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Wood chips for kraft and sulfite pulping: evaluation of novel forest-industrial drum-chipping technology
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2020 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Flis för sulfatmassa- och sulfitmassaprocesserna : utvärdering av ny skogsindustriell trumhuggningsteknik (Swedish)
Abstract [en]

Wood chipping and the supply of high-quality wood chips are of critical importance for most forest-industrial processes. The quality of wood chips affects product yield, product quality, and processability. Wood chips from a novel type of forest-industrial drum chipper, with a large drum and specially designed wood-chip channels, were evaluated with regard to wood chips for the Kraft and sulfite processes. Wood chips from a full-scale demonstration version of the drum chipper and from a conventional disc chipper at a Kraft mill were compared. The average bulk density and the fractions of oversized and overthick wood chips were similar, but the demonstration drum chipper produced 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. A pilot-scale drum chipper based on the new technology was used to produce short wood chips designed for acidic processes. When the drum velocity was 30-34 m/s and the average wood-chip length 21-22 mm, the fraction of pin chips and fines was 4.2% and the fraction of total accept was 89-90%. When the average wood-chip length was decreased to 17 mm, the fraction of pin chips and fines increased to 8.5% and the fraction of total accept decreased to 80-82%. The pilot drum chipper was used to investigate the influence of using different tree species (aspen, birch, pine, and spruce), processing of wood with different moisture content, and frozen wood. For hardwood (aspen and birch), the fraction of total accept reached ~90% when the average wood chip length was 17 mm. The pilot drum chipper was also used to generate wood chips of heartwood of pine for a comparison of 15 sulfite-process reaction conditions that differed with regard to impregnation and cooking procedures. The analyses included absorption of liquid in a specially designed impregnation reactor, pulp yield, reject, viscosity, kappa number, brightness, fiber properties, and chemical composition as determined using compositional analysis based on two-step hydrolysis with sulfuric acid and pyrolysis-gas chromatography/mass spectrometry. The results reveal in detail how the individual wood constituents were affected by the different treatments, and demonstrate the benefits of using a pressurized impregnation step prior to sulfite cooking.

Abstract [sv]

När vi producerar massa till papper och kartong vill vi använda så mycket av vedråvaran som möjligt, dvs. ha ett högt utbyte när råvaran konverteras till produkt. Det är viktigt för att minimera transporter, råvaruåtgång och kemikalieåtgång, vilket bidrar till en ekonomiskt bärkraftig process. Ett av processens första steg är att sönderdela stockarna till flis. Hur jämn flisen är i storlek, dess fukthalt och dess packdensitet påverkar hur bra massa det blir.

Idag huggs nästan all flis som blir massa med skivhuggsteknik. Skivhuggen uppvisar en hastighetsgradient, vilket leder till att en större andel av råvaran blir till pinnflis och spån. Pinnflis och spån har för små dimensioner för att fungera bra som råvara vid impregnering med kokkemikalier och vid massakok.

En ny typ av trumhugg har utvecklats. Trumman har inte den hastighetsgradient som skivhuggen har och borde teoretiskt sett kunna producera en mindre andel pinnflis och spån. För att utvärdera den nya tekniken så jämfördes en fullstor demonstrationshugg baserad på den nya trumhuggstekniken med en konventionell skivhugg på ett sulfatmassabruk. För att utvärdera effekten av trummans hastighet och stockens inmatningsvinkel användes istället en pilothugg baserad på den nya tekniken. Med hjälp av pilothuggen undersöktes också hur fliskvalitén påverkades av stockarnas fukthalt, vilket trädslag det var och om veden var fryst eller tinad.

Den nya trumhuggstekniken skapade flis som visuellt liknade den från skivhuggen. För att få bra massa behöver en andel på ungefär 85% av flisen vara acceptflis, dvs. dess dimensioner ligger inom de storleksintervall som industrin har valt att definiera som acceptabel. Den nya trumhuggen gav en andel på 85% acceptflis direkt efter huggning i demonstrationsskala, ett värde som brukar uppnås först efter sållning av flis. Framför allt minskade andelarna av de fraktioner som kan ses som förlust, pinnflis och spån. Dessa småfraktioner stör massaprocessen och även om de kan användas som bränsle innebär det en värdeförlust. Bra huggresultat gick också att få med andra inställningar och varierande råvara. När flis som var betydligt kortare än normalt producerades gick som väntat andelen acceptflis ner, dock fortfarande inom gränser som är industriellt acceptabla. Detta pekar på att den nya trumhuggstekniken kan vara speciellt fördelaktig för sura processer där kortare flis är att föredra.

