How white cement kilns work
White cement clinker is made from very low-iron raw materials, such as white limestone, kaolin and silica sand, and burnt at about 1,450 to 1,550°C, hotter than grey clinker because there is little iron to act as a flux. Fuel must be low in ash and iron, so furnace oil, petcoke or natural gas is used rather than coal. Kilns are smaller than grey kilns, typically 300 to 1,500 tpd, with a cyclone preheater. The hot clinker is quenched in water or cooled under reducing conditions to keep it white, then finished in an air cooler. The kiln gas leaves the top cyclone at about 300 to 380°C, is cooled in a conditioning tower and cleaned in a bag filter. The kiln ID fan draws gas through the preheater; the burner primary air fan and the cooler fans supply air.
Where the ID fan sits
- Kiln and calciner
- Cyclone preheater
- Kiln ID fan
- Conditioning tower
- Bag filter
- Stack
The fan sits at the top of the preheater tower or at ground level next to it, drawing gas directly from the top cyclone. Upstream are the kiln, riser, calciner where fitted and four to five cyclone stages, so the suction is high, typically 450 to 650 mmWC on a modern preheater. The gas still carries most of the meal that escapes the top cyclone. The fan is placed here because it must create the draft for the kiln itself, while a smaller fan after the bag filter handles the clean side.
Gas at the ID fan
| Gas temperature, normal | 300 to 380°C after the top cyclone |
| Maximum or upset | Up to 450°C during cyclone blockage or feed interruption |
| Dust at the fan | Fine white raw meal, typically 50 to 100 g/Nm³ |
| Corrosive species | SO₂ and SO₃ from petcoke or oil firing; sulphates in the dust |
| Moisture and dew point | Low; the gas stays well above its dew point at the fan |
| Density at the design temperature | About 0.57 kg/m³ at 350°C, 47% of standard air. Pressure developed and power drawn scale with density, so the fan is selected at this condition and the motor is checked at the coldest operating or start-up condition. |
ID Fan selection for white cement kilns
| Blade form | Backward curved with thick blades and wear allowance, or radial-tipped where build-up is severe |
| Material of construction | Boiler quality or high-tensile plate designed for strength at 450°C; wear plate on blade leading edges |
| Drive and arrangement | Direct coupled, arrangement 8 or double inlet with pedestal bearings, variable speed drive |
| Bearings and cooling | Shaft cooling disc and heat shield; oil-lubricated bearings with temperature monitoring |
| Flow control | Variable speed drive on kiln inlet or preheater outlet pressure |
| Also specified | Cleaning doors on the casing, water washing connections and a turning gear for hot stops |
What this ID fan has to cope with
Sulphate build-up on the impeller
Petcoke and oil firing raise the sulphur in the kiln gas, and white cement meal carries sulphates that deposit on blades in layers. Uneven shedding of these layers causes sudden vibration. Blade forms that shed dust, regular washing at kiln stops and vibration monitoring keep the rotor running between cleanings.
Higher draft for harder burning
White clinker needs a hotter burning zone and more combustion air per tonne than grey clinker. The fan must provide this extra draft without running at its limit, especially when the cooler and quench system add air leakage.
Hot stop and shaft bow
If the kiln trips and the fan stops full of gas at 350°C, the shaft bows. A turning gear or slow-speed running until the gas cools prevents heavy vibration at restart.
Iron contamination concerns
Rust and wear debris from fans and ducts do not reach the clinker on the gas side, but returned filter dust does go back to the kiln feed. Keeping the collector and fan casings in sound condition avoids iron-bearing scale finding its way into the product.
Energy and control
White cement kilns are smaller than grey kilns and often run below rated output to match market demand, so the ID fan spends long periods at part load. A variable speed drive matched to kiln draft saves heavily against damper control. Controlling false air at the preheater and kiln inlet seals reduces both fan power and the fuel that a hot, hard-burning white kiln uses.
ID fan and FD fan in white cement kilns
| ID fan | FD fan | |
|---|---|---|
| Position | After the top cyclone of the preheater | On the firing floor, feeding the burner |
| What it handles | Hot kiln gas with fine meal dust | Ambient air |
| Temperature at the fan | 300 to 380°C, up to 450°C upset | Ambient |
| Main design concern | Sulphate build-up and hot strength | High pressure and steady flame shaping |
| Control | Kiln draft | Burner air pressure |
See also the Forced Draft (FD) Fan for white cement kilns.
Questions buyers ask
What temperature does a white cement kiln ID fan handle?
Typically 300 to 380°C at the outlet of the top cyclone, with upsets to about 450°C. The impeller and shaft are designed for strength at the upset temperature, and the bearings are protected by a cooling disc and heat shield.
Why does the ID fan on a petcoke-fired white cement kiln build up dust?
Petcoke adds sulphur to the kiln gas, and the fine meal picks up sulphates that stick to the blades. The deposits grow and break off unevenly, unbalancing the rotor. Washing at stops and a blade form that sheds dust are the usual responses.
Is the white cement kiln ID fan different from a grey cement preheater fan?
The type of fan is the same, but it is smaller and works with finer, often stickier meal and higher sulphur fuels. The draft needed per tonne of clinker is also higher because white clinker is burnt harder.
Information needed to quote an ID fan for white cement kilns
- Duty point. Gas volume in m³/h or Am³/h at the fan inlet and the static pressure the fan must develop, with the margin you want on each.
- Gas condition. Normal and maximum gas temperature at the fan, dust loading after the collector, moisture and any acid gases such as SO₂ or HCl.
- System. Boiler or furnace capacity and fuel, collector type and its pressure drop, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), rotation and discharge orientation, and a layout drawing or site photograph.
- Fuel and sulphur. Fuel type, sulphur content and any history of build-up on the existing fan.
- Preheater. Number of cyclone stages, calciner type and the pressure at the top cyclone outlet.
Built and tested in Chennai
Adroit Fantech Engineers has designed and manufactured industrial fans at Ayanambakkam, Chennai since 2004. Each impeller, casing and shaft is built for the gas and temperature it will see, performance tested as per IS 4894 or BS 848 Part I, and balanced to grade G 6.3 or G 2.5 as per ISO 21940-11, with the records supplied with the fan. We also replace rotors and retrofit existing fans of any make.