Woodchips are a medium-sized solid material made by cutting, gold chipping, larger pieces of wood .

Woodchips can be used as a biomass solid fuel and raw material for producing wood pulp . They can also be used as an organic mulch in gardening , landscaping , ecological restoration , bioreactors for denitrification and mushroom cultivation. According to the different chemical and mechanical properties of the masses, the wood logs are mostly peeled, and the bark chips and the wood chips are processed in different processes. The process of making wood chips is called woodchipping and is done with a woodchipper .

Raw materials

The raw materials of wood chips can be pulpwood , wood plantations , waste wood and residuals from construction , agriculture , landscaping , logging , and sawmills and locally grown and harvested fuel crops . quote needed ]


A woodchipper is a machine used for reducing wood to smaller pieces. There are several types of woodchippers [1] depending on the further processing of the woodchips. For industrial use, the woodchippers are wide, stationary facilities.

Pulp and paper industry

Wood chips used for chemical pulp must be relatively uniform in size and free of bark. The optimum size varies with the species. [2] It is important to avoid damage to the wood fibers as it is important for the pulp properties. For roundwood it is most common to use disk chippers. A typical size of the disk is 2.0 – 3.5 m in diameter, 10 – 25 cm in thickness and weight is up to 30 tons. The disk is fitted with 4 to 16 knives and driven with motors of ½ – 2 MW. [2] Drum chippers are normally used for wood residues. [2]

Methods of conveyance

There are four potential methods to move woodchips: pneumatic , belt conveyor , hopper with direct fall, batch system (manual conveyance). [3] [4]


Woodchips are used as a raw material for technical wood processing. In industry, processing of bark chips is often separated after peeling the logs due to different chemical properties.

Wood pulp

Main article: Wood pulp

Only the heartwood and sapwood are useful for making pulp. Bark contains relatively few useful fibers and is used in the pulp mill . Most pulping processes require that the wood be chipped and screened to provide uniform sized chips. quote needed ]


Aussi woodchips are used as landscape and garden mulch , Producing benefits Such As water conservation , weed control, Reducing and Preventing soil erosion , and for Supporting germination of native seeds and acorns in habitat revegetation- ecological restoration projects. As the ramial chipped wood decomposes and improves the soil structure, permeability, bioactivity, and nutrient availability. Woodchips when used as a mulch are at least three inches thick. quote needed ]

Playground surfacing

Wood chips can be reprocessed into an extremely effective playground surfacing material, or impact-attenuation surface. [5] When used as playground surfacing (soft fall, cushion fall, or play chip, as it is known), woodchips can be very effective in the impact of falls of playground equipment. When spread to depths of one foot (30 centimeters) playground wood chips can be effective at reduced impacts in falls up to 11 feet (3 meters). Playground woodchip is also an environmentally friendly alternative to rubber type playground surfaces. quote needed ]


Woodchip batteries at the edge of a field can inhibit nitrates from running off into water tiles. They are a simple measure for farmers to reduce the pollution of the watershed. A 2011 study showed that most of the nitrate removal was due to heterotrophic denitrification. [6] A 2013 experiment from Ireland showed that after 70 days of startup, a woodchip stack loaded with liquid pig manure at 5 L / m 2 / day removed an average of 90% of nitrate in the form of ammonium after one month. [7] A January 2015 study from the Ohio State University showed very low nitrogen gas, ie greenhouse gas emissionsfrom nitrate transformation under the anaerobic conditions of the wood chip bioreactor. Scientists constructed a model for water flow and nitrate removal kinetics which can be used to design denitrification beds. [8] It is unknown if other nutrients like phosphorus or pathogens are affected by the bioreactor as well.


