How wood pellets are made

A wood pellet sinks in water, because the press packs sawdust denser than water itself.

stations: 5
things upstream: 1
raw source: 1
step from the ground: 1

The short version

Wood pellets are made from sawdust and other wood-milling waste. The material is dried, ground to a uniform dough-like mass in a hammer mill, and squeezed through a die with holes about 6 millimeters wide. The heat and pressure make the wood's own lignin act as glue, and the rods are cooled and bagged.

Gather the sawdust

Pellet mills use sawdust and waste from lumber mills, furniture plants and construction. Tree tops and shells are also used.

Goes in
Timber
Dry it out

Wet feedstock is dried so that pellets leave with a moisture content below 10 percent. Dry pellets burn at very high efficiency.
Hammer it uniform

A hammer mill breaks the material into a uniform, dough-like mass. Even size makes the press work smoothly.
Squeeze through a die

A press forces the mass through a die with holes of about 6 millimeters. High pressure heats the wood, softening its lignin so the particles bind.

6 mm die holes
Cool and bag the rods

Hot pellets are cooled so the lignin hardens, then screened and bagged or blown into bulk trucks.

End of the lineWood pellets

Worth repeating

Pellets meeting European norms are denser than 1 ton per cubic meter, so they sink in water.
Drying, pelletizing and transporting pellets takes less than 11 percent of the energy the pellets contain, if the wood waste is pre-dried.
High-efficiency pellet stoves and boilers reach combustion efficiencies of over 85 percent.