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Pellet fuel

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Wood pellets.
Fuels for heating

Wood pellets are a type of wood fuel, generally made from compacted sawdust or other wastes from sawmilling and other wood products manufacture,[1] but also sometimes from sources such as whole-tree removal or tree tops and branches leftover after logging and which otherwise help replenish soil nutrients.[citation needed] Pellets are manufactured in several types and grades as fuels for electric power plants, homes, and other applications in between.[2] Pellets are extremely dense and can be produced with a low moisture content (below 10%) that allows them to be burned with a very high combustion efficiency.[3]

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.[citation needed] Their high density also permits compact storage and rational transport over long distance.[citation needed] They can be conveniently blown from a tanker to a storage bunker or silo on a customer's premises.[citation needed]

A broad range of pellet stoves, central heating furnaces, and other heating appliances have been developed and marketed since 1999.[citation needed][example needed] With the surge in the price of fossil fuels in 2005, the demand for pellet heating has increased in Europe and North America, and a sizable industry is emerging.[citation needed]

Production

Pellets are produced by compressing the wood material which has first passed through a hammer mill to provide a uniform dough-like mass.[4] 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.[3] A report to the Massachusetts Department of Energy Resources estimates the energy required to manufacture and transport pellets is less than 2% of the energy content of the pellets.[3]

Pellets conforming to the norms commonly used in Europe (DIN 51731 or Ö-Norm M-7135) have less than 10% water content, are uniform in density (higher than 1 ton per cubic meter, thus it sinks in water)(bulk density about 0.6-0.7 ton per cubic meter), have good structural strength, and low dust and ash content.[2] Because the wood fibres are broken down by the hammer mill, there is virtually no difference in the finished pellets between different wood types.[citation needed] 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.[citation needed]

Pellets conforming to the European standards 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 uncontrolled variations in the burning characteristics of the pellets.[citation needed]

Standards used in the United States are different, developed by the Pellet Fuels Institute, are not mandatory, and are generally less strict than those of Europe; for example, it is accepted that pellets exposed to large volumes of water in the US may significantly degrade (turning into "mush").[citation needed] Still, many manufacturers comply, as warranties of US-manufactured or imported combustion equipment may not cover damage by pellets non-conformant with regulations.[citation needed] Prices for US pellets surged during the fossil fuel price inflation of 2007–2008, but subsequently have decreased significantly in late 2008 and early 2009, and are generally lower on a per-BTU basis than most fossil fuels, excluding coal,[citation needed] which is not an option highly favored for heating by many residential and commercial consumers, due to frequent maintenance and tending requirements for end users, high carbon emissions, air pollution (often leading to nuisance complaints from neighbors and investigation by boards of health and environmental agencies), the mess generated by coal dust and improper storage, as well as potentially dangerous fly ash.[citation needed]

Pellet stove operation

A fully automated pellet stove requires filling up with the pellets and turning on, the stove does the rest: it automatically lights, automatically feeds the pellets into the flame with an auger, automatically adjusts the rate to keep the room at a pre-set temperature with an electric thermostat.[citation needed]

Energy output and efficiency

Wood-pellet heater

The energy content of wood pellets is approximately 4.7 – 4.9 MWh/tonne[5] (~7450 BTU/lb).

High-efficiency wood pellet stoves and boilers have been developed in recent years, offering combustion efficiencies of over 90%.[citation needed] Wood pellet boilers, having limited control over the rate and presence of combustion compared to liquid or gaseous-fired systems; however, for this reason they are better suited for hydronic heating systems due to the hydronic system's greater ability to store heat.[citation needed] Pellet burners capable of being retrofitted to oil-burning boilers are predicted to be available on the market within the next several years.[citation needed]

Air pollution emissions

Emissions such as NOx, SOx and volatile organic compounds from pellet burning equipment are in general very low in comparison to other forms of combustion heating.[6] An additional consideration, though, is such air pollutant emissions caused in producing the energy used to manufacture pellets. A recognized problem is the emission of fine (particulate matter) to the air, especially in urban areas that have a high concentration of pellet heating systems or coal or oil heating systems in close proximity. This PM2.5 emissions of older pellet stoves and boilers can be problematic in close quarters, especially in comparison to natural gas (or renewable biogas), though on large installations electrostatic precipitators or baghouse particle filters may reduce the problem if installed and properly maintained and operated.[citation needed] Research is particularly needed concerning the health effects of ultrafine particles produced by the high burn temperatures of wood pellets.[7][failed verification] These nano-scale particles are substantially smaller than PM2.5, and can penetrate into the smallest passages of the lungs and in some cases directly into the bloodstream.[7][dubious – discuss] They have unique physical and chemical properties because of their extremely high surface area per unit of mass, an inherent consequence of their nano-scale size. Even a very small mass of such particles constitutes a very large number of them.[7][dubious – discuss]

