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Reduction of refining energy during mechanical pulping: using pressurised chip compression and sulphite pre-treatment
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The effects of pressurised compressive chip pre-treatment and low dosage sulphite pre-treatment were evaluated for production of thermomechanical pulp in mill scale trials using Norway spruce (Picea abies) at the Braviken paper mill (Holmen Paper AB, Sweden). The general aim of the study was to improve the energy efficiency during the production of mechanical pulps suitable for news and improved news grade papers.  The pressurised compressive chip pre-treatment performed in an Impressafiner, resulted in a reduced acetone extractive content for first stage blow line pulp by up to 24%. Furthermore, pulp produced from mechanically pre-treated chips had higher tensile- and tear indices, elongation and light scattering and lower freeness compared to pulps from untreated chips produced with equal total specific energy consumption. The total specific energy consumption was reduced by 120 kWh/bone dry ton (6%) at equal tensile index, when pulps were produced together with the Impressafiner pre-treatment. Sulphite pre-treatment increased tensile index, elongation, density and brightness and reduced light scattering and shive content compared to pulps produced with only mechanical pre-treatment at equal specific energy consumption. The increase in tensile index and reduction in light scattering followed linear relations to the dosage of sodium sulphite in the measured dosage range (0-1.2% Na2SO3). The addition of ~1.2% sodium sulphite gave a sulphur content in pulp of ~0.67% (as Na2SO3) and reduced the specific energy consumption by 210-320 kWh/bdt (12-15%) when compared at equal tensile index. However, light scattering was not retained for this energy reduction.  Further analyses showed that sulphite pre-treatment did not significantly affect the distribution of the Bauer-McNett fractions or the fibre length for pulps refined with equal specific energy consumption but did increase fibre delamination/internal fibrillation as measured by Fernando and Daniel’s (2010) version of Simons’ staining. The specific energy consumption for pulps produced with sulphite pre-treatment (1.2% Na2SO3) and double disc refining were 650 kWh/bdt (30%) lower than for pulps produced in a two stage single disc refiner line (no pre-treatment), when compared at a similar tensile index and light scattering coefficient.

Place, publisher, year, edition, pages
Uppsala: Sveriges Lantbruksuniversitet, 2011. , p. 62
Keywords [en]
Chip pre-treatment, double disc refiner, energy efficiency, Impressafiner, low dosage, Norway spruce, refining intensity, single disc refiner, sulphite pre-treatment, thermomechanical pulp
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:miun:diva-21428ISBN: 978-91-576-9049-4 (print)OAI: oai:DiVA.org:miun-21428DiVA, id: diva2:698845
Supervisors
Available from: 2014-02-27 Created: 2014-02-25 Last updated: 2017-05-03Bibliographically approved
List of papers
1. Optical properties of thermomechanical pulp (TMP) obtained from sulfite-pretreated Norway spruce with focus on two-photon spectral imaging (TPSI)
Open this publication in new window or tab >>Optical properties of thermomechanical pulp (TMP) obtained from sulfite-pretreated Norway spruce with focus on two-photon spectral imaging (TPSI)
2012 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, ISSN 0018-3830, Vol. 66, no 7, p. 817-824Article in journal (Refereed) Published
Abstract [en]

Chips of Norway spruce have been impregnated with Na2SO3 and refined at two specific energy consumptions levels at full mill scale. The optical properties of thermomechanical pulps (TMPs) obtained were analyzed in terms of brightness, light scattering, opacity, and autofluorescence by spectral imaging. Even at low sulfite dosage (0.24% sulfite by dry weight) light absorption was reduced, and the brightness was elevated, and a clear dose-response effect was observed. Two-photon spectral imaging (TPSI) showed that sulfonation, impregnation, and refining affect the fluorescence properties differently. Compared to native wood, both processed wood chips and pulp fibers revealed blue-shifted fluorescence maxima, a characteristic of shortened conjugated systems. Two subpopulations of fibers with different optical properties were observed, and the fluorescence of one fiber population was red shifted.

Keywords
microscopy; optical properties; pulp; refining, spectral imaging; sulfonation; two-photon excitation; wood
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-21422 (URN)10.1515/hf-2011-0184 (DOI)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-12-05Bibliographically approved
2. Mill scale experiences of combined low dosage sulphite pre-treatment and high intensity refining of spruce
Open this publication in new window or tab >>Mill scale experiences of combined low dosage sulphite pre-treatment and high intensity refining of spruce
Show others...
(English)Manuscript (preprint) (Other academic)
Keywords
chip pre-treatment, double disc refiner, energy reduction, refining intensity, single disc refiner, sulphite, thermomechancial pulp
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-21425 (URN)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2014-03-06Bibliographically approved
3. Pressurised compressive chip pre-treatment of Norway spruce with a mill scale Impressafiner
Open this publication in new window or tab >>Pressurised compressive chip pre-treatment of Norway spruce with a mill scale Impressafiner
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, ISSN 0283-2631, Vol. 27, no 1, p. 056-062Article in journal (Refereed) Published
Abstract [en]

Mill scale trials were performed to evaluate pressurised compressive chip pre-treatment with the Impressafiner installed in one of the thermomechanical pulp lines at Braviken paper mill (Holmen Paper AB). The aim of the study was to determine if earlier reported effects of the Impressafiner pre-treatment on spruce chips from pilot scale trials (i.e. energy reduction and extractives removal) could also be attained with the mill scale Impressafiner.The mill scale Impressafiner pre-treatment resulted in partial disintegration of chips into a material consisting of fragmented chips with cracks running along the longitudinal fibre axis. Splits or evidence for weaknesses were observed between the primary and secondary fibre walls of pre-treated chips. An increase in water uptake for pre-treated chips was also observed. The extractive content was reduced by up to 24% for pulps produced with pre-treated chips compared to pulps from untreated chips. Pulp produced from pre-treated chips had higher tensile- and tear indices, elongation and light scattering and lower freeness compared to pulps from untreated chips produced with the same total specific energy consumption. The total specific energy needed to reach a tensile index of 47 Nm/g was reduced by 120 kWh/bone dry ton (6%) with Impressafiner pre-treatment. A smaller refiner plate gap was needed to reach the same specific energy consumption for pre-treated chips compared to untreated chips.

Keywords
Chip pre-treatment, Energy reduction, Extractives, Fibre microstructure, Impressafiner, Norway spruce, Thermomechanical pulp
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-21421 (URN)10.3183/NPPRJ-2012-27-01-p056-062 (DOI)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-12-05Bibliographically approved

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Nelsson, Erik

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