Woodchips / REF / 471 / 2014

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

Woodchips may be used as a biomass solid fuel and are raw material for producing wood pulp. They may also be used as an organic mulch in gardening, landscaping, restoration ecology 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 woodchips processed in different processes. The process of making wood chips are called woodchipping and are done with a woodchipper.

Raw materials

    Pulpwood

    Wood plantations

    Waste wood and residuals from construction, agriculture, landscaping, logging, and sawmills.

    Locally grown and harvested fuel crops.

Production

A woodchipper is a machine used for reducing wood to smaller pieces. There are several types of woodchippers depending of the further processing of the woodchips. For industrial use, the woodchippers are large, stationary installations.

Woodchips for 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 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.[1] Drum chippers are normally used for wood residuals from saw mills or other wood industry.

Possible Methods of Woodchip Conveyance

    Pneumatic

    Conveyor belt

    Hopper with direct chute

    Batch system (manual conveyance)

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.

Mulch

Woodchipping is also used to produce landscape and garden woodchips mulch. It is used for 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 decompose it improve the soil structure, permeability, bioactivity, and nutrient availability. Woodchips when used as a mulch are at least three inches thick.

Playground surfacing

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

Fuel

Traditional use of woodchips is as a solid fuel for heating in buildings or in energy plants for generating electric power from renewable energy. During the last years, the main source of forest chips in Europe and in most of the countries are logging residues. However, 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 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.

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.

The size of the woodchips is particularly important when burning woodchip in small plants. Unfortunately there is not so many standards set to decide the fractions of woodchip. One standard though is the GF60. GF60 is commonly used in smaller plants. (Villas, small industries and apartment buildings)

GF60 is commonly known as "Fine, dry, small chips". The requirements for GF60 is that the moisture is between 10–30% and the fractions of the woodchips is distributed as follows:

    0–3.5mm: <8%

    3.5–30mm: <7%

    30–60mm: 80–100%

    60–100mm: <3%

    100–120mm: <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 is taken down in the winter and is left to dry under the summer, with tears in the bark and covered so rain cant reach to them and then is chipped in the fall the woodchip will get an moisture of approx. 20–25%. The energy content is then approx 3.5–4.5kWh/kg (~150–250 kg/cubic metre)

In a number of cases, coal power plants have been converted to run on woodchips. This 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.

Solid biomass is an attractive fuel for addressing the concerns of the energy crisis and climate change, since the fuel is affordable, widely available, and is carbon neutral and sustainable as long as the crops are allowed to regrow. In most cases, biomass is not carbon neutral as wood is not regrown and the efficiency of biomass operations produce more pollutants than the processes they replace. Compared to coal and nuclear fuels, woodchip biomass does not have waste disposal issues, since wood ash can be used directly as a mineral-rich plant fertilizer.

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. This 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, 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.

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 increasingly used for heating applications. This will reduce the demand for heating oil, and thereby allow a greater percentage of fuel oil to be used for applications such as internal combustion engines, which are less 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.

Comparison to other Fuels

Woodchips are less expensive than wood pellets. Also, woodchips are theoretically more energy efficient than pellets, because less energy is required for manufacturing, processing, and transportation; however, this assumes that they are consumed in an appropriately designed burner, and as of 2008, these are mostly only available in large systems designed for commercial/institutional use. In contrast to the lack of residential systems, commercial heating installations have been very successful in terms of performance, cost, reliability, and efficiency.

Woodchips are also less expensive than cord wood, because the harvesting is faster and more highly automated. Also there is a greater supply, partly because all parts of a tree can be chipped, whereas small limbs and branches can require too much labor to be worth converting to cord wood. Woodchips are similar to wood pellet, in that the movement and handling is more amenable to automation than cord wood, particularly for smaller systems. Cordwood 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 and woodgas)

Environmental Issues

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

Theoretically, whole-tree chip harvesting does not have as high a solar energy efficiency, as compared to short 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 often associated with clear cutting, and perhaps other questionable forestry practices.

Woodchips for waste processing

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

Woodchip biomass does not have the waste disposal issues of coal and nuclear power, since wood ash can be used directly as a mineral-rich plant fertilizer.

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.

Market Products, Supply and Demand

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

Woodchip prices in the United States

"Wood chip 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.

European Perspective

Large woodchipper in Germany

In several well wooded European countries (e.g. 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 it is estimated to be 913 million m3.

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