Woodchips

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Woodchips, with hand for scale Woodchip.jpg
Woodchips, with hand for scale

Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste. [1] [2]

Contents

Woodchips may be used as a biomass solid fuel and are raw material for producing wood pulp. [3] They may also be used as an organic mulch in gardening, landscaping, and ecosystem restoration; in bioreactors for denitrification; [4] and as a substrate for mushroom cultivation. [5]

The process of making woodchips is called wood chipping and is done using a wood chipper. The types of woodchips formed following chipping is dependent on the type of wood chipper used and the material from which they are made. [6] Woodchip varieties include: forest chips (from forested areas), wood residue chips (from untreated wood residues, recycled wood and off-cuts), sawing residue chips (from sawmill residues), and short rotation forestry chips (from energy crops). [6]

Raw materials

Woodchips waiting to be loaded at Albany Port in Western Australia Woodchips at Albany Port.JPG
Woodchips waiting to be loaded at Albany Port in Western Australia

The raw materials of woodchips can be pulpwood, waste wood, and residual wood from agriculture, landscaping, logging, and sawmills. [7] Woodchips can also be produced from remaining forestry materials including tree crowns, branches, unsaleable materials or undersized trees. [8]

Wood chipper Bandit Model 1290H drum chipper.jpg
Wood chipper

Forestry operations provide the raw materials needed for woodchip production. [9] Almost any tree can be converted into woodchips, however, the type and quality of the wood used to produce woodchips depends largely on the market. [1] Softwood species, for instance, tend to be more versatile for use as woodchips than hardwood species because they are less dense and faster growing. [1]

Production

A wood chipper is a machine used for cutting wood into smaller pieces (chips). [10] There are several types of wood chippers, each having a different use depending on the type of processing the woodchips will undergo. [11]

Pulp and paper industry

Woodchips used for chemical pulp must be relatively uniform in size and free of bark. The optimum size varies with the wood species. [12] It is important to avoid damage to the wood fibres as this 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. [12] Drum chippers are normally used for wood residuals from saw mills or other wood industry. [12]

Methods of conveyance

There are four potential methods to move woodchips: pneumatic, conveyor belt, hopper with direct chute, and batch system (manual conveyance). [13] [ unreliable source? ] [14]

Types of wood chippers

Disk

A disk wood chipper features a flywheel made of steel and chopping blades with slotted disks. The blades slice through the wood as the material is fed through the chute. Knives located in the throat of the chipper cuts the wood in the opposite direction. The design is not as energy efficient as other styles but produces consistent shapes and sizes of woodchips. [15] [16]

Drum

A drum wood chipper has a rotating parallel-sided drum attached to the engine with reinforced steel blades attached in a horizontal direction. Wood is drawn into the chute by gravity and the rotation of the drum where it is broken up by the steel blades. The drum type is noisy and creates large uneven chips but are more energy efficient than the disk type. [15] [16]

Screw-type

A screw-type wood chipper contains a conical, screw-shaped blade {citation needed}. The blade rotation is set parallel to the opening so wood is pulled into the chipper by the spiral motion. Screw-type, also called high-torque rollers, are popular for residential use due to being quiet, easy to use and safer than disk and drum types. [15] [17]

Applications

Woodchips are used primarily 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

Only the heartwood and sapwood are useful for making pulp. Bark contains relatively few useful fibres and is removed and used as fuel to provide steam for use in the pulp mill. Most pulping processes require that the wood be chipped and screened to provide uniform sized chips.[ citation needed ]

Mulch

Woodchips are also used as landscaping and garden mulch, for water conservation, weed control, and reducing and preventing soil erosion. Woodchips when used as a mulch are at least three inches thick. It has a mixed reputation in gardening.

It has been promoted for use in habitat restoration projects. As the ramial chipped wood decomposes it improves the soil structure, permeability, bioactivity, and nutrient availability of the soil.

