![Woodchip](https://upload.wikimedia.org/wikipedia/commons/9/9c/Woodchip.jpg)
Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
such as
trees
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are u ...
,
branches
A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term ''twig'' usually ...
, logging residues,
stump
Stump may refer to:
* Stump (band), a band from Cork, Ireland and London, England
* Stump (cricket), one of three small wooden posts which the fielding team attempt to hit with the ball
*Stump (dog): Clussexx Three D Grinchy Glee (born 1998), 200 ...
s,
root
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...
s, and wood waste.
Woodchips may be used as a
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
solid fuel
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 ...
and are raw material for producing
wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw mate ...
. They may also be used as an organic
mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A m ...
in
gardening
Gardening is the practice of growing and cultivating plants as part of horticulture. In gardens, ornamental plants are often grown for their flowers, foliage, or overall appearance; useful plants, such as root vegetables, leaf vegetables, fruits ...
,
landscaping
Landscaping refers to any activity that modifies the visible features of an area of land, including the following:
# Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal o ...
, and
ecosystem restoration
Restoration ecology is the scientific study supporting the practice of ecological restoration, which is the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human interrupt ...
; in bioreactors for
denitrification
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 denitr ...
; and as a substrate for
mushroom cultivation
Fungiculture is the cultivation of fungi such as mushrooms. Cultivating fungi can yield foods (which include mostly mushrooms), medicine, construction materials and other products. A ''mushroom farm'' is involved in the business of growing fun ...
.
The process of making woodchips is called wood chipping and is done using a
wood chipper
A tree chipper or woodchipper is a machine used for reducing wood (generally tree limbs or trunks) into smaller woodchips. They are often portable, being mounted on wheels on frames suitable for towing behind a truck or van. Power is general ...
. The types of woodchips formed following chipping is dependent on the type of wood chipper used and the material from which they are made.
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).
Raw materials
![Woodchips at Albany Port](https://upload.wikimedia.org/wikipedia/commons/d/d2/Woodchips_at_Albany_Port.JPG)
The raw materials of woodchips can be
pulpwood
Pulpwood is timber with the principal use of making wood pulp for paper production.
Applications
* Trees raised specifically for pulp production account for 15% of world pulp production, old growth forests 9% and second- and third- and more gener ...
, waste wood, and residual wood from
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
,
landscaping
Landscaping refers to any activity that modifies the visible features of an area of land, including the following:
# Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal o ...
,
logging
Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidding, on-site processing, and loading of trees or logs onto trucks or skeleton cars.
Logging is the beginning of a supply chain ...
, and
sawmill
A sawmill (saw mill, saw-mill) or lumber mill is a facility where logs are cut into lumber. Modern sawmills use a motorized saw to cut logs lengthwise to make long pieces, and crosswise to length depending on standard or custom sizes (dimensi ...
s. Woodchips can also be produced from remaining forestry materials including
tree crown
The crown of a plant refers to the total of an individual plant's aboveground parts, including stems, leaves, and reproductive structures. A plant community canopy consists of one or more plant crowns growing in a given area.
The crown of a wo ...
s, branches, unsaleable materials or undersized trees.
![Bandit_Model_1290H_drum_chipper](https://upload.wikimedia.org/wikipedia/commons/b/b8/Bandit_Model_1290H_drum_chipper.jpg)
Forestry operations provide the raw materials needed for woodchip production.
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.
Softwood
file:Pinus sylvestris wood ray section 1 beentree.jpg, Scots Pine, a typical and well-known softwood
Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The main diff ...
species, for instance, tend to be more versatile for use as woodchips than
hardwood
Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood (which comes from ...
species because they are less dense and faster growing.
Production
A
wood chipper
A tree chipper or woodchipper is a machine used for reducing wood (generally tree limbs or trunks) into smaller woodchips. They are often portable, being mounted on wheels on frames suitable for towing behind a truck or van. Power is general ...
is a machine used for cutting wood into smaller pieces (chips). There are several types of wood chippers, each having a different use depending on the type of processing the woodchips will undergo.
Pulp and paper industry
Woodchips used for chemical
pulp
Pulp may refer to:
* Pulp (fruit), the inner flesh of fruit
Engineering
* Dissolving pulp, highly purified cellulose used in fibre and film manufacture
* Pulp (paper), the fibrous material used to make paper
* Molded pulp, a packaging material
* ...
must be relatively uniform in size and free of bark. The optimum size varies with the wood species.
