How to Separate Ultra-Fine Particles from Green Coke During Shaping

During green coke spheroidization, sharp edges are abraded by inter-particle friction, continuously generating large quantities of ultra-fine debris. If these ultra-fines remain mixed in the quasi-spherical green coke product, they will reduce D10 value, raise BET specific surface area, destabilize tap density, and worsen electrochemical performance of the final artificial graphite anode. Separating ultra-fine particles online during the shaping process, rather than only after spheroidization, is critical to maintain target PSD and consistent precursor quality. JACAN circulating spheroidizer integrates built-in dynamic classification plus secondary fine separation to continuously remove ultra-fine fractions while retaining qualified quasi-spherical green coke.

Source of Ultra-Fines in Green Coke Shaping

Ultra-fine particles mainly come from edge abrasion of angular green coke particles. Brittle petroleum coke or needle coke easily sheds micro-fragments under particle-to-particle rubbing.
Key risks of residual ultra-fines:

• D10 decreases, PSD span becomes wider
• BET rises sharply
• Higher electrolyte consumption and low initial coulombic efficiency in finished anode
• False tap density readings caused by fine powder filling particle voids

Core Separation Principle

Adopt closed-loop staged air classification inside the spheroidization system, using airflow and classifier wheel centrifugal force to split powder into three streams simultaneously:

1. Oversized, under-shaped green coke: returned to shaping chamber for re-polishing
2. Qualified quasi-spherical green coke (target D50 6–18 μm): collected as intermediate product
3. Ultra-fine abrasive debris: captured and discharged out of the shaping loop, not returned back

Step-by-Step Method for In-Line Ultra-Fine Separation During Shaping

1. Pre-remove excess fines before entering spheroidizer

Do not rely only on the spheroidizer to handle all ultra-fines. The upstream air classifier mill must strip most pre-existing ultrafine fines before feeding green coke powder into the shaping unit.

• Control green coke moisture ≤0.3% to prevent agglomeration; agglomerated fines will re-attach to coarse particles and evade separation.
• Use magnetic separation to eliminate metal impurities that cause random particle fracture and extra fine generation.
  Narrow the incoming PSD before shaping to reduce the total fine load entering the spheroidization loop.

2. Built-in dynamic turbo classifier inside circulating spheroidizer

This is the primary on-line fine separation unit during shaping:

• Adjust classifier wheel rotation speed and primary/secondary airflow to set the fine cut point.
• Higher classifier wheel speed increases centrifugal force; only extremely fine particles can escape through the classifier along with airflow.
• Tuned airflow carries ultra-fine abrasion products away immediately after they are generated.
  The classifier distinguishes between intact quasi-spherical coke particles and tiny edge fragments. Qualified shaped particles drop back to the shaping chamber or go to product collection, while ultra-fines are transported to the dust collection system.

3. Optimize airflow balance for fine particle extraction

Airflow is the carrier for ultra-fine separation.

• Increase fine extraction airflow to enhance the capture capacity of submicron and micro-fines.
• Avoid excessive turbulence that blows qualified medium-sized green coke powder into the fine fraction.
• Stabilize negative pressure of the whole closed system; pressure fluctuation will cause fines back-mixing and unstable separation efficiency.

4. Secondary fine classification after spheroidization

For high-spec anode precursors, add an independent multi-stage air classifier after the spheroidizer as polishing separation:

• Primary separation: reject coarse, incompletely shaped particles and send them back to spheroidizer.
• Secondary fine cutting: further strip residual ultra-fines that escaped the built-in classifier.
  This two-stage classification greatly reduces fine tail fraction and stabilizes D10.

5. Pulse dust collection for ultra-fine powder collection

Ultra-fine coke powder carried by airflow enters high-efficiency pulse bag dust collectors with fine-grade filter media. The separated ultra-fines are collected as by-products and isolated from qualified quasi-spherical green coke. Regular filter bag maintenance prevents fines leakage and re-contamination of main product.

Key Parameter Tuning Guidelines

1. Classifier wheel speed: Raise speed to intercept more green coke particles and allow only ultra-fines to pass into the fine stream. Do not over-speed, otherwise qualified medium particles will also be wasted.
2. Extraction airflow: Increase airflow to improve fine removal; test incrementally to avoid loss of target product.
3. Spheroidizer rotor speed: Keep rotor at minimum speed required for edge rounding. Higher rotor speed generates more fines and overloads the classification system.
4. Circulation cycles: Avoid redundant circulation passes, which continuously produce extra ultra-fine debris.

Common Troubleshooting

1. Ultra-fines cannot be fully separated, D10 keeps dropping
   Cause: Fine extraction airflow insufficient; classifier cut point not properly set.
   Solution: Boost fine extraction airflow, adjust classifier wheel speed to tighten fine cut.
2. Product yield loss, qualified green coke is taken away together with ultra-fines
   Cause: Airflow too high or classifier speed too high.
   Solution: Reduce extraction airflow and lower classifier wheel speed moderately.
3. Fines re-attach onto particle surfaces after separation
   Cause: High powder moisture.
   Solution: Re-dry feedstock to ≤0.3%.
4. Fines accumulate inside shaping chamber
   Cause: Poor negative pressure balance, blocked filter bags.
   Solution: Check dust collector, clean filter bags, stabilize system negative pressure.

Separating ultra-fine particles from green coke during shaping is realized by combining pre-fine removal from the upstream air classifier mill, built-in dynamic classification inside the circulating spheroidizer, airflow fine extraction and post multi-stage classification. The system continuously extracts edge-generated abrasive fines online during spheroidization rather than after the whole shaping process. By tuning classifier wheel speed and extraction airflow, manufacturers remove ultra-fine debris without losing qualified quasi-spherical green coke. This method stabilizes D10, controls BET and PSD span, ensuring the shaped green coke precursor meets the strict requirements of lithium battery artificial graphite anode.