Ferro Silicon Manufacturing Process - Submerged Arc Furnace

Ferro silicon is widely used in metal smelting, serving as an important deoxidizer in steelmaking, a crucial reducing agent in light metal smelting, and an indispensable raw material in the metallurgical industry. 

Due to its high energy consumption, the vast majority of ferrosilicon production worldwide takes place in developing and underdeveloped regions, requiring a guaranteed supply of electricity, coal, and mineral resources. 

The core of this production chain is the submerged arc furnace. It is through this unique and highly efficient electrothermal metallurgical equipment that ferrosilicon is produced from ore.

Characteristics of Submerged Arc Furnaces: 

A submerged electric furnace is essentially a giant resistance-heated reactor. Its outer shell is made of thick steel plates, while the inner lining is constructed of high-quality carbon or magnesia bricks capable of withstanding temperatures approaching 2000°C.

Conductive copper or self-baking electrodes are embedded deep within the furnace charge at the bottom. 

When a powerful current is introduced through the electrodes into the furnace charge, the resistance of the material itself generates enormous Joule heat, creating a sustained high-temperature reaction environment deep within the furnace. 

A large-scale ferrosilicon smelting SAF transformer can have a capacity of tens of thousands of kilovolt-amperes, consuming a huge amount of electrical energy day and night, making it a veritable "electricity hog" in the industrial field [2].

Submerged Arc Furnace Ferro Silicon Manufacturing Process - From Ore to Alloy

The smelting of ferrosilicon is essentially a complex high-temperature chemical process in which silicon in silica (mainly SiO₂) is reduced by carbonaceous reducing agents (usually coke, semi-coke, etc.), and then melted with iron (from iron-containing materials such as steel scrap) to form a ferrosilicon alloy. 

Its core chemical reaction can be simplified as: SiO₂ + 2C → Si + 2CO. This process is not instantaneous in the ferrosilicon furnace, but is accompanied by multiple intermediate reactions and drastic physicochemical changes. 

The standard smelting process is a rigorous closed-loop operation:

1. Raw material preparation and batching: 

Silica requires a SiO₂ content higher than 97% and a suitable particle size (typically 20-80mm); the reducing agent requires high fixed carbon, high resistivity, and good reactivity; steel scrap is used to adjust the alloy composition. These three are mixed in precise proportions to ensure a balanced chemical reaction within the furnace.

2. Charge feeding and preheating: 

The mixture is continuously added to the furnace through a charging system. During its descent, the charge is preheated by the rising high-temperature furnace gas below, causing moisture and volatiles to volatilize.

3. High-temperature reduction and smelting (core area): 

In and near the electrode arc zone, the temperature reaches over 1800℃. Solid silicon dioxide is violently reduced by carbon, generating liquid silicon and carbon monoxide gas. Simultaneously, iron oxides are reduced to iron and mix with silicon to form ferrosilicon molten metal.

4. Melt Accumulation and Tapping: 

The high-density molten ferrosilicon sinks into the bottom molten pool and accumulates, then is periodically tapped out and flows into the ladle.

5. Casting and Finishing: 

Molten ferrosilicon is poured into a cast iron mold, cooled and solidified, then crushed and finished to obtain finished ferrosilicon ingots within a specified particle size range.

6. Furnace Gas Treatment and Utilization: 

The large amount of high-temperature carbon monoxide furnace gas (rich in CO) generated during smelting is discharged from the top of the furnace. After dust removal and purification, it can be recycled as a valuable secondary energy source.

SAF Process Data: 

Modern ferrosilicon smelting is a precision operation that heavily relies on data support. The various operating parameters of the ferrosilicon furnace directly determine the technical and economic indicators:

• Electricity Consumption: 

The comprehensive electricity consumption for producing one ton of standard 75% ferrosilicon is typically between 8200-8800 kWh, with electricity costs accounting for 50%-70% of the total cost [3]. This is the direct reason why ferrosilicon is defined as a "high-energy-consuming product". 

• Silicon recovery rate: 

Under advanced submerged electric furnace operation, the silicon recovery rate from silica to alloy can reach over 92% [4]. Each percentage point increase in recovery rate signifies significant resource savings and cost reduction.

• Electrode consumption: 

The consumption of self-baking electrodes is approximately 40-60 kg/ton of iron. Their management and maintenance are crucial for ensuring smooth furnace operation [2].

• Furnace gas volume and calorific value: 

For every ton of ferrosilicon produced, approximately 1200-1500 standard cubic meters of furnace gas are generated, with a calorific value exceeding 8000 kJ/standard cubic meter. Efficient recovery and utilization are key to energy conservation and consumption reduction [3].

Although the submerged arc furnace ferro silicon manufacturing process is mature, it faces increasingly severe challenges. On the one hand, under the "dual carbon" target, how to further reduce unit product power consumption and improve energy efficiency has become a core issue for the industry's survival and development. 

Intelligent power distribution systems, full recovery of waste heat and gas, and the widespread adoption of large-capacity closed furnaces are the main directions. On the other hand, increasingly stringent environmental requirements are driving innovation in ultra-low emission technologies across the entire process, particularly in the control of fugitive emissions and fine particulate matter.

Every spark that flashes at the tapping of iron is a concrete manifestation of the deep integration of energy, resources, and technology within the modern industrial system.

The continuous "elemental alchemy" within the submerged electric furnace is not only smelting ferrosilicon but also constantly forging a more efficient and cleaner industrial future.

References

[1] Li Xiaoming, Wang Gang. Analysis of the global ferrosilicon market pattern and China's industrial competitiveness[J]. China Metallurgy, 2022, 32(5): 1-8.

[2] Zhang Jianguo. Ferroalloy Smelting Technology[M]. Beijing: Metallurgical Industry Press, 2019: 145-178.

[3] International Ferroalloys Association (IFA). Energy Consumption in Ferroalloy Production: Best Practice Guidelines[R]. 2020.

[4] Zhao Wei, Liu Tao. Technological progress and practice of smelting high-purity ferrosilicon in large closed submerged arc furnaces[J]. Ferroalloys, 2021, 52(4): 1-6.

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