The raw materials for producing graphite electrodes include petroleum coke, needle coke and coal tar pitch:

Petroleum coke is a combustible solid product obtained by coking petroleum residue and petroleum pitch. The color is black and porous, the main element is carbon, and the ash content is very low, generally below 0.5%. Petroleum coke is a kind of easily graphitized carbon. Petroleum coke is widely used in chemical industry, metallurgy and other industries. It is the main raw material for the production of artificial graphite products and carbon products for electrolytic aluminum.

According to the heat treatment temperature, petroleum coke can be divided into green coke and calcined coke. The former is petroleum coke obtained by delayed coking, which contains a large amount of volatile matter and has low mechanical strength. Calcined coke is obtained by calcining green coke. Most refineries in China only produce green coke, and most of the calcination operations are carried out in carbon plants.

Petroleum coke can be divided into high sulfur coke (more than 1.5% sulfur content), medium sulfur coke (0.5%-1.5% sulfur content) and low sulfur coke (less than 0.5% sulfur content). Graphite electrodes and other artificial graphite products are generally produced using low-sulfur coke.

Needle coke is a kind of coke with obvious fibrous texture, low thermal expansion coefficient and easy graphitization. When the coke block is broken, it can be divided into long and thin strip particles (length to width ratio is generally above 1.75) according to the texture. The anisotropic fibrous structure can be observed under the polarizing microscope, so it is called needle coke.

The anisotropy of the physical and mechanical properties of needle coke is very obvious. The direction parallel to the long axis of the particles has good electrical and thermal conductivity, and the coefficient of thermal expansion is low. During extrusion molding, the long axes of most particles are arranged in the direction of extrusion. Therefore, needle coke is the key raw material for manufacturing high-power or ultra-high-power graphite electrodes. The graphite electrodes made have low resistivity, small thermal expansion coefficient, and good thermal shock resistance.

Needle coke is divided into oil-based needle coke produced from petroleum residue and coal-based needle coke produced from refined coal tar pitch.

Coal tar pitch is one of the main products of coal tar deep processing. It is a mixture of a variety of hydrocarbons, black high viscosity semi-solid or solid at room temperature, without fixed melting point, softening after heat, and then melting, with a density of 1.25-1.35g/cm3. According to its softening point is divided into low temperature, moderate and high temperature asphalt three. The yield of medium temperature asphalt is 54-56% that of coal tar. The composition of coal bitumen is very complex, which is related to the properties of coal tar and the content of heteroatoms, and is also affected by the coking technology system and the processing conditions of coal tar. There are many indexes to characterize the properties of coal asphalt, such as asphalt softening point, toluene insoluble matter (TI), quinoline insoluble matter (QI), coking value and rheological property of coal asphalt.

Coal pitch is used as binder and impregnating agent in carbon industry. Its properties have great influence on the production process and quality of carbon products. Binder asphalt generally uses moderate softening point, high coking value, high beta resin medium temperature or medium temperature modified asphalt, impregnating agent to use lower softening point, low QI, rheology can be good medium temperature asphalt.

• Graphite electrode application

Graphite electrode has a wide range of uses, mainly used in electric furnace steelmaking, ore thermal furnace, resistance furnace, etc.

1. Graphite electrode is used in arc steelmaking furnace

Main users of electric furnace steelmaking, electric furnace steelmaking is the use of graphite electrode into the furnace current, strong current at the lower end of the electrode through the gas arc discharge, the use of arc generated heat for smelting, according to the size of the electric furnace capacity, with different diameters of graphite electrodes, in order to make continuous use of electrodes, electrodes by electrode thread joint connection, The graphite electrode used in steelmaking accounts for about 70-80% of the total amount of graphite electrode.

2. User mineral heat electric furnace

Mineral furnace is mainly used for the production of ferroalloy, pure silicon, yellow phosphorus, matte and calcium carbide. Its characteristics are that the lower part of the conductive electrode is buried in the charge, so in addition to the heat generated by the arc between the plate and the charge, the current through the charge by the resistance of the charge also generate heat, each ton of silicon needs to consume about 150kg/ graphite electrode, each ton of yellow phosphorus needs to consume about 40kg graphite electrode.

3, for resistance furnace

Production of graphite products with graphitization furnace, melting glass furnace and the production of silicon carbide furnace are resistance furnaces, furnace installed boring heating resistance, is also the object of heating. Generally, the conductive graphite electrode is inserted into the furnace head wall at the end of the hearth, so the conductive electrode is not continuously consumed.

In addition, a large number of graphite electrode blanks are also used for processing into a variety of crucible, graphite boat, hot casting mold and vacuum electric furnace heating body and other special-shaped products. For example, in the quartz glass industry, 10t graphite electrode blank is required for every 1t capacitor tube production, and 100kg electrode blank is consumed for every 1t quartz brick production.

#carbon raiser #graphite electrode #carbon addictive # graphited petroleum coke # needle coke #petroleum coke