Petroleum Coke: What You Need to Know

What is Petroleum coke?

Petroleum coke is a black or dark gray solid carbon material, which is a by-product of petroleum refining. The main component of petroleum coke is carbon, which is usually high in carbon content and has unique physical and chemical properties, which plays an important role in many industrial fields.

How is Petroleum coke produced?

Production Process Overview

The production process of petroleum coke is relatively complex and is usually carried out in refineries. Firstly, crude oil has been processed by a series of distillation, cracking and other processing processes to obtain heavy oil components such as residual oil. These heavy oils are then subjected to delayed coking reactions at high temperatures (usually between 480 and 550) and high pressures (usually several megabits).

In this process, heavy oil molecules undergo pyrolysis and condensation reactions to form coke and oil and gas. Oil and gas will be further separated and processed, while coke will be treated by cooling, cutting and other treatment to obtain petroleum coke products.

Raw Materials Used

The main raw materials used in the production of petroleum coke are residual oil or coke oil in the process of petroleum refining. Residual oil is the heavy material part of crude oil after many times of distillation. Its composition is complex. It contains a large number of polymer hydrocarbons and a small amount of sulfur, nitrogen, metal and other impurities.

The content of these impurities will have an impact on the quality of petroleum coke, for example, the high sulfur content of residual oil may also be higher, and environmental problems may be caused in subsequent applications.

Different types of petroleum coke

Calcined petroleum coke

It is a product obtained by heating raw petroleum coke at high temperature (generally 1200-1350℃). The calcining process can remove the volatiles from petroleum coke, improve its fixed carbon content, reduce resistivity, and improve its chemical stability and physical properties.

After calcining, the petroleum coke density is large, and the pore structure is more stable. Its specifications vary according to different application requirements, and the price will vary depending on quality, specification and other factors.

Graphite petroleum coke

Graphite fossil oil pyrographite fossil oil coke is an oil coke treated by high temperature graphitization (usually at 2500-3000℃). In the process of graphitization, the crystal structure of petroleum coke is rearranged and the carbon atoms are arranged more orderly.

These make it have higher conductivity, thermal conductivity, better chemical stability, and closer to the properties of graphite. Graphite fossil oil coke has been widely used in iron and steel, metallurgy and other industries. The degree of graphitization will affect its performance and price. And the price of high quality graphite fossil oil coke is relatively high.

Green delayed petroleum coke

t is a kind of petroleum coke produced by selecting specific technological conditions and raw materials in the process of delayed coking. It has relatively low sulfur content and volatile matter content. And it has certain application in the field with high environmental requirements.

Its production process pays attention to the impact on the environment, tar, dust and other pollutants. So pollutants are relatively few in the production process. In some areas with strict emissions requirements, the market demand for green delayed oil coke gradually increases. So its specifications and prices will fluctuate according to market supply and demand and quality standards.

Petroleum needle coke

It is a kind of pet coke with special acicular structure, with obvious acicular texture. And it is produced by specific raw materials and processes. It has he advantages of low sulfur, low nitrogen, low ash, high conductivity, high thermal conductivity, high purity. It is mainly used to produce ultra-high power graphite electrode, which is an indispensable key material in steel and steel industry. Its production process is complex. The raw materials and production conditions are strict. So the price is relatively high and the specification also strictly controlled according to the electrode production requirements.

Physical and chemical properties of petroleum coke

Density Characteristics

Density characteristics the density of petroleum coke is related to the production process, type and impurities and other factors. Generally, the density of calcined petroleum coke and graphite fossil oil coke is relatively high, while the density of raw pet coke without calcining is low.

Density affects the volume and weight ratio of pet coke, which needs to be considered in the storage, transportation and application. For example, anode materials used in aluminum electrolytic cells may affect their conductivity and stability if the density is not appropriate.

Porosity Features

The porosity characteristic of petroleum coke has a certain pore structure, and the porosity size will affect its adsorption performance, reaction activity and interaction with other substances. Pet coke with high porosity may have greater contact area in some chemical reactions, which is conducive to the reaction.

But in some applications that require high strength and low permeability, lower porosity is more appropriate. The porosity characteristics of different types of petroleum coke are different, which is closely related to the production process and subsequent treatment process.

Carbon Content and Other Chemical Compositions ( chemical formula)

Carbon content and other chemical components (chemical formula) petroleum coke is mainly composed of carbon. Its carbon content is usually between 80% and 97%, depending on the type and production process of petroleum coke. Besides, it contains a small amount of hydrogen, oxygen, nitrogen, sulfur and metal elements. (such as vanadium, nickel, etc).

The chemical formula can be roughly expressed as “Cₓ Hᵧ OₛNₜ”. T is the number of atoms. X is much higher than y, s, t. Among them, sulfur content is an important index. High sulfur pet coke may produce sulfur dioxide and other pollutants in the process of combustion or processing. It  will cause harm to the environment. So there are strict restrictions on sulfur content in some applications.

Identify different types of petroleum coke

By Appearance

There are certain differences in appearance through different types of petroleum coke. Calcined petroleum coke has a relatively deep color and dense surface. Graphite fossil oil coke usually presents a metallic sheen, more uniform texture. The color of green delayed oil coke may be lighter and the appearance is relatively regular.

Oil needle coke has obvious acicular texture. It is one of the important characteristics that is different from other types of oil coke. By observing the appearance characteristics such as color, luster and shape of petroleum coke, it can be preliminarily judged. But the accuracy of this method is limited. And other methods need to be combined with comprehensive judgment.

