Ferro-Alloy Refining Furnace Electric Arc Furnace Equipment

Ferro-Alloy Refining Furnace Electric Arc Furnace Equipment

Ferroalloy refining furnace is the main equipment for smelting ferroalloy. Ferroalloy electric furnace is divided into two categories: reduction furnace and refining furnace. Reduction furnace is also called submerged arc furnace. It adopts submerged arc operation with electrodes inserted into the charge. Reduction furnace has open, closed (or semi-closed) and fixed, rotating and other forms. Refining furnace is used to refine medium-carbon, low-carbon and micro-carbon ferroalloys. The capacity of the electric furnace is generally 1500~6000 kVA, and it adopts open fixed or covered tilting form. The former is similar to the reduction furnace and can be equipped with continuous self-baking electrodes; the latter is similar to the electric arc steelmaking furnace and uses graphite or carbon electrodes.

Ferroalloy refining furnace is mainly used for desiliconization and refining of ore, high-silicon low-carbon ferroalloy refining products and solvents and other charges, so as to obtain medium-carbon, low-carbon, micro-carbon and other ferroalloy products. Its production process is characterized by intermittent periodic charging and furnace discharge operation.

Ferroalloy refining electric furnaces are usually divided into open type, covered type and semi-enclosed type with low smoke hood; the furnace body is also divided into three types: fixed type, tilting type and rotary type. Electric furnace equipment mainly includes furnace body, furnace cover (or smoke hood), electrode system, charging system, hydraulic system and water cooling system, etc.

Ferroalloy refining electric furnace uses low-carbon silicon-containing alloy products (such as manganese silicon alloy, silicon chromium alloy, etc.) of submerged arc reduction electric furnace as raw materials, adds necessary ore and slag-making agent, and uses electric energy to directly heat and oxidize and desiliconize the furnace. It is often used to produce medium, low and micro-carbon ferroalloys.

Ferroalloy refining electric furnaces are similar to steelmaking electric arc furnaces and submerged arc reduction electric furnaces. The capacity of the electric furnace is usually measured by the apparent power kilovolt-ampere of the capacity of the selected special transformer, generally between 1500 and 6000kVA.

The world's largest ferroalloy refining furnace has a capacity of 10,000 kVA. The two largest and most common furnace types in China are 1,500 kVA and 3,500 kVA respectively (see table). Electric furnace production is intermittent operation. Each furnace is regularly loaded, and smelting is generally divided into a melting period and a refining period. After passing the refining, the metal and slag are discharged to form a production cycle. Usually, low-carbon and micro-carbon products are refined by tilting steelmaking electric arc furnaces; the advantage of tilting is that the ferroalloy melt in the furnace can be poured out at once, and the quality of the next furnace product will not be affected by the unqualified products of the previous furnace. For the refining of medium-carbon products, a small submerged arc reduction furnace with a solid or rotating furnace body is selected; there are many types of furnaces with this structure. 

From the 1950s to the late 1960s, open fixed or rotating furnace bodies were used. By the late 1970s and early 1980s, with the development of technology and the improvement of environmental protection requirements, most of them were changed to semi-enclosed furnace mouths, which not only improved the operating environment, but also facilitated smoke and dust removal. The difference between the two refining furnaces lies mainly in the electrode equipment. The steelmaking electric arc furnace type refining furnace uses graphite electrodes, and its electrode lifting mechanism moves along the pillar through a cantilever frame, and the gripper is mostly a pneumatic spring pull rod type. The submerged arc reduction furnace uses self-baking electrodes, and the electrode lifting adopts a hanging structure, and the gripper is a pressure ring type.

According to the characteristics of ferroalloy refining products, the lining of the refining furnace should be alkaline, and magnesia bricks are mostly used for masonry. When smelting medium-carbon products, the lining is consumed quickly, and the refractory material masonry of the furnace part is usually thicker, and even a margin of corrosion depth during the furnace age should be reserved.

Modern ferroalloy electric furnaces are generally circular furnace bodies with three electrodes. Large ferromanganese electric furnaces use rectangular multi-electrodes. Some large ferrosilicon electric furnaces are equipped with a rotating mechanism, and the furnace body rotates or swings back and forth in the horizontal direction at a speed of 360° in 30 to 180 hours. The closed electric furnace is equipped with a sealed furnace cover, and the semi-closed electric furnace is equipped with an operating door with adjustable opening degree under the smoke hood to control the amount of air drawn in and the flue gas temperature.

Continuous self-baking electrodes are widely used in the electrode system of ferroalloy refining electric furnaces. The largest diameter can reach 2000 mm, and some are made into hollow types. The continuous self-baking electrode consists of a thin steel plate electrode shell and an electrode paste. During operation, the electrode paste is self-baked using the heat generated when the current passes through and the conduction radiation of the furnace heat. As the electrode is consumed, the electrode shell should be welded section by section and the electrode paste should be filled into the shell. The electrode holder is composed of contact cheek plates (conductive copper tiles), copper tubes and holding rings. Its function is to transmit current to the electrode and clamp the electrode at a certain height. It can also adjust the sintering state of the electrode paste. The electrode lifting and pressing device hangs the entire electrode to adjust the electrode insertion depth.

The feeder line from the low-voltage side of the transformer to the electrode holder of the ferroalloy refining electric furnace equipment is generally called a short network, which is a large-section conductor used to transmit large current to the furnace. Most of the secondary windings of large electric furnace transformers complete the triangle connection on the electrode through a short network. The entire network consists of a hard busbar bundle, a soft busbar bundle and a copper tube.