Submerged Arc Furnace: Structural Design, Operating Principles, and Core Equipment Analysis

Overview and Smelting Principles of the Submerged Arc Furnace

A Submerged Arc Furnace (SAF) is a large-scale electric smelting furnace that utilizes electrical energy to carry out high-temperature reduction smelting. It is widely used in the production of ferrosilicon, silicomanganese, high-carbon ferrochrome, silicon metal, calcium carbide, and other ferroalloy products. As a critical piece of equipment in the metallurgical industry, the SAF enables the conversion of metal oxides contained in ores into target metals or alloys through high-temperature reduction reactions, facilitating efficient resource utilization and large-scale industrial production.

The operating principle of a submerged arc furnace is based on submerged-arc smelting technology and selective oxidation-reduction reactions. During production, raw materials—including ores, carbonaceous reducing agents, and fluxes—are continuously charged into the furnace according to predetermined process ratios. Self-baking electrodes are immersed deep within the burden, creating a submerged-arc condition. Once electrical current is supplied through the electrodes, both arc heat and resistance heat generated within the burden act simultaneously to progressively heat, melt, and reduce the charge materials.

Under high-temperature conditions, metal oxides in the ore react with carbon, producing the desired metallic elements along with gaseous by-products such as carbon monoxide. Molten metal accumulates at the furnace hearth and is periodically tapped through the taphole, while slag is intermittently discharged through a dedicated slag outlet. This process enables a production mode characterized by continuous charging and smelting with periodic tapping operations.

Main Structural Components of a Submerged Arc Furnace

From a structural perspective, a submerged arc furnace is a highly integrated system combining mechanical, electrical, hydraulic, automation, and environmental protection technologies. Its principal components include the furnace body, furnace roof, electrode system, secondary conductor (short network) system, power supply system, cooling water system, off-gas handling system, and charging/tapping equipment.

The furnace body serves as the foundation of the entire installation and consists of a steel shell and refractory lining. The steel shell bears the mechanical loads and thermal stresses generated during operation and is typically designed as a cylindrical welded structure to ensure adequate strength and stability. The refractory lining, constructed from materials such as high-alumina bricks, magnesia bricks, and carbon bricks, protects the furnace from molten metal and slag attack, thermal shock, and excessive heat loss, ensuring long-term operational reliability.

The furnace roof is another essential component, particularly in closed-type SAFs. It is generally composed of a water-cooled steel framework lined with refractory materials. Openings for electrodes, temperature monitoring, and off-gas extraction are incorporated into the roof structure. In addition to minimizing heat loss, the roof facilitates the efficient collection of high-temperature process gases, thereby improving overall energy utilization. Together with the hood, ductwork, and dust collection system, it forms a complete off-gas handling unit that captures dust-laden furnace gases under negative pressure and conveys them to air pollution control equipment for treatment, ensuring compliance with modern environmental regulations.

Electrode System and Power Supply System

The electrode system is often regarded as the “heart” of the submerged arc furnace, as it has a direct impact on furnace stability, productivity, and energy efficiency. The system primarily consists of the electrode casing, electrode slipping device, electrode holder, current-carrying components, and electrode lifting mechanism.

Most SAFs employ self-baking Söderberg electrodes, which are continuously formed in situ through the baking and sintering of electrode paste under high-temperature operating conditions. The electrode holder is responsible for both mechanically gripping the electrode and transmitting extremely high electrical currents into the furnace. Its conductive components typically include copper contact shoes, copper conductor tubes, and current-collecting rings. Internal cooling-water passages are incorporated into the copper contact shoes to maintain acceptable operating temperatures while ensuring reliable current transfer.

The electrode regulation system, generally driven by hydraulic cylinders, provides precise control of electrode position. By adjusting electrode immersion depth and arc length, operators can regulate furnace voltage, current distribution, and thermal balance, thereby maintaining optimal smelting conditions.

The secondary conductor system, commonly referred to as the short network, forms the electrical connection between the furnace transformer and the electrodes. This circuit operates at low voltage and extremely high current. Because the resistance and reactance of the short network account for a significant portion of the overall electrical circuit, its design has a major influence on energy efficiency and power factor. Optimizing the short-network configuration to minimize resistance and inductive reactance can reduce power losses, improve phase-current balance, and enhance electrical energy utilization within the furnace.

The power supply system generally includes high-voltage incoming switchgear, vacuum circuit breakers, current transformers, voltage transformers, surge protection devices, and a dedicated furnace transformer, providing a stable and reliable source of electrical power for continuous operation.

Automation and Auxiliary Equipment

Modern submerged arc furnaces have increasingly adopted advanced automation and intelligent control technologies. Automated batching systems accurately control raw material proportions according to process requirements, enabling fully automated weighing, conveying, and charging operations. Vibratory charging equipment or automated overhead crane systems distribute burden materials uniformly into the furnace, helping maintain stable furnace conditions.

The tapping system typically includes hydraulic taphole openers, oxygen lances or burn-through devices, and ladles for the safe discharge and transfer of molten metal. In addition, furnace poking and maintenance machines are used to address issues such as crust formation and burden hanging, thereby enlarging the effective reaction zone and improving smelting efficiency.

Because SAFs operate continuously under conditions of extremely high temperatures and electrical currents, many critical components require forced cooling. The cooling water system supplies circulating water to the short network, water-cooled cables, copper contact shoes, pressure rings, furnace hood, and ductwork, ensuring that component temperatures remain within safe operating limits. Furnace transformers are typically equipped with forced oil circulation and water-cooling systems to maintain long-term operational stability.

Energy-Saving, Environmental Protection, and Maintenance Practices

As environmental regulations and energy-efficiency requirements continue to become more stringent, waste heat recovery systems have become an important feature of modern submerged arc furnace operations. Large volumes of high-temperature process gas generated during smelting can be directed through waste heat boilers to recover thermal energy and produce low- to medium-pressure steam, which can then be used to drive steam turbine generators for power generation. This approach enables effective cascading utilization of energy resources and improves overall plant efficiency.

At the same time, baghouse dust collection systems efficiently capture particulate matter from furnace off-gases, significantly reducing emissions and supporting environmentally responsible production practices.

As a key piece of equipment in the ferroalloy and calcium carbide industries, the performance of a submerged arc furnace depends not only on its engineering design but also on effective operation and maintenance management. Regular inspections of the refractory lining, furnace hood, short-network connections, electrode system, cooling water circuits, and hydraulic equipment are essential. Prompt correction of wear, deformation, leakage, and insulation degradation helps ensure safe, reliable, and uninterrupted operation.

Through systematic maintenance programs and the application of intelligent process control technologies, submerged arc furnaces can achieve highly efficient, low-consumption, and environmentally sustainable production, delivering greater economic and social value to the metallurgical industry.