HELSINKI UNIVERSITY OF

TECHNOLOGY

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ABSTRACT OF DOCTORAL

DISSERTATION

ABSTRACT

Author Topi Helle

Name of the dissertation

Characterisation and removal of gas in papermaking

Date of manuscript 27.9.2007

Date of the dissertation 18.1.2008

Monograph

x Article dissertation (summary + original

articles)

Department Forest Product Technology

Laboratory Paper and Printing Technology

Field of research Paper Technology

Opponent(s) Professor Jari Käyhkö and D.Sc. Ulrich Weise

Supervisor Professor Hannu Paulapuro
Abstract

The objective of this dissertation was to characterise gas in papermaking and to study the effects of centrifugal

force on flotation fibre recovery and the removal of gases from fibre suspensions. In order to reach these goals,

laboratory and pilot paper machine trials with dispersed and precipitated gas bubbles were carried out.

Laboratory and mill trials subjecting the fibre suspension to centrifugal force were also made.

Entrained gas bubbles had mostly adverse effects on papermaking, which was to be expected from previous

studies reported in the literature. Even quite low entrained gas contents were found to affect papermaking.

Precipitated gas bubbles appeared to have largely the same effect on papermaking as dispersed gas bubbles.

However, differences were found in their effects on tear and wet tensile strength.

In this study, centrifugal force was found to remove gas bubbles effectively, so it can be used to remove gas

from a papermaking fibre suspension. Centrifugal force did not remove dissolved gas effectively, but with

correct process design sufficient removal of entrained air should be enough. In addition, it is possible to remove

dissolved gas with centrifugal force with the help of turbulence or vacuum. According to the results in this

study, centrifugal force cannot be used to improve flotation fibre recovery.

Keywords papermaking, gas, air, degassing, deaeration, flotation

ISBN (printed) 978-951-22-9155-7

ISSN (printed) 1796-7414

ISBN (pdf) 978-951-22-9156-4

ISSN (pdf)

ISBN (others)

Number of pages 51 p. + app. 28 p.

Publisher Helsinki University of Technology, Laboratory of Paper and Printing Technology

Print distribution Helsinki University of Technology, Laboratory of Paper and Printing Technology

x The dissertation can be read at http://lib.tkk.fi/Diss/