How tyre curing press boilers work
Tyre plants use steam at typically 14 to 20 bar to heat the curing presses, both through the platens or moulds and, on many presses, inside the bladder. Each press takes a large draw of steam at the start of its cure and much less afterwards, so a curing shop with dozens of presses produces a steam demand that swings sharply through the day. Larger tyre plants generally use coal or biomass fired AFBC or travelling grate boilers; smaller tyre, tube and retread plants use oil or gas fired packaged boilers. In either case the flue gas passes the boiler, economiser and air heater where fitted, then a dust collector on solid fuels, before the ID fan and chimney. The FD fan supplies combustion air to the grate, bed or burner.
Where the FD fan sits
- Inlet screen
- FD fan
- Air heater
- Air ducts
- Windbox or burner
- Furnace
The fan sits at ground level and pushes ambient air through the air heater, where fitted, into the windbox under an AFBC bed or grate, or into the burner on oil and gas boilers. On fluidised bed boilers it works against the distributor plate and bed, typically 700 to 1,100 mmWC. On packaged boilers the burner fan is often integral to the burner and handles 100 to 300 mmWC.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air after the air heater | 120 to 180°C, downstream of the fan |
| Dust | Clean air; carbon black and rubber dust in tyre plant air can enter an unscreened inlet |
| Pressure at the fan outlet | 100 to 300 mmWC on packaged boilers; 700 to 1,100 mmWC on AFBC |
| Load profile | Follows the frequent press-driven swings in firing rate |
| 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 tyre curing press boilers
| Blade form | Backward curved for efficiency; high-pressure radial or backward curved for AFBC beds |
| Material of construction | Mild steel throughout |
| Drive and arrangement | Direct coupled or direct mounted on the motor shaft |
| Bearings and cooling | Standard pedestal or motor bearings; no cooling needed |
| Flow control | Variable speed drive on the combustion control loop with oxygen trim |
| Also specified | Inlet screen and silencer; airflow measurement in the duct for accurate ratio control |
What this FD fan has to cope with
Air-fuel ratio drift through load swings
If the FD fan responds slower than the fuel feed, the boiler runs short of air at each press start and produces smoke and CO. An airflow measurement and a drive tuned to lead fuel on rising load keep the ratio correct.
Bed slumping at low load on AFBC
When press demand falls, reducing air too far can drop below minimum fluidising velocity. The FD control needs a floor on airflow, and bed compartments are taken out of service rather than starving the whole bed.
Carbon black and rubber dust
Tyre plant air carries fine carbon black and rubber particles that can coat the impeller and choke inlet screens. Taking air from a clean location and cleaning the screen on a schedule prevents unbalance and loss of flow.
Energy and control
The FD fan follows the same rapid load pattern as the ID fan. A variable speed drive with oxygen trim keeps excess air low through the swings, which saves both fan power and fuel. On AFBC boilers the high bed pressure makes the FD fan one of the largest auxiliary loads, so its efficiency at the typical part-load point matters more than at the rated point.
ID fan and FD fan in tyre curing press boilers
| ID fan | FD fan | |
|---|---|---|
| Position | After the dust collector or economiser, before the chimney | Ahead of the air heater, feeding bed, grate or burner |
| What it handles | Flue gas, with fly ash on solid fuels | Clean ambient air |
| Temperature at the fan | 150 to 190°C, up to 240°C upset | Ambient, 25 to 45°C |
| Main design concern | Draft through rapid load swings | Air-fuel ratio through rapid load swings |
| Control | Furnace draft, following the FD fan | Steam header pressure with oxygen trim |
See also the Induced Draft (ID) Fan for tyre curing press boilers.
Questions buyers ask
How fast should the FD fan respond on a tyre curing boiler?
Fast enough to keep the air-fuel ratio within limits as firing rises at press start. In practice this means drive ramp times of a few seconds, airflow measurement and a control strategy where air leads fuel on rising load and lags it on falling load.
Does the FD fan on an AFBC tyre plant boiler need high pressure?
Yes. The fluidised bed and distributor plate need typically 700 to 1,100 mmWC at the fan outlet, far more than a grate or burner. This needs a high-pressure impeller and a robust motor.
Can the existing FD fan be retrofitted with a VFD?
Usually yes, if the motor is suitable for variable speed duty. We check the fan curve against the actual operating range and confirm that the impeller is not close to a resonance in the new speed range.
Information needed to quote an FD fan for tyre curing press boilers
- 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.
- Firing system. AFBC, grate or oil and gas burner, with windbox or burner pressure.
- Air measurement. Whether the duct has an airflow measurement and oxygen trim.
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.