Biomass fuel metering bins dose fuel into a furnace to maintain a process setpoint, such as pressure or temperature. Their design must account for changes in the wood fuel being handled, not just a single nominal feed rate.
Five fuel properties directly influence the requirements for reliable metering.
1. Fuel heating value
For a given furnace heat input, a lower fuel heating value requires a higher fuel feed rate. The metering equipment must accommodate that demand across the expected range of fuel sources.
2. Moisture content
Moisture affects bulk density, heating value and the force needed to shear the material. It can also increase clumping. These changes influence how reliably fuel moves through the bin and into the furnace.
3. Particle size distribution
Long strands and oversized particles can reduce conveying capacity and interrupt fuel delivery. The maximum expected particle size is an important consideration when selecting screw pitch and feeder geometry.
4. Ash and sand content
Silica and other abrasive material increase wear on rotating and fixed parts. Limiting screw speed can help control wear, but maintaining the required throughput at a lower speed may call for larger screws.
5. Angle of repose
The angle a loose pile forms under gravity helps describe how the fuel behaves during handling. A steeper angle can indicate a greater tendency to bridge, which must be considered in the metering-bin design.
One more factor: equipment vibration
Vibration can cause fines to settle into the spaces between larger particles. Across multiple metering bins, that segregation can create uneven particle-size distributions and inconsistent fuel beds. The resulting imbalance in combustion can contribute to unpredictable emissions and slagging.
Design for the fuel you actually handle
Reliable metering depends on matching the equipment to the range of fuel properties it will encounter. Reviewing heating value, moisture, particle size, abrasive content and flow behavior together helps identify where changes can improve reliability and throughput.