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Extraction of logging residues for bioenergy: effects of operational methods on fuel quality and biomass losses in the forest
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.ORCID iD: 0000-0002-2990-3559
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Uttag av skogsbränsle : hanteringens och lagringens inverkan på grotens bränslekvalitet samt biomassaförluster i skogen (Swedish)
Abstract [en]

Wood products play a key role in the transformation to a more sustainable society based on renewable bio-based resources, together with the positive effects on climate mitigation by replacing fossil fuels. However, to increase the use of forest fuel in practice it is important to understand the effects of handling and storage on its quality and removal of nutrients from the forest. This thesis addresses these effects with special focus on a comparative evaluation of the traditional dried-stacked with “new” and to some extent more controversial fresh-stacked methods for extraction of logging residues from Norway spruce (Picea abies (L.) Karst).

The results indicate that a normal extraction of logging residues will leave at least 20% of logging residues at the clear-felled area, in accordance with Swedish Forest Agency recommendations. However, the results also indicate that the ambition of the dried-stacked method to leave the majority of the needles well spread over the clear-felled area does not meet these recommendations. In fact, the harvesting operation is more important than the extraction method, with respect to how much logging residues (nutrients) being left in the forest. The results also show that the quality of fuel yielded by the two handling methods differs only to minor extent, indicating that other factors have stronger effects, where “dried-stacked” and “fresh-stacked” logging residues from different clear-felling areas is often similar. Generally, logging residues stored over summer (regardless method), seem to provide sufficiently dry forest fuel, with a needle content of about 5–10%. There is a clear correlation between drying and effective loss of needles from twigs, but the loss does not necessarily mean that the needles will remain in the forest.  However, needle color (green or brown) is not a strong indicator for a reduction in needle content.

Acceptance of the fresh-stacked method would provide opportunities for the development of new technologies, more efficient use of machinery throughout the whole year, reduced costs, shorter lead times and increased amounts of logging residues extracted from each clear-felled area. This is mainly because it would enable extraction at optimal times from a logistical, financial and/or forestry perspectives.

Written in English with summary and conclusion in Swedish.

Abstract [sv]

Skogen och dess produkter har en nyckelroll i omställningen till ett framtida hållbart samhälle eftersom användande av träråvara har en positiv effekt på klimatet, t.ex. genom träbyggande eller att fossila bränslen ersätts med bioenergi. Men för att kunna ta tillvara mer skogsbränsle i form av grenar och toppar (grot) från bestånd dominerade av gran (Picea abies (L.) Karst) är det viktigt att förstå hur hanteringen påverkar såväl bränslekvalitet som bortförsel av näringsämnen från skogen. Denna avhandling belyser hanteringens effekter på bränslekvalitet och näringsförluster genom att jämföra den traditionella metoden (skotning av torkad grot, ”brunrisskotning”), med den ”nya” och till viss del ifrågasatta skotningen av färsk grot (”grönrisskotning”).

Resultatet visar att ett normalt grot-uttag kommer att lämna minst 20 % av groten kvar på hygget, helt i linje med Skogsstyrelsens rekommendationer. Däremot uppfylls inte rekommendationerna med avseende på att lämna merparten av barren väl spridda på hygget, detta trots att det är ambitionen med den traditionella hyggestorkningen av grot. Hur mycket grot (och således näringsämne) som lämnas kvar på hygget påverkas i själva verket mer av hur avverkningen utförs, än när groten skotas ihop. Resultatet visar också en skillnad i bränslekvalitet mellan de båda beskrivna hanteringsmetoderna. Denna skillnad är dock så liten att andra faktorer sannolikt påverkar mer än hanteringsmetoden. Hyggestorkad grot från ett enskilt hygge i södra Sverige, kan i verkligheten ofta vara ganska likt färskskotad grot från ett annat hygge. Grot som har lagrats över sommaren kan alltså förväntas ha torkat tillräckligt, samt ha en barrandel på ca 5–10 % oavsett hanteringsmetod. Det verkar också finnas ett klart samband mellan torkning och att barren släpper från kvisten, men det betyder inte nödvändigtvis att barren blir kvar i skogen. Hur som helst, barrens färg (gröna eller bruna) är inte en rättvisande indikator på avbarrning.

Om skotning av färsk grot accepteras ger det möjligheter för utveckling av ny teknik, effektivare användning av maskinresurser över hela året, minskade kostnader, kortare ledtider, samt möjligt ökat grot-uttag från enskilda hyggen. Detta beror främst på att det skulle vara möjligt att utföra grot-uttaget när det passar bäst ur ett logistiskt, ekonomiskt och/eller skogligt perspektiv.