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.
Drum chippers are normally used for wood residuals from saw mills or other wood industry.
Methods of conveyance
There are four potential methods to move woodchips:
pneumatic
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air.
Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...
,
conveyor belt
A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred to ...
,
hopper
Hopper or hoppers may refer to:
Places
*Hopper, Illinois
* Hopper, West Virginia
* Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan
* Hopper (crater), a crater on Mercury
People with the name
* Hopper (surname)
* Grace H ...
with direct chute, and batch system (manual conveyance).
[VTHR Green wood Chip Furnace](_blank)
Types of wood chippers
Disk
A disk wood chipper features a
flywheel
A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
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.
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.
Screw-type
A screw-type wood chipper contains a conical, screw-shaped blade . 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.
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
A pulp mill is a manufacturing facility that converts wood chips or other plant fiber sources into a thick fiber board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical, or ful ...
. Most pulping processes require that the wood be chipped and screened to provide uniform sized chips.
Mulch
Woodchips are also used as landscaping and garden
mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A m ...
, for
water conservation
Water conservation includes all the policies, strategies and activities to sustainably manage the natural resource of fresh water, to protect the hydrosphere, and to meet the current and future human demand (thus avoiding water scarcity). Populati ...
, weed control, and reducing and preventing
soil erosion
Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and ...
. Woodchips when used as a
mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A m ...
are at least three inches thick. It has a mixed reputation in gardening.
It has been promoted for use in
habitat restoration
Restoration ecology is the scientific study supporting the practice of ecological restoration, which is the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human interrupt ...
projects. As the
ramial chipped wood
Ramial chipped wood (RCW), also called BRF (from the French name, bois raméal fragmenté, "chipped branch-wood"), is a type of woodchips made solely from small to medium-sized branches. The adjective "ramial" refers to branches (rami). RCW is a ...
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
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
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.
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.
Denitrifying woodchip bioreactor
Woodchips can be loaded into a 'denitrifying woodchip
bioreactor
A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, ...
' which has been used for several decades as an emerging biotechnology to treat agricultural wastewater by
removing nitrates.
It is a subsurface system where
denitrification
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 denitr ...
by micro-organisms utilizing a carbon source (as electron donor) reduces the
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
into a harmless
nitrogen gas
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...
.
Denitrifying woodchip bioreactor have a low construction and operational costs with a comparatively long lifespan going up to 15 years. The interest in such a technique has grown in recent years and has expanded into the mining industry.
A 2013 experiment showed that after 70 days of startup, a woodchip pile loaded with liquid pig manure at 5 L/m
2/day removed an average of 90% of nitrate after one month. However, if the environmental conditions do not support complete denitrification, undesirable
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
such as
nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...
gas and
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
could be produced.
Fuel
![Heaps of chipped woody biomass in Namibia](https://upload.wikimedia.org/wikipedia/commons/0/07/Heaps_of_chipped_woody_biomass_in_Namibia.jpg)
Woodchips have been traditionally used as solid fuel for
space heating
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
or in energy plants to generate
electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
from
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
. The main source of forest chips in Europe and in most of the countries have been logging residues. It is expected that the shares of stumps and roundwood will increase in the future.
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 m
3, for above ground biomass and 585 million m
3 for total biomass.
The newer fuel systems for heating use either woodchips or
wood pellets
Pellet fuels (or pellets) are biofuels made from compressed organic matter or biomass. 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 ...
. 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.
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. 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%.
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).
Coal power plant
A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts capacity. They generate about a th ...
s have been converted to run on woodchips, which is fairly straightforward to do, since they both use an identical
steam turbine
A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
heat engine
In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state ...
, and the cost of woodchip fuel is comparable to
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
.
Solid
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
is an attractive fuel for addressing the concerns of the
energy crisis
An energy crisis or energy shortage is any significant bottleneck in the supply of energy resources to an economy. In literature, it often refers to one of the energy sources used at a certain time and place, in particular, those that supply n ...
and
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, since the fuel is affordable, widely available, close to
carbon neutral
Carbon neutrality is a state of net-zero carbon dioxide emissions. This can be achieved by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the "p ...
and thus climate-neutral in terms of carbon dioxide (CO
2), 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.
