How vertical shaft kiln mini cement plants work
A vertical shaft kiln makes clinker in a refractory-lined shaft, typically 2 to 3 m in diameter and 8 to 10 m high. Raw meal is ground with fine coal or coke breeze, the black meal process, and formed into moist nodules with 12 to 14% water. The nodules are fed at the top onto a shallow burning zone just below the surface, where the fuel inside them burns at about 1,300 to 1,400°C. Combustion air is blown in at the bottom by a high pressure blower and passes up through the clinker, cooling it and preheating itself. The gas leaves the top of the bed at 100 to 250°C, laden with moisture and dust. Older VSKs used only a stack; current plants add a dust collector and an ID fan to meet emission limits.
Where the ID fan sits
- Kiln shaft and bed
- Kiln hood
- Cyclone
- Bag filter or wet scrubber
- ID fan
- Stack
The fan sits after the dust collector at ground level near the kiln. Upstream are the kiln hood, a cyclone and a bag filter or scrubber, with a total resistance of typically 150 to 250 mmWC. The air blower at the bottom pushes the gas through the bed, so the ID fan only needs to take the gas away from the kiln top and overcome the collector, while keeping the open feeding area at a slight suction so that dust does not spill onto the charging floor.
Gas at the ID fan
| Gas temperature, normal | 80 to 150°C at the fan |
| Maximum or upset | Up to 300°C when the bed thins or a blow-through occurs |
| Dust at the fan | Low after a bag filter; wet, sticky raw meal and coal dust if it fails |
| Moisture and dew point | High from nodule water; dew point about 55 to 65°C |
| Corrosive species | SO₂ from coal sulphur; CO from incomplete combustion |
| Density at the design temperature | About 0.90 kg/m³ at 120°C, 75% 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 vertical shaft kiln mini cement plants
| Blade form | Radial-tipped or backward inclined with thick blades, tolerant of wet deposits |
| Material of construction | Mild steel with corrosion allowance; SS 304 or coated wetted parts after a wet scrubber |
| Drive and arrangement | Belt driven or direct coupled, arrangement suited to cleaning access |
| Bearings and cooling | Standard bearings outside the gas stream |
| Flow control | Variable speed drive on kiln top suction |
| Also specified | Casing drain, large inspection door and water wash connection |
What this ID fan has to cope with
Condensation and mud on the impeller
Kiln top gas from wet nodules is close to saturation. Where it cools in long ducts or at stops, water condenses and wets the dust into mud on the blades. Insulated ducts, a drain, and a blade form that does not hold deposits keep the fan in balance.
Blow-through and hot gas
If the bed thins or channels, hot gas from the burning zone short-circuits to the top and the fan sees temperatures well above normal. The fan is stress-checked at the upset temperature and the bag filter needs a temperature trip or dilution damper.
Acid corrosion after a scrubber
A wet scrubber absorbs SO₂ into the water, and the saturated gas carries acid droplets into the fan. Stainless or coated wetted parts and a mist eliminator before the fan prevent rapid corrosion.
Energy and control
A VSK runs continuously but its output follows the bed condition, and the operator adjusts air and draft often. A variable speed drive on the ID fan, controlled on kiln top suction, follows the air blower without manual damper changes. Keeping suction low saves power and reduces dust pull-out from the bed, which also lowers the load on the collector.
ID fan and FD fan in vertical shaft kiln mini cement plants
| ID fan | FD fan | |
|---|---|---|
| Position | After the cyclone and bag filter or scrubber | At the kiln bottom, below the clinker bed |
| What it handles | Cool, humid kiln top gas | Ambient air |
| Temperature at the fan | 80 to 150°C | Ambient |
| Main design concern | Condensation and wet dust deposits | High pressure against a changing bed |
| Control | Kiln top suction | Air flow through the bed |
See also the Forced Draft (FD) Fan for vertical shaft kiln mini cement plants.
Questions buyers ask
Does a vertical shaft kiln need an ID fan?
Older VSKs ran on natural draft with a short stack. To meet dust emission limits most plants now add a bag filter or scrubber, and the extra resistance needs an ID fan after the collector, while the bottom blower still supplies all the combustion air.
Why do VSK ID fans clog and vibrate?
The kiln top gas is cool and very humid from the nodule water. Fine meal and coal dust that passes the collector becomes wet and sticks to the blades, especially after stops, and the uneven deposit unbalances the rotor.
What temperature is the VSK exhaust gas?
Usually 100 to 250°C at the kiln top, and 80 to 150°C at the ID fan after the collector. The heat exchange between the rising gas and the fresh nodules keeps the exit temperature low.
Information needed to quote an ID fan for vertical shaft kiln mini cement plants
- 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.
- Collector. Bag filter or wet scrubber, its pressure drop and the gas temperature after it.
- Kiln data. Kiln diameter, clinker output and the air blower flow and pressure.
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.