what is the pre-crushing requirement for artificial graphite anode raw materials

1. Definition & Core Purposes of Pre-Crushing

Pre-crushing (coarse crushing / primary crushing) is the front-end crushing process for bulk calcined petroleum coke / needle coke before fine jet milling, including multi-stage crushing + initial sieving + impurity removal.
Core objectives:

1. Reduce 50–200 mm bulk coke lumps into uniform small particles, stable feeding for downstream roller mill / jet mill, prevent equipment blockage and uneven grinding load.
2. Expose wrapped mineral gangue, refractory brick debris and metal foreign bodies for front-end magnetic separation & screening removal.
3. Shorten subsequent fine grinding time, narrow particle size distribution (PSD), reduce ultra-fine dust generation and control BET surface area.
4. Create uniform particle gaps for later pitch kneading homogenization, improve pitch coating uniformity and tap density of granulated precursors.

Raw feed: Calcined petroleum coke / needle coke (bulk lump size 50–200 mm, moisture ≤3.0% after calcination cooling).

2. Full Pre-Crushing Process Flow Standard

Raw coke feeding → primary magnetic iron removal → jaw primary coarse crushing → vibrating initial sieving → secondary hammer/roller medium crushing → secondary magnetic separation → secondary sieving → qualified pre-crushed intermediate stock silo
All equipment contact surfaces adopt zirconia ceramic / PU lining to avoid secondary iron contamination.

3. Tiered Particle Size Standard (Critical Technical Index)

3.1 Primary Jaw Coarse Crushing (1st Stage Pre-Crushing)

• Incoming lump size: 50–200 mm bulk coke
• Discharge target particle size: All particles ≤10 mm
• Oversize control standard: Material >10 mm residue on screen ≤2.0% by mass; oversized lumps loop back to jaw crusher for re-crushing
• Gap adjustment: Jaw discharge gap set 8–12 mm according to raw coke hardness
• Supporting equipment: Permanent magnetic separator at discharge port to remove steel fragments from calcination furnace lining

3.2 Secondary Medium Crushing (2nd Stage Pre-Crushing, Mandatory for Battery-Grade)

Adopt sealed hammer crusher or double roller crusher after primary sieving to further reduce particle size:

• Target finished pre-crushed particle size: All particles ≤5 mm (0–5 mm)
• Optimal main fraction distribution: 1–3 mm accounts for 60–75% of total mass
• Fine powder control: Fraction <0.5 mm ≤10% (excess fine powder causes high BET after fine milling, low initial Coulombic efficiency)
• Oversize index: Residue >5 mm after secondary sieving ≤1.0%

3.3 Unified Pre-Crushed Finished Particle Acceptance Standard

4. Equipment Selection & Anti-Contamination Mandatory Requirements

4.1 Standard Pre-Crushing Equipment Matching

1. Primary crushing: Jaw crusher (all lining plates zirconia / high manganese non-magnetic alloy)
2. Secondary crushing: Double roller crusher (low dust generation, controllable particle grading) or closed hammer mill (for high-hardness needle coke)
3. Screening: 10 mesh (2.0 mm) + 5 mesh (4.0 mm) double-layer linear vibrating screen, 316L stainless steel anti-wear mesh
4. Magnetic separation: Double-stage strong magnetic separator (magnetic field strength ≥12000 Gs) before & after crushing

4.2 Strict Anti-Iron Contamination Rules (Battery-Grade Hard Requirement)

1. No carbon steel contact liners inside crushing cavity; replace worn metal liners immediately to avoid iron powder mixing into coke.
2. Two-stage magnetic iron removal:
   • Front feeding magnetic separator: Remove calcination furnace refractory iron scraps, conveying equipment wear debris
   • Post-crushing magnetic separator: Eliminate iron micro-particles generated by crusher liner friction
3. Control target: Total iron impurity of pre-crushed coke ≤8 ppm before fine milling

5. Raw Material Pre-Conditioning Requirements Before Crushing

5.1 Moisture Control

• Calcined coke incoming moisture ≤3.0%
• If moisture >3.0%, equip low-temperature rotary dryer (100–130°C nitrogen hot air) before crushing to eliminate screen mesh blinding and coke agglomeration.
• Pre-crushed finished material moisture stabilized ≤2.0% before entering homogenization silo.

5.2 Foreign Body Removal Standard

1. Manual pre-sorting before feeding: Remove refractory brick, plastic, wood, stone gangue mixed in coke lumps.
2. After two-stage crushing + screening: No visible hard rock, metal blocks, organic foreign bodies in pre-crushed coke.
3. Foreign body inspection limit: ≤2 visible impurities per 100 kg pre-crushed material.

5.3 Raw Coke Batch Homogenization Before Crushing

Stack multi-batch calcined coke by ash, volatile content, true density; cross-layer reclaiming homogenization ≥12 h to avoid large performance fluctuation of pre-crushed material from different batches.

6. Operation & Process Control Parameters

1. Feeding speed: Uniform continuous feeding, avoid instantaneous over-feeding causing crusher cavity blockage; install buffer silo + quantitative screw feeder.
2. Crushing temperature: Closed nitrogen circulation inside crusher to isolate air; material surface temperature ≤150°C to prevent coke surface oxidation.
3. Circulation re-crushing rule: All oversize particles >5 mm automatically return to secondary roller crusher via belt conveyor closed loop, no manual open circulation.
4. Sampling frequency: Test particle size distribution every 30 min at secondary screening discharge port; record oversize residue rate, fine powder proportion.

7. Post Pre-Crushing Intermediate Storage Requirements

1. Sealed nitrogen-blanketed silo storage, internal RH ≤35% to prevent moisture re-absorption.
2. Pre-crushed coke stored in silo for ≥8 h circulation homogenization to eliminate particle size segregation (large/small particle layering).
3. Silo discharge magnetic separation again before feeding to jet mill fine grinding station.

8. Common Unqualified Defects & Adjustment Standards

1. Excess oversize >5 mm (residue >1.0%)
   • Causes: Excessive crusher discharge gap, fast feeding speed, worn screen mesh
   • Solutions: Narrow roller/jaw gap, reduce feeding rate, replace deformed screen cloth
2. Too much superfine powder <0.5 mm (>10%)
   • Causes: Over-crushing, too small roller gap, long hammer impact time
   • Solutions: Widen secondary roller gap, reduce hammer mill rotation speed
3. Excess iron impurities (>8 ppm)
   • Causes: Worn metal liners, insufficient magnetic separator magnetic strength
   • Solutions: Replace ceramic lining, upgrade high-strength magnetic separator, increase magnetic separation times
4. Mesh blinding during screening
   • Causes: Raw coke moisture >3.0%, static agglomeration
   • Solutions: Pre-dry coke, install ultrasonic anti-blocking vibration device on screen

9. Full Pre-Crushing Standard Summary

1. Two-stage crushing flow: Jaw primary crush (≤10 mm) → roller secondary crush (final Dmax ≤5 mm).
2. Grading target: 1–3 mm main fraction 60–75%, fine powder <0.5 mm ≤10%, oversize >5 mm ≤1.0%.
3. Hard quality limits: Fe impurity ≤8 ppm, moisture ≤2.0%, no metal/rock foreign bodies.
4. Supporting configuration: Double-stage magnetic separation, full non-magnetic ceramic lining, closed nitrogen circulation, automatic oversize loop re-crushing.

Qualified pre-crushed coke with uniform particle grading lays a foundation for narrow PSD fine grinding, stable kneading homogenization and consistent electrochemical performance of finished artificial graphite anode. All pre-crushing system design complies with JACAN full-line low-contamination coke pretreatment standards.