How ceramic tile roller kilns work
Floor, wall and vitrified tiles are fired in single-layer roller kilns 100 to 300 m long, with cycles of about 35 to 70 minutes and peak temperatures of 1,150 to 1,220°C. Tiles ride on ceramic rollers through preheating, firing, rapid cooling, slow cooling and final cooling sections. Burners above and below the roller plane fire natural gas, LPG or, in some clusters, producer gas from coal gasifiers. Flue gas moves back towards the entry and is drawn off by the fume exhaust fan, while cooling sections have their own fans. Hot air from the cooling zone is often used for the dryers, and on some kilns as preheated combustion air. Clays release fluorine and sulphur during firing.
Where the ID fan sits
- Firing section
- Preheating section
- Fume offtakes
- Fume duct
- Fume exhaust (ID) fan
- Scrubber or stack
The fan is at the entry end, drawing fumes through offtakes above and below the rollers. The roller kiln has small cross section, open ends and many roller penetrations, so pressure must be held close to neutral to prevent hot gas leaking out or cold air leaking in. Kiln resistance is low, usually 40 to 120 mmWC, but a lime or alkali scrubber for fluoride removal can add 100 to 200 mmWC.
Gas at the ID fan
| Gas temperature, normal | 180 to 250°C at the fume offtakes |
| Maximum or upset | Up to 300°C when the kiln runs with gaps between tiles |
| Dust at the fan | Light glaze and engobe fines; soot and tar on producer gas firing |
| Moisture and dew point | Water from the tile body and combustion; acid dew point raised by SO₂ and HF |
| Corrosive species | HF from fluoride in clays, SO₂ from the body and fuel, chlorides; tar from producer gas |
| Density at the design temperature | About 0.73 kg/m³ at 210°C, 61% 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 ceramic tile roller kilns
| Blade form | Backward curved, or backward inclined flat blades where tar deposits are expected |
| Material of construction | Mild steel with corrosion allowance; SS 316 where a scrubber or condensing duty is involved |
| Drive and arrangement | Direct coupled, arrangement 8 |
| Bearings and cooling | Pedestal bearings with a shaft cooling disc |
| Flow control | Variable speed drive on entry section pressure, with fast response |
| Also specified | Insulated casing, drain, inspection door and dilution damper |
What this ID fan has to cope with
Pressure balance in a long, open kiln
A roller kiln is open at both ends and the fume fan, cooling fans and burners together fix the pressure profile. Small changes in fume fan speed shift the neutral point and cause hot gas leakage or cold air ingress, both of which affect tile size and flatness. A fast speed loop on entry section pressure keeps the profile steady.
Fluoride and sulphur corrosion
Tile clays release HF and SO₂ during firing, and both condense as acid when the fume cools. Keeping the gas above the acid dew point, insulating the fan and duct, and using SS 316 where a scrubber is installed protect the fan. Fluoride also attacks glass fibre and some coatings.
Tar on producer gas firing
Where kilns fire producer gas from coal gasifiers, tar and soot condense on fan blades, build up and cause unbalance. Flat blades that shed deposits, an access door for cleaning and keeping the gas above the tar dew point reduce the problem. Clean producer gas, well filtered, makes the largest difference.
Energy and control
Roller kilns run around the clock, but output and the gas volume change with tile size and product mix. A variable speed drive on the fume fan follows these changes and saves power. Using cooling zone air for combustion or for the dryers reduces fuel, and tight control of excess air reduces the gas volume the fume fan must move.
ID fan and FD fan in ceramic tile roller kilns
| ID fan | FD fan | |
|---|---|---|
| Position | At the kiln entry, after the preheating section | Beside the firing section, feeding burner headers |
| What it handles | Fumes with HF, SO₂ and sometimes tar | Ambient or preheated air |
| Temperature at the fan | 180 to 250°C | Ambient, or 150 to 250°C preheated |
| Main design concern | Pressure profile and acid corrosion | Burner balance, hot air volume |
| Control | Entry section pressure | Header pressure |
See also the Forced Draft (FD) Fan for ceramic tile roller kilns.
Questions buyers ask
What is the fume exhaust fan on a tile roller kiln?
It is the ID fan of the kiln. It draws the combustion gas and fumes from the firing section back through the preheating section and discharges them to the stack or scrubber. It also sets the pressure profile along the kiln, which affects tile quality.
Why does the fume fan on my tile kiln corrode?
Tile clays release fluorine and sulphur compounds during firing. When the fume gas cools below its acid dew point, especially in a scrubber or on cold duct surfaces, it forms corrosive acid. Insulating the fan and duct, keeping the gas warm, and using stainless steel where needed prevent this damage.
Does producer gas firing affect the tile kiln fume fan?
Yes. Producer gas from coal gasifiers carries tar and soot, which condense on fan blades and build up. The fan needs blades that shed deposits, a cleaning access door and a gas temperature above the tar dew point. Clean, well-filtered producer gas reduces the problem considerably.
Information needed to quote an ID fan for ceramic tile roller 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.
- Kiln data. Kiln length, width, output, firing cycle and fuel.
- Fume treatment. Whether a fluoride scrubber is fitted and the gas temperature at the fan.
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.