A direct current plasma arc furnace includes a tank having a crucible delimiting a chamber to receive material to be melted and/or treated; refractory walls surrounding the crucible outer surface; a metallic frame covering the refractory walls; and a heating system for heating the received material. The heating system includes two electrodes acting as cathode and anode, respectively, wherein the first electrode is a movable electrode to project vertically into the chamber. The crucible is part of an anode system also having the second electrode and at least one part connecting the crucible and second electrode. The crucible receives and holds material to be melted and/or treated and provides electric conduction for the flow of current to heat the material, such that the voltage potential difference between the cathode and any point of the crucible surface defined to be in contact with the material is the same.

A method for preparing needle coke for ultra-high power (UHP) electrodes from heavy oil is provided. In this method, heavy oil is used as a raw material. The size exclusion chromatography (SEC) is conducted with polystyrene (PS) as a packing material to separate out specific components with a relative molecular weight of 400 to 1,000. The ion-exchange chromatography (IEC) is conducted to remove acidic and alkaline components to obtain a neutral raw material. The neutral raw material is subjected to two-stage consecutive carbonization to obtain green coke, and the green coke is subjected to high-temperature calcination to obtain the needle coke for UHP electrodes. The needle coke has a true density of more than 2.13 g/cm.sup.3 and a coefficient of thermal expansion (CTE) of ≤1.15×10.sup.−6/° C. at 25° C. to 600° C.

Coke including additives that are accumulated at the yield points or in the regions surrounded by the yield points. For homogeneous distribution, the additives are continuously dosed into the delayed coker during the filling time. The dosing can be carried out by powdery blowing with an inert gas (nitrogen) or also distributed in a slurry consisting of the reaction components and a partial flow of the coker feed (vacuum resid, pytar, decant oil or coal-tar distillates). According to an advantageous form of embodiment, the additives may optionally have a diameter of between 0.05 mm and 5 mm, preferably between 1 mm and 3 mm. Advantageously, the additives can be selected from at least one of acetylene coke, fluid coke, flexi coke, shot coke, carbon black, non-graphitisable carbons (chars), non-graphitic anthracite, silicon carbide, titanium carbide, titanium diboride or mixtures thereof.

Coke including additives that are accumulated at the yield points or in the regions surrounded by the yield points. For homogeneous distribution, the additives are continuously dosed into the delayed coker during the filling time. The dosing can be carried out by powdery blowing with an inert gas (nitrogen) or also distributed in a slurry consisting of the reaction components and a partial flow of the coker feed (vacuum resid, pytar, decant oil or coal-tar distillates). According to an advantageous form of embodiment, the additives may optionally have a diameter of between 0.05 mm and 5 mm, preferably between 1 mm and 3 mm. Advantageously, the additives can be selected from at least one of acetylene coke, fluid coke, flexi coke, shot coke, carbon black, non-graphitisable carbons (chars), non-graphitic anthracite, silicon carbide, titanium carbide, titanium diboride or mixtures thereof.

Provided is impregnated pitch having a high fixed carbon content despite being petroleum-based pitch. The method for producing impregnated pitch for graphite electrode production according to one embodiment includes heat treatment of ethylene bottom oil and distillation of the heat-treated product to remove low-boiling-point compounds.

Provided is impregnated pitch having a high fixed carbon content despite being petroleum-based pitch. The method for producing impregnated pitch for graphite electrode production according to one embodiment includes heat treatment of ethylene bottom oil and distillation of the heat-treated product to remove low-boiling-point compounds.

Described are graphite-containing electrodes comprising zirconium-based coatings, which slow the loss of material from the electrodes when used at high temperatures, for example when used in arc furnaces between 1000 and 2000° C. The zirconium-based coating may be disposed on a graphite-containing surface of the electrode, or on a pre-coating disposed on a surface of the electrode. The zirconium-based coatings include one or more zirconium compounds such as zirconia. Also described are compositions and methods to coat graphite-containing electrodes with zirconium-based coating compositions.

Described are graphite-containing electrodes comprising zirconium-based coatings, which slow the loss of material from the electrodes when used at high temperatures, for example when used in arc furnaces between 1000 and 2000° C. The zirconium-based coating may be disposed on a graphite-containing surface of the electrode, or on a pre-coating disposed on a surface of the electrode. The zirconium-based coatings include one or more zirconium compounds such as zirconia. Also described are compositions and methods to coat graphite-containing electrodes with zirconium-based coating compositions.

The present invention provides a method for producing an artificial graphite electrode that enables kneading and subsequent mixing to be carried out without having to increase an amount of binder pitch used even in the case of needle coke having a large pore volume. An artificial graphite electrode is produced by kneading binder pitch with needle coke, and performing extrusion molding and then performing baking and graphitization process on the same, wherein a process for kneading the binder pitch with needle coke includes at least two separate kneading stages, and the amount of binder pitch added and kneading time in these kneading stages satisfy a kneading index as represented by formula (1) below within a range of 0.1 to 0.7.
Kneading index=(a1/A)×(t1/T)  (1)

A method for preparing needle coke for ultra-high power (UHP) electrodes from heavy oil is provided. In this method, heavy oil is used as a raw material. The size exclusion chromatography (SEC) is conducted with polystyrene (PS) as a packing material to separate out specific components with a relative molecular weight of 400 to 1,000. The ion-exchange chromatography (IEC) is conducted to remove acidic and alkaline components to obtain a neutral raw material. The neutral raw material is subjected to two-stage consecutive carbonization to obtain green coke, and the green coke is subjected to high-temperature calcination to obtain the needle coke for UHP electrodes. The needle coke has a true density of more than 2.13 g/cm.sup.3 and a coefficient of thermal expansion (CTE) of ≤1.15×10.sup.−6/° C. at 25° C. to 600° C.