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Optical properties of thermomechanical pulp (TMP) obtained from sulfite-pretreated Norway spruce with focus on two-photon spectral imaging (TPSI)
Sveriges lantbruksuniversitet (SLU).
Utrecht university, The Nederlands.
Utrecht university, The Nederlands.
2012 (English)In: Holzforschung, ISSN 0018-3830, ISSN 0018-3830, Vol. 66, no 7, 817-824 p.Article 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.

Place, publisher, year, edition, pages
2012. Vol. 66, no 7, 817-824 p.
Keyword [en]
microscopy; optical properties; pulp; refining, spectral imaging; sulfonation; two-photon excitation; wood
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-21422DOI: 10.1515/hf-2011-0184OAI: oai:DiVA.org:miun-21422DiVA: diva2:698828
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2016-03-24Bibliographically approved
In thesis
1. Reduction of refining energy during mechanical pulping: using pressurised chip compression and sulphite pre-treatment
Open this publication in new window or tab >>Reduction of refining energy during mechanical pulping: using pressurised chip compression and sulphite pre-treatment
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. 62 p.
Keyword
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:nbn:se:miun:diva-21428 (URN)978-91-576-9049-4 (ISBN)
Supervisors
Available from: 2014-02-27 Created: 2014-02-25 Last updated: 2017-05-03Bibliographically approved
2. Improved energy efficiency in mill scale production of mechanical pulp by increased wood softening and refining intensity
Open this publication in new window or tab >>Improved energy efficiency in mill scale production of mechanical pulp by increased wood softening and refining intensity
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on the electric energy efficiency of single stage double disc refining for production of printing grade mechanical pulp from Norway spruce wood chips. The thesis is based on the hypothesis, that more energy efficiency refining can be attained by balanced increases of wood softening and refining intensity. Five mill scale trials were performed where wood softening and refining intensity was varied by applying or changing the following process parameters and variables:

  • Chip pretreatment/impregnation with water
  • Low dosages of sodium sulfite (Na2SO3) added to impregnation
  • Temperature and retention time in the atmospheric preheater bin
  • Refining temperature (housing pressure)
  • Feeding segment design combined with increased production rate

By combining suitable increases in wood softening and refining intensity, it was possible to reduce the specific electric energy consumption in refining by 15% (~290 kWh per bone dry ton (bdt)) while preserving important pulp properties within ±5%, compared to the standard double disc refining process. This was done by combining chip impregnation, using an addition of 0.36% (on bone dry basis) sodium sulfite, with a new feeding segment design which enabled 25% higher production rate.

When using the new feeding segment design at an increased production rate at unchanged wood softening, it led to reduced fiber length and increased sheet light scattering coefficient at certain tensile index, compared with the standard segment design at normal production rate. This is consistent with the effects normally seen when the refining intensity is increasing. The specific electric energy consumption was 8% lower at a tensile index of 43.5 Nm/g (on Rapid Köthen laboratory sheets) compared to refining at lower intensity using the standard segment design at normal production rate.

Mechanical chip pretreatment with subsequent water impregnation showed a reduction in specific electric energy consumption of 6% (~120 kWh/bdt). When chip impregnation was applied in a later trial with a milder chip compression, it led to increased wood softening seen as better preserved fiber length and reduced light scattering coefficient. This resulted in a reduction in tensile index at certain specific electric energy consumption when applied with the standard refining condition but to an increase in tensile index when applied with refining at higher intensity using the feeding segment design at higher production rate.

An addition of 1.2% sodium sulfite during impregnation led to a sulfonate content of pulps of ~0.28% (as Na2SO3 equivalents, including post sulfonation) and an average increase in tensile index of about 8.3 Nm/g, when compared to unsulfonated pulps at certain specific electric energy consumption. The increase in tensile index correlated with increased delamination and internal fibrillation of fibers (measured by Simon’s staining), which indicate that the increase in tensile index for sulfonated pulps was a result of improved fiber flexibility and collapsibility. The reduction in disc gap at certain specific electric energy consumption in refining due to an increased wood softening after sulfonation may explain the increase in delamination and internal fibrillation for sulfonated pulps. The smaller disc gap probably led to a more intense refining, i.e. loading at higher deformation rates due to a higher degree of deformation in bar crossings.

Different temperatures (80 vs. 97°C) and retention times (6 vs. 9 min.) in the atmospheric preheater bin were studied. This showed that the lower temperature and shorter retention time was beneficial for the tensile strength and light scattering of pulp when applying low dosage sodium sulfite pretreatment. This was most likely a result of too high degree of wood softening prior to defibration in the breaker bar zone when combining low dosage sodium sulfite pretreatment with the higher preheating bin temperature at longer retention time.

Different refining temperatures (4.6 and 6.4 bar(g) refiner housing pressure) were evaluated both without and with low additions (0.6% and 1.2%) of sodium sulfite. Raising the refining temperature increased tensile index by 3.2 Nm/g and the addition of 1.2% sodium sulfite by 8.6 Nm/g. The combined increase (~12 Nm/g) was similar to the effect of increasing the specific electric energy consumption by 380 kWh/bdt, when comparing pulps at equal tensile index. However, the pulps produced with increased refining temperature and sodium sulfite addition had lower light scattering coefficient at certain tensile index. The combination of increased refining temperature and addition of 0.6% sodium sulfite was interesting and resulted in pulp with higher tensile index, light scattering coefficient and brightness together with lower shives content at certain specific electric energy consumption, compared with pulp produced at the lower refining temperature without addition of sodium sulfite.

Finally, an implementation of the technology presented here is discussed in relation to the Braviken mill (Holmen Paper AB, Norrköping, Sweden) concerning reduction in electric energy consumption and steam recovery. The technology has potential to reduce the electrical energy use by ~100 GWh/year at the Braviken paper mill, where this study was performed.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2016. 124 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 242
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-27322 (URN)978-91-88025-59-3 (ISBN)
Public defence
2016-04-21, O102, Holmgatan 10, Sunsvall, 10:00 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 3 och 4 inskickat.

At the time of the doctoral defence the following papers were unpublished: paper 3 and 4 submitted.

Available from: 2016-03-24 Created: 2016-03-22 Last updated: 2016-03-24Bibliographically approved

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