Dilution Air Blower for Waste Heat Recovery Boilers

The process

A waste heat boiler sits on the exhaust of a kiln, furnace or engine and lowers the gas temperature before the dust collector and fan. The ID fan after the boiler handles the gas of the source process at reduced temperature, and dampers divert the gas around the boiler when it is out of service.

The gas at the fan

Exhaust from a kiln, furnace or engine after a waste heat boiler. Temperature and dust depend on the upstream process; the fan is selected at the hot condition with the dust load of the source.

Selection for this duty

Blade form	Radial tipped, or backward inclined where the fan sits after the collector
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 200°C the gas density is close to 0.75 kg/m³, 62% 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 waste heat recovery boilers

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.