Raw material and manufacturing process of graphite electrode
Graphite electrode is a high temperature resistant graphite conductive material produced by petroleum knead, needle coke as aggregate and coal bitumen as binder, which are produced through a series of processes such as kneading, molding, roasting, impregnation, graphitization and mechanical processing. material.
The graphite electrode is an important high-temperature conductive material for electric steelmaking. The graphite electrode is used to input electric energy to the electric furnace, and the high temperature generated by the arc between the electrode end and the charge is used as a heat source to melt the charge for steel making. Other ore furnaces that smelt materials such as yellow phosphorus, industrial silicon, and abrasives also use graphite electrodes as conductive materials. The excellent and special physical and chemical properties of graphite electrodes are also widely used in other industrial sectors.
The raw materials for the production of graphite electrodes are petroleum coke, needle coke and coal tar pitch.
Petroleum coke is a flammable solid product obtained by coking coal 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 belongs to the class of easily graphitized carbon. Petroleum coke has a wide range of uses in chemical and metallurgical industries. It is the main raw material for producing artificial graphite products and carbon products for electrolytic aluminum.
The petroleum coke can be divided into two types: raw coke and calcined coke according to the heat treatment temperature. The former petroleum coke obtained by delayed coking contains a large amount of volatiles, and the mechanical strength is low. The calcined coke is obtained by calcination of raw coke. Most refineries in China produce only coke, and calcination operations are mostly carried out in carbon plants.
Petroleum coke can be divided into high sulfur coke (containing more than 1.5% sulfur), medium sulfur coke (containing 0.5%-1.5% sulfur), and low sulfur coke (containing less than 0.5% sulfur). The production of graphite electrodes and other artificial graphite products is generally produced using low sulfur coke.
Needle coke is a kind of high quality coke with obvious fibrous texture, very low thermal expansion coefficient and easy graphitization. When the coke is broken, it can be split into slender strips according to texture (the aspect ratio is generally above 1.75). An anisotropic fibrous structure can be observed under a polarizing microscope, and is therefore referred to as needle coke.
The anisotropy of physico-mechanical properties of needle coke is very obvious. It has good electrical and thermal conductivity parallel to the long axis direction of the particle, and the coefficient of thermal expansion is low. When extrusion molding, the long axis of most particles is arranged in the extrusion direction. Therefore, needle coke is the key raw material for manufacturing high-power or ultra-high-power graphite electrodes. The graphite electrode produced has 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 pitch raw materials.
Coal tar is one of the main products of coal tar deep processing. It is a mixture of various hydrocarbons, black at high temperature, semi-solid or solid at high temperature, no fixed melting point, softened after heating, and then melted, with a density of 1.25-1.35 g/cm3. According to its softening point, it is divided into low temperature, medium temperature and high temperature asphalt. The medium temperature asphalt yield is 54-56% of coal tar. The composition of coal tar is extremely complicated, which is related to the properties of coal tar and the content of heteroatoms, and is also affected by the coking process system and coal tar processing conditions. There are many indicators for characterizing coal tar pitch, such as bitumen softening point, toluene insolubles (TI), quinoline insolubles (QI), coking values, and coal pitch rheology.
Coal tar is used as a binder and impregnant in the carbon industry, and its performance has a great impact on the production process and product quality of carbon products. The binder asphalt generally uses a medium-temperature or medium-temperature modified asphalt having a moderate softening point, a high coking value, and a high β resin. The impregnating agent is a medium temperature asphalt having a low softening point, a low QI, and good rheological properties.
Post time: Sep-23-2019