Wood Chips & Sawdust

Biomass plants spend more time clearing blockages than almost any other bulk handling operation, and the cause is usually particle shape rather than capacity.

Interlocking and bridging

Slivers and long chips form stable arches over openings many times their nominal size.

• Screw dischargers, walking floors or sliding frames rather than gravity cones.
• Screening to remove oversize before storage.
• Generous chute cross sections with no converging corners where fibres can wedge.

Moisture variation

A delivery at 50 percent moisture and one at 15 percent are different materials in weight, flow and energy content.

Storage design, feeder sizing and combustion control all have to cope with the range, and inline moisture measurement pays for itself at the boiler.

Fire and dust

Dry sawdust is a classic explosible dust, and stored chip piles can self-heat through biological activity and oxidation.

Temperature monitoring in piles, spark detection before filters and explosion protection on milling and collection equipment are standard.

Tramp material

Forest and recycled wood streams carry stones, nails and occasional steel.

Magnets and stone traps protect downstream equipment, and their absence is usually discovered through a damaged screw or a fire.

What to establish before buying equipment

• Particle size distribution including the longest slivers.
• Moisture range across suppliers and seasons.
• Bulk density at both moisture extremes.
• Tramp metal expectation and the detection method.

Wood chips and sawdust interlock rather than flow, and they are biologically active.

A chip pile composts, generating heat deep inside, and the moisture content that arrives with the material drives both the heating and the handling behaviour. Fresh chips and dry sawdust are different materials in the same bin.

• Avoid deep storage of damp material; the heating is slow, internal and invisible.
• Monitor temperature in significant stores and agree the response in advance.
• Plan mechanical discharge from the start; gravity does not move interlocked chips.

Mechanical discharge and oversize tolerance set the design.

Chips bridge, wrap and jam, and a single oversize piece can stop a screw. Equipment has to be sized for the worst piece that can arrive, not for the average.

• Live-bottom, sweep or screw discharge with torque reserve.
• Generous clearances and accessible blockage clearing points.
• Screening to remove oversize before it reaches the narrow part of the line.

Wood dust is explosible and a chip store can self-heat and off-gas.

• Explosion protection on filters, cyclones and silos.
• Temperature and gas monitoring in large stores; carbon monoxide rises before anything is visible.
• Entry procedures assuming a depleted atmosphere and an unstable mass.

Hardwood dust is also a recognised carcinogen by inhalation, which makes capture at the source a health control rather than housekeeping.