Wood chip harvester
A wood chip harvester is a combination of a wood harvester and a mobile chopping machine . Harvesters are mainly used for forest maintenance in coniferous forests and cut the trees to be harvested into industrially usable lengths. Mobile chippers then chop up unmarketable residual wood into wood chips, which are then used to produce chipboard or cellulose or to obtain bioenergy through combustion. The wood chip harvester combines both operations.
History and Development
The first machines of this type came from the Danish forest machine manufacturer Silvatec in the early 1990s. These machines were built exclusively for thinning young coniferous trees and were initially only equipped with a timber grapple, mounted on a seven-meter-long crane, to feed whole trees that had been felled manually to the chipper. Individual models had a felling head with which it was possible to fell trees in the immediate working area of the machine. Processing the tree into different lengths of wood was just as impossible as delimbing. The maximum possible wood chip diameter was 28 cm. In 1993 J. Greß and U. Jacobsen developed the first machine that was equipped with a harvester head for processing fixed lengths and at the same time had a powerful large chopper. Features of this machine were:
- Working or swivel range of the machine = 270 ° (Silvatec = 60 °)
- Max. Wood chips diameter = 65 × 50 cm (Silvatec = 28 cm)
- compact design (length 7.8 m - Silvatec = 9.8 m, Volvo BM = 11.30 m)
- In terms of production data, it is comparable to the individual harvesters and mobile chippers
- manual preparatory work was no longer necessary
- Production of round wood and recycling of waste wood in one operation
- can also be used in hardwood forests
Comparison of working methods
In order to achieve the same results when harvesting wood with conventional machines, at least three machines are necessary. The harvester fells the tree and sawed it into usable lengths, the forwarder collects the timber and transports it to the forest road and the mobile chipper then moves repeatedly through the skid trails to waste wood to chop or crown material. This work step is not necessary with the wood chip harvester, since residual wood is chopped immediately during processing. A forwarder with a tipping container takes over the transport of the wood chips from the harvester to the skip container provided on Waldstrasse .
Valuable wood produced was loaded during the drive to Waldstrasse. This so-called "shuttle" was equipped with a hook lift that enabled the container and stanchion frame to be changed quickly for moving short timber . In multiple long-term tests by well-known forest institutes such as KWF or LWF Uni Munich, this technology was classified as a particularly soil-friendly wood harvesting process, as the machine only had to drive down the work aisle once. In addition, only two special machines were required for production, which reduces operating and material costs.
use
The wood chip harvester was used and produced between 1995 and 2000 in various areas of Germany, the Netherlands and, for a short time, in France. Today it is also used in Switzerland to produce wood chips to supply local small- scale thermal power stations. A total of ten machines were built according to this idea, which were running or are still in operation in various versions in Sweden (1), Estonia (6), Denmark (1), Switzerland (1) and Germany (1).
Disadvantages of the system
- high logistical effort required, both in the planning phase and in daily operation
- in this design can only be transported with a special low loader
- Due to the lack of options for aligning the machines (crane tilt, bogie lift), it can only be used in flat areas or at low-mountain workplaces
Further developments
In addition to the Danish manufacturer Silvatec (machine model CH 878 and its successor model Grane 8325 CH), the Finnish forest machine manufacturer Komatsu (formerly Valmet) has launched the Valmet 801 Combi, a machine that uses the same technology. In the meantime, the production of both machines has been discontinued due to a lack of demand. The storm damage of recent years required large chippers that can process as much wood as possible in a short time. These manufacturers are now concentrating on special harvester heads that allow the removal of several trees in one operation. Other well-known manufacturers rely on coordinators. These special superstructures for forwarders collect residual wood and crown material from the felling area and compress them into bundles suitable for transport, which are then burned in biomass power plants to generate energy.
literature
- Martin Kaltschmitt , Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures , Springer Vieweg, Berlin / Heidelberg 2016, ISBN 978-3-662-47437-2 , p. 437 f.
- Stefan Feller, Norbert Remler, Helmut Weixler: Fully mechanized forest woodchip provision. Results of a work study on the wood chip harvester , reports from the Bavarian State Institute for Forests and Forestry 16, Freising 1998, ISSN 0945-8131 .
