Grinding dried lignite coal requires proper equipment and safety precautions due to its low rank (high moisture and volatile content) and potential for spontaneous combustion. Here’s a step-by-step guide:
1. Pre-Grinding Preparation
– Dry the Lignite: Ensure the coal is sufficiently dried (moisture content <15%) to improve grindability and reduce clogging.
– Remove Impurities: Screen out rocks, debris, or large chunks that could damage grinding equipment.
2. Choosing the Right Grinding Equipment
Lignite is softer than bituminous or anthracite coal but can be abrasive. Recommended grinders include:
– Hammer Mill: Best for coarse to medium grinding (ideal for lignite due to its brittleness).
– Ball Mill or Vertical Roller Mill: Suitable for fine grinding (if needed for industrial processes like pulverized coal combustion).
– Impact Crusher: For initial size reduction before fine grinding.
3. Grinding Process
1. Crushing (If Necessary): Use a jaw crusher or impact crusher to break large chunks into smaller pieces (~1–2 inches).
2. Primary Grinding:
– Feed dried lignite into a hammer mill or ball mill.
– Adjust the mill settings to achieve the desired particle size (e.g., 0.5–5 mm for boiler fuel, <200 mesh for pulverized coal).
3. Fine Grinding (Optional):
– For ultra-fine powder, use a Raymond mill or vertical roller mill with air classification.
– Control temperature to prevent overheating (lignite can ignite at ~50–60°C).
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4. Safety & Handling Considerations
– Dust Control: Use dust collection systems (cyclones, bag filters) to minimize explosion risks.
– Fire Prevention:
– Avoid excessive heat buildup during grinding.
– Store ground lignite in cool, dry conditions away from ignition sources.
– Monitor for spontaneous combustion.
– Personal Protection: .jpg)
r respirators, gloves, and eye protection due to coal dust hazards.
5. Post-Grinding Steps
– Screening: Use sieves or air classifiers to separate particles by size.
– Storage: Store in sealed containers or silos with inert gas if long-term storage is needed.
Applications of Ground Lignite
– Fuel for power plants (after drying & pulverization)
– Briquette production