Woodchips

Woodchips are a solid fuel made from woody biomass. They are made in the process of woodchipping with a woodchipper. They are used primarily as a heating fuel in a few commercial institutions, such as schools, and in some industrial plants for generating electric power from renewable energy. The use of woodchips in automated heating systems, is based on a relatively new technology.

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, clean burning, and is carbon neutral and sustainable as long as the crops are allowed to regrow.

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.

Fuel Availability

In some countries, such as the United States, wood is widely abundant in many areas. In the small American state of Vermont, it has been estimated that low-grade timber could provide 1.5 million tons per year of renewable green wood fuel. [ [http://www.sredmond.com/vthr_index.htm VTHR Green wood Chip Furnace] ]

Short rotation coppice (SRC) is a fast growing, and efficient wood fuel energy crop.

Environmental Issues

If woodchips are harvested through sustainable forestry practices, then this is a 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. It is believed that environmentally responsible forestry practices can make woodchip energy one of the more environmentally benign sources of energy, particularly in the context of climate change, since it is a carbon neutral source, and does not require fertilizers.

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.

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.

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.

Fuel Sources

* Waste wood and residuals from construction, agriculture, landscaping, logging, and sawmills.
* Locally grown and harvested fuel crops

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. [http://www.biomasscenter.org/pdfs/Wood-Chip-Heating-Guide.pdf]

Woodchips are also less expensive than cordwood, 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). [ [http://www.sredmond.com/vthr_index.htm VTHR Green wood Chip Furnace] ] (see gasification and woodgas)

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 $18 to $30 per (wet)-ton delivered." [ [http://www.burlingtonelectric.com/specialtopics/mcneil.htm Woodchip price factors for a power Generating Station in Burlington, VT, US] ]

In 2006, prices were $15 and $30 per wet-ton in the northeast. [ [http://www.sredmond.com/vthr_index.htm Vermont Heat Research - An Experimental Wood Chip Furnace] ]

In the 20 years leading up to 2008, prices have fluctuated between $60-70/oven-dry metric ton (odmt) in the southern states, and between $60/odmt and $160/odmt in the Northwest. [ [http://forestnewswire.com/index.php?option=com_content&view=article&id=118:first-quarter-wood-chip-costs-up-almost-50-in-western-us-but-pulpmills-in-the-us-south-experienced-only-small-upward-price-adjustments&catid=1:latest First quarter wood chip costs up almost 50% in western US, but pulpmills in the US South experienced only small upward price adjustments] ]

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 whom are experienced with woodchips, say they are not compatible with the 2 inch (5 cm) auger used in pellet stoves. [ [http://www.sredmond.com/vthr_index.htm VTHR Green wood Chip Furnace] ]

Possible Methods of Woodchip Conveyance

* Pneumatic
* Conveyor belt
* Hopper with direct chute
* Batch system (manual conveyance) [ [http://www.sredmond.com/vthr_index.htm VTHR Green wood Chip Furnace] ] [ [http://www.stiltman.com/html/doe_report_part_ii.html US Dept. of Energy report,... Fuel Handling Equipment] ]

ee also

* Renewable heat
* Woodchipping in Australia‎

References

External links

* [http://www.biomasscenter.org/pdfs/Wood-Chip-Heating-Guide.pdf Commercial Heating Installations]
* [http://www.sredmond.com/vthr_index.htm Vermont Heat Research - An Experimental (inverted downdraft) Woodchip Furnace]