What is Petcoke? And What is it Used For?

The demand for petroleum products worldwide is enormous. A barrel of crude oil hides a number of those products in its depths. Petroleum refining produces over 2500 of them, one of which is Petcoke. It has been in production since the 1930s. The growing demand for Petcoke due to industrialization and modernization led to innovations in the bitumen (a sticky, black, highly viscous liquid or semi-solid form of petroleum) extraction process, which have given an impetus to Petcoke production in recent years. 

The crude oil extracted from Earth is processed or refined to get gasoline, lubricating oils, waxes, and jet fuel. The residual crude undergoes further processing or “Coking” to get Petcoke. Often referred to as Petroleum Coke , it is a highly stable, carbonaceous solid fuel which is not considered hazardous.

A thermo-based chemical engineering process, called cracking, is used to break down long petroleum hydrocarbons into smaller chains in coker units. This process occurs at a high temperature and pressure and drives off the gases and other volatiles, separating light and heavy oils and leaving behind the solid Petcoke . The entire process is called Coking. Petcoke is also produced during the making of synthetic crude oil (syncrude) from bitumen.

The raw coke obtained straight out of the coker is called Green Coke . You could also say it is the primary solid carbonization product obtained from the coker. Here the term “green” refers to the coke being unprocessed.

1. Fuel Grade Petcoke – The coke that has a high content of sulphur and metals is called fuel grade Petcoke. Green coke having excessive metal content because it has not yet been calcined, is used as fuel-grade coke. It is considered a very desirable direct replacement of coal.

2. Anode Grade Petcoke – The coke that is low in sulphur and metals is called anode grade Petcoke. Sometimes additional processing of green coke is done by calcining in a rotating furnace to eliminate lingering hydrocarbons. This calcined Petcoke is further processed in an anode baking klin to get anode coke, primarily used in the steel and aluminium industry.

Petcoke can be divided into four main types based on its microstructure. These are:

1. Needle Coke – Needle coke is also called acicular coke. It is a highly crystalline petroleum coke used for manufacturing electrodes. Needle coke is made solely from either Fluid Catalytic Cracking (FCC) decant oil or coal tar pitch.

2. Honeycomb Coke – Honeycomb coke is an in-between or transitional coke. It has uniformly distributed ellipsoidal pores. In comparison to needle coke, it has a lower coefficient of thermal expansion as well as a lower electrical conductivity.

3. Sponge Coke – Sponge coke is a consistent, dull black permeable delayed petroleum coke. The individual spheres are not prominent in it, and the coke has a continuum of form or structure. You could say it is an intermediary between honeycomb coke and shot coke.

4. Shot Coke – Shot coke is an unfavourable grade of Petcoke. It is produced from a delayed coker. It has an irregular structure and is tricky to handle, making it unsuitable for specialty uses.

Petroleum coke is a useful and critical commercial product that finds usage in a wide variety of applications. Some of which include aluminium manufacturing, fuels, and various other products like glass, steel, paint, and fertilisers. Petroleum coke or Petcoke is also used as a fuel in cement ovens, power generation, and various other industries.

1. Fuel – Almost 80% of the worldwide Petcoke production is “Fuel-grade,” which is used to generate electricity and in cement furnaces.
2. Paint And Colourings – Calcined Petcoke is used to make titanium dioxide or TiO2. It is a mineral that substitutes harmful lead in paints. It is also used as a pigment in sunscreens and colourant in food and plastics.
3. Steel – Calcined Petcoke partially replaces coal in metallurgical processes. It takes the form of feedstock for coke furnace batteries. It is also a partial alternative for pulverised coal and is directly infused into blast ovens. In the steel industry, electrodes used in EAC (Electric Arc Furnace) are manufactured from Needle coke.
4. Aluminium – Calcined Petcoke is essential to make anodes for smelting. It is the only commercially feasible method because calcined Petcoke has an exceptional blend of electrical conductivity and resistance or aversion to physical and chemical degradation in the smelting pot. Also, it contains low levels of contaminants.
5. Brick And Glass – Brick and glass manufacturers use calcined Petcoke because it has very little ash content in comparison to other fuels.
6. Fertiliser – Ammonia and urea-ammonium nitrate is produced by gasification of calcined Petcoke. These are then used for making fertiliser.
7. Paper – Ammonia and urea-ammonium nitrate are also used for producing paper and pulp. The titanium dioxide (TiO2) produced from calcined Petcoke is used as a mineral that makes the paper appear white.

1. Petcoke is an alternative to coal fuel with a higher calorific value (>7800 Kcal/Kg compared to 3500-4500 Kcal/Kg for coal).
2. Petcoke is hydrophobic while coal is hydrophilic, giving it a definitive edge over coal during the rainy season.
3. Petcoke is a solid fuel, and hence, has low volatile matter. It means there are no evaporation losses.
4. When it comes to transportation, Petcoke is a blessing. It saves transportation costs because of its higher density than liquid fuels.
5. Petcoke has low ash content.

Petcoke is a very stable fuel and carries minimal risk of combustion during transportation. Nevertheless, it has high carbon content, so when it combusts, it releases up to 10% more carbon dioxide (CO2) per unit of energy than regular coal. This makes Petcoke an enormous contributor to the creation of greenhouse gases. Also, stringent pollution controls are required to capture the sulphur produced during Petcoke combustion, particularly the low-grade Petcoke.

In spite of the environmental concerns, the demand for Petcoke is still very high. Its inexpensive manufacturing, easy availability, stability, convenient transportation, and low price make it a desirable option for all developing countries. As long as the demand for Petroleum Coke remains high, there will not be any decrease in its production even in the foreseeable future.