The process of making calcined petroleum coke (CPC) involves a series of steps where petroleum coke is subjected to high heat in a controlled environment to remove volatile substances and impurities, resulting in a product with a higher carbon content.
Here is an overview of the typical process for producing calcined petroleum coke:
1. Production of Green Petroleum Coke (GPC)
Before calcination can occur, petroleum coke (often referred to as "green petroleum coke" or GPC) must first be produced. This step occurs during the refining of crude oil, specifically during the delayed coking or fluidized catalytic cracking (FCC) process. The process involves breaking down heavy crude oil fractions into lighter products and petroleum coke as a byproduct.
Coking Process: In the coking process, heavy residual oils are heated and cracked in a furnace, leading to the formation of petroleum coke. The coke that results from this process is called "green" coke, and it contains a significant amount of volatile matter (mainly hydrocarbons) that need to be removed.
2. Calcination
The green petroleum coke is then subjected to calcination-a high-temperature treatment process that drives off volatile hydrocarbons and impurities from the coke.
Steps in the Calcination Process:
Furnace: The GPC is placed into a rotary kiln or a vertical shaft furnace. A rotary kiln is the most common and involves rotating the coke inside a cylindrical kiln that is heated externally by burning fuel (natural gas, oil, or other fuels).
Heating: The temperature inside the kiln is gradually increased to around 1200°C to 1400°C (2200°F to 2550°F). This is high enough to break down the remaining volatile materials in the coke, leaving behind a more pure form of carbon (calcined coke).
Volatilization: During the heating process, the volatile matter (such as sulfur, hydrogen, and other impurities) in the coke vaporizes and is expelled from the kiln. This results in a more stable, dense, and carbon-rich product.
Purification: The calcining process also reduces the sulfur, nitrogen, and metal content, further enhancing the purity and properties of the CPC.
Cooling: After calcination, the hot calcined coke is cooled down in a controlled environment. This cooling can take place in the kiln itself or in a separate cooling section, often using air or water.
3. Quality Control and Screening
After cooling, the calcined petroleum coke is typically screened to ensure uniform particle size, as the material can be used in various industries with different requirements for particle size and purity.
Screening: The coke is passed through sieves or screens to separate fine particles from larger chunks. The fine particles may be further processed or used for specific applications, while larger chunks may be processed into various forms (like anode-grade CPC).
Testing: Samples of CPC are often tested for carbon content, sulfur levels, ash content, particle size distribution, and other impurities (such as metals like vanadium, nickel, and iron) to ensure it meets the quality requirements for its intended use.
4. Storage and Packaging
Finally, calcined petroleum coke is stored in silos or other storage units. It may be packaged for shipment or transported directly to industries (like aluminum smelting or steel production) where it will be used in the production of electrodes, anodes, or other products.
Key Equipment Used in the Calcination Process:
Rotary Kiln: A rotating cylindrical furnace that provides a controlled temperature environment for calcining.
Vertical Shaft Furnace (VSF): A furnace where the coke is fed vertically, and hot gases flow around the coke to provide heat.
Cooling Units: Systems to lower the temperature of calcined coke after the process.
Sieves or Screens: Used to sort the coke by particle size.
Sampling and Testing Tools: For ensuring the quality of the final product.
Summary of the Calcination Process:
Green Petroleum Coke Production: Derived from crude oil refining.
Calcination: The GPC is heated in a rotary kiln or shaft furnace to 1200–1400°C, volatilizing impurities.
Cooling: The calcined coke is cooled down and prepared for further processing.
Screening and Testing: To ensure quality, the coke is screened and analyzed.
Storage and Shipment: The final product is stored and packaged for its intended industrial use.
