This article's table of contents introduction:
- The numbers: 20-800 Tons
- The Fan Type: Induced Draft (ID) Fan
- The Fan Design: Centrifugal Fan
- Summary of Specifications
- Typical Manufacturers (for this range)
This phrase refers to a specific type of heavy-duty industrial fan used in power plants and large industrial boiler systems.
Here is the breakdown of what this specification means and the type of fan you are looking for.
The numbers: 20-800 Tons
This refers to the boiler capacity (steam generation rate), not the physical weight of the fan.
- 20 Tons: A small industrial boiler (e.g., for a factory or hospital).
- 800 Tons: A very large utility or power plant boiler (generating ~240 MW of electricity or more).
- Implication: This is a massive size range. The fan for an 800-ton boiler could be the size of a small room and require a motor of 500 HP to 2,000+ HP.
The Fan Type: Induced Draft (ID) Fan
This is the critical operational function.
- Position: Located at the exit of the boiler (between the boiler and the chimney/stack).
- Function: It pulls hot, dirty flue gas (exhaust) through the boiler, creating negative pressure (suction) inside the furnace.
- Challenges:
- High Temperature: Handles gas from 150°C to 250°C (300°F - 480°F) for normal operation, up to 400°C (750°F) for emergency bypass.
- Abrasion: Gas contains fly ash and particulates that erode fan blades.
- Corrosion: Acidic condensation can occur if gas cools below the dew point.
The Fan Design: Centrifugal Fan
This is the mechanical construction.
- Why Centrifugal? For "Induced Draft" applications, centrifugal fans are preferred over axial fans because:
- High Pressure: They can overcome the high resistance of the boiler's heat exchangers, economizers, and scrubbers.
- Robustness: They handle high temperatures and dust loads better than axial fans.
- Stability: Their performance curve is stable for the variable flow requirements of a boiler.
Specific Centrifugal Fan Blade Types (for ID Service):
For a 20-800 Ton boiler, the specific blade shape is critical. The most common choices are:
| Feature | Radial (Radial Tip) Fans | Backward Inclined (BC/FC) Fans |
|---|---|---|
| Best for | Small & Medium boilers (20-200 Tons) | Large & High-efficiency boilers (200-800+ Tons) |
| Blade Shape | Straight, paddle-wheel design. | Blades curve away from direction of rotation. |
| Efficiency | Low (60-72%) | High (80-88%) |
| Pressure | Very High | High |
| Dust/Ash Handling | Excellent (self-cleaning, non-clogging) | Moderate (dust can stick) |
| Material | Heavy steel plate | High-strength alloy steel |
- For a 20-200 Ton boiler (Dusty / Coal / Biomass): You likely need a Radial Tip or Paddle Wheel fan. These are tough and handle ash well.
- For a 400-800 Ton boiler (Cleaner gas / High efficiency): You likely need a Backward Inclined or Airfoil fan. These are more energy efficient, saving significant electricity costs over time.
Summary of Specifications
If you are sourcing this fan, you need to provide the following data:
- Boiler Capacity: 20 Ton/hr or 800 Ton/hr?
- Fuel Type: Coal, Biomass, Oil, or Gas? (Determines dust level).
- Gas Temperature: Normal operating temp and max peak temp.
- Flow (Volume): Expressed in m³/hr or CFM (Cubic Feet per Minute).
- Static Pressure: Expressed in mmWC (mm Water Column) or Pa (Pascals). (Typically 200-800 mmWC for ID fans).
- Gas Composition: Is it corrosive (sulfur content)?
Typical Manufacturers (for this range)
- Howden (Global leader for large utility fans)
- Clyde Bergemann (Formerly SE Zhangjiagang)
- China-based OEMs: Shanghai Blower Works, Shenyang Blower Works, Chongqing General Industry (CQGI) – very common for 20-800 Ton range in Asian markets.
- ABB / TLT-Babcock (Large axial designs)
- New York Blower / Garden City (Smaller to mid-range industrial)
