Cement
Rotary kiln
Also known as cement kiln, rotary cement kiln.
A rotary kiln is a long (typically 50–100 m), large-diameter (typically 4–6 m), gently inclined rotating steel cylinder lined with refractory brick where preheated raw meal is burned at flame temperatures of ~2,000 °C and material temperatures of ~1,450 °C to form clinker. The rotary kiln is the heart of every cement plant.
Layout
The kiln is fed at its upper end by raw meal pre-calcined in the preheater tower and calciner. The main burner fires at the lower (clinker discharge) end, opposing the gas flow direction. Discharged clinker falls into the clinker cooler below.
Why kiln stops are catastrophic
A cement kiln is designed for continuous operation. Stopping and restarting the kiln means cooling and re-heating massive refractory mass, which damages the lining and incurs substantial fuel cost. A typical unplanned kiln stop loses 24–72 hours of clinker production, equivalent to thousands of tonnes of lost output.
What stops the kiln
Most unplanned kiln stops trace to upstream or downstream problems rather than the kiln itself:
- Preheater pluggage — see preheater tower
- Kiln-inlet ring / snowman formation
- Clinker cooler upset — bridging in the cooler hopper
- Calciner pluggage — accreted build-up from AFR firing
- ID-fan trip — fouled blades causing vibration
Sonic horns installed across the preheater, calciner and kiln-inlet area address several of these directly.
Related terms
Related terms
- 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.
- Clinker coolerA clinker cooler quenches hot clinker discharged from the rotary kiln using forced ambient air. Hot air recovered is sent to the calciner via the TAD; cooler dust hoppers benefit from sonic horns.
- Kiln inlet and riser ductThe kiln inlet / riser duct is the connection between the rotary kiln and the calciner / preheater. It is the most-fouled location in any cement plant, the focal point for sonic-horn cleaning.
- 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.
- Alternative fuelAlternative fuels (AFR) replace fossil fuel in cement kilns. They cut CO2 emissions and waste-disposal cost but increase chlorine, sulphur and alkali loading in the kiln gas.