DC Submerged Arc Furnaces

The core strengths of DC submerged arc furnaces lie in three key dimensions: energy consumption, operational stability, and cost control. These advantages can be broken down into the following five aspects:

1. Lower Energy Consumption and Higher Energy Utilization Efficiency

DC current exhibits no skin effect, allowing uniform current distribution throughout the furnace charge. This eliminates localized overheating and energy waste caused by the skin effect in AC current. – Compared to AC submerged arc furnaces, DC furnaces typically achieve 5%-10% higher electrical efficiency. For a 100,000-ton annual industrial silicon production line, this translates to millions of kilowatt-hours saved annually. – Higher power factor, generally exceeding 0.9-0.98, eliminates the need for substantial reactive power compensation equipment, further reducing overall energy consumption.

DC EAF Natural Power Factor up to 0.95-0.98

2. More stable furnace conditions and enhanced product quality control

DC arcs exhibit minimal length and temperature fluctuations, far less affected by grid voltage variations than AC arcs, resulting in a more uniform temperature distribution within the furnace. – Stable arcs reduce abnormal conditions like “material collapse” and “spattering,” enabling more complete material reactions and narrowing product composition variations by 10%-15%. – For high-purity products (e.g., high-purity industrial silicon), stable furnace conditions effectively reduce impurity content and improve product yield rates.

3. Reduced electrode consumption and lower consumable costs

DC arcs cause less electrode erosion due to stable operation without frequent flickering and slower oxidation rates on electrode surfaces under DC current. – Electrode consumption per ton is 15%-30% lower than AC submerged arc furnaces. Taking ferrosilicon production as an example, AC furnaces consume approximately 50kg of electrodes per ton of product, while DC furnaces can reduce this to below 35kg. Calculated annually, this yields significant savings in electrode procurement costs.

DC Submerged Arc Furnaces

4. Reduced grid impact and enhanced environmental performance

DC submerged arc furnaces deliver stable current output, eliminating grid harmonic issues caused by three-phase imbalance in AC equipment. This minimizes impact on both plant and surrounding power grids, eliminating the need for additional harmonic mitigation equipment. – Reduced electromagnetic interference and operational noise: AC furnaces generate strong electromagnetic radiation due to alternating arcs, whereas DC furnaces reduce radiation by over 40%, better meeting modern factory environmental and occupational health standards.

5. Extended furnace lining lifespan and reduced maintenance costs

The relatively fixed “anode spots” of DC arcs prevent the localized repeated erosion and high-temperature damage caused by alternating polarity in AC arcs. – Average furnace lining lifespan increases by 20%-30%. For large ferroalloy furnaces, AC furnace lining replacement cycles occur approximately every year, while DC furnaces extend this to 14-16 months, reducing downtime for maintenance and refractory material consumption.

DC Submerged Arc Furnaces

DC submerged arc furnace is the application of direct current to the smelting of the submerged arc furnace. Its main feature is the use of graphite electrodes or self-baking electrodes, and the bottom of the furnace is connected to one pole of the power supply, and the bottom of the furnace is both a conductor and a smelting crucible.

The main heat conduction mechanism of the DC electric furnace is direct and stable unidirectional convection. This heat transfer is superior to that of AC arcs in metallurgical processes. It has applications in the production of ferrochromium, ferrosilicon, silicon and ferromanganese in I industry.

Advantage
Compared with the AC submerged arc furnace, the direct current submerged arc furnace has the advantages of simple structure (one electrode is commonly used in small and medium-sized direct current submerged arc furnaces, and the hood part is well sealed, which is convenient for maintenance and flue gas treatment), and the arc is stable (its flicker effect is only 50%~70% of the AC furnace), concentrated power, high thermal efficiency (the center temperature of the DC SAF electrode is high, the heat is concentrated, it is easy to bury the electrode deeply, and the bottom of the furnace is not easy to rise), high power factor (the natural power factor of the DC submerged arc furnace can be up to 0.94~0.96) and other characteristics. And it has the advantages of low smelting power consumption, low electrode consumption (electrode consumption is about 30% to 50% of AC furnace), low operating noise (noise during submerged arc operation is more than 20dB lower than AC submerged arc furnace), and high production efficiency.

Structure
Structural characteristics of once-through submerged arc furnace
The structure of DC SAF is basically similar to that of AC submerged arc furnace. The main electrical equipment includes rectifier transformer, rectifier cabinet, high and low voltage electrical equipment and electronic control system.

The main mechanical equipment includes single-phase self-baking electrode or graphite electrode, electrode holder, electrode lifting structure and electrode pressing and releasing device, semi-closed low smoke set, conductive furnace body, hydraulic system, water cooling system, feeding device and smoke exhaust system, etc. .

The self-baking electrode or graphite electrode used in the DC submerged arc furnace is connected with the negative electrode (cathode) of the rectifier, and the “bottom electrode” is connected with the positive electrode (anode) of the rectifier. Hollow electrodes are commonly used on the cathode to add cold fine powder to the end of the electrode to reduce the temperature of the arc zone at the end of the electrode, thereby further reducing the consumption of the electrode.

The special part of the structure of the DC submerged arc furnaces is the conductive bottom and the bottom anode, which are not only the melting crucible, but also an input end of the DC power supply.

The conductive furnace bottom should have good electrical conductivity to reduce power loss; good insulation to ensure safe production and high temperature in the reaction zone; uniform electrical distribution to make the temperature distribution of the smelting molten pool relatively close; long service life, to Reduce downtime maintenance and replacement manufacturing, and obtain higher economic benefits. Therefore, the conductive furnace bottom and its anode technology are the key to the design of the DC reduction furnace.

DC submerged arc furnace can be divided into single electrode, double electrode and three electrode electric furnace.

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