operation can lead to uneven melting—one side fully molten while the other remains solid. To counter this, we developed a polarity-switching system that periodically reverses electrode polarity, ensuring uniform melting temperatures.

YND DC EAF power factor of at least 0.95

Natural Power Factor

YND DC EAF power factor achieves at least 0.95. While this is not just a little higher than 0.9, the underlying technology is fundamentally different. It’s akin to automotive engine thermal efficiency: while other brands achieve only 0.35–0.37, Toyota engines reach 0.4. This requires substantial investment in research and development—the essence of technological superiority.

The exceptional operational flexibility of YND DC EAF

The primary advantage of YND DC EAF lies in its exceptional operational flexibility. It allows arbitrary adjustment of arc length, enabling both open-arc and submerged-arc processes. Current intensity can be freely modified without altering arc length. Consequently, our equipment can smelt any material you can find. You can process any ore, any metal, or even solid and hazardous waste. For instance, if you find ferroalloy smelting profitable now, you can do that. Should the market shift and precious metal ore processing become lucrative, you can immediately switch to smelting precious metals without replacing equipment.