Pellet fuel

Pellet fuels (or pellets ) are biofuels made from compressed organic matter or biomass. [1] Pellets can be made of any of the following general categories of biomass: industrial waste and co-products, food waste , agricultural residues , energy crops, and virgin lumber . [2] Wood pellets are the most common type of pellet fuel and are made from compacted sawdust [3] and related industrial products of the milling of lumber, manufacture of wood products and furniture , andconstruction . citation needed ] Other industrial waste sources include empty bunches, palm kernel shells, coconut shells, and tree tops discarded during logging operations. [4] [5] So-called “black pellets” are made of biomass , refined to resemble hard coal and have been developed into existing coal-fired power plants . [6] Pellets are categorized by their heating value , moisture and ashcontent, and dimensions. They can be used as power generation, commercial or residential heating, and cooking . [7] 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 . [8]

Further, their regular geometry and small size allow very fine calibration. They can be fed to a feeder by auger feeding or by pneumatic conveying. Their high density also permits compact storage and long distance transport. They can be conveniently blown from a tanker to a storage bunker or silo on a customer’s premises. [9]

A broad range of pellet stoves , central heating furnaces, and other heating appliances have been developed and marketed since the mid-1980s. [10] In 1997, fully automatic wood pellet boilers with similar comfort levels and oil boilers became available in Austria . [11] With the surge in the price of fossil fuels since 2005, the demand for pellet heating has increased in Europeand North America , and a sizable industry is emerging. According to the International Energy Agency Task 40 , wood pellet production has more than doubled between 2006 and 2010 to over 14 million tones. [12]In a 2012 report, the Biomass Energy Resource Center says it expects wood pellet production in North America to double again in the next five years. [13]


Pellet truck being filled at a plant in Germany.

Pellets are produced by compressing the wood material which has passed through a hammer mill to provide a uniform dough-like mass. [14] This mass is fed to a press, where it is squeezed through a hole having the required size (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 plasticizes slightly, forming a natural “glue” that holds the pellets together as it cools. [8]

Pellets can be made from grass and other non-woody forms of biomass that do not contain lignin: distiller’s dried grains can be added to provide the necessary durability. [15] A 2005 news story from Cornell UniversityNews suggests that grass pellet production was more advanced in Europe than North America. It suggests the benefits of grass as a feedstock included its short growing time (70 days), and ease of cultivation and processing. The story quoted Jerry Cherney, an agriculture professor at the school, stating that greasy produce 96% of the heat of wood and that “any mixture of fat can be used, cut in mid-late summer, left in the field to leach out minerals, then baled and pelleted. “Drying of the hay is not required for pelleting, making the cost of processing less than with wood pelleting.” [16] In 2012, the Department of Agriculture of Nova Scotia announced a project to convert an oil fired boilerto grass pellets at a research facility. [17]

Rice-husk fuel-pellets are made by compacting rice-husk obtained by-product of rice -growing from the fields. It also has similar characteristics to the wood-pellets and more environment-friendly, as the raw material is a waste-product . The energy content is about 4-4.2 kcal / kg and the moisture content is typically less than 10%. The size of pellets is usually kept in the form of a cylinder; however larger cylinder or briquette forms are not uncommon. It is much cheaper than similar energy-pellets and can be compacted / manufactured from the husk itself, using cheap machinery. They are more environment-friendly as compared to wood-pellets. [18] In the regions of the world where wheatis the predominant food-crop, wheat husk can also be compacted to produce energy-pellets, with similar characteristics to rice-husk pellets.

A report by CORRIM (Consortium on Research on Renewable Industrial Material) for the Life-Cycle Inventory of Wood Pellet Manufacturing and Utilization estimates the energy required to dry, pelletize and transport pellets is less than 11% of the energy content of the pellets if using pre-dried industrial wood waste. If the pellets are made directly from forest materials, it takes up to 18% of the energy to dry the wood and additional 8% for transportation and manufacturing energy. An environmental impact assessment of exported wood by the Department of Chemical and Mineral Engineering, University of Bologna , Italy and the Clean Energy Research Center, University of British ColumbiaCanadian wood pellets from Vancouver to Stockholm (15,500 km via the Panama Canal ), about 14% of the total energy content of the wood pellets. [19] [20]

Pellet standards

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 (greater than 1 ton per cubic meter, thus it sinks in water) about 0.6-0.7 ton per cubic meter), have good structural strength, and low dust and ash content. [7] Because the wood fibers are broken down by the hammer mill, there is virtually no difference in the pellets between different wood types. citation needed ]Pellets can be made from a wide variety of materials, and can be used in many countries. quote needed ]. In Europe, the main production areas are located in Scandinavia , Finland , Central Europe , Austria , and the Balticcountries. [21] [22]

Pellets conforming to the European standards which are considered class B pellets. [7] Recycled materials such as particle board, treated or painted wood, melamine resin -coated panels and the like are particularly useful for pellets, since they can produce noxious emissions and uncontrolled variations in the burning characteristics of the pellets. quote needed ]

Standards used in the United States are different, developed by the Pellet Fuels Institute and, as in Europe, are not mandatory. citation needed ] Still, many manufacturers comply, as warranties of non-conforming with regulations. Citation needed ] Prices for pellets US surged During the fossil fuel price inflation of 2007-2008, aim later dropped markedly lower and are Generally we per- BTU basis Than Most fossil fuels, excluding coal .