Global warming

There is controversy over whether and to what degree making heat or electricity by burning wood pellets contributes to global climate change, as well as how the impact on climate compares to the impact of using competing sources of heat.[3][8][9][10]

Factors in the controversy include the wood source, carbon dioxide emissions from production and transport as well as from final combustion, and what time scale is appropriate for the consideration.[3][8][11][12]

Central to the on-going controversy throughout the United States, but specific to circumstances in Massachusetts, is a report[3] by the Manomet Center for Conservation Sciences,[13] "Biomass Sustainability and Carbon Policy Study," issued in June 2010. It was commissioned by the Massachusetts Department of Energy Resources,[14] and concludes that burning wood pellets or wood chips releases a large amount of CO2 into the air, creating a "carbon debt" that is not retired for many decades and in some cases more than a century.[3] In June 2011 the department was preparing to file its final regulation, expecting to significantly tighten controls on the use of biomass for energy, including wood pellets.[15] Biomass energy proponents have disputed the Manomet report's conclusions,[16][17] and scientists have pointed out oversights in the report, suggesting that climate impacts are worse than reported.[8][18]

Until ca. 2008 it was commonly assumed, even in scientific papers, that biomass energy (including from wood pellets) is carbon neutral, largely because regrowth of vegetation was believed to recapture and store the carbon that is emitted to the air.[19] Then, scientific papers began to appear which took at the climate implications of biomass and refuted the simplistic assumption of its carbon neutrality.[3][11][12][20]

In 2011 twelve prominent U.S. environmental organizations adopted policy setting a high bar for the use of biomass energy, including wood pellets. It states in part that, "[b]iomass sources and facilities qualifying for (government) incentives must result in lower life-cycle, cumulative and net GHG and ocean acidifying emissions, within 20 years and also over the longer term, than the energy sources they replace or compete with."[21]

Sustainability

The wood products industry is concerned that if large-scale use of wood energy is instituted, the supply of raw materials for construction and manufacturing will be significantly curtailed.[3][22] forests will no longer be able to be Ecological sustainability of large-scale use of wood energy has also been a topic of concern from divergent points of view.[3][23][24][25]

Cost

Due to the rapid increase in popularity since 2005, pellet availability and cost may be an issue.[26] This is an important consideration when buying a pellet stove, furnace, pellet baskets or other devices known in the industry as Bradley Burners.[27] However, current pellet production is increasing and there are plans to bring several new pellet mills online in the US in 2008–2009.[28]

The cost of the pellets can be effected by the building cycle leading to fluctuations in the supply of sawdust and offcuts.[29]

Usage by region

Europe

Pellet Use (ton)[30]
Country 2006
Sweden 1 400 000
Italy 550 000
Germany 450 000
Austria 400 000
Denmark* n. 400 000
Finland* n. 50 000
*Households 2005.[31]

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.[citation needed]

New Zealand

The total sales of wood pellets in New Zealand was 3–5,000 tonnes in 2003. Recent construction of new wood pellet plants has given a huge increase in production capacity.[32]

United States

Some companies import European-made boilers. As of 2009, about 800,000 Americans were using wood pellets for heat.[6]

Retail cost

United States

In 2009, the cost for heating with pellets was $15.15 per million BTU.[6]

Europe

In 2009, the cost of woodpellets was 4 eurocent per kWh or 16 $ per million BTU.[33] Retail prices depend on the size and specifications of the order (bulk, big bag, 15 kg sacks,...).