Playground surfacing

Woodchips do not meet American Society for Testing and Materials standards for use as playground surfacing material, and as of 2011 are illegal to use as playground surfacing in the US, not being ADA-approved according to US department of Justice guidelines. [18]

Barbecuing

Woodchips can also be used to infuse flavor and enhance the smoky taste to barbecued meats and vegetables. Several different species of wood can be used depending on the type of flavor wanted. For a mild, sweet fruity flavor, apple wood can be used while hickory gives a smoky, bacon-like flavor. Other different types of wood used are cherry, mesquite and pecan. [19]

Denitrifying woodchip bioreactor

Woodchips can be loaded into a 'denitrifying woodchip bioreactor' which has been used for several decades as an emerging biotechnology to treat agricultural wastewater by removing nitrates. [20] [21] [22] [23] It is a subsurface system where denitrification by micro-organisms utilizing a carbon source (as electron donor) reduces the nitrate into a harmless nitrogen gas. [21] Denitrifying woodchip bioreactor have a low construction and operational costs with a comparatively long lifespan going up to 15 years. [24] The interest in such a technique has grown in recent years and has expanded into the mining industry. [25] [26]

A 2013 experiment showed that after 70 days of startup, a woodchip pile loaded with liquid pig manure at 5 L/m2/day removed an average of 90% of nitrate after one month. [27] However, if the environmental conditions do not support complete denitrification, undesirable greenhouse gas such as nitrous oxide gas and methane could be produced. [20] [28] [29] [30] [31]

Fuel

Woody chips left for drying before transport to industrial off-takers in Namibia Heaps of chipped woody biomass in Namibia.jpg
Woody chips left for drying before transport to industrial off-takers in Namibia

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. [32] As of 2013 in the EU, the estimates for biomass potential for energy, available under current 2018 conditions including sustainable use of the forest as well as providing wood to the traditional forest sectors, are: 277 million m3, for above ground biomass and 585 million m3 for total biomass. [33]

The newer fuel systems for heating use either woodchips 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. [32]

The size of the woodchips, moisture content, and the raw material from which the chips are made are particularly important when burning wood chips in small plants. Unfortunately, there are not many standards to decide the fractions of woodchip. However, as of March 2018, The American National Standards Institute approved AD17225-4 Wood Chip Heating Fuel Quality Standard. The full title of the standard is: ANSI/ASABE AD17225-4:2014 FEB2018 Solid Biofuels—Fuel Specifications and classes—Part 4: Graded wood chips. [34] One common chip category 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 that the moisture is between 10 and 30% and the fractions of the woodchips are distributed as follows: 0–3.5mm: <8%, 3.5–30mm: <7%, 30–60 mm: 80–100%, 60–100 mm: <3%, 100–120 mm: <2%. [32]

The energy content in one cubic metre is normally higher than in one cubic metre 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 down in the winter and left to dry for the summer (with teas in the bark and covered so rain can't reach to them), and is 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 metre). [32]

Coal power plants have been converted to run on woodchips, which is fairly straightforward to do, since they both use an identical steam turbine heat engine, and the cost of woodchip fuel is comparable to coal. [32]

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 was drawn in during the tree's growth and stored in the wood is released into the atmosphere again. [32]

Waste and emissions

Compared to the solid waste disposal problems of coal and nuclear fuels, woodchip fuel's waste disposal problems are less grave; in a study from 2001 fly ash from woodchip combustion had 28.6 mg cadmium/kg dry matter. Compared to fly ash from burning of straw, cadmium was bound more heavily, with only small amounts of cadmium leached. It was speciated as a form of cadmium oxide, cadmium silicate (CdSiO3); authors noted that adding it to agricultural or forest soils in the long-term could cause a problem with accumulation of cadmium. [35]

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. [36]

When wood burning is used for space heating, indoor emissions of 1,3-butadiene, benzene, formaldehyde and acetaldehyde, which are suspected or known carcinogenic compounds, are elevated. The cancer risk from these after exposure to wood smoke is estimated to be low in developed countries. [37]

Certain techniques for burning woodchips result in the production of biochar – effectively charcoal – which can be either utilised as charcoal, or returned to the soil, since wood ash can be used as a mineral-rich plant fertilizer. The latter method can result in an effectively carbon-negative system, as well as acting as a very effective soil conditioner, enhancing water and nutrient retention in poor soils. [38]

