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 FD fan sits
- Cooling section hot air or inlet filter
- FD fan
- Combustion air header
- Burner valves
- Burners above and below rollers
The fan feeds headers on both sides of the kiln, supplying burners above and below the roller plane along the firing section. Where it takes air from the cooling section, the air enters at 150 to 250°C, saving fuel but increasing the volume and requiring a heat-resistant fan. The fan typically works against 300 to 600 mmWC, including the header, valves and burners.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C, or 150 to 250°C with cooling section air |
| Dust | Clean ambient air; some fines in recovered cooling air |
| Pressure at the fan outlet | Typically 300 to 600 mmWC |
| Burner count | Often over a hundred burners on a large kiln |
| Density at the design temperature | About 1.13 kg/m³ at 40°C, 94% 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. |
FD Fan selection for ceramic tile roller kilns
| Blade form | Backward curved high-pressure, with a stable curve |
| Material of construction | Mild steel for ambient air; heat-resisting steel for preheated air |
| Drive and arrangement | Direct coupled |
| Bearings and cooling | Standard bearings; cooling disc and heat shield for preheated air |
| Flow control | Variable speed drive on header pressure |
| Also specified | Inlet filter on ambient duty, standby fan on large kilns |
What this FD fan has to cope with
Hot air volume and density
With combustion air taken from the cooling section at 200°C, the volume is about 50% more than at ambient, and the fan must be sized for it. A fan selected at ambient density falls short at full firing. The selection is made at the actual air temperature, with a check at cold start when the air is ambient.
Burner balance above and below the rollers
Burners above and below the rollers fire into different spaces, and uneven air supply leads to temperature differences that curl or warp tiles. Separate headers or zone valves for top and bottom burners, fed by a fan with pressure margin, keep each side under control.
Many burners on one fan
On a large kiln, over a hundred burners share one fan. Any instability in its pressure affects them all. A fan with a steadily rising curve, operating at a point well away from the peak, gives the burner controls a reliable supply to work with.
Energy and control
Fuel is by far the largest energy cost on a tile kiln, so the combustion air system is designed around fuel saving. Using hot air from the cooling section reduces fuel considerably, though it increases fan volume. A variable speed drive on header pressure saves fan power, and keeping excess air low at the burners saves fuel and reduces fume volume.
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 Induced Draft (ID) Fan for ceramic tile roller kilns.
Questions buyers ask
What is the FD fan on a tile roller kiln?
It is the combustion air fan that supplies air to the burners above and below the rollers in the firing section. It can take ambient air or hot air from the cooling section. The cooling and fume exhaust fans are separate machines with their own duties.
Can a tile kiln combustion air fan use hot air from the cooling zone?
Yes, many kilns do this to save fuel. The fan must then be designed for air at 150 to 250°C, with heat-resisting materials, a cooling disc on the shaft and selection at the hot air density. The fan is also checked at ambient air for start-up conditions.
How many burners can one combustion air fan serve on a roller kiln?
One fan commonly serves all the burners on a kiln, often over a hundred. It is sized for the total air at full firing, with headers designed to give even pressure along the kiln. Large kilns sometimes split the burners between two fans for redundancy.
Information needed to quote an FD fan for ceramic tile roller kilns
- Duty point. Combustion air quantity in m³/h or kg/h and the static pressure at the fan outlet, with the margins you want.
- Air condition. Site ambient temperature range and altitude, and whether the fan takes ambient air or air already heated.
- System. Boiler or furnace capacity and fuel, resistance of the air heater, windbox, grate or burner, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), noise limit, rotation and discharge orientation.
- Air source. Whether combustion air is ambient or recovered from the cooling section, and its temperature.
- Burner layout. Number of burners above and below the rollers and the required air 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.