Regulatory agencies in Europe and North America are in the process of tightening the emissions for all forms of wood heat, including wood pellets and pellet stoves. These standards will become mandatory. [23] [24] In the United States, the new rules were introduced in the EPA regulatory review process, [25] with final new rules issued for comment on June 24, 2014. [26] [27] [28] The American Lumber Standard Committee will be the independent certification agency for the new pellet standards. [29]


Wood pellets, in particular freshly made, are chemically active and can deplete the atmosphere of the oxygen required to sustain life. Wood pellets can also emit large quantities of poisonous carbon monoxide . Fatal accidents have taken place in private storerooms [30] and onboard marine vessels. [31] When handled, wood pellets give off dust which can cause serious dust explosions . [32]

Pellet stove operation

Main article: Pellet stove

There are three general types of pellet heating appliances, free standing pellet stoves, pellet stoves inserts and pellet boilers . Pellet stoves “look like a traditional wood stoves but operate more like a modern furnace. [Fuel, wood or other biomass pellets, is stored in a storage bin called a hopper. The hopper can be located on the top of the appliance, the side of it or remotely.] A mechanical auger [automatically feeds] the pellets into a burn pot, where they are incinerated at such a high temperature that they create no wind-clogging creosote and very little ash or emissions … “Heat-exchange tubes”: “Convection fan”: Circulates air through heat-exchange tubes and into … The biggest difference between a pellet stove and … a woodstove , that is, inside, the pellet stove is a high-tech device with a circuit board, a thermostat, and fans-all of which work together to [regulate temperature and heat your space efficiently. ” [33]

pellet stove insert is a stove that is inserted into an existing masonry or prefabricated wood fireplace . See Fireplace insert

Pellet boilers are standalone central heating and hot water systems designed to replace traditional fossil fuel systems in residential, commercial and institutional applications. Automatic or auto-pellet boilers include silos for bulk storage of pellets, a fuel delivery system that moves the fuel from the silo to the hopper, a logic controller to regulate temperature over multiple heating zones and an automated ash removal system for long-term automated operations. [34]

Pellet sneakers allow a person to heat their home with pellets in existing stoves or fireplaces. [35]

Energy output and efficiency

Wood-pellet heater

The energy content of wood pellets is approximately 4.7 – 5.2 MWh / ton [36] [37] (~ 7450 BTU / lb).

High-efficiency wood pellet stoves and boilers have been developed in recent years, typically offering combustion efficiencies of over 85%. [38] The newest generation of wood pellet boilers can work in condensing mode and therefore achieve 12% higher efficiency values. [39] Wood pellet boilers have limited control over the spleen 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 also available. [9]

Air pollution emissions

Emissions such as NO x , SO x and volatile organic compounds from pellet burning are in general very low in comparison to other forms of combustion heating. [40] Highly concentrated particulate matter in 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 PM 2.5 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 facilitieselectrostatic precipitators , cyclonic separators , or baghouse particle filterscan control particulate When Properly maintained and operated. [41]

Global warming

Main article: Global warming

There is uncertainty in the degree of heat transfer, which contributes to the global warming of the environment. [8] [42] [43] [44] Factors in the uncertainty include the wood source, carbon dioxide emissions and production of final combustion, and what time scale is appropriate for the consideration. [8] [42] [45]

A report [8] by the Manomet Center for Conservation Sciences , “Biomass Sustainability and Carbon Policy Study” issued in June 2010 for the Massachusetts Department of Energy Resources, concludes that a large biomass of CO2 a net profit, which is not retired for 20-25 years. [8] In June 2011 the department was preparing for its final regulation, expecting to sharpen the controls of the biomass for energy, including wood pellets. [46] Biomass energy proponents have disputed the Manomet report’s conclusions, [47] [48]and scientists have pointed out that the impacts are worse than reported. [42] [49]

Until ca. It has been widely assumed, even in scientific papers, that biomass energy (including from wood pellets) is carbon neutral, and is more likely to be reclaimed from the air. [50] Then, scientific papers studying the climate implications of biomass, which appeared to be refuting the simplistic assumption of its carbon neutrality . [45] [51] According to the Biomass Energy Resource Center, the assumption of carbon neutrality “has shifted to a recognition that the carbon implications of biomass depend on the fuel is harvested, from what forest types, what types of forest management are? applied, and how biomass is used over time and across the landscape. ” [41]

