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Designing grinding tools to control and understand fibre release in groundwood pulping
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.ORCID-id: 0000-0002-7432-592X
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2019. , s. 59
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1817
Emneord [en]
Groundwood pulping, Grinding mechanisms, Diamond grinding tool, Energy efficiency
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial
Identifikatorer
URN: urn:nbn:se:uu:diva-382719ISBN: 978-91-513-0672-8 (tryckt)OAI: oai:DiVA.org:uu-382719DiVA, id: diva2:1312993
Disputas
2019-08-23, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Energy Agency, 37206-2Tilgjengelig fra: 2019-05-29 Laget: 2019-05-02 Sist oppdatert: 2019-08-15
Delarbeid
1. Initiation of wood defibration in groundwood pulping, single asperity indentation and scratching
Åpne denne publikasjonen i ny fane eller vindu >>Initiation of wood defibration in groundwood pulping, single asperity indentation and scratching
2016 (engelsk)Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, nr 3, s. 401-406Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
Defibration, Scratching, Strain analysis
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot tribomaterial
Identifikatorer
urn:nbn:se:uu:diva-310478 (URN)000387974800001 ()
Forskningsfinansiär
Swedish Energy Agency
Tilgjengelig fra: 2016-12-16 Laget: 2016-12-16 Sist oppdatert: 2019-05-02bibliografisk kontrollert
2. Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale
Åpne denne publikasjonen i ny fane eller vindu >>Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale
2019 (engelsk)Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434XArtikkel i tidsskrift (Fagfellevurdert) Epub ahead of print
Abstract [en]

With industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.

Emneord
CT; Defibration; DVC; FE; Grinding; Wood
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382716 (URN)
Forskningsfinansiär
Swedish Energy Agency, 37206-2
Tilgjengelig fra: 2019-04-29 Laget: 2019-04-29 Sist oppdatert: 2019-11-20
3. Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
Åpne denne publikasjonen i ny fane eller vindu >>Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools
2019 (engelsk)Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
Computed tomography, Energy efficiency, Groundwood pulping, Lab scale equipment, Test method
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382698 (URN)10.1515/npprj-2019-0063 (DOI)
Forskningsfinansiär
Swedish Energy Agency, 37206-2
Tilgjengelig fra: 2019-04-29 Laget: 2019-04-29 Sist oppdatert: 2019-11-12
4. Influences of load and temperature on groundwood pulping with well-defined tools
Åpne denne publikasjonen i ny fane eller vindu >>Influences of load and temperature on groundwood pulping with well-defined tools
2019 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 438-439, artikkel-id 203051Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Groundwood pulping is an industrial process with a high energy demand, although only a minor part of the energy is used for actually separating the fibres and the rest for working them. Traditionally, the separation process employs a grinding stone having particles embedded in a softer matrix. The position and distribution of the particles have been random, causing their interaction with the wood to also be random. This makes studies of the mechanisms during the separation process difficult. Knowledge of the mechanisms in the separation process helps when designing future tools aimed at energy efficiency or tailored fibre properties. Recently, grinding surfaces having diamond particles brazed to a steel backing at fixed positions have been developed and commercialised. In this work, individual particles are not positioned at the tool surfaces. Instead, well-defined structured diamond films, soldered to a backing, are used as grinding tools. The grinding asperities of such films can be tailored to shapes that are not possible to achieve by using particles. Using this kind of tool in a lab scale grinding equipment, confirms the well-known fact that increased load or increased temperature both lead to lower energy consumption for fibre separation and longer, less damaged fibres.

Emneord
Grinding, Pulping, Wood tomography, Energy savings, Tool design
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382700 (URN)10.1016/j.wear.2019.203051 (DOI)
Forskningsfinansiär
Swedish Energy Agency, 37206-2
Tilgjengelig fra: 2019-04-29 Laget: 2019-04-29 Sist oppdatert: 2019-11-12
5. Evaluation of well-defined tool surface designs for groundwood pulping
Åpne denne publikasjonen i ny fane eller vindu >>Evaluation of well-defined tool surface designs for groundwood pulping
2019 (engelsk)Inngår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, nr 4, s. 9575-9587Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Groundwood pulping is a process in which logs are pressed against a rotating grinding stone. A conventional grinding stone is generally made of grinding particles in a vitrified matrix. As the particles are practically round, their contact with the wood is limited to occasional point contacts. The interaction between the particles and the wood occurs at random positions and at random times, only intermittently contributing to the defibration process. In this work, well-defined grinding tools with asperities giving line contacts rather than point contacts were tested. The tool surface asperities were elongated in shape and positioned with different density over the surface. The tools were tested in a lab-scale equipment at elevated temperatures, and their performance was compared to that of a conventional grinding stone. The grinding mechanisms varied between the different tools, and the specific grinding energy was reduced compared to the conventional tool.

Emneord
Groundwood pulping, Diamond tools, Energy consumption, Tomography, Grinding mechanisms
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382701 (URN)10.15376/biores.14.4.9575-9587 (DOI)000493997400141 ()
Forskningsfinansiär
Swedish Energy Agency, 37206-2
Tilgjengelig fra: 2019-04-29 Laget: 2019-04-29 Sist oppdatert: 2019-12-05bibliografisk kontrollert
6. Influence of alignment between extended tool ridges and the wood structure on the defibration mechanisms in groundwood pulping experiments
Åpne denne publikasjonen i ny fane eller vindu >>Influence of alignment between extended tool ridges and the wood structure on the defibration mechanisms in groundwood pulping experiments
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382709 (URN)
Forskningsfinansiär
Swedish Energy Agency, 37206-2
Tilgjengelig fra: 2019-04-29 Laget: 2019-04-29 Sist oppdatert: 2019-09-10

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