Wood chips
Wood chips (also wood chips , wood chips or wood chips ) are wood chopped up with cutting tools . Shredded wood, on the other hand, is produced by chopping wood with blunt, shattering tools. Wood chips are primarily used as a raw material for the wood processing industry and as a biogenic and renewable fuel .
Depending on the origin and the names are bark wood chips or wood chips (wood chips) are used.
production
Wood chips are produced with chippers . Mobile or stationary disc, drum or screw Hacker crushing waste wood (e.g., cut branches), small timber (too small diameter) and other low-quality wood (for example, a thinning , clippings from landscape maintenance measures or angemorschtes waste wood ), which is not to higher value by the industry Products can be processed. With the increasing number of short rotation plantations , these become a source of raw material for wood chips.
properties
Wood chips consist of 100% wood . They have a calorific value of around 4.0 kWh (= 14.4 MJ ) per kg (depending on the type of wood , with approx. 20% water content ) and are used for automatic loading, for example, of heating systems using screw conveyors , spring tine discharges, push rod discharges and conveyor belts suitable.
Water content
| Water content w | 0% | 15% | 20% | 30% | 50% |
|---|---|---|---|---|---|
| Humidity and | 0% | 18% | 25% | 43% | 100% |
| Calorific value of coniferous wood [kWh / srm] | 840 | 820 | 815 | 800 | 730 |
| Calorific value hardwood (hard) [kWh / srm] | 1130 | 1100 | 1090 | 1060 | 970 |
| Calorific value hardwood (soft) [kWh / srm] | 700 | 690 | 680 | 665 | 610 |
| standard | Main faction | Fines | Coarse fraction | Extreme values |
|---|---|---|---|---|
| P | > 80% | <5% | <1% | |
| P16 | 3.15 ... 16 mm | <1 mm | > 45 mm | <85 mm |
| P45 | 3.15… 45 mm | > 63 mm | <120 mm | |
| P63 | 3.15 ... 63 mm | > 100 mm | <350 mm | |
| P100 | 3.15 ... 100 mm | > 200 mm | <350 mm |
| standard | Main faction | Fines | Coarse fraction | Extreme values |
|---|---|---|---|---|
| G | > 60% | <20% | <20% | |
| G30 | 2.8… 16 mm, ø 30 mm² | <2.8 mm | > 16 mm | <85 mm |
| G50 | 5.6… 31.5 mm, ø 50 mm² | <5.6 mm | > 31.5 mm | <120 mm |
| G100 | 11.2… 63 mm, ø 100 mm² | <11.2 mm | > 63 mm | <250 mm |
Depending on the tree species, various central properties of the wood chips can vary and thus influence the calorific value. This applies in particular to the water content, which has an important influence on the calorific value of the wood chips and influences the shelf life. Wood chips with a water content of less than 30% are considered "suitable for storage" and no or no significant microbial degradation of the chips is expected. Therefore, drying is recommended before storage. Wood chips fresh from the forest, on the other hand, contain 50 to 60% water. Freshly harvested coniferous wood has a calorific value that is around 2 kWh / kg, with 20% water the calorific value is twice as high and is around 4 kWh / kg.
Fire behavior
The lower its oxygen index, the better a substance burns . If oxygen is chemically bound in a substance, it can be released in the event of a fire and react with the carbon it contains. Wood, for example, contains around 42% oxygen. In maple, birch or pine as a solid therefore the oxygen index is lower than that of nylon , PVC PVC hard, soft, polyester or wool and can therefore also known as green wood a fire load form, which fires clearly in chips camps. See also haystack spontaneous combustion .
Size and size distribution
Further properties are the size and size distribution and the bulk density of the wood chips and the energy density as fuel as well as the room size necessary for transport and storage. The very dense oak and beech wood (571 and 668 kg DM / m3 ) with a water content of 20% has a calorific value of 1103 kWh / cubic meter, whereas the less dense poplar wood (353 kg DM / m3 ) has a calorific value with the same water content from only 682 kWh / cubic meter.
Bark content
The bark content also has an impact on the quality of the wood chips . If debarked wood is usually used for wood chips that are used as fuel in smaller wood chip heating systems, the lower-quality bark wood chips contain larger amounts of bark. They are mainly produced from residual forest wood , small-volume wood and other inferior wood (for example from thinning , cuttings from landscape conservation measures). They can be used for the production of chipboard or for generating energy in larger systems such as biomass heating plants or biomass heating power plants .
Norms
For wood chips which applies European Standard EN 14961, the characteristics and classes for water content, ash content, particle size distribution, bulk density space, nitrogen and chlorine content and heating or calorific value of wood chips as biofuel sets. In practice, the classification according to the older Austrian standard ÖNORM M 7133 is also widespread in Germany.
Wood chips in practice
In practice, wood chips are classified in different product categories depending on their source and purpose. In the chipboard and wood-based materials industry, for example, a distinction is made between MDF wood chips and chipboard wood chips. These names indicate the different production processes in which the wood chips are processed into high-quality products such as table tops and insulation boards. Since every production process, usually even every factory, has individual requirements for the raw material, the wood chip market is highly fragmented. Another reason for the fragmentation of the market is the diverse sources of wood chips. Forest wood chips are differentiated from sawmill wood chips , for example.
use
Wood chips serve as a raw material for the wood processing industry ( e.g. pressboard , wood fiber insulation boards , paper industry ) and as fuel for thermal power stations or for wood chip heating systems . They are also used as a substrate in mushroom cultivation and as a material for soil cover, for example in gardening and landscaping .
fuel
As a fuel wood chips are primarily used in wood chip heating plants and - thermal power stations , in addition to wood chip. The feeding is mostly done with electric screw conveyors or scraper chain conveyors.