In 2011 twelve prominent US environmental organizations adopted policy setting a high bar for government incentives of biomass energy, including wood pellets. It states in part, “[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. ” [52]


The wood products industry is concerned that if large-scale use of wood is established, the supply of raw materials for construction and manufacturing will be significantly curtailed. [8] [53]


Due to the rapid increase in popularity since 2005, pellet availability and cost may be an issue. [54] This is an important consideration when buying pellet stoves, furnaces, pellet baskets or other devices known in the industry as Bradley Burners. [55] However, current pellet production is increasing and there are plans to bring new pellets into the US in 2008-2009. [56]

The cost of the pellets can be affected by the building cycle leading to fluctuations in the supply of sawdust and offcuts. [57]

The new Hampshire Office of Energy and Planning released on October 5, 2015, the cost of # 2 Fuel Oil delivered to the cost of Bulk Delivered Wood Fuel Pellets using their BTU equivalent: 1 ton pellets = 118.97 gallon of # 2 Fuel Oil. This assumes that one ton of pellets produces 16,500,000 BTU and one gallon of # 2 Fuel Oil produces 138,690 BTU. Thus if # 2 Fuel Oil delivered costs $ 1.90 / Gal, the price is for breakeven pellets is $ 238.00 / Ton delivered.

Usage by region


EU Pellet Use (your) [58]
Country 2013
UK 4,540,000
italy 3,300,000
denmark 2,500,000
Netherlands 2,000,000
Sweden 1,650,000
germany 1,600,000
belgium 1,320,000

Usage across Europe varies due to government regulations. In the Netherlands , Belgium , and the UK , pellets are widely used in large-scale power plants. The UK’s largest power plant, the Drax power station , converted some of its units to pellet burners starting in 2012; by 2015 Drax had made the UK the largest container of exports of wood pellets from the US. [59] In Denmark and Sweden , pellets are used in large-scale power plants, medium-scale district heating systems, and small-scale residential heat. In Germany , Austria , Italy , and France, pellets are mostly used for small-scale residential and industrial heat. [58]

The UK HAS Initiated a grant scheme called Expired the Renewable Heat Incentive (RHI) Allowing non-domestic and domestic wood pellet boiler installations recevoir payments over a period of 7-20 years entre It is the first scheme in the world Such AIMS and pour augmenter the amount of renewable energy generated in the UK, in line with EU commitments. Scotland and Northern Ireland have separate but similar schemes. From spring 2015, any biomass or domestic purchaser must buy their fuel from BSL (Biomass Suppliers List). [60]

Pellets are widely used in Sweden, the main pellet producer in Europe, [21] as an alternative to oil-fired central heating. In Austria, the leading market for pellet central heating furnaces (relative to icts population), it is Estimated That 2 / 3 of all new domestic heating furnaces are pellet burners. In Italy, a large market for fed pellet stoves has developed. Italy ‘s main use for pellets is small – scale private residential and industrial boilers for heating. [61]

In 2014 in Germany the overall wood pellets per year consumption 2.2 mln tones. These pellets are consumed predominantly by residential small scale heating sector. The co-firing plants which are used in the field of energy production are not widespread in the country. The largest amount of wood pellets is certified with DINplus and these are the pellets of the highest quality. As a rule, the pellets of lower quality are exported. [62]

New Zealand

The total sales of wood pellets in New Zealand was 3-5,000 tons in 2003. [63]

United States

Some companies import European-made boilers. As of 2009, about 800,000 Americans were using wood pellets for heat. [40] It is estimated that 2.33 million tons of wood pellets will be used for heat in the US in 2013. [64] The US wood pellet export to Europe grew from 1.24 million tons in 2006 to 7 million tons in 2012, but forests grew even more. [65]

Other uses

Horse bedding

When small amounts of water are added to wood pellets, they expand and revert to sawdust. This makes them suitable for use as a horse bedding. The ease of storage and transportation are additional benefits over traditional bedding. However, some species of wood, including walnut, can be toxic to horses and should not be used for bedding. [66]

In Thailand , rice husk pellets are being produced for animal bedding. They have a high absorption rate which makes them ideal for the purpose. [67]


Wood pellets are also used to absorb water when drilling oil or gas wells. [68]


Wood Pellet grills have gained popularity as a versatile way to grill, bake, and smoke. The size of the pellets makes it useful for creating a wood that still controls its temperature. < [69]

See also

  • Solid fuel
  • Renewable heat
  • Pellet mill
  • Pellet stove
  • woodchips
  • Firelog
  • biochar


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