The petroleum coke from the delayed coking unit is called raw coke, and the process of heat treatment of high temperature (1250~1380 °C) under the condition of insulating air is called calcination. The petroleum coke after calcination is called calcined petroleum coke, also called Calcined coke and calcined petcoke, they have different names but are the same product. The purpose of calcination is to discharge moisture and volatiles in the raw materials, so that the petroleum coke raw materials are sufficiently shrunk to improve their physical and chemical properties.
Under normal circumstances, the petroleum coke starts to escape volatiles from 200 ° C. When the temperature reaches 1100 ° C, the volatiles basically escape. In the range of 500 ° C to 800 ° C, the volatiles of petroleum cokes escape the most. At about 700 °C, the petroleum coke volatiles are mainly hydrogen decomposed by hydrocarbons and hydrocarbon pyrolysis. As the temperature continues to increase, the gas escape amount decreases, and the pyrolysis temperature increases, further promoting the structure. Tightening. In the calcination of petroleum coke, the O2, N2, CO, CO2, and S elements are sequentially removed by heat, and a planar network structure is formed inside the petroleum coke at 1350 °C. This change in microstructure reflects an improvement in the physical properties of the calcined coke (such as true density, electrical conductivity, strength, etc.).
Calcined petroleum coke is mainly used for prebaked anode and cathode used in electrolytic aluminum, carbonizing agent for production in metallurgical steel industry, graphite electrode, carbon electrode for industrial silicon, yellow phosphorus and iron alloy. Therefore, both electrolytic aluminum plants, independent carbon plants and refineries are concerned about the progress and development of petroleum coke calcination technology.
Why is petroleum coke need calcined?
The purpose of calcination:
1. Eliminate volatiles and moisture in petroleum coke raw materials. After calcination, the volatile matter is 0.5% or less, and the water content is 0.3% or less.
The calcined volatiles and moisture represent the degree of calcination, which does not require secondary shrinkage and crack formation during calcination.
2. Improve the density and mechanical strength of petroleum coke raw materials. The true density is 2.00 g/cm3 or more.
The true density of the calcined coke affects the true density of the final product, and the mechanical strength is low. The bulk density is low, which affects the molding. The main performance is difficult to form. The height of the green block does not meet the requirements within the required time, which affects the operation of the aluminum electrolytic cell.
3. Improve the electrical conductivity of petroleum coke raw materials.
The calcined coke specific resistance affects the final product resistivity.
4. Improve the chemical stability of petroleum coke raw materials. Improved oxidation resistance.