How textile stenters work
A stenter dries, heat-sets and finishes woven and knitted fabric held by clips or pins on two chains running through a row of heated chambers, typically six to ten. Each chamber has recirculation fans blowing hot air through nozzles above and below the fabric. The air is heated by thermic fluid coils or direct gas burners to about 120 to 160°C for drying and 180 to 210°C for heat-setting polyester and blends. The fabric gives off water, finishing chemicals, spinning oils and plasticisers, which leave as a hot, oily, smoky exhaust. One or two exhaust fans per machine draw this air from the chambers, through any heat recovery unit or exhaust cleaner, to the roof. There is no FD fan in the usual sense: fresh air enters through the fabric slots and chamber openings.
Where the ID fan sits
- Stenter chambers
- Exhaust collection duct
- Lint screen
- Heat recovery or exhaust cleaner
- Exhaust (ID) fan
- Roof stack
The exhaust fan sits on the stenter roof or beside the machine, drawing from a collection duct connected to each chamber. On many stenters it follows a lint screen and sometimes an air-to-air heat exchanger or an electrostatic or scrubbing exhaust cleaner. Suction is moderate, typically 50 to 150 mmWC depending on what is upstream, and the fan is set to hold the chambers slightly negative so smoke and vapour do not escape at the fabric entry and exit.
Gas at the ID fan
| Air temperature, normal | 120 to 180°C at the exhaust duct |
| Maximum or upset | Up to about 220°C during heat-setting at the highest chamber settings |
| Dust at the fan | Lint and fibre fly, with oil mist and condensate that stick to surfaces |
| Moisture and dew point | Humid during drying; water and oil condense on any cold surface |
| Fire risk | Oil-soaked lint in ducts and fan can ignite at stenter temperatures |
| Density at the design temperature | About 0.82 kg/m³ at 160°C, 68% 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 textile stenters
| Blade form | Backward curved or radial, with smooth blades chosen to shed oil and lint |
| Material of construction | Mild steel, or SS 304 where oily condensate persists |
| Drive and arrangement | Belt driven arrangement 9 or direct coupled, with the motor outside the hot air |
| Bearings and cooling | Shaft cooling disc and heat shield |
| Flow control | Variable speed drive controlled from exhaust humidity |
| Also specified | Cleaning doors, oil drain at the casing bottom, insulated casing, and a fire damper in the duct |
What this ID fan has to cope with
Oil and lint deposits
Spinning oils and finishing chemicals condense as the exhaust cools in the duct and fan, and bind lint into a sticky layer. The layer grows unevenly on the blades and causes unbalance. Insulated ducts, a lint screen, cleaning doors and a cleaning interval set by the fabric mix keep the fan running smoothly.
Stenter exhaust fires
Oil-soaked lint in the exhaust duct and fan can ignite at heat-setting temperatures or from a burner flame on gas-fired machines. Fire dampers, temperature monitoring in the duct, a fixed cleaning schedule and a fan casing without ledges or crevices for deposits reduce the risk of a fire spreading along the roof.
Excess exhaust and wasted heat
Many stenters run their exhaust fans at full speed, removing far more air than the evaporation needs. The exhaust then carries little moisture, and the thermic fluid heater or burners heat fresh air that leaves almost at once. Humidity-based speed control saves both fan power and heating energy.
Blue smoke from the stack
Visible blue haze during heat-setting is oil mist. Electrostatic or scrubbing exhaust cleaners remove it, but they add resistance and need to be cleaned themselves. The fan is selected for the cleaner's pressure drop when dirty, not when new, or chamber suction is lost between cleans.
Energy and control
Stenter exhaust is one of the largest heat losses in a finishing plant. Measuring humidity in the exhaust and running the fan at the speed that holds it near the best value for drying can cut heating energy considerably compared with a fan at full speed. Heat recovery from the exhaust to fresh air or process water saves more, provided the exchanger is kept clean of oil.
Questions buyers ask
How much exhaust does a stenter need?
It depends on the moisture in the fabric, the machine speed and the process. Drying needs enough exhaust to carry away the evaporated water, while heat-setting needs less. Most stenters run more exhaust than they need. Measuring exhaust humidity and setting fan speed to hold it near the target is the reliable way to find the right flow.
Why does the stenter exhaust fan vibrate?
Oil and lint build up unevenly on the impeller and change its balance. Regular cleaning through access doors, a lint screen before the fan and insulated ducts that limit condensation reduce the build-up. Balancing the wheel after cleaning restores smooth running, and the vibration trend shows when the next clean is due.
Does a stenter have an FD fan?
Not usually. Fresh air enters through the fabric entry and chamber openings, drawn in by the exhaust fan. Each chamber has recirculation fans that blow hot air onto the fabric, but these are not forced draft fans. If the stenter is heated by a thermic fluid heater, that heater has its own combustion air fan.
Information needed to quote an ID fan for textile stenters
- 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.
- Stenter details. Number of chambers, fabric types, drying and heat-setting temperatures, and the heating system.
- Exhaust treatment. Heat recovery unit or exhaust cleaner downstream, and its resistance clean and dirty.
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.