Glossary
Cement
Raw mill, cement mill and coal mill
Also known as raw mill, cement mill, coal mill, ball mill (cement).
Cement plants run three principal mills, each grinding a different material:
| Mill | Input | Output | Destination |
|---|---|---|---|
| Raw mill | Limestone + clay + sand + iron | Raw meal (cement-fineness powder) | Preheater tower feed |
| Cement mill | Clinker + gypsum + additives | Finished cement powder | Bagging / despatch |
| Coal mill | Raw coal or petcoke | Pulverised fuel | Rotary kiln main burner |
Mill technology
Two technologies dominate:
- Ball mill — rotating cylinder containing steel balls; mature, robust, energy-intensive
- Vertical roller mill (VRM) — modern preferred design; 30–40% lower energy use; dominant for raw and coal mills
Mill-related fouling
- Mill duct fouling — fine powder coats hot-gas ducts, reducing flow
- Coarse-fines bridging in mill discharge silos
- Sticky cement coating in cement-mill ducting during high-humidity periods
- Coal-mill blade and classifier fouling — fire hazard
Sonic horns on mill exhaust ducting and discharge silos prevent the build-up that disrupts mill throughput.
Related terms
Related terms
- Vertical roller millA vertical roller mill grinds material between rotating tyres and a static table inside a single vertical housing. 30–40% lower energy than ball mills; dominant for raw and coal grinding.
- ClinkerClinker is the dark, hard nodular intermediate product of cement manufacture, formed by burning raw meal at 1,450 °C in the rotary kiln before grinding to cement powder.
- Preheater towerA preheater tower is a vertical stack of cyclone separators that pre-heats raw meal with kiln exhaust gas before it enters the rotary kiln. The most fouling-prone section of any cement plant.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.