University of Oulu

Mechanisms of thermomechanical pulp refining

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Author: Illikainen, Mirja1
Organizations: 1University of Oulu, Faculty of Technology, Department of Process and Environmental Engineering
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.2 MB)
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Language: English
Published: 2008
Publish Date: 2008-10-21
Thesis type: Doctoral Dissertation
Defence Note: Academic dissertation to be presented, with the assent of the Faculty of Technology of the University of Oulu, for public defence in Auditorium TA105, Linnanmaa, on October 31st, 2008, at 12 noon
Reviewer: Doctor Kari Luukko
Professor Bruno Lönnberg


The objective of this thesis was to obtain new information about mechanisms of thermomechanical pulp refining in the inner area of a refiner disc gap by studying inter-fibre refining and by calculating the distribution of energy consumption in the refiner disc gap.

The energy consumption of thermomechanical pulping process is very high although theoretically a small amount of energy is needed to create new fibre surfaces. Mechanisms of refining have been widely studied in order to understand the high energy consumption of the process, however, phenomena in the inner area of disc gap has had less attention. It is likely that this important position is causing high energy consumption due to the high residence time of pulp located there.

The power distribution as a function of the refiner disc gap was calculated in this work. The calculation was based on mass and energy balances, as well as temperature and consistency profiles determined by mill trials. The power distribution was found to be dependent on segment geometry and the refining stage. However, in the first stage refiner with standard refiner segments, a notable amount of power was consumed in the inner area of the disc gap.

Fibre-to-fibre refining is likely to be the most important mechanism in the inner area of disc gap from the point of view of energy consumption. In this work the inter-fibre refining was studied using equipment for shear and compression. Fibre-to-fibre refining was found to be an effective way to refine fibres from coarse pulp to separated, fibrillated and peeled fibres if frictional forces inside the compressed pulp were high enough. It was proposed that high energy of today’s thermomechanical pulping process could derive from too low frictional forces that heated pulp and evaporated water without any changes in fibre structure.

The method to calculate power distribution and results of fibre-to-fibre refining experiments may give ideas for developing today’s thermomechanical pulp refiners’ or for developing totally new energy saving mechanical pulping processes.

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Series: Acta Universitatis Ouluensis. C, Technica
ISSN-E: 1796-2226
ISBN: 978-951-42-8906-4
ISBN Print: 978-951-42-8905-7
Issue: 305
Copyright information: © University of Oulu, 2008. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.