Petroleum coke and its many types and uses

Most people are familiar with coal and its uses, however, a perfect alternative to coal is available.

Petroleum coke is in many different industries to a great effect. This is due to its desirable properties which make it a powerful energy source, but also a key raw material in production of different electrical components.

While the production of petroleum coke has been steadily increasing for over four decades, advancements in production methods made it even cheaper to produce, and today, this material is also a profitable export.

Let’s learn how petroleum coke is made, how many types of it are out there, and the industries in which it’s most commonly used.

Petroleum coke, also known as pet coke, is a solid, rocklike byproduct of refining bitumen in oil sands into crude oil. In this vein, it’s similar to other products created by refining crude oil, such as gasoline or diesel fuel.

Petroleum coke is ‘’engineered’’ in the so-called coker units in which a process of cracking occurs. This is a thermic process in which petroleum’s longer chain hydrocarbons are split into shorter chains. In other words, the residual oils from the distillation of petroleum refinement are treated under high pressure and high temperatures which eliminate the volatiles and gasses separating the light and heavy oils that remain.

Depending on the raw materials used in the ‘’coking’’ process, pet coke can have different kinds of chemical compositions. But generally, it can consist of as much as 95% carbon with hydrogen concentrations sitting around 3%.

There are four basic types of pet coke. They all have varying microstructures due to differences in the nature of the raw materials and operating conditions. However, there are also small differences in the properties of pet coke regarding the contents of volatile materials and substances like ash. 

The four types of coke are as follows:

1. Needle coke

This grade of coke has a crystalline structure, making it a favorable material in the production of components such as electrodes. It’s manufactured from a low-sulfur FCC slurry processed in a specific type of coker.

2. Honeycomb coke

Honeycomb coke is considered an intermediate type. It consists of uniformly distributed ellipsoidal pores. It’s characterized by low electrical conductivity and low coefficient of thermal expansion.

3. Shot coke

This type is undesirable as it has an irregular structure that makes it very difficult to handle. As such, it’s unacceptable for most applications. When manufacturing petroleum coke, refiners control the feed of vacuum resid to avoid producing shot coke. 

4. Sponge coke

Physically sponge coke can be described as porous. The individual spheres are not apparent and the coke itself has a continuous structure. While the electrical conductivity of this type of coke is low, its structure makes it appropriate for the production of anodes. 

Green (raw) pet coke results from delayed coking during crude oil processing. The quality of green coke that depends on the quality of the crude oil used in its production determines its application. According to the sulfur content in the coke, there are two categories:

1. High sulfur/fuel-grade coke

This type is less expensive than coke used for other applications due to high levels of sulfur. It also contains a high metal content making it unusable for making components such as carbon anodes.

However, due to its higher heat content, it’s perfect solid fuel, and its characteristics can go head to head with coal. 

Since the high sulfur content decreases the market value of petroleum coke and poses a significant environmental risk, multiple methods of desulfurization were proposed in the last few. Including techniques such as solvent extraction, thermal desulfurization, desulfurization in an oxidizing atmosphere, etc. However, no methods yielded favorable results so far.

2. Low sulfur coke and calcination

Lower sulfur content and low level of impurities in this type of petroleum coke make it valuable because it can be thermally treated and turned into calcinated or crystalized coke. It can then be used to create anodes for steel and aluminum extraction. 

Low sulfur pet coke is rare as only about 20% of manufactured material has a low sulfur/low metal impurity content.

This material is a commercial product used in different industries and a wide range of products,  most notably:

1. Fuel

Since 80% of pet coke produced is fuel-grade, this material is widely used in clement clinks and electricity production as it’s a perfect substitute for coal in boilers and furnaces.

2. Aluminum

At the moment, the only commercially viable method to make anodes for aluminum smelting. This is thanks to calcinated pet coke’s superior electrical resistance and conductivity, as well as its resistance to physical and chemical degradation in the smelting pot.

3. Steel

Calcinated pet coke is a viable substitute for different types of coal used in the metal industry. For instance, pet coke can replace coal as a raw material for coke oven batteries, but it can also replace pulverized coal injected into blast furnaces.

Needle coke is also often used to produce electrodes for electric arc furnaces due to its electrolytic properties.

4. Glass and brick

Due to the low ash content of calcinated coke, glass, and brick manufacturers value it above other fuel sources.

5. Colorings

One of the crucial materials in the production of titanium oxide is calcinated coke. Titanium oxide is most often used as a substitute material for lead in paint, additionally, it’s a key material of pigment in different kinds of colorings, such as food, plastic, and even sunscreen.

6. Fertilizer

When calcinated coke is carbonized, it produces urea ammonium nitrate and ammonia which can then be used as fertilizer. 

7. Paper

The aforementioned titanium dioxide is used in the production of paper and as a whitener for paper products. But ammonium urea nitrate and ammonia are also widely used in the paper industry for paper and pulp production.

Petroleum coke is everywhere, making it quite sought after (especially the coke with low sulfur content). The only concern is the potential environmental impact of this material, as when it combusts, it releases more CO2 than coal.

However, it doesn’t pose any significant risks to the human respiratory system and it’s stable, so there are no problems with transportation.

The most important factor in its popularity and worldwide use is its cost-effectiveness. It’s easy and cheap to manufacture, it’s easy to transport, and this makes it a great source of energy, especially for developing countries. For example, India imports over 10 million tons of pet coke from the United States anually.

Since it’s favorable for both exporters and importers, the positive sides of this material outweigh the environmental factors by a wide margin.