How to Homogenize Artificial Graphite Anode Raw Materials

Artificial graphite anode raw materials mainly include calcined petroleum coke/needle coke (solid carbon aggregate) and coal tar/petroleum pitch (binder). Raw material homogenization eliminates batch-to-batch differences in particle size, volatile content, impurity distribution, and pitch coating uniformity. Inconsistent homogenization leads to unstable tap density, uneven graphitization, large fluctuation of capacity & cycle life, and poor electrode coating performance.

The full homogenization system is divided into four core stages: raw coke batch homogenization (dry powder pre-homogenization), formula batching & low-temperature dry mixing, high-temperature thermal kneading homogenization (core), and post-granulation re-homogenization, matched with industrial low-iron sealed mixing equipment and uniformity testing standards for JACAN graphite production lines.

1. Stage 1: Raw Coke Batch Homogenization (Upstream Pre-Homogenization)

Purpose

Unify multi-batch calcined coke with varying volatile matter, particle size, ash content, and true density to eliminate raw material inherent fluctuations before crushing & milling.

Process Flow

1. Raw material incoming classification & stacking homogenization
   • Separate calcined coke by origin, calcination furnace batch, and volatile index; stack in layered stock silos (layer thickness ≤ 50 cm).
   • Multi-layer vertical cutting reclaiming: cross-cut top-to-bottom layers to mix different batches continuously; homogenization cycle ≥ 24 h.
   • Control target: Volatile matter fluctuation of mixed coke ≤ ±0.1%, ash content difference ≤ ±5 ppm.
2. Closed silo powder circulation homogenization (after crushing & classification)
   After jet milling, coke powder with D50 8–20 μm is transported to large sealed homogenization silos with nitrogen protection.
   • Circulation mode: Bottom air lift + top falling material closed loop circulation, circulation times ≥ 6 full cycles.
   • Environment control: Silo internal RH ≤ 35%, powder moisture ≤ 0.3% to avoid agglomeration blocking circulation pipes.
3. Magnetic separation interlock
   Multi-stage magnetic separators are installed on circulation pipelines to remove iron wear debris, preventing local metal impurity enrichment in mixed powder.

Uniformity Inspection Standard

Sampling from silo top, middle, bottom; D50 deviation ≤ ±0.5 μm, total metal impurity difference ≤ 3 ppm between samples.

2. Stage 2: Precision Batching & Low-Temperature Dry Mixing (Formula Homogenization)

Core Function

Accurately proportion multi-grade coke powder (bimodal PSD large/small fractions) and pre-mix solid coke with solid pitch powder before thermal kneading to avoid local pitch agglomeration.

Equipment & Standard Parameters

1. Double-shaft sealed dry mixer (full zirconia lining, no iron pollution)
2. Batching precision: MES automatic loss-in-weight feeding system, single component feeding error ≤ ±0.2%
3. Formula matching rules:
   • High-power artificial graphite: Large coke D50 16–22 μm + fine coke D50 7–12 μm bimodal blend ratio 7:3 ~ 8:2
   • Energy-type artificial graphite: Single medium-size coke D50 12–16 μm
   • Pitch solid powder addition: 10–18 wt% of total coke mass (adjust by pitch softening point)
4. Dry mixing process parameters:
   • Mixing temperature: 60–90°C (lower than pitch softening point to prevent premature melting & agglomeration)
   • Mixing speed: 40–60 rpm, holding time 30–45 min
   • Nitrogen closed circulation to isolate oxygen, avoid coke surface oxidation

Homogenization Judgment Index

Randomly extract 5 samples from mixer discharge; pitch residue distribution deviation ≤ ±0.3 wt% across samples, no visible pitch particle agglomerates.

3. Stage 3: High-Temperature Thermal Kneading Homogenization (Most Critical Core Step)

This step melts solid pitch into liquid binder under heating, fully coats every coke particle surface, and forms a uniform plastic paste—decisive for consistent granulation and post-graphitization performance.

Industrial Kneading Equipment

Double Z-blade high-temperature kneader with jacket heat conduction oil heating, sealed nitrogen atmosphere, full PU lining to avoid metal contamination.