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
Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...
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 oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with octahedral cation and anion centers. It occurs na ...
, cadmium silicate (CdSiO
3); authors noted that adding it to agricultural or forest soils in the long-term could cause a problem with accumulation of cadmium.
Like coal, wood combustion is a known source of
mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
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.
When wood burning is used for space heating, indoor emissions of
1,3-butadiene
1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two viny ...
,
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
,
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
and
acetaldehyde
Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
, 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.
Certain techniques for burning woodchips result in the production of
biochar
Biochar is the lightweight black residue, made of carbon and Ash (analytical chemistry),
ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the th ...
– effectively charcoal – which can be either utilised as charcoal, or returned to the soil, since
wood ash
Wood ash is the powdery residue remaining after the combustion of wood, such as burning wood in a fireplace, bonfire, or an industrial power plant. It is largely composed of calcium compounds along with other non-combustible trace elements presen ...
can be used as a mineral-rich plant
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. 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.
Automated handling of solid fuel
Unlike the smooth, uniform shape of manufactured
wood pellets
Pellet fuels (or pellets) are biofuels made from compressed organic matter or biomass. 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 ...
, 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.
Comparison to other fuels
Woodchips are similar to
wood pellets
Pellet fuels (or pellets) are biofuels made from compressed organic matter or biomass. 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 ...
, 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
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
and higher moisture content of woodchips reduces their
calorific value
The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it.
The ''calorific value'' is the total energy rele ...
, 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).
(see
gasification
Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
and
woodgas
Wood gas is a fuel gas that can be used for furnaces, stoves, and vehicles. During the production process, biomass or related carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce a comb ...
)
Environmental aspects
Compared to conventional timber harvesting, woodchip harvesting has a greater impact on the environment, since a larger proportion of biomass is removed.
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.
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.
If woodchips are harvested as a by-product of
sustainable
Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livin ...
forestry practices, then this is considered a source of
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
.
Theoretically, whole-tree chip harvesting does not have as high a
solar energy
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essenti ...
efficiency compared to
short rotation coppice
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 ...
; however, it can be an energy-efficient and low-cost method of harvesting.
Waste processing
Woodchips and bark chips can be used as bulking agents in
industrial composting
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting m ...
of municipal
biodegradable
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
waste, particularly
biosolids
Biosolids are solid organic matter recovered from a sewage treatment process and used as fertilizer. In the past, it was common for farmers to use animal manure to improve their soil fertility. In the 1920s, the farming community began also to use ...
.
Forest fire prevention
Woodchip harvesting can be used in concert with creating man-made
firebreak
A firebreak or double track (also called a fire line, fuel break, fireroad and firetrail in Australia) is a gap in vegetation or other combustible material that acts as a barrier to slow or stop the progress of a bushfire or wildfire. A firebre ...
s, which are used as barriers to the spread of
wildfire
A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a 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
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.
In 2006, prices were US$15 and US$30 per wet-ton in the northeast.
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.
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.
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.
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.
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.
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.
Europe
![Forsthäcksler Hubertushof](https://upload.wikimedia.org/wikipedia/commons/7/73/Forsth%C3%A4cksler_Hubertushof.jpg)
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 m
3.
Japan
Woodchips are used in Japan for the paper manufacturing industry. Large supplies of
softwood
file:Pinus sylvestris wood ray section 1 beentree.jpg, Scots Pine, a typical and well-known softwood
Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The main diff ...
chips are imported from countries such as the United States and Australia for this purpose.
See also
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Barkdust
In agriculture, gardening, and landscaping, barkdust (also bark dust, bark chips, bark mulch, beauty bark or simply bark) is a form of mulch produced out of chipped or shredded tree Bark (botany), bark. Coarser forms of barkdust may be known as ba ...
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Renewable heat Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technol ...
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Woodchipping in Australia
Woodchipping is the act and industry of chipping wood for pulp. Timber is converted to woodchips and sold, primarily, for paper manufacture. In Australia, woodchips are produced by clearcutting or thinning of native forests or plantations. I ...
References
External links
Commercial Heating Installations
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Biomass
Wood fuel
Wood products