The coke produced by most petroleum coke plants is black-brown porous solid irregular block, also called sponge coke. The second kind of petroleum coke with better quality is called the ratio of needle coke to sponge coke. Because of its low resistance and thermal expansion coefficient, it is more suitable as an electrode. Sometimes another kind of hard petroleum coke is produced, which is called shot coke. This kind of coke, like a projectile, has a small surface area and is not easy to coke, so it is of little use.
Petroleum coke has its unique physical, chemical and mechanical properties. It is non-volatile carbon in the heating part. Volatiles and mineral impurities (sulfur, metal compounds, water, ash, etc. ) to determine the chemical properties of coke. Porosity and density in physical properties determine the reactivity and thermophysical properties of coke. Mechanical properties include hardness, wear resistance, strength and other mechanical properties, particle composition and other processing, transportation, stacking and storage properties.
Petroleum coke usually has the following four classification methods:
According to the processing method of the invention
It can be divided into raw coke and cooked coke.
The former is taken from the coke tower of delayed coking unit, also known as green coke, which contains more volatile matter and has poor strength; The latter is obtained by calcining green coke (1300℃), also known as calcined coke.
According to the level of sulfur content
It can be divided into high sulfur coke (sulfur content is higher than 4%), medium sulfur coke (sulfur content is 2% ~ 4%) and low sulfur coke (sulfur content is lower than 2%).
The sulfur content of coke mainly depends on the sulfur content of raw oil. With the increase of sulfur content, the quality of coke decreases and its use changes.
According to the different microstructure and morphology
It can be divided into sponge coke and needle coke. The former is porous as sponge, also known as ordinary coke. The latter is as dense as fiber, also known as high-quality coke;
It is obviously different from sponge coke in nature, and has the characteristics of high density, high purity, high strength, low sulfur content, low burning loss, low thermal expansion coefficient and good thermal shock resistance. It has obvious anisotropy in thermal conductivity, electrical conductivity, magnetic permeability and optics; The holes are large and few, slightly oval, with clear fracture texture and lubrication to the touch. Needle coke is mainly made of residual oil with high aromatic content and low non-hydrocarbon impurities.
According to different forms
It can be divided into needle coke, pellet coke or spherical coke, sponge coke and powdered coke.
⑴ Needle coke: It has obvious needle structure and fiber texture, and is mainly used as high-power and ultra-high-power graphite electrode for steelmaking.
⑵ Sponge coke: high sulfur content, high moisture content, rough surface and high price.
⑶ Pellet coke or spherical coke: spherical in shape, 0.6 ~ 30mm in diameter, smooth in surface and low in water content. Usually, it is produced from high-sulfur and high-asphaltene residues and can only be used as industrial fuels, such as power generation and cement.
⑷ Powder coke: produced by radial coking process, its particles have high thermal expansion coefficient (diameter 0. 1~0.4mm) in volatile matter, so it can not be directly used in electrode preparation and carbon industry.