How sinter plants work
A sinter plant agglomerates iron ore fines, return fines, limestone, dolomite and coke breeze into a strong, porous burden for the blast furnace. The mix is laid 500 to 700 mm deep on a travelling grate sinter machine and ignited by a gas-fired ignition hood. The main exhaust fan then draws air down through the bed, and the burning front moves through it as the pallets travel towards the discharge end. Waste gas leaves the windboxes at about 80 to 150°C, hotter near burn-through, collects in the main gas duct and passes an ESP before the main exhaust fan and stack. Hot sinter is crushed and cooled on a circular or straight-line cooler, where cooling air fans blow ambient air up through the bed.
Where the FD fan sits
- Inlet filter
- FD (cooler) fan
- Air duct
- Cooler air box
- Sinter bed
- Hood or heat recovery
The cooler fans stand in a row beside the cooler, typically three to five fans, each feeding a section of the air box beneath the pallets. They push air up through 1 to 1.5 m of hot sinter, which arrives at 600 to 800°C. The air leaves the first sections at 300 to 450°C and on many plants goes to a heat recovery boiler; later sections exhaust to atmosphere. The fans work against the air box, grate and sinter bed, typically 300 to 500 mmWC.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air leaving the bed | 300 to 450°C in the first sections, downstream of the fan |
| Dust | Sinter dust in the plant air; inlets need screening |
| Recirculated air | 120 to 180°C where the fan returns air from a heat recovery boiler |
| Pressure at the fan outlet | Typically 300 to 500 mmWC |
| 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 sinter plants
| Blade form | Backward curved, for efficiency on ambient air at high flow |
| Material of construction | Mild steel; wear plate on blades for recirculation fans that see sinter dust |
| Drive and arrangement | Arrangement 8, one fan per cooler section |
| Bearings and cooling | Pedestal bearings; a cooling disc on recirculation fans |
| Flow control | Variable speed drive or inlet vanes on sinter discharge temperature |
| Also specified | Inlet screen and silencer, and isolation dampers so a fan can be maintained while the cooler runs |
What this FD fan has to cope with
Uneven cooling and hot sinter
If one fan loses capacity, its section cools poorly and hot sinter reaches the conveyor belts and burns them. Matched fans, flow measurement per section and alarms on discharge temperature protect the belts. Section air flow trending reveals a failing fan early.
Recirculation with dust
When air from a heat recovery boiler is returned through the fan, it carries sinter dust and is warm. A dust collector ahead of the fan, wear plate and a hot air design are then needed, unlike the ambient fans.
Leakage at cooler seals
Worn seals between the moving pallets and the air box let air escape without passing through the sinter. The fans work harder for the same cooling, so seal maintenance is part of keeping fan power down. Seal wear is checked at every shutdown.
Energy and control
Cooler fans run whenever the strand runs, and their air demand follows sinter production and the temperature of the sinter coming off the machine. A variable speed drive on each fan, controlled by discharge temperature, avoids over-cooling at reduced output. Recovering heat from the first sections into steam also turns part of the fan duty into useful output.
ID fan and FD fan in sinter plants
| ID fan | FD fan | |
|---|---|---|
| Position | After the ESP, before the stack | Beside the cooler, below the pallets |
| What it handles | Waste gas with alkali chloride dust | Ambient air, or recirculated warm air |
| Temperature at the fan | 110 to 150°C | Ambient, 25 to 45°C |
| Main design concern | Erosion and deposits at high suction | Even cooling and dusty intake |
| Control | Windbox suction | Sinter discharge temperature |
See also the Induced Draft (ID) Fan for sinter plants.
Questions buyers ask
What are the FD fans in a sinter plant?
They are the cooler fans, which blow ambient air up through hot crushed sinter on the circular or straight-line cooler. A sinter plant has no conventional boiler FD fan; the ignition hood has a small combustion air fan of its own. That fan is small by comparison.
What pressure do sinter cooler fans need?
Typically 300 to 500 mmWC, to push air through about a metre of sinter on the cooler grate. Exact pressure depends on bed depth, sinter size and the cooler design. Section pressures differ, so each fan is matched to its section rather than all being identical.
Can sinter cooler air be used for waste heat recovery?
Yes. Air from the first cooler sections at 300 to 450°C can raise steam in a heat recovery boiler. The air is often returned to the cooler, which means the fans handle warm, dusty air and need a different design. The heat recovered offsets the fan power.
Information needed to quote an FD fan for sinter plants
- 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.
- Cooler data. Cooler type and area, number of sections, sinter rate and inlet temperature.
- Heat recovery. Whether air is recirculated through a heat recovery boiler, and its temperature and dust 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.