How to Maintain Proper Humidity Levels in Graphite Grinding Environment (Vertical Roller Mill)

Core Standards (Graphite-Specific)

1. Workshop Ambient RH: 40% – 55% (optimal; <40% = high static/explosion risk; >60% = condensation, agglomeration, flake damage)
2. Raw Material Moisture: ≤0.5% (ASTM C562; max 1.0% for coarse grinding)
3. Mill Internal Control: Keep equipment surface temperature 3–5°C above dew point to eliminate condensation (sweating) on rollers/table
4. Temperature Baseline: 20–25°C stable; avoid >5°C temperature fluctuations

1. Risks of Uncontrolled Humidity

2. Workshop Ambient Humidity Control (Passive + Active)

2.1 Sealing & Isolation (First Step)

• Seal all mill openings, duct joints, and workshop doors/windows to block outdoor humid air
• Install air curtains at material inlets/outlets; use closed-loop air circulation for the grinding zone
• Lay moisture-proof flooring; avoid water cleaning during production

2.2 Active Dehumidification/Humidification

2.3 Ventilation Rules

• Use recirculated dry air instead of fresh outdoor air
• Keep workshop negative pressure (-50 to -100 Pa) to prevent dust leakage and moisture ingress

3. Mill Internal Humidity & Condensation Control (Critical for VRM)

This eliminates mill sweating and ensures stable grinding for graphite.

3.1 Process Air Temperature Tuning

• Control mill inlet air temperature: 60–80°C (fine graphite) / 40–60°C (flake graphite, avoid over-drying)
• Adjust air heater output to keep outlet air temp 10–15°C above dew point
• Do NOT use cold unprocessed air directly into the grinding chamber

3.2 Raw Material Pre-Drying

• Install a rotary dryer before feeding; dry graphite to ≤0.5% moisture
• Avoid feeding wet raw materials (moisture >2% causes immediate agglomeration)

3.3 Anti-Condensation Measures

1. Insulate mill housing, ducts, and classifier with 20–30mm thermal insulation cotton
2. Install electric heat tracing on bearing seats and discharge pipes in winter
3. Drain condensed water from air ducts/cyclones every shift (install automatic steam traps)
4. Purge the mill with dry air for 10 mins before startup/shutdown

3.4 Dust Collector Humidity Control

• Use waterproof/anti-static filter bags; replace damp filters immediately
• Keep dust collector temperature 5–10°C above ambient to avoid internal condensation
• Empty ash hoppers daily to prevent moisture accumulation

4. Real-Time Monitoring & Auto-Control

1. Sensor Placement
   • RH/temp sensors: Workshop, mill inlet, mill outlet, classifier, dust collector
   • Dew point meter: Mill internal (PLC-linked for alarm)
2. Alarm Thresholds
   • High humidity alarm: >58% RH
   • Low humidity alarm: <38% RH
   • Condensation risk alarm: Surface temp ≤ dew point +2°C
3. Auto-Regulation: PLC links dehumidifiers/heaters to adjust humidity without manual operation

5. Routine Maintenance SOP

Daily (Every Shift)

1. Record RH/temp data at 6 key points; drain condensed water
2. Check filter bags for dampness; clean dust accumulation
3. Inspect mill seals for air/moisture leakage

Weekly

1. Calibrate humidity/temp sensors; clean dehumidifier filters
2. Inspect thermal insulation and heat tracing for damage

Monthly

1. Test raw material moisture content (ASTM C562)
2. Full inspection of duct sealing and air circulation system

6. Troubleshooting Common Issues

7. Safety & Compliance

1. Use explosion-proof electrical equipment for all humidity control devices (graphite dust is combustible)
2. No open flames; ground all equipment to eliminate static
3. Comply with NFPA 652 (combustible dust) and GB 50058 standards
4. Dispose of damp graphite waste separately to avoid secondary moisture