Wood pellets are a type of wood fuel, generally made from compacted sawdust. They are usually produced as a byproduct of sawmilling and other wood transformation activities. The pellets are extremely dense and can be produced with a low humidity content (below 10%) that allows them to be burned with a very high combustion efficiency. Further, their regular geometry and small size allow automatic feeding with very fine calibration. They can be fed to a burner by auger feeding or by pneumatic conveying.
Their high density also permits compact storage and rational transport over long distance. They can be conveniently blown from a tanker to a storage bunker or silo on a customer's premises. As the price of heating with fossil fuels increases, more capacity for pellet heating has been installed. A large number of models of pellet stoves, central heating furnaces and other heating appliances have been developed and marketed since about 1999. With the surge in the price of fossil fuels in 2005, the demand has increased all over Europe and a sizable industry is emerging. The reason being is that customers on oil or LPG could be saving from 35-50% on their heating bill in the United Kingdom.
With the high efficiency burners developed in recent years, other emissions such as NOx and volatile organic compounds are very low, making this one of the most non-polluting heating options available. One remaining problem is emission of fine dust in urban areas due to a high concentration of pellet heating systems. Electrostatic particle filters for pellet heaters have however been developed and considerably reduce the problem when installed as standard.
The energy content of wood pellets is approximately 4.7-4.9 MWh/tonne (~7450 BTU/lb).
The climate impact of wood pellets is disputed. Some argue that there is a very low net carbon footprint because trees are a renewable resource, and, in the process of growing, consume the carbon dioxide released by their combustion. Others counter that the source sawdust would not otherwise have contributed to greenhouse gases, and that burning fuel pellets releases a large amount of CO2 into the air. The fact is, wood is made up of mostly carbon (and water), that carbon came from the atmosphere through the process of photosynthesis, and its carbon gets returned to the atmosphere when the wood is either burned or left to decompose. While it is true that in burning, most of the carbon joins with oxygen and returns to the atmosphere as carbon dioxide, left to decompose, the carbon still returns to the air in the form of methane, which has over 20 times more heat trapping characteristics than CO2 does.
Due to the rapid increase in popularity since 2005, Pellet availability and cost may be an issue. This is an important consideration when buying a pellet stove, furnace, pellet baskets or other devices known in the industry as Bradley Burners. However, current pellet production is increasing and there are plans to bring several new pellet mills online in 2008-2009, in the US alone.
Cost of the pellets has begun to rise as less wood by-products are being created due to the slowing of the housing boom.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)
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