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The burning of wood results in about 6–10% ashes on average. [2] The residue ash of 0.43 and 1.82 percent of the original mass of burned wood (assuming dry basis, meaning that H 2 O is driven off) is produced for certain woods if it is pyrolized until all volatiles disappear and it is burned at 350 °C (662 °F) for 8 hours.
The moisture content of firewood determines how it burns and how much heat is released. Unseasoned (green) wood moisture content varies by the species; green wood may weigh 70 to 100 percent more than seasoned wood due to water content. Typically, seasoned (dry) wood has 20% or less moisture content.
Outdoor wood boilers also typically have short stack heights in comparison to other wood-burning appliances, contributing to ambient levels of particulates at ground level. An increasingly popular alternative is the wood gasification boiler, which burns wood at very high efficiencies (85-91%) and can be placed indoors or in an outbuilding.
In this process the wood is submerged in a tank of water-preservative mix, and allowed to soak for a longer period of time (several days to weeks). This process was developed in the 19th century by John Kyan. The depth and retention achieved depends on factors such as species, wood moisture, preservative and soak duration.
Deeper ponding exerts pressure that forces water into the ground faster. Faster flow dislodges contaminants otherwise adsorbed on soil and carries them along. This can carry pollution directly to the raised water table below and into the groundwater supply. Thus, the quality of water collecting in infiltration basins is of special concern.
There are no binders involved in this process. The natural lignin in the wood binds the particles of wood together to form a solid. Burning a wood briquette is far more efficient than burning firewood. Moisture content of a briquette can be as low as 4%, whereas green firewood may be as high as 65%.
Further drying of the wood results in strengthening of the wood fibres, [1] and is usually accompanied by shrinkage. Wood is normally dried to a point where it is in equilibrium with the atmospheric moisture content or relative humidity, and since this varies so does the equilibrium moisture content. Laboratory testing has found the average FSP ...
The chemical potential of sorbed water is a function of wood moisture content. Therefore, a gradient of wood moisture content (between surface and centre), or more specifically of water activity, is accompanied by a gradient of chemical potential under isothermal conditions. Moisture will redistribute itself throughout the wood until its ...