ABOUT WOOD PELLETS
Producing wood pellets
Wood pellets are usually
made from compressed sawdust and wood shavings. However, they can
be made from most biomass material (e.g. straw, forestry residues,
specially grown energy crops etc.) and hence have the potential to
be sourced from locally unused material, which can then give
considerable benefit to the local economy.
Pellets are typically 6-10mm in diameter (depending on the size of the heating system) and resemble animal feed. In fact the manufacturing process is similar in many ways. A pellet production facility will traditionally be a large production facility producing tens of thousands of tonnes per year such as at Balcas, Northern Ireland. However, new technology is becoming available to enable wood pellet production on a smaller scale (hundreds to a few thousand tonnes per year), such as Eco Wood Fuels at Brookridge Timber, Hemyock, Devon.
Wood pellets are now a major fuel source used in many parts of Europe (Sweden, Austria, Norway, Germany, Denmark, France) as well as in the US and Canada. Wood pellets are made to a strict standard in terms of size, moisture content and energy density. This is a major advantage over the main biomass alternative, wood chips, which can vary significantly in size and moisture content between suppliers and from batch to batch. The low moisture content of wood pellets also reduces the relative cost of fuel transportation since less water is present, and they are easier to transport and store than wood chips.
The 'bulk density' of the wood fuel has very important implications for both storage and transport. This is one of the major advantages of wood pellets compared to wood chips. It is important here to make the distinction between density and bulk density.
For example, good quality wood pellets when put in water sink like a stone i.e. they have a density greater than that of water (i.e. >1000kg/m3). However, when put in a container you will find a volume of 1m3 will have a mass of somewhere between 600-700kg depending on the density and size (diameter and length).
Wood pellets have a bulk density of about 600-700kg/m3. Seasoned wood chips (at 25% moisture content) will have a bulk density of between 150-250kg/m3 depending on species.
Transportation
Wood pellets improve the economics of biomass fuel transportation. A 20m3 trailer/lorry will contain about 12-13 tonnes of wood pellets with about three times as much energy as the same trailer with wood chips.
