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A way of reducing the energy demand in TMP by shear/compression deformation
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

One of the major cost factors in mechanical pulp production is the electrical energy input. Much of the research in this field has therefore been devoted to an understanding of the mechanisms in the refining process and, consequently, to find ways of reducing the electrical energy consumption. Shear and compression are probably the main types of fibre deformation occurring in refiners for collapsing and fibrillating the fibres into a suitable pulp. In current refiners, the repeated mechanical action of the bars on the fibres consumes large amounts of energy in a treatment of mechanical fibres that is almost random.

Fundamental studies of the deformation of wood have indicated that a combination of shearing and compression forces is highly beneficial in terms of fibre deformation with a low energy demand. Pure compression is able to permanently deform the fibre but requires a substantial amount of work, while pure shearing, although being much less energy demanding, does not lead to any permanent deformations. A more suitable application of the shear and compression forces on the wood fibres during the refining process could be a way to develop fibres at a lower energy demand. These ideas have been studied in this work trying to find new ways of saving energy in the mechanical pulping process.

The first paper in this thesis discusses the way of producing wood shavings and the introduction of shear/compression deformations in these, as well as the potential benefits of using them instead of wood chips as raw material for TMP production. With the shaving process, high deformations in the wood cells were achieved by the shear and compression forces. This led to energy savings of about 25% at a given tensile index, when compared to traditional chips. The quality of the pulp produced from wood shavings was found to be better than that of the pulp produced from wood chips, when it came to strength properties (except for tear index) and optical properties at comparable energy levels.

Another way of reducing energy consumption in refining involving a limited shear combined with compression forces for the mechanical treatment of both wood chips and coarse fibres was also studied. This work shows that such a kind of treatment resulted in a high degree of fibre collapse at low energy demands. The thick-walled transition fibres could even be permanently deformed. Furthermore, refining trials, utilising shear and compression pre-treated chips, showed that the strength properties, except for tear index, along with the optical properties of a TMP could be improved and the electrical energy consumed could be reduced by approx. 100 kWh/tonne, when compared to untreated chips.

The results from the pilot trials described in this work could be used as a starting point for further implementation in the industry, in order to identify the most efficient way of producing mechanical pulp with a lower consumption of electrical energy.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 22 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:01
Keyword [en]
shear, compression, pulses, wood chips, coarse fibre, mechanical pulping, wood cells
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-4282ISBN: 978-91-7178-573-2 (print)OAI: oai:DiVA.org:kth-4282DiVA: diva2:11615
Presentation
2007-02-23, STFI-salen, STFI-Packforsk AB, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101119Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2010-11-19Bibliographically approved
List of papers
1. From wood shavings to mechanical pulp - a new raw material?
Open this publication in new window or tab >>From wood shavings to mechanical pulp - a new raw material?
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, ISSN 0283-2631, Vol. 20, no 4, 418-422 p.Article in journal (Refereed) Published
Abstract [en]

Wood chips used in the thermomechanical pulping (TMP) process were originally designed to suit the chemical pulping process. The production of small wood pieces more suitable for the TMP process could lead to an energy saving in this energy-intensive process. This paper discusses the potential benefits of using wood shavings instead of chips as the raw material for TMP production. In some exploratory trials, wood shavings with a thickness of about 2 mm and wood chips were refined in two steps under normal TMP process conditions in a pilot refiner. The first-stage refining was performed under pressurized conditions at 130°C. The second-stage refining was performed at atmospheric pressure at approximately 100°C at four different energy levels. The quality of the pulp produced from wood shavings was found to be better than that of the pulp produced from wood chips, with respect to both strength properties (except tear index) and optical properties at comparable energy levels. The potential for energy savings at a given tensile index using wood shavings instead of the traditional chips is estimated to be about 25%.

Keyword
Shaving, Metal lathe, Energy consumption, Energy saving, Fibre dimension, Collapse
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6800 (URN)10.3183/NPPRJ-2005-20-04-p418-422 (DOI)000235258200007 ()2-s2.0-30344434073 (Scopus ID)
Note

QC 20101119

Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2014-04-07Bibliographically approved
2. Shear/compression of chips for lower energy consumption in TMP-refining
Open this publication in new window or tab >>Shear/compression of chips for lower energy consumption in TMP-refining
2008 (English)In: Appita journal, ISSN 1038-6807, Vol. 61, no 1, 49-55 p.Article in journal (Refereed) Published
Abstract [en]

Fundamental studies of the deformation behaviour of wood show that combining small amounts of shear along with compression within a roll press reduces the work required for cell wall deformation. This permanent deformation can be increased by: increased number of passes through the nip reduced roll speed increased process temperature. Refining trials showed that the strength properties (except for the tear index), as well as the optical properties of TMP produced from these shear/compression pretreated chips are improved, with the potential of reducing electric energy by approx. 100 kWh/tonne, when compared to untreated chips.

Keyword
wood, shear, compression, energy, Picea abies, deformation, energy consumption, mechanical properties, thermomechanical pulp
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6801 (URN)000252686700009 ()
Note
Uppdaterad från submitted till published(20101119) QC 20101119Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2010-11-19Bibliographically approved
3. Optimal shear/compression forces: a way of collapsing coarse TMP fibres
Open this publication in new window or tab >>Optimal shear/compression forces: a way of collapsing coarse TMP fibres
2007 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 1, 22-28 p.Article in journal (Refereed) Published
Abstract [en]

Fundamental studies of wood have indicated that, with a proper combination of shear and compression forces, it might he possible to collapse wood fibres effectively. To study the applicability of such a combination of shear and compression forces for fibre deformation, a laboratory device for carrying out tests continuously on coarse fibre mats was constructed. Coarse mechanical pulp fibres in the form of sheets were fed through the device, applying differential speeds on two rolls for providing various combinations of shear and compression forces. With the application of a limited shear force, as compared to the compression forces, fibre collapse and bonding could he improved with only a limited amount of work. This indicates a potential for improved paper strength properties in mechanical pulp fibres. Reducing the speeds of the rolls and increasing the temperature proved to he favourable for improving fibre collapse.

Keyword
thermomechanical pulps, fibers, pressure, collapse, compression, shear stress, strength properties
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6802 (URN)000246589100004 ()
Note
QC 20101119Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2010-11-19Bibliographically approved

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