How to Control D10 D50 D90 of Green Coke During Grinding Shaping

D10, D50 and D90 are the core particle size indicators for green coke precursors of artificial graphite anode. D50 represents the median particle size, D10 reflects the fine tail fraction, and D90 represents the coarse tail fraction. Stable control of these three values guarantees a narrow PSD span, consistent tap density, and predictable morphology after spheroidization. Poor control will lead to excessive ultrafine fines (low D10) or residual large angular particles (high D90), both of which degrade the electrochemical performance of final graphite anodes. During the integrated grinding-shaping process, D10, D50 and D90 are regulated jointly by pre-treatment, air classifier mill parameters, spheroidization conditions and closed-loop classification.

Understanding D10, D50, D90 for Green Coke

• D50: Median particle size, target range 6–18 μm for anode green coke.
• D10: 10% of particles are smaller than this value. A too-low D10 means excessive ultrafine powder, raising BET and causing severe side reactions in batteries.
• D90: 90% of particles are smaller than this value. A too-high D90 indicates leftover oversized angular coke particles, which cannot be fully rounded in subsequent spheroidization and reduce tap density.
  Span = (D90−D10)/D50; lower span means more concentrated particle size distribution. For green coke precursor, the preferred span ≤0.9.

Root Factors Affecting D10, D50, D90 in Grinding & Shaping

1. Feed PSD and moisture: broad incoming PSD or high moisture leads to agglomeration and unstable particle breakage.
2. Air classifier mill rotor speed: higher speed generates more impact, reduces D50 and D10 simultaneously.
3. Dynamic classifier wheel speed: the most direct parameter to adjust cut point, controlling both coarse tail (D90) and fine tail (D10).
4. Feed rate: faster feeding reduces particle residence time, increases D50 and D90; slower feeding extends grinding time and creates more fines, dropping D10.
5. Spheroidization rotor speed and circulation cycles: excessive impact in shaping stage breaks coke particles, shifts D10 and D50 downward.
6. Airflow balance: primary and secondary airflow control particle transport and fines removal.

Step-by-Step Control Method for D10, D50, D90

1. Stabilize Feedstock to Eliminate Baseline Fluctuation

• Dry green coke to moisture ≤0.3% to prevent agglomeration. Agglomerates are counted as large particles during laser testing but break into fines inside the mill, causing inconsistent D10 / D90 readings.
• Pre-crush bulk coke and remove oversize lumps, narrow raw feed PSD before entering ACM.
• Remove ferromagnetic impurities by magnetic separation; metal contaminants cause random particle fracture.
  The feed material must have a stable particle size band before fine grinding, otherwise D10, D50 and D90 will drift continuously.

2. Tune Air Classifier Mill (Grinding Stage) to Lock Baseline PSD

This stage sets the primary D10/D50/D90 target before spheroidization.

1. Grinding rotor speed: Controls particle breakage intensity.
   • Increase rotor speed: particles get finer; D50, D90 and D10 all decrease.
   • Reduce rotor speed: weaker impact; D50, D90 and D10 rise.
2. Classifier wheel speed: Main lever to cut coarse tail and limit fines.
   • Higher classifier speed: only finer particles pass through; D90 drops, D10 may decrease. Oversized coke is returned for regrinding.
   • Lower classifier speed: allows coarser particles to pass; D90 increases.
3. Quantitative screw feeder: Maintain constant feed rate. Sudden feed surge raises D90; underfeeding generates excess fines and pulls D10 down.
4. Airflow adjustment: Increase fine extraction airflow to continuously remove ultra-fine debris, preventing D10 from falling too low.

3. Adjust Spheroidization Parameters to Avoid PSD Drift in Shaping

Spheroidization’s purpose is edge polishing, not particle crushing. Over-shifting parameters will change D10/D50/D90:

• Keep spheroidizer rotor speed at the minimum level required for quasi-spherical shaping. High rotor speed fractures brittle green coke, produces more fines, reduces D10 and slightly lowers D50.
• Control circulation cycles. Too many cycles abrade particles continuously, generating fine fragments and dragging D10 down.
• Maintain stable airflow to extract edge-generated fines separately, so these fine abrasion products do not mix into qualified powder and distort D10.

Key rule: The PSD after spheroidization should remain close to the PSD exiting the air classifier mill. Significant PSD shift means over-grinding during shaping.

4. Multi-Stage Post Classification to Trim D10 and D90 Tails

After grinding and shaping, multi-stage air classification polishes the two tails:

1. Coarse classification: intercept residual oversized particles to cap D90. Unqualified coarse coke returns to the spheroidizer or ACM.
2. Fine classification: strip excess ultrafine powder to stop D10 from being too small.
   This separates coarse tail and fine tail independently to compress PSD span, instead of only adjusting D50.

5. Sampling, Testing and Closed-Loop Feedback

• Take representative samples after grinding and after spheroidization for laser particle size analysis, record D10, D50, D90 and span.
• If D90 exceeds target: raise classifier wheel speed or reduce feed rate.
• If D10 is too low (too many fines): lower grinding rotor speed, increase fine discharge airflow.
• If D50 deviates: adjust rotor speed first, then fine-tune classifier speed.
  Build a parameter matrix for green coke of different hardness (petroleum coke vs needle coke).

Common Troubleshooting of D10 / D50 / D90 Deviation

1. D90 too high, D50 above target, D10 normal
   Cause: insufficient grinding, classifier speed too low or feed rate too high.
   Solution: increase classifier wheel speed; reduce feed volume.
2. D10 too low, D50 slightly fine, span large
   Cause: over-grinding in ACM or over-circulation in spheroidizer; excess ultrafine fines.
   Solution: lower grinding rotor speed, enhance fine powder extraction airflow, reduce spheroidization cycles.
3. D10 normal, D90 normal, but D50 drifting batch to batch
   Cause: unstable feed moisture or fluctuating feeding rate.
   Solution: stabilize drying system and adopt variable-frequency quantitative feeding.
4. PSD changes after spheroidization, D10 drops obviously
   Cause: spheroidizer speed too high; brittle green coke is fractured during edge polishing.
   Solution: reduce spheroidizer rotor speed and shorten circulation time.

Controlling D10, D50 and D90 of green coke during grinding-shaping relies on separating the two tasks: the air classifier mill sets the baseline particle size distribution, while the spheroidizer only performs mild edge rounding without major particle breakage. Stabilizing feed moisture and feed PSD is the foundation. Operators adjust grinding rotor speed, dynamic classifier wheel speed, feed rate and airflow to set D10/D50/D90, then limit spheroidization impact strength to avoid shifting PSD. Multi-stage classification trims coarse and fine tails separately, and regular laser particle testing provides closed-loop parameter correction. This workflow keeps D10, D50 and D90 within specification, delivering green coke precursors with narrow PSD for artificial graphite anode production.