miun.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Measurement of the Power Distribution in a Single Disc Refiner
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
Sunds Defibrator AB.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (Ved- och fibermekanik)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
Responsible organisation
1999 (English)In: Journal of Pulp and Paper Science, ISSN 0826-6220, Vol. 25, no 11, 384-387 p.Article in journal (Refereed) Published
Abstract [en]

A vital parameter in the production of mechanical pulp through refining is the energy consumption. Until recently, the pulping industry has focused on the total energy consumed, without a full understanding of how this energy is distributed in the refiners. In this paper two methods are suggested by which it is possible to estimate the energy supplied at an arbitrary point along the disc radius on refiner segments. The methods are based on instrumented bar with strain gauges. In the first method, a bar is slotted so that the sensor can be viewed as consisting of a number of cantilever beams separated by slots. In the second method, the sensor consists of one continuous bar along the disc radius. The sensors are calibrated such that influence coefficients are obtained for the slotted case and an influence function is obtained for the continuous one. The tangential forces are obtained directly in the first method, while in the second they are given by an integral equation which can be solved numerically. From the knowledge of the tangential force the power distribution can be calculated. Experimental results from the use of the slotted sensor are also given.

Place, publisher, year, edition, pages
1999. Vol. 25, no 11, 384-387 p.
Keyword [en]
Disc refiners, Energy consumption, Force sensors, Mathematical analysis, Picea abies, Thermomechanical pulping
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-1641ISI: 000083844000003Local ID: 245OAI: oai:DiVA.org:miun-1641DiVA: diva2:26673
Available from: 2008-09-30 Created: 2008-10-21Bibliographically approved
In thesis
1. Wood and fibre mechanics related to the thermomechanical pulping process
Open this publication in new window or tab >>Wood and fibre mechanics related to the thermomechanical pulping process
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner.

 

The thesis comprises the following parts:

–A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process

–An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners

–An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner

–A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone

–Measurements of the power distribution in a refiner.

 

The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given.

 

The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy.

In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data.

Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone.

Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position.

The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.

 

 

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2008. 65 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 63
Keyword
Acoustic emission, Chips, Compression tests, Defibration, Disc refiners, Energy consumption, Fibre structure, Force sensors, Fracture, Impact strength, Mathematical analysis, Moisture content, Picea abies, Refining, Stiffness degradation, Strains, Temperature, Thermomechanical pulping, Velocity
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-6725 (URN)978-91-86073-15-2 (ISBN)
Public defence
2008-11-21, O 102, SCA-salen, Holmgatan 10, Åkroken, Sundsvall, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2008-10-24 Created: 2008-10-22 Last updated: 2009-06-08Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Gradin, Per A.Berg, Jan-ErikNyström, Staffan
By organisation
Department of Engineering, Physics and MathematicsDepartment of Natural Sciences
Mechanical Engineering

Search outside of DiVA

GoogleGoogle Scholar

Total: 970 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf