The process
Annealing, normalising and tempering furnaces need recirculation fans inside the chamber for temperature uniformity, combustion air for the burners, and a flue fan where the furnace is under draft. The recirculation fan is a plug fan running inside the hot zone.
The gas at the fan
Clean air at elevated temperature from a dryer, oven or cooling duty. The selection is made at the hot density, with the shaft and bearings arranged for continuous hot running.
Selection for this duty
| Blade form | Backward curved or aerofoil for the best efficiency on clean gas |
| Material of construction | Mild steel |
| Drive and bearings | Direct coupled, shaft cooling disc, bearings in a pedestal outside the gas stream, allowance for thermal growth |
| Density at the fan | At about 250°C the gas density is close to 0.67 kg/m³, 56% 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. |
Sits at the outlet of a boiler, kiln or furnace and draws the flue gas through the plant to the stack. It handles hot, dust-laden gas at large volume, so it is sized at the hot condition and checked at cold start. Client-stated blade types for the ID Fan in general: Backward curved, backward inclined and radial tipped.
Industries
Other fans in heat treatment furnaces
ID 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.