Fly ash grinding in a Vertical Roller Mill (VRM) is an efficient process for improving the fineness and reactivity of fly ash, making it suitable for use in cement and concrete applications. Here’s an overview of the key aspects:
1. Why Grind Fly Ash?
– Fly ash (a byproduct of coal combustion) often has inconsistent fineness.
– Grinding improves its Blaine fineness (typically to 400–600 m²/kg), enhancing pozzolanic activity.
– Ground fly ash can replace cement more effectively, reducing CO₂ emissions.
2. Advantages of VRM for Fly Ash Grinding
– Energy Efficiency: VRMs consume 30–50% less energy than ball mills.
– Drying Capability: Can handle moist fly ash (up to ~15% moisture) with integrated hot gas drying.
– Compact Design: Smaller footprint compared to traditional ball mills.
– Adjustable Fineness: Easy control over particle size distribution.
.jpg)
3. Challenges & Solutions
| Challenge | Solution |
|———–|———-|
| Low grindability (hard particles) | Optimize grinding pressure, roller speed |
| High abrasiveness (SiO₂/Al₂O₃) | Use wear-resistant materials (e.g., high-chrome rollers/tables) |
| Moisture content | Pre-drying with hot gas (~200–300°C) |
| Segregation risks | Proper air classification and circulation |
4. Process Flow in VRM
1. Feed System: Fly ash is fed into the mill via a screw conveyor or pneumatic system.
2. Grinding Zone: Rollers compress and shear material against the rotating table.
3. Classification: Ground particles are separated by an internal/external classifier; coarse particles are recycled.
4. Drying (if needed): Hot gases dry moisture during grinding.
5. Product Collection: Fine fly ash is collected in a baghouse or cyclone.
5. Operational Parameters
– Grinding Pressure: 50–120 bar (adjust based on fineness).
– Gas Temperature: 150–300°C (for drying).
– Mill Speed: 30–60 rpm (table rotation).
– Classifier Speed: Adjust to target fineness.
6. Applications of Ground Fly Ash
– Cement Replacement (20–35% in blended cement).
– High-Performance Concrete (improves workability