| Of all the biomass resources, woodfuel has the greatest ability to deliver immediate and significant carbon savings throughout the South East.
The main types of woodfuel are logs, wood chip and wood pellets. In a domestic setting, logs can be used in open fires, stoves and manually fed boilers, for space and water heating and cooking. Woodchip is mainly used in community to commercial scale boilers and for power generation. Wood pellets can be used at any level – from domestic pellet stoves to very large boilers. As a compressed form of wood with very low moisture content they burn very efficiently. These three main types of woodfuel are discussed in more detail below.
Logs
Wood in the form of logs is the simplest and most common form of wood. Logs used for fuel will normally be described
by their species (or simply hardwood or softwood) and classified as either ‘seasoned’ (meaning partially
dried) or ‘green’ (meaning wet). Sometimes additional information will be provided such as the duration
of seasoning (e.g. ‘one year seasoned’) and the log dimensions. Stoves and boilers will usually specify
the maximum length of log they can take.
Ideal moisture content: <20%
Energy content: ~ 14GJ/t or 3,900kWh/t (at MC20)
Density: ~ 475kg/m3
Price: Will vary considerably according to location/supplier – can be free
Chip
With wood chip, fuel quality is vitally important. Particle size and
moisture content cannot be compromised or the user is likely to encounter
problems. In addition, chip used for fuel should come from clean, untreated
sources. Chip suppliers should be well acquainted with the relevant
specifications for different boiler types. Normally, fuel grade wood chip
will need to have dimensions of around 3cm and be of less than 30% moisture
content.
Ideal moisture content: <30%
Energy content: ~ 12GJ/t or 3,400kWh/t (at MC30)
Density: ~ 250kg/m3
Price: ~ £75/tonne
Pellet
Wood pellets are the most dense biomass fuel (both in terms of weight and
energy). They have low moisture content and good flow properties so are easy
to deliver and store. Normally made from compressed sawdust, they can have
diameters of 6, 8 or 10mm. The smaller diameter pellets are usually needed
for smaller (domestic scale) stoves and boilers.
Moisture content: <8%
Energy content: ~ 17GJ/t or 4,700kWh/t (at MC8)
Density: ~ 650kg/m3
Price: ~£175/t
Please note, the prices shown here are meant to provide a rough guide only, approximate as of November 2008. Actual costs may vary with location, delivery method, quality and quantity of fuel purchased and may rise or fall over time.
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