Automated handling of solid fuel

Unlike the smooth, uniform shape of manufactured wood pellets, woodchip sizes vary and 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. [13]

Comparison to other fuels

Woodchips are similar to wood pellets, in that the movement and handling 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 physical volume requirements also increase the expense and emissions 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, partly because all parts of a tree can be chipped, whereas small limbs and branches can require substantial labor to convert to cord 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 cleanly and efficiently burn "green chips" with very high moisture content of 43–47% (wet basis). [13] (see gasification and woodgas)

Environmental aspects

Compared to conventional timber harvesting, woodchip harvesting has a greater impact on the environment, since a larger proportion of biomass is removed. [39] Increased use of woodchips can have negative effects on the stability and long-term growth of the forests in which they're removed from. For instance, chipping of trees from forests has been shown to increase the removal of plant nutrients and organic matter from an ecosystem, thereby reducing both the nutrients and humus content of the soil. [39] One option to balance the negative effects of woodchip harvesting is to return the woodchip ash to the forest which would restore some of the lost nutrients back into the soil. [39]

If woodchips are harvested as a by-product of sustainable forestry practices, then this is considered a source of renewable energy. [40]

Theoretically, whole-tree chip harvesting does not have as high a solar energy efficiency compared to short rotation coppice; however, it can be an energy-efficient and low-cost method of harvesting. [41]

Waste processing

Woodchips and bark chips can be used as bulking agents in industrial composting of municipal biodegradable waste, particularly biosolids. [42]

Forest fire prevention

Woodchip harvesting can be used in concert with creating man-made firebreaks, which are used as barriers 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.[ citation needed ]

Market products, supply and demand

United States

Woodchip costs usually depend on such factors as the distance from the point of delivery, the type of material (such as bark, sawmill residue or whole-tree chips), demand by other markets and how the wood fuel is transported. Chips delivered directly to the (powerplant) station by truck are less expensive than those delivered ... and shipped by railcar. The range of prices is typically between US$18 to US$30 per (wet)-ton delivered. [43]

In 2006, prices were US$15 and US$30 per wet-ton in the northeast. [44]

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. [45]

Canada

Wood chips have been used as a source of single-dwelling heating in Canada since the early days of settling but the development of oil and natural gas has dramatically decreased its usage. Most of the wood chip usage is by installations such as schools, hospitals and prisons. Prince Edward Island (PEI) has the most wood-chip plants due to high electricity rates and subsidies from the federal government. Nova Scotia has a 2.5 MW wood chip burning system that provides power to a textile factory as well as systems that provide power to a poultry processing plant, two hospitals and an agricultural college. [46]

The University of New Brunswick operates a wood chip burning furnace system to supply heat to the university, several industrial buildings, an apartment complex and a hospital. [46] Usage of wood chips for heat is low in Quebec due to low hydroelectricity rates but a small town is using wood chips as an alternative to road salt for icy roads. EMC3 Technologies started producing wood chips coated with magnesium chloride in November 2017 for the town and has claimed it maintains traction in -30 degrees Celsius compared to regular road salt at -15 degrees Celsius. [47] In Ontario, wood chip operations include a college in Brockville, a few secondary schools in Northern Ontario as well as a chip-fired boiler at the National Forestry Institute in Petawawa. [46] In the late 1980s, the Ontario provincial government in conjunction with the federal government subsidized building three co-generation plants next to sawmills. The first one was constructed in 1987 in Chapleau followed by a plant built in Cochrane in 1989 and the largest one in Kirkland Lake which was built in 1991. [46]

Europe

Large wood chipper in Germany Forsthacksler Hubertushof.jpg
Large wood chipper in Germany

In several well wooded European countries (e.g. Austria, Finland, Germany, Sweden) woodchips are becoming an alternative fuel for family homes and larger buildings due to the abundant availability of woodchips, which result in low fuel costs. The European Union is promoting woodchips for energy production in the EU Forest action plan 2007–2011. The total long term potential of woodchips in the EU is estimated to be 913 million m3. [33]

Japan

Woodchips are used in Japan for the paper manufacturing industry. Large supplies of softwood chips are imported from countries such as the United States and Australia for this purpose. [48]

See also

Related Research Articles

<span class="mw-page-title-main">Pulpwood</span> Timber intended for processing into wood pulp for paper production

Pulpwood can be defined as timber that is ground and processed into a fibrous pulp. It is a versatile natural resource commonly used for paper-making but also made into low-grade wood and used for chips, energy, pellets, and engineered products.

