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 ID fan sits
- Furnace
- Boiler bank
- Economiser
- Air heater
- Dust collector
- ID fan
- Chimney
The fan sits after the dust collector on coal and biomass units and directly after the economiser on oil and gas packaged boilers. Suction at the fan inlet is typically 150 to 250 mmWC on a fluidised bed or grate boiler with a bag filter, and 50 to 120 mmWC on a packaged boiler. Because the presses change load quickly, the fan and its drive must follow the FD fan within seconds to keep the furnace under slight suction and avoid puffing at the doors and ports.
Gas at the ID fan
| Gas temperature, normal | 150 to 190°C after the economiser or air heater |
| Maximum or upset | Up to 240°C on fouled surfaces or at peak steam draw |
| Dust at the fan | Coal or biomass fly ash at 50 to 150 mg/Nm³ after a bag filter or ESP; negligible on oil or gas |
| Moisture and dew point | Acid dew point matters on furnace oil and high-sulphur coal; the gas must stay above about 140 to 160°C at the fan |
| Load profile | Rapid swings between about 40 and 100% of rated steam as presses start their cures |
| Density at the design temperature | About 0.80 kg/m³ at 170°C, 67% 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 tyre curing press boilers
| Blade form | Backward curved for efficiency, with wear liners on coal or biomass behind a bag filter |
| Material of construction | Mild steel; wear-resistant plate on the blades for solid fuels; corten class steel where oil firing brings acid dew point risk |
| Drive and arrangement | Direct coupled, arrangement 8, with a motor and drive rated for frequent acceleration |
| Bearings and cooling | Pedestal bearings outside the gas stream with a cooling disc |
| Flow control | Variable speed drive on furnace draft with fast ramp settings tuned to the FD fan |
| Also specified | Inlet damper for isolation, vibration monitoring, and an inspection door |
What this ID fan has to cope with
Furnace puffing during press start-up
When several presses open their steam valves together, the firing rate jumps and the FD fan responds before the ID fan, so the furnace goes briefly positive. Tuning the ID fan drive to lead or match the FD fan, with feed-forward from the FD speed, keeps draft negative through the swing.
Low-load acid condensation
Long periods at low press demand, such as weekends or changeovers, lower the gas temperature at the fan. On oil firing this can put the casing and ducts below acid dew point. Holding a minimum economiser outlet temperature and using corrosion-resistant steel for the casing protect the fan.
Drive and motor heating from cycling
Repeated acceleration and deceleration through the shift heats the motor and stresses couplings. A motor rated for variable speed duty, a flexible coupling and a drive with suitable ramp rates avoid premature failure.
Energy and control
Because press demand swings so often, a damper-controlled ID fan spends most of its time throttled and wastes considerable power. A variable speed drive following furnace draft brings fan power down with the steam load. Steam accumulators or a header pressure strategy that smooths boiler firing also reduce the size and frequency of the swings, which helps both fans and the combustion efficiency.
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 Forced Draft (FD) Fan for tyre curing press boilers.
Questions buyers ask
Why does my tyre plant boiler furnace go positive when presses start?
The steam demand rises suddenly when presses begin their cure, the combustion control increases fuel and air, and the ID fan lags behind. The fix is drive tuning and feed-forward so the ID fan follows the FD fan quickly, with enough fan margin to cover the peak.
Is a VFD worthwhile on an ID fan for a tyre curing boiler?
Yes, in most cases. The load pattern from curing presses keeps the boiler away from full load for much of the time, and a variable speed drive saves energy while giving faster, smoother draft control than a damper.
What size ID fan does a tyre plant boiler need?
It depends on the fuel, excess air, gas temperature and system resistance at peak press demand. Send the boiler data, fuel analysis and the existing fan nameplate, and we will calculate the duty and margin for the swings.
Information needed to quote an ID fan for tyre curing press boilers
- 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.
- Press load pattern. Number of curing presses, cure cycle time and the observed range of steam flow.
- Fuel. Fuel fired now and any planned change, such as from oil to biomass.
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.