Boiler fan

Boiler fan (boiler drum induced draft fan, core auxiliary equipment of boiler air and smoke system) is a specialized fan that is matched with coal-fired, biomass, and gas-fired boilers. It is the power core of the entire air and smoke system, with one supply and one exhaust working together to maintain furnace negative pressure, ensure full combustion of fuel, and achieve standard emissions of flue gas. It is widely used in industrial boiler rooms, thermal and electric heating stations, and power plants, mainly centrifugal type. Large power plant boilers use axial flow.

1、 Classification and Function of Boiler Fans

1. Supply fan (blower, FD)

Installed at the front end of the boiler, it delivers fresh air at room temperature as secondary air into the furnace for combustion assistance, overcoming air preheater and duct resistance, and operating under positive pressure conditions.

Medium: Room temperature clean air; Good working conditions with low requirements for wear resistance. Small boilers commonly use 9-19 and 9-26 centrifugal fans.

2. Induced draft fan (ID, the most critical fan of the boiler)

Installed in the tail flue of the boiler, under negative pressure conditions, extracting high-temperature flue gas, and sending it into the chimney after dust removal and desulfurization; Maintain negative pressure in the furnace to prevent smoke from escaping.

Medium: High temperature flue gas at 150-220 ℃, containing dust and acidic corrosive components; The blades must be wear-resistant sprayed, and the bearing box can choose a water-cooled structure.

Key point: The air volume of the induced draft fan should be slightly larger than that of the supply fan to ensure stable negative pressure in the furnace.

3. Primary fan (for coal powder furnace/circulating fluidized bed)

Provide primary air to dry coal powder and carry it into the furnace. Mix cold/hot primary air and adjust the temperature of the coal mill.

4. Other auxiliary fans

Secondary fan: circulating fluidized bed boiler, fluidized air at the bottom of the furnace

Sealed fan: coal feeder and coal mill are sealed to prevent coal powder leakage

Denitrification dilution fan: providing dilution air for denitrification process

2、 Structural characteristics (mainly boiler centrifugal induced draft fan)

Shell+wear-resistant impeller+air inlet+bearing box+coupling+base

Impeller: Rear curved blades, induced draft fan blades are welded with tungsten carbide wear-resistant layer; Factory dynamic balance verification G4, 0

Bearing box: Under high temperature conditions of induced draft fan, equipped with water-cooled bearing seat to prevent bearing overheating

Adjustment method: imported air damper, variable frequency speed regulation (mainstream energy-saving transformation)

Complete set of accessories: import and export soft connections, spring shock absorbers, mufflers, coupling guards, variable frequency control cabinets

3、 Material selection

Supply fan: Q235 carbon steel, ordinary spray painted

Induced draft fan: shell Q235; Blade Q345, surface wear-resistant spray coating; Low temperature corrosion caused by sulfur-containing flue gas can choose 304 stainless steel

High temperature condition: heat-resistant steel plate, water-cooled bearing seat

4、 Key parameters for selection

1. Fan type: supply fan/induced draft fan/primary fan

2. Airflow, total pressure, medium temperature

3. Dust content and sulfur (corrosion) content in flue gas

4. Negative pressure requirement for furnace

5. Adjustment method: imported baffle/frequency converter

6. Resistance of supporting dust removal and desulfurization system

7. Motor power and voltage

5、 Installation points

1. On the negative pressure side of the induced draft fan, the inlet flange is tightly sealed to prevent the leakage of cold air and reduce dust removal efficiency

2. The fan base is equipped with spring shock absorbers, and non-metallic soft connections are installed at the inlet and outlet to block vibration transmission through the flue

3. Independent support for flue, the weight of the pipeline cannot be pressed against the fan body

4. Reserve thermal expansion compensation for induced draft fan under high temperature conditions

5. Supporting muffler to reduce factory noise and meet environmental impact assessment requirements

6、 Common faults

1. Wear and dust accumulation of impeller: Dust erosion, disruption of dynamic balance, and soaring vibration (highest occurrence of induced draft fan)

2. Excessive temperature rise of bearings: high temperature conduction, insufficient cooling water, lubrication failure

3. Smoke leakage: Poor inlet sealing, large amount of cold air entering, insufficient fan output, and increased power consumption

4. Blade corrosion: Low temperature acid corrosion, thinning and perforation of blades

5. Blocker jamming: Ash accumulation in the flue, malfunction of the inlet air damper action