Refractory For Smelting Ferrosilicon Furnace

Ferrosilicon furnace, a type of submerged arc furnace, are typical high-power-consuming industrial electric furnaces. They are primarily used for smelting ferrosilicon, ferromanganese, ferrochrome, ferrotungsten, and ferrosilicon-manganese alloys, employing a continuous feeding and intermittent tapping and slag removal operation, classifying them as continuous production equipment.

Ferrosilicon smelting furnaces have complex structures, generally including a furnace shell, furnace cover, furnace lining, short mesh, water cooling system, flue gas and dust removal system, electrode system (electrode shell, pressing and lifting devices), loading and unloading system, handles, burn-through device, hydraulic system, transformer, and other electrical equipment. Due to the extremely high temperatures, thermal shock, chemical erosion, and mechanical scouring during the smelting process, the selection and configuration of refractory materials are extremely demanding.

Proper selection of refractory materials can not only effectively extend the furnace lining life and improve operating efficiency, but also significantly reduce energy consumption and production costs, and reduce solid waste emissions caused by frequent maintenance.

The following systematically describes the selection scheme of refractory materials based on the actual operating conditions and temperature distribution of various zones within a ferrosilicon smelting furnaces. All temperature ranges and material recommendations are based on common industry smelting practices and refractory material performance data.

Refractory For Smelting Ferrosilicon Furnace

1. Preheating Zone (Upper Burden)

This zone is located approximately 500mm thick at the top of the furnace charge, with a temperature of approximately 500–1000℃. This area is mainly affected by high-temperature exhaust gases, electrode conduction heat, and combustion heat from the charge surface. The temperature is relatively low but fluctuates frequently. Clay bricks with good thermal shock stability and low cost are generally selected as the lining.

2. Preheating Zone (Burn Charge Drying and Crystal Transformation Zone)

After the furnace charge falls into this zone, the moisture evaporates completely, and silica undergoes a crystal transformation (such as the transformation from α-quartz to β-quartz), accompanied by volume expansion, which easily leads to cracking or bursting. The temperature in this zone is approximately 1300℃. It is recommended to use high-alumina bricks (Al₂O₃ content ≥55%) with high refractoriness and thermal shock resistance for construction.

3. Sintering Zone (Crust Shell Formation Zone)

The temperature is between 1500–1700℃. Here, the furnace charge softens and sinters, forming initial liquid silicon and iron beads that drip into the molten pool. This zone has poor permeability, requiring timely breaking up of clumps to improve ventilation and increase electrical resistance. Due to the high temperature and strong erosive effect of the initial slag, semi-graphite carbon-silicon carbide bricks (containing 30–50% SiC) with excellent impermeability and high-temperature strength are recommended.

4. Reduction Zone (Main Reaction Zone)

Located in the lower middle part of the crucible zone, the temperature reaches 1750–2000℃. This is the area of intense chemical reactions such as SiC decomposition, ferrosilicon formation, and the reaction of SiO₂ with C and Si. Erosion and scouring are extremely severe. In ferrosilicon furnace, semi-graphite calcined carbon bricks with stable high-temperature performance and strong resistance to metal and slag penetration must be used in this area.

5. Arc Zone (High-Temperature Cavity Below Electrode)

This zone is the hottest point in the submerged arc furnace, reaching over 2000℃, and is the main heat source area of the furnace. The electrode insertion depth directly affects the position of the high-temperature zone; 

Generally, the bottom of the electrode should be 400-500mm away from the furnace bottom. Too shallow a distance can cause the high-temperature zone to shift upwards, the furnace bottom temperature to be too low, and slag discharge to be obstructed, forming a "false furnace bottom." While a false furnace bottom provides some protection, it will cause the taphole to shift upwards, affecting normal operation.

Semi-graphite calcined carbon bricks are also recommended for this area to ensure structural stability under extremely high temperatures and arc radiation.

6. Permanent Layer

Located between the working lining and the furnace shell, this layer mainly serves to insulate and protect the furnace shell. It is often constructed using phosphate-bonded refractory castables or clay bricks.

7. Furnace Door Area

This area experiences frequent opening and closing, as well as erosion from high-temperature airflow, resulting in drastic temperature fluctuations. It is recommended to use high-strength, wear-resistant corundum castable for monolithic casting, or to use precast silicon carbide bricks for lining to ensure erosion resistance and structural integrity.

The selection of refractory for smelting furnaces requires a comprehensive consideration of factors such as furnace volume, operating temperatures of various parts, type of chemical erosion, thermomechanical stress, and environmental requirements, scientifically matching different types of refractory bricks and castables.

Optimizing the lining configuration not only improves the lifespan of the submerged arc furnace & other smelting ferrosilicon furnace lining and smelting efficiency but also has significant practical implications for achieving energy conservation, emission reduction, and cleaner production.