Through Chemical Analysis

Chemical analysis is one of the important methods to accurately identify petroleum coke types. By determining the content of carbon, hydrogen, oxygen, nitrogen, sulfur and other elements in pet coke, the chemical composition can be understood and its type can be inferred.

For example, high carbon content, low sulfur content and less impurities may be high quality graphite fossil oil coke; The higher sulfur content may be ordinary delayed oil coke. In addition, the analysis of the content of metal elements is also helpful to determine the quality and applicability of petroleum coke, such as vanadium and nickel, which may affect the application of it in some special fields.

Using Physical Testing Methods

The use of physical test methods physical testing methods can provide information on the physical properties of petroleum focus and help identify their types. For example, physical parameters such as measuring the density, porosity, resistivity of petroleum coke are measured.

The measurement of density and porosity can be used by drainage method, gas adsorption method, etc. The measurement of resistivity can use special resistivity test instruments. These physical parameters are closely related to the type and quality of it. By comparing with the physical parameter standard of known pet coke, it can be classified and evaluated.

Comparing Petroleum Coke with Other Carbon Materials

Petroleum Coke vs. Coal – based Coke

They are important carbon materials, but they have some differences in the source, nature and application of raw materials.

From the source of raw materials, petroleum coke comes from the process of petroleum refining. While coal-based coke is produced by coal as raw material. In terms of nature, the volatile content of petroleum coke is relatively low. And the sulfur content may vary from crude oil quality.

Its structure is relatively dense. The volatile content of coal coke is high and the sulfur content is usually higher. And the structure is relatively loose.

Application

In application, petroleum coke is widely used in some high-end fields in aluminum industry and steel industry. (Such as graphite electrode production for electric furnace steelmaking). Coal-based coke is widely used in some fields with relatively cost sensitivity and low sulfur content requirements. Such as some fuel and reducing agent in iron smelting blast furnace.

Petroleum Coke vs. Graphite in Some Aspects

The graphitized petroleum coke in some aspects of the petroleum coke after graphitization treatment. Its performance is close to graphite in many aspects. Compared with ordinary non-graphite fossil oil coke, the crystal structure of graphite fossil oil coke is more orderly. Carbon atoms are arranged in a layered structure, and the interlayer pressure is weak. This makes it have good conductivity, thermal conductivity and lubrication.

In terms of thermal conductivity, the thermal conductivity of graphite fossil oil coke is significantly improved. It can transfer heat more effectively. This makes it have advantages in some applications that require high efficiency heat dissipation. Such as heat dissipation parts in electronic equipment. However, compared with natural graphite, there may still be a certain gap in the integrity and stability of crystal structure. But it may have certain advantages in cost and machinability.

Applications of Pet Coke

In the Aluminum Industry

In aluminum industry pet coke in aluminum industry is mainly used in the production of aluminum electrolytic anode materials. The anode plays an important role in conducting electricity and participating in chemical reactions in the process of aluminum electrolysis. Petroleum coke is the main component of anode material. Its quality directly affects the performance of anode and the efficiency of aluminum electrolysis.

The anode made of high quality calcining petroleum coke or graphite fossil oil coke has a low resistivity, which can reduce power loss and improve electrolytic efficiency. At the same time, its good chemical stability can resist the strong corrosive environment in the electrolytic process and prolong the service life of the anode. In the aluminum industry, the specification of petroleum coke is strictly required, such as low impurity content and uniform particle size, so as to ensure the quality of the anode is stable.

 For the Steel Industry

In the steel industry, pet coke has many applications. On the one hand, it can be used as a carbon enhancer in the process of steelmaking. In the process of steelmaking, the carbon content of molten steel is adjusted by adding oil coke to meet the production requirements of different steel varieties.

Graphite Electrode

On the other hand, the graphite electrode made from graphite fossil oil coke plays a key role in the furnace steelmaking. Graphite electrode has high conductivity and high temperature resistance. They can conduct strong current in the electric furnace, produce high temperature to make scrap steel and other raw materials melt. And conduct steelmaking operation.

The steel industry has a large demand for oil coke. And its price fluctuation will have a certain impact on the production cost. At the same time, in the process of steel production, the use of petroleum coke also needs to consider its impact on the environment. Such as the emission control of dust and sulfur oxides generated by combustion.

In the Power Generation Sector

Petroleum coke in the power generation industry can be used as fuel in the power generation industry. And its calorific value is high, which can provide a large amount of thermal energy for power generation. In general, the calorific value of petroleum coke is about 30-35mj/kg, which is competitive with traditional fuels such as coal.

However, the burning of pet coke will produce dust, sulfur dioxide and other pollutants. These need to be equipped with corresponding environmental protection equipment for treatment to meet strict environmental emission standards. Changes in prices relative to fuels such as coal will also affect fuel selection decisions for power generation companies.

Other Industrial Applications

In addition to the above major industries, have also been widely used in other industrial fields. For example, in the chemical industry, it can be used as raw material for producing silicon carbide and other chemical products.

In the casting industry, it can be used to make casting core, etc.

In the glass industry, it can be used as fuel for glass furnaces to provide the required heat.

And its burning ash can be used as one of the raw materials of glass to participate in the glass production process.

In these applications, the characteristics of petroleum coke, such as high carbon content and certain calorific value, have been fully utilized. And its specifications and quality requirements vary according to different industrial application requirements.

Conclusion

Petroleum coke is an important by-product of petroleum refining, which has many types and rich physical and chemical properties. It plays an irreplaceable role in many industrial fields. By understanding its production process, type characteristics, identification methods, comparison with other carbon materials and extensive application fields, we can better understand the value and importance of pet coke.