A pulverizer (also called a coal mill) is a mechanical device used to grind coal into fine powder for combustion in coal-fired power plants. The pulverized coal is then blown into the boiler furnace for efficient burning.
Types of Coal Pulverizers
1. Ball and Tube Mill
– Uses steel balls to crush coal inside a rotating drum.
– Commonly used in older power plants.
2. Vertical Spindle (Roller) Mill
– Uses rollers to press and grind coal against a rotating table.
– More energy-efficient than ball mills.
3. Impact (Hammer) Mill
– Uses hammers or beaters to pulverize coal by impact.
– Suitable for softer coals but produces coarser particles.
4. Bowl Mill (Raymond Mill)
– Uses grinding rollers and a bowl to crush coal into fine powder.
– Widely used in modern power plants due to efficiency.
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Key Components of a Coal Pulverizer
– Grinding Elements (Rollers, Balls, Hammers) – Crush the coal.
– Classifier – Separates fine particles from coarse ones, returning larger pieces for regrinding.
– Air Flow System – Transports pulverized coal to the furnace.
– Drive Mechanism – Rotates the grinding components.
Factors Affecting Pulverizer Performance
– Coal Hardness & Moisture Content – Affects grinding efficiency.
– Fineness Requirement – Typically 70-80% passing through a 200-mesh sieve (~75 microns).
– Wear & Tear – Erosion of grinding elements reduces efficiency over time.
– Air-to-Fuel Ratio – Ensures proper combustion and prevents explosions.
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Common Issues & Solutions
| Problem | Possible Cause | Solution |
|———|————–|———-|
| Low Fineness | Worn rollers/balls, improper classifier setting | Replace grinding parts, adjust classifier |
| High Vibration | Unbalanced load, misalignment | Check alignment, balance load |
| Coal Blockage | Moisture buildup, foreign material | Improve drying, remove debris |
| Excessive Wear | Abrasive coal quality | Use wear-resistant materials |
Applications
– Thermal power plants (for pulverized coal combustion)
– Cement industry (coal grinding for kilns)
– Industrial boilers