What are wood pellets?

General Information Sheet - Wood Pellets

Staffan Melin Delta Research Corporation, Delta, British Columbia, Canada 

Wood pellets are generally produced out of wood waste such as saw dust and shavings. The raw material is dried, mechanically fractioned to size and thereafter extruded under intense pressure into pellets. In the process the raw material is densified approximately 3.7 times and the product produced in Western Canada has a bulk density of approximately 705 kg/m3 and a bulk stowage factor of approximately 52-56 ft3/metric tonne. 

Wood pellets are primarily used as a fuel and has a calorific (heat) value of around 5 MWh/metric tonne (18 GJ/metric tonne) which is approximately half that of fuel oil. In North America the wood pellets are used in stoves and fireplaces. In Europe, particularly Scandinavia , the bulk of the pellets produced are used as fuel in central heating stations supplying heat for entire communities or even entire cities.

Wood pellets is a renewable energy source with a zero net contribution of green house gases. Wood pellets is one of many fuel products classified as bio-fuel which is considered the only sizeable alternative to fossil fuel in the short and medium term.

High quality wood pellets have a moisture content of 3 to 7% and are hydrofilic and therefore sensitive to water droplets. The shiny surface of the pellets is caused by partial plasticizing of the lignin in the wood due to high pressure and the evaporation of terpenes during the production process. The surface protects the pellets from absorbing any significant amount of airborne water vapor under normal atmospheric conditions. However, wood pellets have to be protected from direct water penetration. If exposed to water droplets, from for example condensation, the pellets will gradually decompose and loose their effectiveness as a fuel. The decomposition involves expanded volume and over time a gradual chemical breakdown followed by a slow temperature increase, as with most wood fiber or organic material. (JRA: This won't happen with Torrefied Wood Pellets).

It is important during loading and discharge as well as during ocean transportation to protect the wood pellets from water droplets. Tight cargo holds with limited influx of unconditioned moist air is recommended considering the very low moisture content of the wood pellets. The charter party may in some cases stipulate sealing of hatch covers with tape to limit exposure to salt and water during transportation. This does not in any way preclude proper safety precautions during voyage and ample ventilation of spaces during discharge. Attention should be paid to any wet and decomposed pellets indicating leakage in the holds. Wet material should be removed.

Wood pellets are transported by ocean vessels in other parts of the world under necessary safety measures without problems and are likely to become a fairly common trading commodity over time. Wood pellets presently manufactured in British Columbia typically do not contain any additives or binders of any sort.