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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.
| Fuels for heating |
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Heating oil |
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Production
Pellets are produced by compressing the wood material which has first passed through a hammer mill to provide a uniform dough-like mass. This mass is fed to a press where it is squeezed through a die having holes of the size required (normally 6 mm diameter, sometimes 8 mm or larger). The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plastifies slightly forming a natural 'glue' that holds the pellet together as it cools.
Pellets conforming to the norms commonly used (DIN 51731 or Ö-Norm M-7135) have less than 10% water content, are uniform in density (density in excess of 1 ton / cubic meter, so they do not float if placed in water), have good structural strength, and low dust and ash content. Because the wood fibres are broken down by the hammer mill, there is virtually no difference in the finished pellets between different wood types. Pellets can be made from nearly any wood variety, provided the pellet press is equipped with good instrumentation, the differences in feed material can be compensated for in the press regulation.
Pellets conforming to the above norms cannot contain any recycled wood or outside contaminants. Recycled materials such particle board, treated or painted wood, melamine resin-coated panels and the like are particularly unsuitable for use in pellets, since they may produce noxious emissions and / or uncontrolled variations in the burning characteristics of the pellets.
New pellet mills are being opened in the United Kingdom every month, lowering the price of a tonne of pellets to as low as £140 per tonne. The scarcity and unreliable supply that used to come with the dependence on wood pellets has vanished.
Energy output
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 9.8 MWh/ton (or about 17 million BTU/ton).
The climate impact of wood pellets is disputed. Some argue that there is a low net carbon footprint because trees are a renewable resource. 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 [1]methane, which has over 20 times more heat trapping characteristics than CO2 does.
Potential issues
- 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, or pellet basket. 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.
Usage by region
Europe
| Pellet Use (ton)1 | ||||
|---|---|---|---|---|
| Land | 2006 | |||
| Sweden | 1 400 000 | |||
| Italy | 550 000 | |||
| Germany | 450 000 | |||
| Austria | 400 000 | |||
| Denmark * | n. 400 000 | |||
| Finland* | n. 50 000 | |||
| *Households 2005.2 | ||||
Pellets are most widely used in Sweden - mainly as an alternative to oil-fired central heating. In Austria, the leading market for pellet central heating furnaces (relative to its population), it is estimated that 2/3 of all new domestic heating furnaces are pellet burners. In Italy, a large market for automatically-fed pellet stoves has developed. Although in the U.S., the inexpensive way of burning wood pellets is with pellet baskets in your existing fireplace or wood stove. Pellets are shoveled manually into the basket.
New Zealand
The total sales of wood pellets in New Zealand was 3-5,000 tonnes in 2003. Recent construction of new wood pallet plants has given a huge increase in production capacity.3
United States
Currently, there are several companies investing in pellet burning technology. TARM USA has been importing European-made boilers for five years, and Maine Energy Systems [2] hopes to convert 10% of Maine households to wood pellet heat in the 2008-2009 heating season. Maine Energy Systems is using a Bosch/Janfire boiler/burner system.
Retail cost
United States
In 2008, it cost $19.59 per million BTUs for heating with pellets.4
See also
References
- ^ Bioenergie: Großes Potenzial für Pellets-Märkte in Europa und weltweit 9.7.2007 Solarserver.de
- ^ Pellets for small-scale domestic heating systems 5/2007, European Biomass Association Aebiom (Resmac project)
- ^ Nielsen, S; George A. Estcourt and Carolyn J. Hodgson (October 2004). "New Bioenergy options for New Zealand - an evaluation of wood pellet opportunities". Forest Research. Retrieved on 2008-10-17.
- ^ Ryan, Matt (June 20, 2008). Homeowners seek cheaper winter heat. Burlington Free Press.
External links
- Fuel Cost Calculator - Compare the cost of wood pellets to other fuels
- Pellet Fuels Institute - Non-profit association that serves the pellet industry
- [3] - Biomass Energy centre, compare costs in GBP
- Pelletsales.com - Compare soft wood pellets to hard wood pellets
Wikipedia content modification information:
- This page was last modified on 18 November 2008, at 16:10.
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