Skriven på engelska, men med sammanfattning och slutsatser på svenska

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2016. , 200 p.
Series
Linnaeus University Dissertations, 270/2016
Keyword [en]
Forest fuel, Storage, Fraction composition, Needles, Defoliation, Moisture content, Nutrients, Nitrogen, Norway spruce, Picea abies
Keyword [sv]
Skogsbränsle, Lagring, Fraktionsfördelning, Barr, Avbarrning, Fukthalt, Näringsämnen, Kväve, Gran, Picea abies
National Category
Forest Science Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
URN: urn:nbn:se:lnu:diva-58307ISBN: 978-91-88357-50-2OAI: oai:DiVA.org:lnu-58307DiVA: diva2:1049815
Public defence
2016-12-16, Wickesell, Hus K, Linnéuniversitetet, Universitetsplatsen, Växjö, 10:00 (Swedish)
Opponent
Supervisors
Note

Tidigare handledare har också varit:

Thomas Thörnqvist, Professor, Linnéuniversitetet

Dick Dandberg, Professor, Linnéuniversitetet

Åsa Blom, Docent, Linnéuniversitetet

Sammanläggningsavhandlingen består av totalt fyra Paper:

Paper I

Nilsson, B., Blom, Å., Thörnqvist, T. 2013. The influence of two different handling methods on the moisture content and composition of logging residues. Biomass and Bioenergy, 52, 34–42.

Paper II

Nilsson, B., Nilsson, D., Thörnqvist, T. 2015. Distributions and losses of logging residues at clear-felled areas during extraction for bioenergy: Comparing dried- and fresh-stacked method. Forests, 6, 4212–4227.

Paper III

Nilsson, D., Nilsson, B., Thörnqvist, T., Bergh, J. 2016. Amount of nutrients extracted and left behind at the clear-felled area using the fresh- and dried-stacked method of logging residue extraction. Submitted to Scandinavian Journal of Forest Research (2016-11-01).

Paper IV

Nilsson, B., Lerman, P. 2016. Experimental study of relations between defoliation, moisture content and color change in logging residues. Department of Forestry and Wood Technology, Linnaeus University, Växjö, Sweden. Manuscript.

Available from: 2016-11-28 Created: 2016-11-25 Last updated: 2016-11-28Bibliographically approved
List of papers
1. The influence of two different handling methods on the moisture content and composition of logging residuals
Open this publication in new window or tab >>The influence of two different handling methods on the moisture content and composition of logging residuals
2013 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 52, 34-42 p.Article in journal (Refereed) Published
Abstract [en]

The most frequently used handling method in Sweden for the extraction of forest fuels is one in which logging residues are piled in harvester heaps to dry within the clear-cutting area before stacking into larger windrows. This handling method, however, requires multiple stages and the amount of handling involved results in a significant loss of biomass that could have been used for energy. This study compares two handling methods for the extraction of logging residues in stands dominated by Norway spruce. The traditional “dried-stacked” method was compared to the “fresh-stacked” method in which logging residues are collected simultaneously during normal logging operations and stacked in windrows at or near the roadside to dry. Determination of fraction composition and moisture content was carried out on the biomass provided to the energy-converting industry shortly after comminuting the logging residues. The results show that the fresh-stacked logging residues contained a higher amount of needles (8%), compared to 4% for the dried-stacked logging residues. However, the amount of needles was considered to be low in both handling methods. Both handling methods were proven to provide adequate drying with moisture content levels at approximately 36% for fresh-stacked and 31% for dried-stacked logging residues. These results indicate that weather and forest conditions have a greater impact on the moisture content than handling method. An acceptance of fresh-stacked logging residues, preferably connected to ash recycling, would afford the energy-converting industries the opportunity to use new technologies, reduce costs and extract a greater biomass total.

Place, publisher, year, edition, pages
Elsevier, 2013
National Category
Other Engineering and Technologies
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-19005 (URN)10.1016/j.biombioe.2013.02.026 (DOI)000319645400005 ()
Available from: 2012-05-29 Created: 2012-05-29 Last updated: 2016-11-25Bibliographically approved
2. Distributions and Losses of Logging Residues at Clear-Felled Areas during Extraction for Bioenergy: Comparing Dried- and Fresh-Stacked Method
Open this publication in new window or tab >>Distributions and Losses of Logging Residues at Clear-Felled Areas during Extraction for Bioenergy: Comparing Dried- and Fresh-Stacked Method
2015 (English)In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 6, no 11, 4212-4227 p.Article in journal (Refereed) Published
Abstract [en]

It is well known that a large proportion of available logging residues intended for extraction will not reach the energy-conversion industry, because some are lost during transportation or left on the clear-felled area. However, there is little understanding of where logging residue losses occur in the supply chain. In this study, the distribution of logging residues for two methods (dried- and fresh-stacked method) to extract logging residues were studied in one clear-felled area. In addition, residue fractions were examined in a detailed comparison. Even though the fresh-stacked method left somewhat more logging residues at the clear-felled area, the differences are small between the methods. Approximately 30% of the total amount of logging residues was left behind between the harvester heaps, with an additional 10%-15% under these heaps and approximately 2%-3% beneath the windrows. The final product that was delivered to the energy-conversion industry was very similar, regardless of the extraction method used. The delivered chipped logging residues had moisture contents of 37% and 36% following fresh- and dried-stacked methods respectively, and in both cases the needle content in the processed logging residues was approximately 10%. However, the total amount of fine fractions (needles and fines) was slightly higher following dried-stacking.

Keyword
forest fuel, storage, quality, needles, moisture content, Norway spruce
National Category
Forest Science Energy Systems
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-48816 (URN)10.3390/f6114212 (DOI)000365704000022 ()
Available from: 2016-01-19 Created: 2016-01-15 Last updated: 2016-11-25Bibliographically approved

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