High-Purity Calcined Anthracite Coke (CAC): New-Generation Carbon Additive for Steelmaking

Calcined Anthracite Coke (CAC) has long been one of the most reliable recarburizers used in steelmaking and foundry industries. Known for its low ash, low sulfur, low phosphorus, and high carbon content, CAC provides stable performance during melting and refining operations. After undergoing high-temperature calcination in electric or dedicated calcining furnaces, the product achieves high strength, low resistivity, and excellent thermal conductivity, making it an ideal material for raising carbon content in molten steel.

However, traditional CAC and conventional carbon raisers often encounter problems during production—especially impurity contamination. These residual impurities not only limit the carbon yield but also require additional purification steps, which increase energy consumption and raise production costs.

To solve these challenges, a more advanced production technology has emerged: graphitized carbon additive manufacturing.

Conventional carbon raiser production can introduce fresh impurities during mixing, shaping, or calcination. Additional impurity-removal steps must then be added, which prolongs the overall production cycle.

The new method fundamentally improves product quality by integrating graphitization treatment, effectively increasing carbon purity while enhancing electrical and thermal properties. As a result, steel mills and foundries obtain a higher-efficiency, cleaner, and more stable carbon additive suitable for high-grade steel production.

Overview of the New Carbon Additive Manufacturing Process

Below is a simplified and optimized description of the improved graphitization-based production method.

1. Raw Material Preparation & Mixing

Petroleum coke is first ground into a 300-mesh fine powder and thoroughly blended with carbon-rich materials. Asphalt is added to enhance binding strength.
Typical formulation (by weight):

• Petroleum coke: 15–25%

• Asphalt: 1–3%

• Carbon-containing materials: 60–80%

• Composite mixture of micropurified graphite + free carbon (ratio 3:2)

This balanced ratio ensures adequate carbon density, mechanical strength, and graphitization response.

2. Granulation Pretreatment

Water is added to the mixture, and the wet blend is fed into a rotary granulator.
This process forms uniform spherical granules that improve thermal distribution during calcination.

3. Surface Smoothing Treatment (4–10 hours)

Granules are placed in a rotating drum to polish the surface.
This step:

• Removes burrs and protrusions

• Improves particle uniformity

• Enhances heating uniformity during graphitization

• Reduces structural defects

Insufficient surface treatment can cause uneven heating and lower final product quality.

4. Sieving & Size Control

Processed granules are screened to remove pieces larger than 8 mm. Oversized particles are crushed and re-treated until the proper size is reached.

Accurate particle sizing ensures consistent carbon uptake and improved melting efficiency.

5. Low-Temperature Drying

Particles are dried in a vertical dryer at 80–120°C for 60–80 minutes until the material reaches ≤1% moisture.
This safeguards structural stability during high-temperature graphitization.

6. High-Temperature Graphitization (8–10 days)

The dried granules are placed into a graphitization furnace and heated between 2300°C and 2800°C.

Benefits of graphitization include:

• Removal of more than 90% of impurities

• Significant reduction in resistivity

• Higher carbon purity

• Improved crystal structure, increasing conductivity and strength

Increasing the temperature toward the upper limit enhances impurity evaporation and structural transformation.

7. Cooling and Final Packaging

After cooling, the graphitized carbon additive is classified and packaged according to size:

• 0–2 mm

• 2–5 mm

• 5–8 mm

These particle sizes are widely used in steelmaking, precision casting, and high-end material manufacturing.

Comparing Four Test Cases: Key Insights

In experimental trials, four production variations were tested. Results indicate:

1. Graphitization Temperature

Higher temperatures (up to 2800°C) significantly increase impurity removal, enabling ultra-high-purity carbon raiseroutput.

2. Surface Treatment Time

Longer smoothing time creates a more uniform particle surface, ensuring:

• Better heat transfer during drying

• Higher uniformity during graphitization

• Improved final product consistency

3. Raw Material Ratios

Adjusting the ratio of petroleum coke, asphalt, and graphite directly affects the mechanical properties and final application range.

Advantages of the New Graphitized Carbon Additive Technology

• Higher purity – impurity removal > 90%

• Lower resistivity – improved electrical and thermal conduction

• Better carbon recovery rate in steelmaking

• Denser carbon structure and improved compressive strength

• Reduced energy waste and lower production costs

• Consistent particle size and uniform structure

• Ideal for high-quality steels and special alloys

This optimized process offers global steel plants and foundries a more stable and efficient carbon solution. The article outlines multiple manufacturing scenarios that engineers worldwide can adapt and refine based on local production conditions.