Wood

What is it?

Wood is a ligno-cellulosic solid matter directly burnt for the heat released. Woody material mostly comes from different parts of a tree or a shrub such as trunk, branches, root, bark and leaves. This definition covers wood chips, sawdust and chopped wood. Firewood, wood-derived fuel, wood-based energy and fuelwood are all synonyms for wood that is combusted directly to produce heat and/or power; or transformed into charcoal energy.
Natural ligneous vegetation, wood plantation and natural wood resource provide the main wood used as fuel.
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Wood characterisitcs

Wood characteristics such as calorific, density, volatile matter, fixed carbon and ash content vary according to the type of wood species, the parts of tree or shrub (for example, branch, trunk, bark and root) and the moisture content of wood.

Woodfuel CharacteristicsUnitMinMax
Calorific valueKcal/Kg27005000
Density
0.310.88
Volatile matter %7580
Fixed carbon%1824
Ash content%1.64.6

From the wide range of fuel, woody biomass has the lowest calorific value, fixed carbon and ash content. Concerning sulphur and phosphorus content, wood value is more significant.

Who uses it?

Who would have thought that "about 55 percent of all the wood harvested in the world is used as fuel?" (A Food and Agriculture Organization of the United Nations Approximation)

A lot of wood is used for fuel.The developing countries in Asia have approximately 3/4 of the world's woodfuel users, but only 1/4 of the forest cover.

But in some cases the wood doesn't come from forests! According to the Food and Agriculture Organization*, an organization that works internationally in agriculture and forestry, "We now know that over 60% of fuelwood originates from non-forest sources and the supply from these non-forest sources appears to be sufficient to 'fill the gap'."

The author continues, offering that "...fuelwood harvesting from forest land is not necessarily non-sustainable, and that fuelwood use is not necessarily linked to deforestation. Now, fuelwood use is no longer generally considered a major or general cause of deforestation."

In Asia at least, most of the wood used as fuel is harvested from tree crops grown on non-forest lands. This includes village lands, agricultural lands, tree plantations, trees in wind rows and fence rows. Worldwide the relationship is probably similar. Wood used for fuel is seldom the main reason forests are cut down.

Wood as fuel worldwide is important, now and in the future. The rise in woodfuel consumption is projected to continue for some years to come in many fast growing, economically developing nations.

Not all wood used for fuel comes from trees harvested specifically for that purpose. For example, wood stoves that burn sawdust or wood pellets are burning industrial "wastes." Mills using "hog fuels" to generate heat and/or steam use these same wastes, generated on-site or shipped in by train and truck. Wood wastes and hog fuels are wood chips or dust burned as fuel.

In developing countries, household, traditional baker, restaurant and artisans represent the greatest wood consumers to meet their energy need. Domestic consumption is more important. In the household sector, cooking remains the main reason to burn wood. Wood is used more in rural areas, where wood is usually free, than in urban areas where wood must be bought.

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Advantages

  • wood is cleaner to handle than wood charcoal;
  • when it burns wood provides more light from its flame

Disadvantages

  • when it burns wood releases more smoke;
  • wood is harder to handle than wood charcoal;
  • to start wood burning it requires more delay than other fuels;
  • wood must be chopped regularly

Devices

A wide range of devices are built to burn wood as energy source. The type of devices includes three stone , the massif and fixed stove, and portative metallic stove. Their energy efficiency is between 18% and 24%.








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