The difference and application of coke, pitch coke, needle coke and petroleum coke

Coke is a solid product formed from coking coal or coal blending of several kinds of coal, heated to 1000 ℃ under oxygen free conditions, and subjected to high temperature retorting. At the same time, it also generates gas, coal tar and other products. Petroleum coke is widely used in the preparation of graphite electrodes for EAF /LF steelmaking. The solid material generated from coal tar pitch after high-temperature carbonization is called pitch coke. Coal tar pitch or petroleum pitch can produce needle texture coke after liquid phase carbonization to produce anisotropic mesophase and high temperature carbonization. Petroleum coke is the coke formed from petroleum residue or petroleum pitch after high-temperature carbonization. The four cokes' characteristics are listed in the following table: 

The main component of coke is carbon, which also contains a small amount of hydrogen, oxygen, nitrogen and sulfur based metal elements. Coke is an indispensable raw material for blast furnace ironmaking. It is also used in metallurgy, casting, synthesis gas production, calcium carbide production, etc. In blast furnace ironmaking, coke provides heat and acts as a reducing agent to reduce iron ore. China's blast furnace ironmaking has a huge demand for coke. In 2016, China's coke output was 449 million tons.

Petroleum coke is used to separate light oil and heavy oil from crude oil by distillation, and then convert the heavy oil into products by thermal cracking process. From the appearance, coke is a kind of black block (or particle) with irregular shape and different sizes, with metallic luster. Coke particles have porous structure. The main element composition is carbon, accounting for more than 80%, containing 1.5% - 8% hydrogen, and the rest are oxygen, nitrogen, sulfur and metal elements.

Petroleum coke belongs to the type of easily graphitized carbon. Compared with metallurgical coke, the microcrystals of petroleum coke have a neat overlap between carbon grid lamellae, and the distance between lamellae is small; At the high temperature of graphitization, the average grain thickness (Lc) and average grain width (La) of carbon lattice lamellae increase, and the lamellar layer spacing (d) decreases; The lattice constants (a0 and c0) are close to those of natural graphite, and the resistivity decreases significantly while the true density increases correspondingly. Therefore, using petroleum coke as raw material can produce graphite electrode with low resistivity.  

Petroleum coke has its unique physical, chemical and mechanical properties. The chemical properties of coke are determined by the nonvolatile carbon, volatile matter and mineral impurities (sulfur, metal compounds, water, ash, etc.) in the heating part. Porosity and density in physical properties determine the reactivity and thermophysical properties of coke. Its mechanical properties are determined by particle composition, processing method, hardness, wear resistance, strength and other mechanical properties.  

The aromaticity of coal tar pitch is higher than that of petroleum tar pitch, and the sulfur content, volatile matter and ash content of pitch coke produced are lower than that of petroleum coke, with relatively dense structure and low porosity.

However, needle coke has high requirements for raw materials, because impurities and heteroatoms in pitch raw materials affect the formation of wide area mesophase, which is a necessary condition for forming high-quality needle coke. Therefore, both coal tar pitch and petroleum tar pitch raw materials need to be pretreated when preparing needle coke. On the one hand, reduce the mechanical impurities and primary QI in the pitch, and on the other hand, reduce the content of sulfur, nitrogen, oxygen and other impurities as much as possible, so as to prepare excellent needle coke. To learn the recent coke market trends, welcome to consult us.