Category Archives: Mechanical

DC Arc Furnace – An Overview

DC Arc Furnace comprises typically of cylindrical refractory lined steel shell. This is with cathode (central graphite) electrode being positioned vertically by means of opening in roof centre. Anode connections in furnace’s hearth are in contact directly with molten metal layers. This is covered by molten slag layer. Energy has been supplied through open plasma arc. This is generated in between cathode’s bottom tip and molten slag’s upper surface. Central portion at least of surface of slag is open. Meaning is that, there is no covering by feed materials. Since, furnace is powered electrically there can be attainment of very high temperature (greater than 1500 degrees). Open bath thereby allows feed fine materials being fed to furnaces with no risk of gas blocking emanating by chemical reactions. Fine ores and requirements of too much high temperatures leads one for choosing open arc furnace (DC or AC either). Fine ores allows utilizing bed-fluidized reactor for pre-reduction or pre-heating purposes. These provide energy saving significantly used in conjunction with DC Arc Furnace. In cases of open-arc furnaces, the DC furnaces have lots of benefits over AC furnaces. 1 important benefit in circular furnaces is that there are no arc repulsions in cases of single DC arcs. Whilst in AC cases, arcs repel each other. They flare towards walls. They lead to hot spots on areas of side walls. They are in close proximity to electrodes. DC furnace experiences also low electrode consumption. In DC large furnaces, high currents are carried per electrodes or small electrode is utilized for same current. This is because there is “skin effect” AC in which currents are concentrated in electrodes outer periphery.

Chromite smelting: Chromite has been smelted together with few carbon forms for producing ferrochromium. This is with some CO gas and some slag. DC Arc Furnace operate with open bath, open arc configurations. Therefore, there are no heaped burdens by which reaction gases need escapes. There are molten baths simply to which fine materials are dropped. It immediately almost assimilates molten bath, dissolving and melting into slag phases in which reactions occurs. Furnaces DC arc do not require cokes. There are no burdens above bath. So it does not need porosity which shall otherwise be required. This is benefit very significantly. It allows usage of reductants less costly. This avoids relative coke scarcity and high costs. Power being supplied to furnaces is independent largely of composition of slag. Open electric arcs allows one adjusting power amounts going to furnace without depending on slag’s electrical resistivity. These provide extra freedom degree and extra flexibility of change in unconstrained slag compositions by electrical property. So, chemical activity of important metals changes for achieving high chromium recoveries. Increase typically in recovery of chromium is about 95% in DC Arc Furnace and 85% in AC Furnace. This is very crucial increase. DC Arc Furnace has low electrode consumption. DC Arc process use unagglomerated chromite fines and cheap non-coking coals. This technology of furnace is considered as one of low costly options for ferrochromium production. As natures of power generation change with respect to challenges environmentally more energy renewable are used. There are abilities of swinging furnace loads likely for bringing economic benefits significantly. This is common practice, though it incurs nuisance factors with plant operation. Large furnaces are better than present furnaces with respect to handling powered dips and out aging long times. DC Arc Furnace offers benefits crucial when question of fast and easy load swinging arises. This type of furnace has wonderful features which are proven in industrial practices over past 30 years. They accommodate fine sized feed materials very nicely.

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