Ferrosilicon Furnace's Different Reaction Temperature

A ferrosilicon furnace is a submerged arc furnace used for smelting ferrosilicon. Ferrosilicon is an important ferroalloy, produced from coke, steel scrap, and quartz (or silica) through a reduction reaction in a SAF.

Common types of ferrosilicon electric furnaces include AC and DC furnaces, with large-scale DC industrial silicon melting equipment representing a significant technological development in recent years. Ferrosilicon, due to its ability to combine with oxygen to form silicon dioxide, is often used as a deoxidizer in steelmaking and can also improve steel properties. It typically occurs as metallic gray lumps or spheres.

Different Reaction Temperature in Ferrosilicon Furnace

The sintering zone temperature in a ferrosilicon submerged arc furnace is typically between 1500℃ and 1700℃, where liquid silicon and iron droplets are generated, but the charge permeability may be poor. 

In contrast, the alkaline slag environment used for smelting high-carbon ferrochrome has a high-temperature magnesia brick load softening temperature of approximately 1550℃. The exhaust temperature of a submerged arc electric furnace flue gas is approximately 650℃, used for waste heat recovery.

The reaction temperature in a ferrosilicon smelting furnace varies depending on the smelting process and location within the furnace. The following are the main temperature ranges and descriptions for different stages and zones:

1. Charge Preheating Zone (Upper Zone)

Temperature Range: 800°C - 1300°C

Reaction Characteristics: 

After the charge (coke, silica, iron source) is added from the top of the electric furnaces, it is heated by the rising high-temperature gas. Moisture evaporates, silica (SiO₂) is partially pre-reduced, and coke volatilizes and is released.

2. Main Reaction Zone (Molten Reduction Zone)

Temperature Range: 1500°C - 1800°C

Key Reactions:

SiO₂ Reduction:

SiO₂ + 2C → Si + 2CO (Above approximately 1700°C)

Si Alloying with Fe:

Si + Fe → FeSi

This zone is concentrated in the arc region near the electrode, where the high temperature provides the necessary conditions for the reduction reaction.

3. High-Temperature Arc Zone (Near the Electrode End)

Temperature Range: 1800°C - 2200°C

Characteristics: 

In submerged arc furnace smelting, the electric arc directly heats this zone, with local temperatures reaching over 2000°C. This promotes the generation of SiO gas, which reacts with carbon, accelerating the reduction process.

4. Hearth Zone (Alloy Accumulation Zone)

Temperature Range: 1400°C - 1600°C

Function: 

The molten ferrosilicon alloy generated during reduction accumulates here. Higher-density alloys settle at the bottom of the SAF furnaces and are periodically discharged from the taphole.

5. Flue Gas Zone (Rising Gas Process)

Temperature Range: 500°C - 800°C (Furnace Throat Exit)

Characteristics: 

The high-temperature furnace gas containing CO and SiO gas preheats the furnace charge as it rises. The temperature gradually decreases before being discharged through the flue.

Key Influencing Factors

1. Silicon Content: 

High-silicon ferrosilicon (e.g., 75% Si) requires higher temperatures (>1800°C) because SiO₂ reduction is more difficult.

2. Raw Material Properties: 

Silica purity and coke reactivity affect the reaction temperature.

3. Operating Parameters: 

Electrode depth, voltage, current, and charge ratio directly determine the temperature distribution.

Key Points for Ferrosilicon Electric Furnaces Temperature Control

• Excessive Temperature: Increased energy consumption, significant SiO volatilization loss, and accelerated furnace lining erosion.

• Excessive Temperature: Incomplete reduction, increased slag volume, and decreased alloy grade.

• Thermal balance needs to be optimized by adjusting the carbon ratio, electrode position, and power supply system.

The temperature inside the ferrosilicon furnace exhibits a gradient distribution, from 800°C in the upper preheating zone to over 2000°C in the bottom arc zone, with the core reduction reaction concentrated between 1500-1800°C. Precise temperature control is crucial for improving silicon recovery and reducing energy consumption. In actual production, adjustments need to be made flexibly based on the furnace type (open or closed), ferrosilicon grade, and raw material conditions.

For any questions or needs regarding SAF and metal melting furnaces, please feel free to contact Sanrui Electric Furnace for further solutions and answers.