Composition and general properties of wood for energy use
Introduction: Average composition of wood
The basic chemical composition resulting from the raw analysis of logged timber under normal conditions (ie in winter in our country).
It was found, by comparing the results obtained with a large number of tree species, a certain consistency in the results and the following figures it can be assumed, by weight representing an average composition.
- 40% water: it is recently felled trees with bark, involving not only the wood of the trunk, but also the branches.
- 1% of mineral or metallic ashes is made completely burn sawdust in a very hot flame and recovering the solid residue consisting solely of non-fuel part.
- 59% of elements "combustible or oxidizing", that is to say transforming into gas during combustion: oxygen, hydrogen, nitrogen and carbon.
These figures are very similar to the results provided by the analysis of beech (40% water - 0,65% ash. - 59,35% of elementary principles)
Let us now examine in more detail each of 3 important points dice composition: water, ash, basic principles.
B - Water
A reduced moisture content is a critical parameter for good firewood: heating capacity, thermal comfort and maintenance of your system depend largely ...
The water forms the major part of the sap, but it also permeates the cell walls.
1 - The water content varies from one species to another. Measurements carried out on trees felled at the same time and in climatic zones almost alike gave:
- 52% for black poplar
- 35% for oak
- 48% for the Italian poplar
- 31% for birch
- 47% for the lime
- 29% for ash
- 45% for the fir
- 27% for the sycamore
- 41% for alder
- 27% for the cormier
- 39.7% for beech
- 19% for the charm
2 - But it varies also within the same species, the following portion of the shaft concerned, the slaughtering season, the time of exposure to the open air, the flow rate etc ...
a) The minimum water content in the trunk, branches and average maximum kids in the branches, and in each part, the sapwood is richer in water than the heart.
Note, however, a difference between softwoods and hardwoods. In the softwood branches contain proportionately less water than hardwoods.
b) At the beginning of vegetation (in April in general) we find the most water in the wood. to 10% is estimated approximately the difference from January to April.
c) Wood exposed to the air dries slowly without ever becoming completely dehydrated. After a period of varying duration with the species and with the general climatic conditions of the region, these "air-dry" woods maintain a grade between 15 and 20%. These are relatively soft woods that tend to retain the most water. Thus maple, which contains on average 28% of water at slaughter, will keep 18% at air drying (a difference of 10%) while oak will change from 35 to 17% (ie difference of 18%).
This residual moisture can only be eliminated by extensive steaming. It would be vain to completely dehydrate the wood because the air in a few days or weeks, it takes some of that moisture.
Drying the wood is accompanied for some species of considerable change in mass! Thus the tree can lose up to 520 kg per cubic meter, which is a percentage of 105% of the weight of dry wood.
d) peeled and timbers quickly lose much more water than wood kept under bark.
Water loss can be even faster at the beginning and cause volumetric changes so brutal that there is interest in keeping some species under bark (fruit ash wood) for a while.
C - The other "simple" elements
Are carbon, oxygen, hydrogen and nitrogen. We have seen that all these die body is 59% of green wood. These elements are found in quantity almost identical in the various species of wood that is for green wood:
- For the 29,5% by weight carbon
- For hydrogen mass 3,5%
- For oxygen and nitrogen 26% by mass
Carbon is the essential element bringing the calories of a wood fire.
More: woodburning file
Links to learn more
1) The choice of material:
- How to correctly choose a heater with wood? (Stove, boiler or boiler)
- List of stoves and boilers labeled "Flamme Verte"
- Help and advice on choosing a wood stove
- Choose the power of his wood stove
- The normalized power heaters Wood
- Choosing a wood boiler
2 Heating with wood every day: maintenance and improvements:
- The different types and prices of firewood fuel
- Heating and wood fireplace: How to avoid chimney fires. Maintenance and dimensions
- Regulation about the chimneys, the standards and the law
- Making a hot water collector on a wood stove
- The manufacture of pellets: a plant scheme
3) The pollution of wood heating:
4) Experience feedback of wood heating:
- Full report on the presentation of a pellet boiler installation at a particular
- Presentation and photos of another pellet boiler plant in Alsace in particular
- Presentation of a wood and solar house
- Auto installation of our wood boiler Deom Turbo explanations and mounting scheme
- effective yield estimate of our stove Boiler Turbo Deom
- Wood heating and insulation forum