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Designing grinding tools to control and understand fibre release in groundwood pulping
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.ORCID iD: 0000-0002-7432-592X
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mechanical pulping is a very energy demanding process in which only a fraction of the energy is used for the actual separation of wood fibres. The rest of the energy is lost, partly in damaging already separated fibres and partly as heat during viscoelastic deformation of the wood. Groundwood pulping is one of the major mechanical pulping processes. In this process, a piece of wood is pressed against a rotating grinding stone. The stone surface has traditionally been made of grinding particles fused to a vitrified matrix. Though the process is close to 200 years old, the detailed mechanisms of the interactions between the grinding particles and the wood surface are still not fully understood. The random nature of the grinding stones combined with the heterogeneous nature of wood creates a stochastic process that is difficult to study in detail. This work utilizes well-defined tools, that facilitate testing and analysis, to increase the understanding of the tool-wood-interaction. In-situ tomography experiments were performed with such well-defined tools, to study the deformations and strains induced in the wood as the tool asperities engage the wood surface. Numerical simulations were used to study the influence of asperity shape, and to show how the induced strains promote intercellular cracks and fibre separation. Several well-defined tool surfaces were designed and tested in a newly developed lab-scale grinding equipment, to study their performance in terms of energy consumption and the quality of the produced fibres. It was shown that the well-defined grinding surfaces, with asperities the same size as a fibre diameter, can be designed both to achieve drastically lower energy consumption compared with that of traditional stones and to produce long and undamaged fibres. This thesis shows that it is possible to design future tools that can help reducing the energy consumption in industrial pulping.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1817
Keywords [en]
Groundwood pulping, Grinding mechanisms, Diamond grinding tool, Energy efficiency
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-382719ISBN: 978-91-513-0672-8 (print)OAI: oai:DiVA.org:uu-382719DiVA, id: diva2:1312993
Public defence
2019-08-23, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 37206-2Available from: 2019-05-29 Created: 2019-05-02 Last updated: 2019-08-15
List of papers
1. Initiation of wood defibration in groundwood pulping, single asperity indentation and scratching
Open this publication in new window or tab >>Initiation of wood defibration in groundwood pulping, single asperity indentation and scratching
2016 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 401-406Article in journal (Refereed) Published
Abstract [en]

To understand how the energy requirements of the mechanical pulping process can be reduced, the fundamental mechanisms behind fiber separation in Norway spruce were studied experimentally and analytically. Single tip scratching in heated water was used to reproduce initial defibration mechanisms found industrially. The resulting scratches were then compared with surfaces ground in a real industrial process. Moreover, the mechanical behavior of the wood microstructure was monitored with X-ray computed microtomography as a single hard tip was pressed into it. Subsequent digital image correlation was applied to estimate the strain field in the region around the indenting tip. Regions in the wood with high tensile or shear strains were identified, i.e. where cracking and fiber separation is believed to initiate.

Keywords
Defibration, Scratching, Strain analysis
National Category
Engineering and Technology Wood Science
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-310478 (URN)000387974800001 ()
Funder
Swedish Energy Agency
Available from: 2016-12-16 Created: 2016-12-16 Last updated: 2019-05-02Bibliographically approved
2. Investigating tool engagement in groundwood pulping – finite element modelling and in-situ observations at the microscale
Open this publication in new window or tab >>Investigating tool engagement in groundwood pulping – finite element modelling and in-situ observations at the microscale
(English)In: Article in journal (Other academic) Submitted
National Category
Paper, Pulp and Fiber Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-382716 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-10
3. Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
Open this publication in new window or tab >>Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
(English)In: Article in journal (Other academic) Submitted
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382698 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-10
4. Influences of load and temperature on groundwood pulping with well-defined tools
Open this publication in new window or tab >>Influences of load and temperature on groundwood pulping with well-defined tools
(English)In: Article in journal (Other academic) Accepted
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382700 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-12
5. Evaluation of well-defined tool surface designs for groundwood pulping
Open this publication in new window or tab >>Evaluation of well-defined tool surface designs for groundwood pulping
(English)In: Article in journal (Other academic) Submitted
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382701 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-10
6. Influence of alignment between extended tool ridges and the wood structure on the defibration mechanisms in groundwood pulping experiments
Open this publication in new window or tab >>Influence of alignment between extended tool ridges and the wood structure on the defibration mechanisms in groundwood pulping experiments
(English)Manuscript (preprint) (Other academic)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:uu:diva-382709 (URN)
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-10

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