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Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial, Ångström Tribomaterials Group)ORCID iD: 0000-0002-7432-592X
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial, Ångström Tribomaterials Group)ORCID iD: 0000-0002-0969-848x
2019 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Refereed) Epub ahead of print
Abstract [en]

Groundwood pulping is a process that employs large machines, making them difficult to use in research. Lab scale grinders exist, but even though they are smaller, the sizes of the grinding stones or segments make them cumbersome to exchange and tailor. This study presents a method and an apparatus for investigating the detailed mechanisms and the energy requirements behind the fibre separation process. A well-defined grinding tool was used at three different temperatures to demonstrate that the equipment can differentiate levels of energy consumption and defibration rates, confirming the well-known fact that a higher temperature facilitates defibration. It is also shown how the equipment can be used to study the influence of grinding parameters, exemplified by the effect of temperature on the way fibres are separated and the character of the produced fibres. A key feature of the equipment is the use and evaluation of small grinding surfaces, more readily designed, produced, evaluated and studied. This reduces both the cost and time necessary for testing and evaluating. At the same time, a technique to produce well defined grinding surfaces was employed, which is necessary for repeatability and robust testing, not achievable with traditional grinding stones.

Place, publisher, year, edition, pages
2019.
Keywords [en]
Computed tomography, Energy efficiency, Groundwood pulping, Lab scale equipment, Test method
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:uu:diva-382698DOI: 10.1515/npprj-2019-0063OAI: oai:DiVA.org:uu-382698DiVA, id: diva2:1307805
Funder
Swedish Energy Agency, 37206-2Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-11-12
In thesis
1. Designing grinding tools to control and understand fibre release in groundwood pulping
Open this publication in new window or tab >>Designing grinding tools to control and understand fibre release in groundwood pulping
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
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:nbn:se:uu:diva-382719 (URN)978-91-513-0672-8 (ISBN)
Public defence
2019-08-23, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 37206-2
Available from: 2019-05-29 Created: 2019-05-02 Last updated: 2019-08-15

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Heldin, MagnusWiklund, Urban

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