Standard Kneading Process Parameters

1. Heating temperature: 150–200°C (matched with pitch softening point; medium-temperature pitch 160–180°C, high-temperature pitch 180–200°C)
2. Kneading rotation speed: Main shaft 20–35 rpm, counter-rotating dual blades for strong shear & folding mixing
3. Total kneading holding time: 60–90 min
   • First 20 min: Uniform melting & spreading of liquid pitch over coke powder surface
   • Middle 30–50 min: Shear break coke agglomerates, eliminate dry coke powder pockets
   • Final 10 min: Low-speed homogenization to release internal bubbles
4. Pressure auxiliary homogenization: Micro positive-pressure nitrogen (0.02–0.05 MPa) inside kneader to suppress volatile escape during mixing

Key Homogenization Mechanism

• Liquid pitch forms continuous thin coating film (0.5–3 μm) on each coke particle; no bare coke particle clusters.
• Shear force breaks coke agglomerates, fills gaps between large coke particles with fine coke + molten pitch, realizing uniform bimodal particle stacking.

Post-Kneading Uniformity Test

Cut paste samples at front, middle, tail of kneader discharge; test tap density of cooled solidified paste: fluctuation ≤ ±0.03 g/cm³, no hard coke lumps or pure pitch blocks.

4. Stage 4: Granulation & Secondary Re-Homogenization

After kneading, the plastic paste is pelletized into secondary spherical particles; re-homogenization eliminates granule size segregation and uneven pitch distribution across granules.

Step 4.1 Thermal Granulation Homogenization

1. Equipment: High-temperature closed granulation reactor (250–350°C)
2. Working principle: Stirring shear cuts large paste blocks into uniform secondary spherical granules (D50 12–25 μm for battery anode)
3. Control: Nitrogen shielding, stirring speed 10–25 rpm, granulation holding time 40–60 min to ensure identical pitch content inside each granule.

Step 4.2 Post-Granulation Cold Homogenization Silo

1. Cool granulated material to ≤80°C under nitrogen protection, then transport to large homogenization silos.
2. Closed air-lift circulation homogenization: ≥4 full circulation cycles to resolve particle size segregation (large/small granules layered during cooling & conveying).
3. Silo storage homogenization holding time ≥ 12 h before feeding to pre-carbonization furnace.

5. Auxiliary Homogenization Supporting Technologies

5.1 Particle Size Homogenization via Multi-Stage Air Classification

Before dry mixing, graded coke powder with narrow PSD (span (D90-D10)/D50 ≤1.2) avoids uneven stacking density caused by excessive particle size difference, laying a foundation for uniform kneading.

5.2 Anti-Agglomeration Control

• All homogenization links maintain powder moisture <0.5% via pre-vacuum drying of coke raw materials.
• Dry mixers and silos install ultrasonic anti-blocking devices to eliminate static agglomeration of fine coke powder.

5.3 Full Anti-Contamination Design

All contact parts of mixing/kneading equipment adopt zirconia ceramic, silicon carbide or PU lining; no carbon steel to prevent secondary iron impurity enrichment in local areas of mixed materials.

5.4 Digital MES Real-Time Homogenization Control

• Real-time monitoring of mixing temperature, rotation speed, circulation times, feeding ratio; automatic alarm if parameter deviation exceeds threshold.
• Full batch traceability: Record raw coke batch, mixing time, kneading temperature, homogenization silo circulation cycles for every production lot.

6. Uniformity Acceptance Standard for Fully Homogenized Artificial Graphite Precursor

7. Common Homogenization Defects & Corrective Measures

1. Local bare coke powder (dry pockets after kneading)
   • Cause: Insufficient kneading time, low heating temperature, uneven pitch feeding
   • Solution: Extend kneading holding time, raise jacket oil temperature, split pitch feeding into multiple batches during dry mixing
2. Particle size segregation after granulation
   • Cause: Short silo circulation times, fast conveying speed leading to gravity stratification
   • Solution: Increase circulation cycles to ≥4 times, lower air-lift conveying velocity
3. Batch-to-batch performance drift after graphitization
   • Cause: Insufficient raw coke stacking homogenization, multi-batch coke mixed without silo circulation
   • Solution: Extend raw coke homogenization silo residence time to ≥24 h, implement cross-layer reclaiming
4. Local high iron impurities in finished powder
   • Cause: Worn metal mixing liner, insufficient intermediate magnetic separation
   • Solution: Replace with ceramic lining, add magnetic separators at silo inlet & outlet

8. Complete Industrial Homogenization Full Flow Summary

Calcined coke multi-batch stacking homogenization → crushing + air classification → sealed silo powder circulation homogenization → automatic precision batching → low-temperature dry mixing of coke + pitch powder → high-temperature thermal kneading homogenization (core) → thermal granulation → cooling silo secondary circulation homogenization → qualified homogenized precursor for pre-carbonization & graphitization.