Smaller forest wood chips (size classes P16 and P45) of high quality are usually required for smaller boilers . Thermal power plants are more flexible with regard to the quality of the raw materials. In large plants, used wood and industrial waste wood ( waste wood ) are used as raw materials. The fuel costs are below those of comparable biofuels such as wood pellets or split logs , but the need for mostly fuel-specific processes must be taken into account.
The use of wood chips as energy wood in private households in Germany was around 580,000 cubic meters in 2005 , which is around 1.1% of the total energy wood use. 9 million cubic meters were burned in cogeneration plants with an output of up to one megawatt, the consumption of larger systems was around 39 million cubic meters of wood chips or shredded material.
Mushroom growing
When growing mushrooms, wood chips of size KL 2-16 are used alone or often in combination with sawdust, straw, dung or other substances. Depending on the type of mushroom, the wood chips come from oak, beech, birch or other trees. The wood chips are watered and then inoculated with mycelium (mushroom network, mushroom spawn ).
Children's playground
Wood chips are also permitted as shock-absorbing flooring in playgrounds. To do this, however, they must meet the requirements of DIN / EN 1176 for playground equipment and playground floors, i.e. H. the grain size must be in the range between 5 and 30 mm. They are made of peeled wood. As a rule, suitable materials are certified by independent institutes (e.g. TÜV) for use as playground flooring.
market
The production of wood chips and, above all, foreign trade are increasing significantly, and market prices have also been rising for years.
price
The prices for wood chips have risen in recent years, between July 2004 and July 2009 the increase was around 80%. Between 2010 and 2013, their price remained largely stable at around 30 euros / MWh.
The end consumer price for dry forest woodchips in Germany in 2009 (4th quarter) was around 119 euros / t (20% water content or 25% wood moisture , 30 m³ delivery volume, including travel up to 20 km and VAT). This corresponds to a price for the heating oil equivalent of 29.71 cents / l. Depending on the region, season, quality, water content and delivery distance, there are significant differences or fluctuations in the price. The delivery quantity is also an important factor, so that large power plants can spend over 40% less on fuel than small plants.
literature
- Peter Wohlleben : HOLZRAUSCH. The bioenergy boom and its consequences. adatia Verlag Marion Zartner, Sankt Augustin 2008, ISBN 978-3-940461-03-2 .
-
Bavarian State Institute for Forests and Forestry (LWF): Leaflets on various topics, also available as PDF , among others
- Leaflet 10: Provision of wood chips from the forest , as of May 2012,
- Leaflet 11: Store wood chips correctly! , As of December 2012,
- Leaflet 12: The energy content of wood , as of July 2014,
- Leaflet 20: Logs , as of July 2014
Individual evidence
- ↑ a b Technologie- und Förderzentrum (TFZ) Straubing, 2008: Classes for wood chips according to DIN CEN / TS 14961 ( PDF ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link accordingly Instructions and then remove this notice. )
- ↑ Leaflet 12 The energy content of wood and its evaluation by the Bavarian State Institute for Forests and Forestry (LWF), as of July 2014, page 3; For the table, rounded and averaged values for the various types of wood from the 2007 leaflet were used.
- ↑ a b Wood structure: fire and explosion protection - fire theory, Kohlhammer-Verlag, Stuttgart, 1998, quoted by: Werner Bauer (fire expert): Risk of fire in wood processing companies , at schadenprisma.de, ( PDF; 2.1 MB ).
- ↑ climate: active management; Calorific value and gross calorific value ( Memento of the original from October 17, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved February 12, 2011.
- ↑ Fachagentur Nachwachsende Rohstoffe e. V. (FNR), 2007: Market overview of wood chip heating systems. P. 9 ( PDF ( Memento of the original from October 12, 2007 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ).
- ↑ Wood chips, biomass and wood for bioenergy, paper & pulp and wood-based materials. Accessed on December 9, 2011.
- ^ Ybbstal news
- ↑ Technologie- und Förderzentrum (TFZ): Development of fuel prices. ( Memento of the original from February 5, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed January 12, 2009.
- ↑ Price development for forest wood chips . Retrieved December 10, 2013.
- ↑ Price development for German wood chips ( Memento of the original from December 20, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (CARMEN - Central Agricultural Raw Material Marketing and Development Network eV) Basis: Prices for Bavaria, 20% water content, 30 m³ delivery quantity, including travel up to 20 km and VAT.
- ↑ Information from the Bavarian State Institute for Forests and Forestry (LWL) on the use of wood chips for heating purposes , accessed on December 30, 2009.
Web links
- Ecological limits of biomass use in forests at www.waldwissen.net.
- Ecological assessment of wood chips on www.waldwissen.net.
- Requirements of the playground equipment standard DIN EN 1176 for shock-absorbing floor coverings made from wood chips underneath playground equipment.
- Holzenergie - Bavarian State Institute for Forests and Forestry at www.lwf.bayern.de.