Woodchips-have-been traditionally used as solid fuel for space heating or in energy plants to generate electric power from renewable energy . The main source of forest chips in Europe and in most of the countries which? ] have been logging residues. It is expected that the shares of stumps and roundwood will increase in the future. citation needed ] As of 2013 in the EU, the estimates for potential biomass for energy, available under current when? ] 277 million m 3 277 million m 3, for above ground biomass and 585 million m 3 for total biomass. [9]

The newer fuel systems for heating or wood pellets . The advantage of woodchips is cost, the advantage of wood pellets is the controlled fuel value. The use of woodchips in automated heating systems, is based on a robust technology. quote needed ]

The size of the woodchips is particularly important when burning woodchip in small plants. Unfortunately there are not many standards to decide the fractions of woodchip. One standard is the GF60 which is commonly used in smaller plants, including small industries, villas, and apartment buildings. “GF60” is known as “Fine, dry, small chips”. The requirements for GF60 are distributed as follows: 0-3.5mm: <8%, 3.5-30mm: <7%, 30-60mm: 80-100 %, 60-100 mm: <3%, 100-120 mm: <2%. quote needed ]

The energy content in one cubic meter is more than one cubic meter wood logs, but can vary greatly depending on moisture. The moisture is decided by the handling of the raw material. If the trees are taken in the winter (with tears in the bark and covered so they can not reach to them), and are then chipped in the fall, the woodchips’ moisture content will be approximately 20-25%. The energy content, then, is approximately 3.5-4.5kWh / kg (~ 150-250 kg / cubic meter). quote needed ]

Coal power plants , which are fairly straightforward to do, since they both use a similar steam turbine engine , and the cost of woodchip fuel is comparable to coal . quote needed ]

Solid biomass is an attractive fuel for addressing the concerns of the energy crisis and climate change , since the fuel is affordable, widely available, close to carbon neutral and thus climate-neutral in terms of carbon dioxide (CO2), since in the ideal case only the carbon dioxide which has been drawn into the tree’s growth and stored in the wood is released into the atmosphere again. [10] It is sustainable as long as crops are allowed to regrow; In most cases, biomass is not carbon neutral contradictory ] as is not regrown and the efficiency of biomass operations produces more pollutants than the processes they replace.quote needed ]

Waste and emissions

Compared to the solid waste disposal problems of coal and nuclear fuel, woodchip fuel is waste disposal problems are less serious; in a study from 2001 fly ash from wood burning chip had 28.6 mg cadmium / kg dry matter. Compared to fly ash from burning straw, cadmium was found to be more prevalent, with only small amounts of cadmium leached. It was speciated as a form of cadmium oxide , cadmium silicate (CdSiO 3 ); It is important to note that adding it to the forest or soils in the long-term could cause a problem with accumulation of cadmium. [11]

Like coal, wood combustion is a known source of mercury emissions, particularly in northern climates during winter. The mercury is both gaseous as elemental mercury (especially when wood pellets are burned) or mercury oxide, and solid PM2.5 particulate matter when untreated wood is used. [12]

When used in the combustion of 1,3-butadiene , benzene , formaldehyde and acetaldehyde , which are known or suspected carcinogenic compounds, are elevated. The cancer risk of these after exposure to wood smoke is estimated to be low in developed countries. [13]

Some techniques for burning woodchips result in the production of biochar – effectively charcoal – which can be used as a charcoal, or returned to the soil, since wood ash can be used as a mineral-rich plant fertilizer . The latter method is an effective carbon-negative system, and it is an effective soil conditioner, enhancing water and nutrient retention in poor soils. quote needed ]

Automated handling of solid fuel

Unlike the smooth, uniform shape of manufactured wood pellets , woodchip and other colors are often mixed with twigs and sawdust. This mixture has a higher probability of jamming in small feed mechanisms. Thus, sooner or later, one or more jams is likely to occur. This reduces the reliability of the system, as well as increasing maintenance costs. Despite what some pellet stove manufacturers may say, researchers who are experienced with woodchips, say they are not compatible with the 2 inch (5 cm) auger used in pellet stoves. [3]