See also

References

  1. ^ "What are pellets". Pellet Fuels Institute. Retrieved 7 November 2011.
  2. ^ a b Alakangas, Eija (18). ["European pellet standards" (PDF). Retrieved 11 December 2011. {{cite web}}: Check |url= value (help); Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |month= ignored (help)
  3. ^ a b c d e f g h i j Manomet Center for Conservation Science. 2010. Biomass sustainability and Carbon Policy Study: Report to the Commonwealth of Massachusetts Department of Energy Resources.[1]
  4. ^ Fuller, Ron. [http:bioenergy.illinois.edu/news/biomass/06Fuller_cpm.pdf "Pelleting Process"] (PDF). University of Illinois. Retrieved 8 December 2011. {{cite web}}: Check |url= value (help)
  5. ^ http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,59188&_dad=portal&_schema=PORTAL
  6. ^ a b c "Buyer's guide to pellet- and wood-burning stoves The pros, cons and costs vs. natural gas, oil, and coal". Consumer Reports. 2009. Retrieved 8 December 2011. {{cite web}}: Unknown parameter |month= ignored (help)
  7. ^ a b c Howard, V. (2009). "Statement of Evidence: Particulate Emissions and Health (An Bord Plenala, on Proposed Ringaskiddy Waste-to-Energy Facility)." [2] Retrieved 2011-04-26.
  8. ^ a b c Booth M (2010). Review of the Manomet Biomass Sustainability and Carbon Policy Study. Report for the Clean Air Task Force. [3]
  9. ^ Lippke, . et al. 2011. Life cycle impacts of forest management and wood utilization on carbon mitigation: knowns and unknowns. [4]
  10. ^ McDermott, Matthew (2009-04-14). "Biomass Can Only Offer Major Emission Reductions if Best Practices Are Followed, New UK Report Says". Treehugger.com. Retrieved 2009-05-16.
  11. ^ a b Searchinger, T.; Hamburg, S.; Melillo, J.; Chameides, W,; Havlik, P.; Kammen, D.; Likens, G; Lubowski, R.; Obersteiner, M.; Oppenheimer, M.; Philip, R.G.; Schlesinger, W.;, Ti, D. (2009). Fixing a Critical Climate Accounting Error. Science (326:5952, p.527-528). [5]
  12. ^ a b Johnson, E. (2009). Goodbye to carbon neutral: Getting biomass footprints right. Environmental Impact Assessment Review (29:3, p.165-168). [6]
  13. ^ URL for the Manoment Center for Conservation Science: [7]
  14. ^ Mass. Dept. of Energy Resources (DOER) website. [8]
  15. ^ Mass. DOER webpage on biomass
  16. ^ http://www.futuremetrics.net/papers/Manomet%20Got%20it%20Backwards.pdf
  17. ^ http://www.futuremetrics.net/papers/Response%20to%20Manomet%20Comments.pdf
  18. ^ Moomaw, W. 2011. Should we get our electricity by burning trees? Presentation at Williams College. [9]
  19. ^ http://www.dovetailinc.org/files/DovetailLCABioenergy0711.pdf
  20. ^ Magelli, F.; Boucher, K.; Bi, H.; Melin, S.; Bonoli, A. (2009). An environmental impact assessment of exported wood pellets from Canada to Europe. Biomass and Bioenergy (33:3, p.434-441). [10]
  21. ^ Principles of Sustainable Biomass; policy of 12 large U.S. environmental oranizations. [11], retrieved from The Wilderness Society website, 27 August 2011.
  22. ^ Large-scale biomass ‘risks UK jobs and carbon emissions.’ Carbon Offsets Daily, 2 July 2010. [12]
  23. ^ http://www.futuremetrics.net/HeatNE%20Vision%20Master%20FINAL%204%2025%2010.pdf
  24. ^ Forest Guild. 2010. Forest Biomass Retention and Harvesting Guidelines for the Northeast. [13]
  25. ^ Massachusetts Forest Watch
  26. ^ http://www.nef.org.uk/logpile/pellets/production.htm
  27. ^ http://www.bradleyburner.com/
  28. ^ http://www.fpl.fs.fed.us/documnts/fplrp/fpl_rp656.pdf
  29. ^ http://thewoodcoaladvocacycouncil.com/images/stories/Development_European_Pellets_Market.pdf
  30. ^ Bioenergie: Großes Potenzial für Pellets-Märkte in Europa und weltweit 9.7.2007 Solarserver.de
  31. ^ Pellets for small-scale domestic heating systems 5/2007, European Biomass Association Aebiom (Resmac project)
  32. ^ Nielsen, S (October 2004). "New Bioenergy options for New Zealand – an evaluation of wood pellet opportunities" (PDF). Forest Research. Retrieved 2008-10-17. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) [dead link]
  33. ^ http://www.pelletinfo.net
  • Pellet Fuels Institute – A non-profit trade association made up of pellet manufacturers and associated industry suppliers
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