Ferro Silicon 75 is produced by high-temperature reduction in a submerged arc furnace. The core process involves reducing SiO₂ in quartz sand with coke and scrap steel at 1700-2000℃ to produce a ferrosilicon alloy:
Main reaction: SiO₂ + 2C → Si + 2CO↑ (ΔG < 0 at high temperature, spontaneous reaction);
Side reaction: SiO₂ + 3C → SiC + 2CO↑ (furnace temperature and raw material ratio must be strictly controlled to avoid the formation of the hard and brittle SiC phase).
Production process: Raw materials - Smelting - Refining - Finished product
(1) Raw material preparation and precise proportioning
Raw material quality is the foundation of FeSi75 performance. The core raw materials and requirements are as follows :
| Raw material type | Core component requirements | Size requirements | Function |
| Quartz sand | SiO₂≥99.0%, Al₂O₃≤0.5%, Fe₂O₃≤0.3% | 50-150mm | Silicon source |
| Coke | Fixed carbon ≥85%, ash ≤10%, volatile matter ≤8% | 20-80mm | Reducing agent, heat source |
| Scrap steel | Fe≥98%, impurities (Cu, Zn)≤0.5% | 50-200mm | Iron source, alloy composition adjusted |
(2) Submerged Arc Furnace Smelting: High-Temperature Reduction and Energy Control
The submerged arc furnace is the core equipment for Ferro Silicon 75% production. The key process parameters are as follows:
Furnace Type Selection:
Generally, a closed or semi-closed submerged arc furnace with a capacity of 12500kVA or higher is used. A closed furnace can reduce heat loss, and the power consumption per ton of product is reduced by 10%-15%;
Furnace Temperature Control:
The temperature in the reaction zone inside the furnace is maintained at 1800-2000℃. Precise temperature control is achieved by adjusting the electrode insertion depth (1.2-1.5m) and transformer power (80%-90% of full load);
Iron Tapping Cycle:
Iron is tapped once every 8-12 hours, with a tapping volume of 5-8 tons each time. The flow rate (0.5-1.0 tons/ton) needs to be controlled during tapping.
(3) Refining and Composition Adjustment After tapping,
the molten iron needs to be refined to ensure the composition meets the standards:
Desulfurization:
When the molten iron temperature is 1400-1500℃, add lime (CaO≥90%) or calcium carbide (CaC₂≥80%). The desulfurization rate can reach 60%-70%, reducing the S content from 0.08% to below 0.03%;
Silicon Content Adjustment:
If the silicon content is too low (<72%), silica (SiO₂≥98%) and coke can be added for secondary reduction in the molten iron ladle, with a silicon recovery rate of about 70%;
Impurity Removal:
Through slag formation (CaO-SiO₂-Al₂O₃ slag system), impurities such as Al and Ca are adsorbed, reducing the Al content from 1.0% to below 0.5% (required for FeSi75-Al0.5 grade).
(4) Casting and Finished Product Processing
Casting:
Molten iron is poured into a mold (cast iron or steel mold) and allowed to cool naturally to room temperature to form ferrosilicon blocks;
Crushing and Screening:
The ferrosilicon blocks are crushed to a particle size of 5-100mm and graded using a vibrating screen to remove powder and oversized particles;
Quality Inspection:
A spectrometer is used to detect the composition of Si, Fe, Al, S, and P, ensuring that Si 72%-80%, Al≤0.5%, S≤0.05%, and P≤0.04% (meeting the requirements of GB/T 2272-2017 FeSi75-Al0.5).
Key Points of Production Process Optimization and Quality Control
(1) Energy Saving and Consumption Reduction Technology
Adopting a "waste heat recovery system" to recover waste heat from the flue gas of the submerged arc furnace (temperature 800-1000℃) for preheating raw materials or power generation, reducing power consumption per ton of product from 8500kWh to 7500kWh;
Optimizing the electrode paste formula to reduce electrode consumption, reducing electrode consumption per ton of product from 25kg to below 20kg.
(2) Handling of Quality Anomalies
If the Si content is too high (>80%), the proportion of scrap steel can be increased in the next batching (for every 0.5% increase in scrap steel, the Si content decreases by approximately 1%);
If the Al content exceeds the standard, high-purity quartz sand (Al₂O₃≤0.3%) needs to be replaced, and the slag basicity (CaO/SiO₂=1.2-1.5) should be adjusted to enhance slag adsorption capacity.
(3) Environmental Protection and Safety Control
A combined dry dust removal and wet desulfurization process is adopted, reducing the dust concentration in the flue gas from 500 mg/m³ to below 10 mg/m³, and the SO₂ emission concentration to <50 mg/m³, meeting environmental protection requirements.
High-temperature resistant gloves and goggles must be worn during furnace operation. A safe distance must be maintained when tapping molten iron to avoid burns from splashing molten iron.
Industry Trends in FeSi 75% Production Processes
Larger-scale and Intelligent Production: New projects increasingly adopt submerged arc furnaces of 30,000 kVA or higher, equipped with DCS control systems to achieve fully automated control of furnace temperature, electrodes, and tapping, increasing production efficiency by 20%-30%;
Green and Low-Carbon Transformation: Exploring "green electricity + green coke" processes, using renewable energy electricity and biomass coke to reduce carbon emissions per ton of product by more than 50%, aligning with the global trend towards carbon neutrality;
High-end Development: Developing, low-sulfur low-aluminum Ferro Silicon 75 (Al≤0.3%, S≤0.03%) to meet the stringent requirements of high-end steel and precision casting, increasing product premium by 15%-20%.
