Dilution Air Blower for Sponge Iron Rotary Kilns

The process

Direct reduction of iron ore in a rotary kiln produces a hot off-gas full of fines that passes through an after-burner chamber and usually a waste heat boiler before the ESP and the ID fan. Shell air fans along the kiln inject air through ports, and shell cooling fans protect the refractory. Hard, continuous duties.

The gas at the fan

Rotary kiln off-gas after the after-burner chamber and waste heat boiler, carrying iron ore and coal fines. Among the harder duties for an ID fan: hot, heavily dust laden and continuous.

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 220°C the gas density is close to 0.72 kg/m³, 59% 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.

Injects ambient air into a hot flue gas stream to bring it down to a temperature the downstream bag filter or fan can accept. Client-stated blade types for the Dilution Air Blower in general: Backward curved.

Industries

Other fans in sponge iron rotary kilns

Dilution 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.