Den nya flisningstekniken användes också för att producera flis från kärnved av tall. En stor andel av vedråvaran i Sverige består av tall, men det är utmanande att använda en stor andel tallkärnved i sulfitprocessen. Flisen användes till försök där 15 olika reaktionsförhållanden jämfördes. Skillnaden mellan de 15 olika reaktionsförhållandena bestod i hur impregnering och sulfitkok utfördes. Resultatet utvärderades genom analys av upptaget av impregneringsvätska i en specialkonstruerad impregneringsreaktor, bestämning av utbytet av massa, rejekt, viskositet, kappatal, ljushet och fiberegenskaper, samt detaljerad analys av råvarans och de 15 produkternas kemiska sammansättning. Försöket gav detaljerad information om hur veden påverkas under olika reaktionsbetingelser och visar tydligt de positiva effekterna av att inkludera ett trycksatt impregneringssteg innan sulfitkoket.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2020. , p. 56
Keywords [en]
wood chip, drum chipper, impregnation, pulping, sulfite process, kraft process, Scots pine, Norway spruce, heartwood, frozen wood, moisture content
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:umu:diva-168634ISBN: 978-91-7855-234-4 (print)ISBN: 978-91-7855-235-1 (electronic)OAI: oai:DiVA.org:umu-168634DiVA, id: diva2:1411918
Public defence
2020-03-27, N360, Kemiska Institutionen, Umeå, 10:15 (English)
Opponent
Supervisors
Funder
Bio4EnergyThe Kempe FoundationsSwedish Energy Agency
Note

Undantagna från kappan t om 2021-03-05: fig. 15 och 16, sid. 47 och 48.

Available from: 2020-03-06 Created: 2020-03-04 Last updated: 2020-03-09Bibliographically approved
List of papers
1. New drum-chipping technology for a more uniform size distribution of wood chips
Open this publication in new window or tab >>New drum-chipping technology for a more uniform size distribution of wood chips
2020 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 74, no 2, p. 116-122Article in journal (Refereed) Published
Abstract [en]

Wood chips from a novel type of drum chipper were compared to wood chips from a conventional disc chipper in an evaluation based on demonstration-scale and industrial-scale machinery. The evaluation was performed as the wood chippers were used as production machines in a kraft pulp mill using softwood. The average bulk density of the wood chips from the disc chipper and the drum chipper was similar and within the range of 138-140 kg/m(3). The size distribution of the wood chips was investigated using a conventional screening method, and by using an automatized image-analysis system based on laser scanning. The average length was set to be the same, but the wood chips from the drum chipper had a more uniform length. The average thickness was similar, but the drum chipper generated slightly more thinner wood chips. Compared to the disc chipper and using the screening method, the drum chipper generated a similar fraction of oversized and over-thick wood chips, 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. Image analysis resulted in similar data. The results indicate that drum chippers warrant further attention as an alternative to conventional industrial-scale disc chippers.

Place, publisher, year, edition, pages
Walter de Gruyter, 2020
Keywords
bulk density, disc chipper, drum chipper, kraft pulping, size distribution, wood chips
National Category
Wood Science Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-168323 (URN)10.1515/hf-2018-0279 (DOI)000510621600003 ()
Conference
15th European Workshop on Lignocellulosics and Pulp (EWLP), JUN 26-29, 2018, Aveiro, PORTUGAL
Note

Special issue: SI

Available from: 2020-02-25 Created: 2020-02-25 Last updated: 2020-03-04Bibliographically approved
2. Evaluation of novel drum chipper technology: pilot-scale production of short wood chips
Open this publication in new window or tab >>Evaluation of novel drum chipper technology: pilot-scale production of short wood chips
2019 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 18, no 10, p. 585-592Article in journal (Refereed) Published
Abstract [en]

Impregnation of wood chips with acidic pulping liquors is improved when using short chip lengths. If the average wood chip length is too short, conventional chipping technology will generate excess small material, such as pin chips and fines. The possibility of using newly developed drum chipping technology to produce short-length wood chips was evaluated with a pilot drum chipper operating at different drum velocities and in-feed angles. With a drum velocity of 30 m/s, the average wood chip lengths and the combined fractions of pin chips and fines were 24 mm and 3.3%, 22 mm and 4.2%, and 17 mm and 8.5%. The highest fractions of total accept chips (large and small accepts), 89% to 90% without screening, were observed for drum velocities of 30-34 m/s and average wood chips lengths of 21-22 mm. The results indicate the potential of drum chipping technology for producing short wood chips with relatively high fractions of accept chips and tolerable fractions of pin chips and fines.

Place, publisher, year, edition, pages
TAPPI Press, 2019
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-165731 (URN)10.32964/TJ18.10.585 (DOI)000496738500002 ()
Funder
The Kempe FoundationsSwedish Energy Agency, P40512-1Bio4Energy
Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-03-05Bibliographically approved
3. The impact of using different wood qualities and wood species on chips produced using a novel type of pilot drum chipper
Open this publication in new window or tab >>The impact of using different wood qualities and wood species on chips produced using a novel type of pilot drum chipper
Show others...
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-168646 (URN)
Available from: 2020-03-04 Created: 2020-03-04 Last updated: 2020-03-05
4. Evaluation of chipping and impregnation of Scots pine heartwood with sulfite cooking liquor
Open this publication in new window or tab >>Evaluation of chipping and impregnation of Scots pine heartwood with sulfite cooking liquor
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-168648 (URN)
Available from: 2020-03-04 Created: 2020-03-04 Last updated: 2020-03-04

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Gard Timmerfors, Jessica

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