<span class="mw-page-title-main">Solid fuel</span> Solid material that can be burnt to release energy

Solid fuel refers to various forms of solid material that can be burnt to release energy, providing heat and light through the process of combustion. Solid fuels can be contrasted with liquid fuels and gaseous fuels. Common examples of solid fuels include wood, charcoal, peat, coal, hexamine fuel tablets, dry dung, wood pellets, corn, wheat, rice, rye, and other grains. Solid fuels are extensively used in rocketry as solid propellants. Solid fuels have been used throughout human history to create fire and solid fuel is still in widespread use throughout the world in the present day.

<span class="mw-page-title-main">Denitrification</span> Microbially facilitated process

Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter. The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO3−), nitrite (NO2−), nitric oxide (NO), nitrous oxide (N2O) finally resulting in the production of dinitrogen (N2) completing the nitrogen cycle. Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO3−, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N2O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.

<span class="mw-page-title-main">Wood fuel</span> Wood used as fuel for combustion

Wood fuel is a fuel such as firewood, charcoal, chips, sheets, pellets, and sawdust. The particular form used depends upon factors such as source, quantity, quality and application. In many areas, wood is the most easily available form of fuel, requiring no tools in the case of picking up dead wood, or few tools, although as in any industry, specialized tools, such as skidders and hydraulic wood splitters, have been developed to mechanize production. Sawmill waste and construction industry by-products also include various forms of lumber tailings. About half of wood extracted from forests worldwide is used as fuelwood.

<span class="mw-page-title-main">Bioenergy</span> Renewable energy made from biomass

Bioenergy is a type of renewable energy that is derived from plants and animal waste. The biomass that is used as input materials consists of recently living organisms, mainly plants. Thus, fossil fuels are not regarded as biomass under this definition. Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms.

<span class="mw-page-title-main">Pellet fuel</span> Solid fuel made from compressed organic material

Pellet fuels are a type of solid fuel made from compressed organic material. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and untreated lumber. Wood pellets are the most common type of pellet fuel and are generally made from compacted sawdust and related industrial wastes from the milling of lumber, manufacture of wood products and furniture, and construction. Other industrial waste sources include empty fruit bunches, palm kernel shells, coconut shells, and tree tops and branches discarded during logging operations. So-called "black pellets" are made of biomass, refined to resemble hard coal and were developed to be used in existing coal-fired power plants. Pellets are categorized by their heating value, moisture and ash content, and dimensions. They can be used as fuels for power generation, commercial or residential heating, and cooking.

Denitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds such as nitrate and nitrite in the absence of oxygen as a terminal electron acceptor. They metabolize nitrogenous compounds using various enzymes, including nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (NOS), turning nitrogen oxides back to nitrogen gas or nitrous oxide.

Energy forestry is a form of forestry in which a fast-growing species of tree or woody shrub is grown specifically to provide biomass or biofuel for heating or power generation.

Pyrolysis oil, sometimes also known as biocrude or bio-oil, is a synthetic fuel with few industrial application and under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C (900 °F) with subsequent cooling, separation from the aqueous phase and other processes. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, partial miscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.

<span class="mw-page-title-main">Lignocellulosic biomass</span> Plant dry matter

Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose and hemicellulose, and an aromatic-rich polymer called lignin. Any biomass rich in cellulose, hemicelluloses, and lignin are commonly referred to as lignocellulosic biomass. Each component has a distinct chemical behavior. Being a composite of three very different components makes the processing of lignocellulose challenging. The evolved resistance to degradation or even separation is referred to as recalcitrance. Overcoming this recalcitrance to produce useful, high value products requires a combination of heat, chemicals, enzymes, and microorganisms. These carbohydrate-containing polymers contain different sugar monomers and they are covalently bound to lignin.

