This article's table of contents introduction:
- Understanding the Application (Boiler Exhaust)
- Typical Technical Specifications
- Key Design Features to Look For
- Common Impeller Types for this Application
- Important Operational Considerations
- Typical Applications for 7.5 kW Boiler Exhaust Fans
- What to Ask the Supplier
- Summary Recommendation:
It sounds like you are looking for a 5 kW Centrifugal Blower designed for use as a Boiler Exhaust Fan. This is a specific type of industrial fan often referred to as an Induced Draft (ID) Fan.
Here is a detailed breakdown of what this specification usually entails, including typical applications, technical specifications, and key purchasing considerations.
Understanding the Application (Boiler Exhaust)
- Purpose: The fan pulls hot flue gases out of the boiler and pushes them up the chimney (stack). It creates a negative pressure (draft) inside the boiler furnace, ensuring safe and efficient combustion.
- The Challenge: The air/gas is hot (typically 150°C to 250°C+ for biomass/coal, slightly lower for gas) and may contain dust, soot, or corrosive chemicals (sulfur, acids).
Typical Technical Specifications
A 7.5 kW centrifugal fan for boiler exhaust is a medium-duty industrial fan. Here is the range of performance you can expect:
| Parameter | Typical Range / Value |
|---|---|
| Power (Motor) | 5 kW (10 HP) |
| Airflow (CFM / m³/hr) | 2,500 – 5,000 CFM (4,250 – 8,500 m³/hr) |
| Static Pressure | 150 – 400 mmWC (mm of Water Column) |
| Impeller Type | Forward Curved (for high air volume, lower pressure) or Radial/Straight Blades (for dirty, sticky dust). For exhaust, Radial is often preferred for durability. |
| Max. Temperature | 150°C (Standard) / 250°C-350°C (High Temp with shaft cooling disc) |
| Voltage / Phase | 415V / 3 Phase (Standard Industrial) |
Key Design Features to Look For
For a Boiler Exhaust Fan, a standard blower will fail quickly. You need a fan specifically designed for high temperatures and harsh environments:
- High-Temperature Bearings: The motor and fan bearings must be externally mounted or have a cooling shaft to transfer heat away.
- Shaft Cooling Disc: A metal disc between the impeller and the bearing housing to radiate heat and prevent heat transfer.
- Material: The impeller and casing should be made of MS (Mild Steel) or Corten Steel (for corrosion resistance). For very high temperatures, SS 310 or SS 316 is used.
- Bearing Type: Heavy-duty Spherical Roller Bearings with high-temperature grease (e.g., Shell Alvania EP or similar).
- Vibration Monitoring: Important for critical boiler applications.
Common Impeller Types for this Application
- Radial Blade (Paddle Wheel): Best for dirty exhaust (wood chips, coal). It is self-cleaning but noisy. High pressure, low volume.
- Backward Inclined (BI): Most efficient for clean gas. Lower noise. Good for gas/oil boilers.
- Forward Curved (FC): High volume, low pressure. Used for clean air or low-static systems.
Important Operational Considerations
- Damper Control: The fan must be controlled by an inlet/outlet damper or a VFD (Variable Frequency Drive) to adjust the exhaust flow rate to match the boiler load.
- Flexible Connection: A flexible connector (usually made of silicone or PTFE-coated fiberglass) must be installed between the boiler exhaust duct and the fan inlet to absorb thermal expansion and vibration.
- Drainage: A drainage hole at the bottom of the fan casing is necessary to allow condensation to drain out during startup.
- Safety: The fan should have a trip/alarm for high vibration and high temperature.
Typical Applications for 7.5 kW Boiler Exhaust Fans
- Small to medium industrial boilers (1 – 5 Ton/hr capacity).
- Solid fuel boilers (Wood Pellets, Biomass, Coal).
- Steam generators in small factories (textile, food processing, rubber).
- Hot air generators.
What to Ask the Supplier
When ordering or quoting, you must provide these parameters to get the correct fan:
- Gas Temperature: (e.g., 180°C maximum)
- Gas Composition: Clean? Dusty? Corrosive?
- Required Airflow: (e.g., 4,000 CFM at 200°C)
- Static Pressure Loss: (Resistance from boiler + duct + chimney)
- Altitude / Density: Air density changes with temperature and altitude.
Summary Recommendation:
For a 5 kW Centrifugal Boiler Exhaust Fan, look for a Radial Blade (Paddle Wheel) type or a Backward Curved type with MS construction, a shaft cooling disc, and external high-temperature bearings. Ensure the motor is suitable for a VFD if you plan to vary speed.
Price Estimate: (Varies heavily by region and manufacturer)
- Standard Model (MS, 150°C): $1,200 – $2,500 USD
- High-Temp Model (SS, 250°C+): $2,500 – $5,000 USD
Would you like help calculating the airflow requirements for a specific boiler size?
