Metla Project 7121
Bundling undelimbed tree sections in the early thinnig of Scots pine
Duration: 2002-2003
Keywords: Harvesting, Scots pine, biomass balance, bundle, early thinning, nutrient balance, pulp properties
Objectives
The project dealt with the feasibility of a conceptual bundle harvester for the integrated production of pulpwood and energy wood in the first commercial thinning of Scots pine (L.). The harvester would operate on the site, and it would be comprised of base machine, an accumulating felling head, and a compacting device. Separation of pulpwood and energy wood would take place at a pulp mill. Integrating pulpwood and energy wood harvesting in this way could possibly reduce relative high procurement costs of timber harvested from young stands. Savings in transportation due to load compaction were estimated to be the foremost advantage of this concept when comparing with the conventional tree-section method.
The bundling operation was simulated by felling and topping the trees using a feller-buncher and forwarding the tree sections to the roadside, where they were bundled using a robust slash bundler originally designed for slash harvesting on final fellings. The harvesting concept was evaluated from an economic and ecological point of view. Furthermore, pulp properties of the bundled tree sections were analysed based on industrial debarking and pulping experiments.
Results
About 63% of the foliage of the removed trees remained in the stand, and only 26% were carried away in the bundles. The total nutrient loss was small compared with the nutrient reserves of mineral soils. Nutrient losses attributable to the adapted tree-section method were significantly lower than those caused by the whole-tree system.
Debarking residue is usually combusted at the pulp mill. The yield of this energy fraction increased by 150% as compared to conventional harvesting shortwood system, in which the trees are delimbed. Its effective oven dry heating value was 22.7 MWh ha-1. When comparing to the conventional cut-to length harvesting, the adjusted tree-section method results in an increase in pulpwood, since it is possible to utilize the tree up to the nominal minimum length. This study indicated that the compaction capacity of the conceptual bundler cannot be fully utilized when processing trees with heavy stem sections, which themselves compact loads by breaking and crushing the branches. Consequently, the bundling concept seems more favorable in harvesting energy wood from dense stands composed of small-diameter trees. The carrying capacity of the trucks could, however, be highly utilized in bundle transportation. A high utilization of the carrying capacity of forwarders seems possible by expanding load space. Bundling system also offers several operational advantages.
The debarking and chipping experiment consisted of three debarking batches, of which two were blend batches composed of bundles and conventional pulpwood (bundle proportions 8% and 16%). The trials were successfully completed without any problems, and all chip samples met the highest cleanliness requirements set for softwood chips. The estimated wood losses of 2-3% did not differ from the values reported on drum debarking of conventional pulpwood. In the pulping trial, average wood consumption of the blend batches was 2.2-2.9% higher than that of the reference batch consisting 100% of conventional pulpwood. The blend pulps seem not to differ from the pulp made of conventional pulpwood.
Project leader:
Jylhä, Paula
The Finnish Forest Research Institute,
Kannus Research Unit,
PL 44, 69101 Kannus
Phone: +358 10 211 3432 Telefax: +358 10 211 3401
E-mail: paula.jylha@metla.fi
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Updated 30.12.2006
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