Classification of Ferroalloy Electric Furnaces

Classification of Ferroalloy Electric Furnaces

Electric furnaces are the primary equipment for producing ferroalloys. They are broadly classified into two main categories: reduction furnaces and refining furnaces.

Reduction Electric Furnaces

Also known as submerged arc furnaces, these furnaces operate with the electrode tips submerged in the charge material. They are designed for the carbothermic reduction of ores. Furnace configurations include open, closed (fully sealed), or semi-closed types, with furnace bodies that can be either fixed or rotating.

Refining Electric Furnaces

This type is used for refining ferroalloys to medium-carbon, low-carbon, and micro-carbon grades. Typically ranging from 1,500 to 6,000 kVA in capacity, refining furnaces are either open and fixed or tilting and covered. The fixed type resembles a reduction furnace and can use continuous self-baking electrodes, while the tilting type is similar to an electric arc steelmaking furnace and employs graphite or carbon electrodes.

---

Detailed Description

1. Reduction Electric Furnace

The reduction furnace, or submerged arc furnace, operates with electrodes immersed in the charge. Open, fixed furnaces were once standard, but advancements in environmental controls and waste heat recovery have led to the adoption of closed furnaces or low-emission hoods for various products. Semi-closed designs are also common.

A rotating furnace body helps prevent charge bridging, reduces localized overheating ("flame jetting" from crust formations), promotes uniform burden distribution, expands the reaction zone, and ensures smooth furnace operation.

Furnace Capacity:

Historically, capacities ranged from a few hundred to ten thousand kilovolt-amperes (kVA). Since the 1950s, the trend has moved toward larger units. By the 1970s, newly built furnaces typically reached 20,000–40,000 kVA, with the largest closed furnaces reaching 75,000 kVA and the largest semi-closed furnaces reaching 96,000 kVA.

Modern Design Features:

Modern ferroalloy reduction furnaces generally feature a circular hearth with three electrodes, although large ferromanganese furnaces may use rectangular designs with multiple electrodes. Some large ferrosilicon furnaces incorporate a rotating mechanism, with the furnace body rotating fully or oscillating slowly over a period of 30 to 180 hours per revolution.

Closed furnaces are equipped with sealed roofs, while semi-closed furnaces have adjustable hood openings to control air ingress and flue gas temperature.

Electrode System:

Continuous self-baking electrodes are widely used, with diameters up to 2,000 mm (some are hollow). These electrodes consist of a cylindrical steel casing filled with electrode paste. During operation, heat from electrical resistance and radiant furnace heat bake the paste into a solid carbon electrode. As the electrode consumes, new sections of casing are welded on and filled with fresh paste.

The electrode holder, comprising contact clamps (conductive copper plates), copper tubing, and holding rings, conducts current to the electrode, clamps it at the desired height, and helps regulate the baking process. An electrode lifting and slipping mechanism supports the entire column and adjusts its immersion depth.

Short Network:

The high-current conductors connecting the transformer's low-voltage side to the electrode holders are termed the "short network." Typically constructed from large-section busbars—including rigid bundles, flexible cables, and copper pipes—this network completes the delta connection of the transformer's secondary windings at the electrodes for most large furnaces.

2. Refining Electric Furnace

Used for refining medium-, low-, and micro-carbon ferroalloys, refining furnaces generally have capacities between 1,500 and 6,000 kVA. They come in two main designs: open fixed furnaces or tilting, covered furnaces.

   Open Fixed Furnace: Similar to a reduction furnace, this type can be equipped with continuous self-baking electrodes.

   Tilting Covered Furnace: Similar to an electric arc steelmaking furnace, this design uses prebaked graphite or carbon electrodes.

We are a professional electric furnace manufacturer. For further inquiries, or if you require submerged arc furnaces, electric arc furnaces, ladle refining furnaces, or other melting equipment, please do not hesitate to contact us at  susan@aeaxa.com