Ferroalloy electric furnaces are the primary equipment used for smelting ferroalloys and can be broadly classified into two main types: reduction electric furnaces and refining electric furnaces.
Reduction electric furnaces, also known as submerged arc electric furnaces, operate by inserting electrodes into the furnace charge, adopting a submerged arc operation mode. These furnaces can be open, closed (or semi-closed), and come in various forms, including fixed and rotating furnace bodies.
Initially, open fixed electric furnaces were commonly used. However, with advancements in environmental protection requirements and waste heat utilization technology, closed electric furnaces or those equipped with low smoke hoods have been increasingly adopted for different products.
Semi-closed electric furnaces feature a rotating furnace body, which helps eliminate suspended materials, reduce "stab fire" caused by encrustation, ensure uniform distribution of the charge, and expand the reaction zone, facilitating smooth furnace operations.
Before the 1950s, the capacity of ferroalloy electric furnaces, measured in kilovolt-amperes (kVA) to indicate their capacity, generally ranged from a few hundred to ten thousand kVA. Over time, there has been a trend towards larger-scale furnaces. In the 1970s, newly constructed electric furnaces typically had capacities of 20,000 to 40,000 kVA, with the largest closed furnace reaching 75,000 kVA and the largest semi-closed furnace reaching 96,000 kVA.
Modern ferroalloy electric furnaces generally feature circular furnace bodies equipped with three electrodes. Large-scale ferromanganese electric furnaces may have rectangular multi-electrode configurations. Some large-scale ferrosilicon electric furnaces are equipped with rotating mechanisms, allowing the furnace body to rotate horizontally or swing back and forth at a speed of 360° over 30 to 180 hours. Closed electric furnaces are fitted with sealed furnace covers, while semi-closed furnaces have adjustable operating doors under the hood to control air intake and flue gas temperature.
The electrode system widely employs continuous self-baking electrodes, which can have diameters up to 2000 mm and may be hollow. These electrodes consist of a thin steel plate electrode shell filled with electrode paste. During operation, the electrode paste is self-baked by the heat generated from current passage and furnace heat conduction radiation. As the electrode is consumed, the electrode shell is welded section by section and refilled with electrode paste.
The electrode holder, composed of components such as contact cheek plates (conductive copper tiles), copper tubes, and holding rings, transmits current to the electrode and clamps it at a specific height. It can also adjust the sintering status of the electrode paste. The electrode lifting and pressure release device hangs the entire electrode to adjust its insertion depth.
The feeder line from the low-voltage side of the transformer to the electrode holder is known as the short network. It consists of large cross-section conductors used to transport large currents into the furnace. Most secondary windings of large electric furnace transformers complete delta connections on the electrodes through short networks, which are composed of hard and soft bus wire harnesses and copper pipes.
Refining electric furnaces are specifically designed for refining medium-carbon, low-carbon, and micro-carbon iron alloys. These furnaces typically have capacities ranging from 1500 to 6000 kVA and come in two main configurations: open fixed or tilting with a cover.
Open fixed refining furnaces are similar in design to reduction electric furnaces and can be equipped with continuous self-baking electrodes.
Tilting refining furnaces with covers resemble electric arc steelmaking furnaces and utilize graphite or carbon electrodes. These furnaces offer precise control over the refining process and are suitable for producing high-quality iron alloys with specific carbon contents.
In summary, ferroalloy electric furnaces are classified into reduction and refining types, each with distinct operational characteristics and design features. The continuous evolution of furnace technology has led to larger capacities, improved environmental performance, and enhanced product quality in the ferroalloy industry.
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