Combustion Air Blower for Heat Treatment Furnaces

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.

Feeds a burner with air at the pressure the burner register needs. Sized for the burner turndown range, and often fitted with an inlet silencer. Client-stated blade types for the Combustion Air Blower in general: Backward curved and radial tipped.

Industries

Other fans in heat treatment furnaces

Combustion Air Blower in other processes

Information needed to select or quote

1. Duty point. Volume flow and static pressure at the fan inlet, with the gas density and temperature or the conditions to derive it.
2. Operating conditions. Site altitude, normal operating temperature and continuous or intermittent duty.
3. Gas stream. Dust loading and particle size, corrosive species, moisture, upset temperature and any tendency of the material to deposit on the impeller.
4. Mechanical. Rotation viewed from the drive end, discharge orientation and motor power.