Differences Between Submerged Arc Furnace and Electric Arc Furnace
The Submerged Arc Furnace (SAF) and the Electric Arc Furnace (EAF) are both industrial electric furnaces that utilize electric arc energy for smelting. The key difference lies in their operating principles, design focus, and primary applications. Fundamentally, a Submerged Arc Furnace is a specialized type of electric arc furnace optimized for a specific process.
(1) Electric Arc Furnace (EAF)
An EAF is a broad category of furnace that uses the high-temperature heat generated by an electric arc to melt ores and metals. Industrial EAFs are classified by their heating method:
Direct Arc Furnace: The arc is struck directly between the electrode(s) and the metallic charge. This is the most common type, predominantly used for steelmaking and refining ferrous and non-ferrous metals.
Indirect Arc Furnace: The arc is struck between two electrodes, and the charge is heated by radiation. This type is less common and used for melting non-ferrous metals like copper alloys.
Submerged Arc Furnace (SAF): A direct arc furnace where the electrodes are typically buried within the charge burden. Heating combines resistive (Joule) heating of the conductive charge material with arc heat beneath the electrodes. This design is specialized for the carbothermic reduction of ores.
The most prevalent EAF is the direct arc furnace for steelmaking. It features a refractory-lined vessel with a water-cooled roof through which graphite electrodes are lowered. Its use of electricity allows precise control of the furnace atmosphere, making it ideal for producing alloy steels. Advances in technology have made EAFs cost-competitive for large-scale production of both carbon and alloy steels.
(2) Submerged Arc Furnace (SAF)
An SAF is a high-power-consumption industrial furnace designed specifically for reduction smelting. It uses carbon or magnesia-based refractories and typically employs continuous self-baking Söderberg electrodes. Its defining operational characteristic is that the electrodes are embedded in the solid or semi-solid charge, creating a "submerged" arc condition. This facilitates the reduction of metal oxides (e.g., in ores) to produce ferroalloys (ferrosilicon, ferromanganese), silicon metal, calcium carbide, and phosphorous.
A critical aspect of SAF design and operation is managing its electrical characteristics. The SAF operates as a very high-current system (tens of thousands of amperes). Over 70% of the furnace's system reactance originates in the low-voltage, high-current busbar system known as the short network. This results in a naturally low power factor (typically 0.7-0.85), leading to significant reactive power consumption, reduced transformer efficiency, and potential utility penalties.
Furthermore, inherent imbalances in the short network layout and charge distribution can create severe three-phase power imbalance (up to 20%+), reducing smelting efficiency and increasing specific energy consumption. Therefore, optimizing the short network's power factor and balancing the phases are paramount for energy efficiency.
Power Factor Correction: High-Voltage vs. Low-Voltage Compensation
High-Voltage (Primary Side) Compensation: A common but limited approach. It improves the power factor on the utility grid side to avoid penalties but does not address the reactive power flow within the furnace's own short network. It does not solve phase imbalance or increase the effective power delivered to the furnace crucible.
Low-Voltage (Secondary Side) Compensation: A more effective solution installed directly on the short network. Its advantages include:
Modern systems use advanced controllers (e.g., BWKN-3500 type) with solid-state switches for fast, reliable, and maintenance-free per-phase, multi-step compensation, directly targeting the furnace's low power factor and imbalance for maximum production and energy savings.
Conclusion:
While both are arc furnaces, the EAF is fundamentally a melting unit for refining metals, and the SAF is a chemical reduction reactor for producing metals and alloys from their ores. The operational need to bury the electrodes in a conductive charge burden defines the SAF's unique design challenges, particularly concerning its high-current short network and the associated electrical optimization requirements.
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