Micro combined heat and power

Main article: Micro combined heat and power

Wood is occasionally used to power engines, such as steam engines , Stirling engines , and Otto engines running on woodgas . As of 2008, these systems are rare, but as technology and the need for it develops, it is likely to be more common in the future. For the time being, wood can be used for heating applications. This invention is intended to provide greater fuel efficiency and allow for greater fuel efficiency in the combustion of fuel , which is compatible with wood based fuel and other solid biomass fuels. Heating applications generally do not require refined or processed fuels, which are almost always more expensive. [quote needed ]

Comparison to other fuels

Woodchips are similar to wood pellets , which is more amenable to automation than cord wood, particularly for smaller systems. Woodchips are less expensive to produce than wood pellets, which must be processed in specialized facilities. While Avoiding the costs associated with refinement, the lower density and Higher moisture content of woodchips Reduces Their calorific value , Substantially Increasing the feedstock needed to generate an equivalent amount of heat. Greater impact of trucking, storing and / or shipping the wood.

Woodchips are less expensive than cord wood , because the harvesting is faster and more highly automated. Woodchips are of greater supply, because they can be chipped, and small limbs and branches can not be less expensive than wood. Cord wood generally needs to be “seasoned” or “dry” before it can be burned cleanly and efficiently. On the other hand, woodchip systems are typically designed to clean and efficiently burn “green chips” with very high moisture content of 43-47% (wet basis). [3] (see gasification and woodgas )

Environmental aspects

If woodchips are harvested by a product of sustainable forestry practices, then this is considered a source of renewable energy . On the other hand, harvesting practices, such as clearcutting large areas, are highly damaging to forest ecosystems .

Theoretically, whole-tree chip harvesting does not have a high energy cost compared to a rotation coppice ; however, it can be an energy-efficient and low-cost method of harvesting. In some cases, this practice may be controversial when whole-tree harvesting may be questionable.

Waste processing

Woodchips, and bark chips, can be used as bulking agents in industrial composting of municipal biodegradable waste, particularly biosolids .

Woodchip biomass can be used as a mineral-rich plant fertilizer.

Forest fire prevention

Woodchip harvesting can be used with man made firebreaks , which are used as a barrier to the spread of wildfire . Undergrowth coppice is ideal for chipping, and larger trees may be left in place to shade the forest floor and reduce the rate of fuel accumulation.

Market products, supply and demand

Currently, domestic or residential sized systems are not available in the market. Homemade devices have been produced, which are small-scale, clean-burning, and efficient for woodchip fuels. Much of the research activities to date, which are of self-funded projects. The majority of funding for energy research has been for liquid biofuels .

United States

“Chips delivered are usually dependent on such points of supply, the type of material (such as bark, sawmill residue or whole-tree chips), Chips delivered. The price is usually between US $ 18 and US $ 30 per (wet) -ton delivered. ” [14]

In 2006, prices were US $ 15 and US $ 30 per wet-ton in the northeast. [15]

In the 20 years leading up to 2008, prices have fluctuated between US $ 60-70 / oven-dry metric ton (odmt) in the southern states, and between US $ 60 / odmt and US $ 160 / odmt in the Northwest. [16]


In several well wooded European countries (eg Austria, Finland, Germany, Sweden) wood chips are becoming an alternative fuel for family homes and larger buildings due to the abundant availability of wood chips, which result in low fuel costs. The European Union is promoting wood chips for energy production in the EU Forest action plan 2007-2011. The total long term potential of wood chips in the EU is estimated to be 913 million m 3 . [9]


After a long period of negative scores, the demand for wood chips Beginning in the last quarter of 2013, for the production of paper and paper, and the production of papers in Japan. Softwood chip prices from United States increased by 7% compared to softwood chip prices from Australia. [17]

