The process
Rice husk burns in a fluidised bed or on a grate and leaves an ash that is largely silica. The ash erodes anything it touches at velocity, so the ID fan is built with wear liners and the dust collector is placed ahead of it. Rice mills and husk-fired captive power plants run these boilers at steady load for long periods.
The gas at the fan
Rice husk ash is high in silica and among the most abrasive fly ashes a boiler fan handles. Blade wear is the limiting factor; wear liners, hard facing and a blade form that resists erosion set the design.
Selection for this duty
| Blade form | Radial tipped with wear liners, or straight radial where the dust is coarse |
| Material of construction | Mild steel with replaceable wear liners on the blades and the scroll at the cut-off |
| Drive and bearings | Direct coupled or belt driven with a shaft cooling disc and bearings outside the casing |
| Also specified | Hard facing or liners on the blade pressure face |
| Density at the fan | At about 180°C the gas density is close to 0.78 kg/m³, 65% of standard air. Pressure developed and power drawn fall in the same ratio, so the selection is made at this density and the motor is checked at cold start. |
Supplies combustion air to a boiler or furnace, pushing ambient air through the air heater and into the windbox against the furnace draft. Clean air, so the blade is chosen for efficiency. Client-stated blade types for the FD Fan in general: Backward curved and backward inclined.
Industries
Other fans in rice husk fired boilers
FD Fan in other processes
Services on this fan
Information needed to select or quote
- Duty point. Volume flow and static pressure at the fan inlet, with the gas density and temperature or the conditions to derive it.
- Operating conditions. Site altitude, normal operating temperature and continuous or intermittent duty.
- Gas stream. Dust loading and particle size, corrosive species, moisture, upset temperature and any tendency of the material to deposit on the impeller.
- Mechanical. Rotation viewed from the drive end, discharge orientation and motor power.