Petroleum Coke: A Comprehensive Guide to Production, Specifications, and Types

Posted on Jan 14, 2024 at 10:01 AM

Petroleum coke and petcoke are all designations that belong to a by-product of the oil refining process. It is a carbon-rich solid. Petroleum coke can be used for various industrial and commercial applications, not to mention as an energy source.

Given the importance of these uses, petroleum coke is an essential part of the global energy landscape.

So, continue reading this guide to explore petroleum coke and enrich it with the necessary information for anyone interested in the oil & gas sector to view this vital resource.

What is Petroleum Coke?

As mentioned above, petroleum coke is a by-product of the oil refining process. It is a carbon-rich material and some other heavy, sulfur, and hydrogen.

It structurally belongs to the Coke family. Petroleum coke is generally used in various manufacturing processes such as smelting, carbon black production, and other industrial processes that require high-temperature activation.

Petroleum coke can also be obtained from some unconventional sources. One of these sources is the manufacture and processing of Bitumen (Asphalt) extracted from oil sands in refineries. However, as a person interested in this field, you can learn more about the different sources of oil derivatives by enrolling in Oil and Gas Training Courses in Dubai.

The production of petroleum coke began in the late 1800s and early 1900s. After that, the areas of its use began to appear worldwide. It was used primarily as an industrial fuel source for boilers and furnaces. Its use has expanded to include a variety of other applications, ranging from industrial to consumer-oriented applications.

Today, it is a fuel source for power plants and boilers due to its high energy content.

It can also be used in cement production as an additive or binder. In addition, Petroleum coke is used to produce graphite, which is used in various products, including pencils and batteries.

How is Petroleum Coke produced and processed?

Petroleum Coke is produced from the petroleum refining process. The first stage is extracting raw materials (crude oil) from the ground after drilling an oil well. The second stage is transporting these materials to the oil refinery.

Oil refineries refine these raw hydrocarbons into usable products for the market—for example, petroleum oils, gasoline, diesel, kerosene, and other derivatives.

Refining petroleum hydrocarbons includes equipment, stages, techniques, and chemical reactions to obtain the final product.

At this stage, raw materials are heated to extremely high temperatures in distillation towers and pressed to high pressures. Then, each hydrocarbon compound separates at a certain pressure and temperature.

The residues of these derivatives remain in the form of petroleum liquids. Here, those liquids are transferred to special units called "coking units" to complete the filtering process. Then, these liquids are processed at a specific temperature and pressure to produce Petroleum coke in the form of solids after purging them of all gases and volatile materials. Finally, all remaining light and heavy oils are separated.

The resulting petroleum coke at this stage is called Green Petroleum Coke (CVP). In short, still needs to be processed. Petroleum Coke can be used here in some applications, but others require more processing and are called “Calcined Coke”. This process means transferring petroleum coke to a rotary kiln to remove the remaining volatile hydrocarbon residues.

The calcined petroleum coke can be further processed in an anode baking oven. It produces coke, which is used mainly in manufacturing steel or aluminium.

For storage and transportation, such as coal, petroleum coke is stored in large piles in bags or silos. Conveyors, hopper belts, and trolleys can easily transport it.

Because petroleum coke is carbon-rich, it must be stored in a dry environment.

It will form a hard solid called "damp coke" if wet. It is a tricky substance that is difficult to remove. It can often be easily broken or removed through the use of a ripper, which is a high-pressure water hose.

What are the Most Important Chemical and Physical Specifications of Petroleum Coke?

The physical and chemical specifications of petroleum coke vary depending on the production method and the final product. Some of the most common specifications for pet coke include:

• Chemistry: Most petcoke consists of carbon 85~99%, and hydrogen in concentrations between 3.0- 4.0%. Raw (or green) coke contains 0.5-1% nitrogen and 0.2- 6.0% sulfur, which become emissions when coke is Calcined.

• Heating Value: Petroleum coke is highly combustible and has a high heating value, often between 8,000 and 10,000 BTU/lb.

• Size: The particle sizes of petcoke are typically in the range of 0-50 mm.

• Ash: Depending on the origin of Petroleum coke, it may range from 0.5~1%.

• Moisture: The moisture content within the Petroleum coke particles varies with the mining place; it may range from under 1% to over 10%.

• Volatile Matter Content: The concentration of volatile matter in Coke varies depending on the place of mining, which is usually found in proportions of less than 10%.

• Hardness: There are two distinct varieties of petcoke: calcined and uncalcined. Calcined petcoke is more complex and denser than regular petcoke due to its increased carbon concentration.

• Sulfur Content: Petcoke sulfur content can vary from 0.2% to 6%, depending on the type of petcoke and the refining process used. 

• Metal Content: The total metal content is typically less than 0.5%. The metals in Petcoke are aluminium, cobalt, iron, chromium, calcium, and others.

• Fixed Carbon: Petcoke's selected carbon content is typically more than 85% and can be as high as 99%.

• Absolute Density typically ranges from 0.8 to 1.0 g/cm3.

What are the Main Types of Petroleum Coke?

There are several types of petroleum coke, which differ according to the method of processing and refining. Among the most important of these types:

• Sponge Coke

It is a petroleum coke produced from heavy residue feedstocks by Pyrolysis in a fluidised bed. The reason why it is called a sponge is due to its high porosity and low bulk density.

Sponge coke is mainly used to produce electrodes for the aluminium industry. Sponge coke is ideal for anodes due to its high purity, low sulfur content, and good electrical conductivity. It is also highly resistant to thermal shock and has a low coefficient of thermal expansion.

Sponge coke is also used as fuel in industrial boilers and cement kilns. Its low sulfur content causes it to produce less sulfur dioxide emissions when burned.

• Shot Coke 

This type is produced during the delayed coking process. The coke particles are rapidly quenching, causing irregularities in their structures. Accordingly, it becomes difficult to handle and unacceptable for special Coke applications. For example, anode production requires high purity low porosity coke.

It can also be used as a fuel in various industrial processes, including cement kilns and power plants. Its high porosity makes it provide good combustion properties and reduces emissions.

• Needle Coke 

It is produced exclusively from fluid catalytic cracking (FCC) decant oil or coal tar pitch.

Its unique structure and high purity make it ideal for producing high-quality graphite electrodes, essential for manufacturing batteries for electric vehicles (EVs) and other energy storage systems.

In Conclusion,

Although petroleum coke is a valuable resource, it can also be life-threatening. It is essential to take the necessary safety precautions when handling petroleum coke, including wearing protective clothing, avoiding skin contact, and using proper ventilation.

Additionally, regular equipment maintenance used in petcoke production should be done to minimise the risk of accidents or exposure to hazardous materials.