See also

  • Barkdust
  • Renewable heat
  • Woodchipping in Australia


  1. Jump up^ Basu, Prabir (2010-07-19). Biomass Gasification and Pyrolysis: Practical Design and Theory . Academic Press. ISBN  9780080961620 .
  2. ^ Jump up to:c Sixta, Herbert, ed. (2006). Handbook of pulp . 1 . Winheim, Germany: Wiley-VCH. pp. 79-88. ISBN  3-527-30997-7 .
  3. ^ Jump up to:c VTHR Green wood chip Furnace unreliable source? ]
  4. Jump up^ BIOMASS ENERGY. State of the Technology, Present Obstacles & Future Potential; Fuel Handling EquipmentReport for: United States Department of Energy, Conservation and Renewable Energy, Office of Energy Related Inventions. Larry Dobson, Northern Light Research & Development. June 23, 1993
  5. Jump up^ Marshall, Mike (March 25, 2011). “ADA-Approved and Non-Appproved Playground Surfacing Materials” (PDF) . Retrieved July 25, 2017 .
  6. Jump up^ Warneke, S; Schipper, LA; Bruesewitz, DA; Baisden, WT (2011). “A comparison of different approaches for measuring denitrification rates in a nitrate removing bioreactor”. Water Research . 45 (14): 4141-51. doi :10.1016 / j.watres.2011.05.027 . PMID  21696799 .
  7. Jump up^ Carney, KN; Rodgers, M .; Lawlor, PG; Zhan, X (2013). “Treatment of separated piggery anaerobic digestate liquid using woodchip biofilters”. Environmental Technology . 34 (5-8): 663-70. doi : 10.1080 / 09593330.2012.710408 . PMID  23837316 .
  8. Jump up^ Ghane, E; Fausey, NR; Brown, LC (2015). “Modeling nitrate removal in a denitrification bed”. Water Research . 71 : 294-305. doi : 10.1016 / j.watres.2014.10.039 . PMID  25638338 .
  9. ^ Jump up to:b Díaz Yáñez-O-Mola Yudego, B; Anttila P, Röser D, Asikainen A. (2013). “Forest chips for energy in Europe: current procurement methods and potentials”. Renewable and Sustainable Energy Reviews . 21 : 562-571. doi : 10.1016 / j.rser.2012.12.016 .
  10. Jump up^ Salthammer, T; Schripp, T; Wientzek, S; Wensing, M (2014). “Impact of operating fireplace wood-burning ovens on indoor air quality”. Chemosphere . 103 : 205-11. doi : 10.1016 / j.chemosphere.2013.11.067 . PMID  24364889 .
  11. Jump up^ Hansen, HK; Pedersen, AJ; Ottosen, LM; Villumsen, A (2001). “Speciation and mobility of cadmium in straw and wood combustion fly ash”. Chemosphere . 45 (1): 123-8. doi : 10.1016 / s0045-6535 (01) 00026-1 . PMID  11572586 .
  12. Jump up^ Huang, J; Hopke, PK; Choi, HD; Laing, JR; Cui, H; Zananski, TJ; Chandrasekaran, SR; Rattigan, OV; Holsen, TM (2011). “Mercury (Hg) emissions from domestic biomass combustion for space heating”. Chemosphere . 84 (11): 1694-9. doi : 10.1016 / j.chemosphere.2011.04.078 . PMID  21620435 .
  13. Jump up^ Rilo, HL; Zeng, Y; Alejandro, R; Carroll, PB; Bereiter, D; Venkataramanan, R; Tzakis, AG; Starzl, TE; Ricordi, C (1991). “Effect of FK 506 on the function of human islets of Langerhans” . Transplantation proceedings . 23 (6): 3164-5. PMC  2965621  . PMID  1721393 .
  14. Jump up^ Woodchip price factors for a Power Generating Station in Burlington, VT, US
  15. Jump up^ Vermont Heat Research – An Experimental Wood Chip Furnace
  16. Jump up^ First Quarter wood chip costs up Almost 50% in western US, Pulpmills goal in the US South Experienced only small upward price adjustments’
  17. Jump up^ “Good development for the Japanese wood chip market” . ITTO . Fordaq SA 15 May 2014.