<span class="mw-page-title-main">Biomass (energy)</span> Biological material used as a renewable energy source

In the context of energy production, biomass is matter from recently living organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.

<span class="mw-page-title-main">Short rotation coppice</span> Coppice grown as an energy crop

Short rotation coppice (SRC) is coppice grown as an energy crop. This woody solid biomass can be used in applications such as district heating, electric power generating stations, alone or in combination with other fuels. Currently, the leading countries in area planted for energy generation are Sweden and the UK.

<span class="mw-page-title-main">Biomass heating system</span>

Biomass heating systems generate heat from biomass. The systems may use direct combustion, gasification, combined heat and power (CHP), anaerobic digestion or aerobic digestion to produce heat. Biomass heating may be fully automated or semi-automated they may be pellet-fired, or they may be combined heat and power systems.

Simultaneous nitrification–denitrification (SNdN) is a wastewater treatment process. Microbial simultaneous nitrification-denitrification is the conversion of the ammonium ion to nitrogen gas in a single bioreactor. The process is dependent on floc characteristics, reaction kinetics, mass loading of readily biodegradable chemical oxygen demand {rbCOD}, and the dissolved oxygen {DO} concentration.

<span class="mw-page-title-main">Bioeconomy</span> Economic activity focused on biotechnology

Biobased economy, bioeconomy or biotechonomy is an economic activity involving the use of biotechnology and biomass in the production of goods, services, or energy. The terms are widely used by regional development agencies, national and international organizations, and biotechnology companies. They are closely linked to the evolution of the biotechnology industry and the capacity to study, understand, and manipulate genetic material that has been possible due to scientific research and technological development. This includes the application of scientific and technological developments to agriculture, health, chemical, and energy industries.

<span class="mw-page-title-main">Forest product</span> Material derived from forestry

A forest product is any material derived from forestry for direct consumption or commercial use, such as lumber, paper, or fodder for livestock. Wood, by far the dominant product of forests, is used for many purposes, such as wood fuel or the finished structural materials used for the construction of buildings, or as a raw material, in the form of wood pulp, that is used in the production of paper. All other non-wood products derived from forest resources, comprising a broad variety of other forest products, are collectively described as non-timber forest products (NTFP). Non-timber forest products are viewed to have fewer negative effects on forest ecosystem when providing income sources for local community.

<span class="mw-page-title-main">Renewable energy in Finland</span>

Renewable energy in Finland increased from 34% of the total final energy consumption (TFEC) in 2011 to 48% by the end of 2021, primarily driven by bioenergy (38%), hydroelectric power (6.1%), and wind energy (3.3%). In 2021, renewables covered 53% of heating and cooling, 39% of electricity generation, and 20% of the transport sector. By 2020, this growth positioned Finland as having the third highest share of renewables in TFEC among International Energy Agency (IEA) member countries.

<span class="mw-page-title-main">Bioenergy with carbon capture and storage</span>

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon dioxide (CO2) that is produced.

<span class="mw-page-title-main">Renewable energy in New Zealand</span>

Approximately 44% of primary energy is from renewable energy sources in New Zealand. Approximately 87% of electricity comes from renewable energy, primarily hydropower and geothermal power.

Bioenergy forms a small part of the Turkish energy sector. There is unrealised potential to generate bioenergy using waste from the country's vast agricultural sector and forest resources. The possibility of expanding biogas, biofuel and bioethanol production and use has been suggested to supplement Turkey's energy needs, reduce dependency on fossil fuel imports and cut greenhouse gas emissions.

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  43. ↑ Woodchip price factors for a power Generating Station in Burlington, VT, US Archived 2008-04-10 at the Wayback Machine
  44. ↑ Vermont Heat Research – An Experimental Wood Chip Furnace Archived 2008-01-19 at the Wayback Machine
  45. ↑ First quarter wood chip costs up almost 50% in western US, but pulpmills in the US South experienced only small upward price adjustments Archived 2012-02-11 at the Wayback Machine
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