Thesis defence in the University of Oulu

Doctoral Candidate

Master of Science in Technology Tuulikki Karvinen

Faculty and research unit

University of Oulu Graduate School, Faculty of Technology, Machine Design

Field of study

Mechanical Engineering

Date and time of the thesis defence

24.5.2019 12:00

Place of the thesis defence

Linnanmaa, hall L10 (OP auditorium)

Topic of the dissertation

Ultra high consistency forming

Opponent

Professor Jari Hämäläinen, Lappeenranta University of Technology

Second opponent

Doctor Ari Kiviranta, Metsä Group

Custos

Professor Juhani Niskanen, University of Oulu

Changing process conditions by tenfold is rare in modern paper making

This doctoral research demonstrated that forming of cardboard and other paper products at ultra high consistency is feasible at commercial speeds. Ultra high consistency signifies a tenfold increase in consistency, i.e. mass fraction of wood fibers, currently used in paper forming. Such an alteration in process conditions is rare in modern process technology.

105 A.D. is cited as the year when paper was invented in China. Modern papermaking began in the early 19th century in England with the development of the Fourdrinier machine, which produces a continuous roll of paper instead of single sheets. Since that time, several gradual developments in papermaking have been introduced, and the width and speed of paper machines have increased tenfold: the width from 1 to 10 m and the speed from 12 to 120 km/h. However, even today, web formation takes place in a low consistency: the mass fraction of wood fibers is about 1% while the rest is water. Research on increasing forming consistency has started in 1980’s. An increase in forming consistency would simplify and compactify the paper making process, resulting in significant economic and environmental benefits.

This doctoral thesis was based on extensive experimental research at pilot scale and studies at laboratory scale. Research on high consistency fiber suspensions is challenging as they are opaque and their flow phenomena depend on both the flow geometry and flow rate range. The pilot scale made it possible to study selected phenomena at commercial speeds and to produce paper sheets. Alongside the standard analysis, sheet properties were analysed utilizing new measurement methods such as X-ray microtomography.

This doctoral research demonstrated that forming at ultra high consistency is feasible at commercial speeds and the required flow geometry is simpler than previously estimated. This research produced new knowledge on the fluidization and forming of ultra high consistency suspensions providing guidelines for future studies. In addition, doctoral research provided new information on the properties of the ultra high consistency sheets and therefore challenges a certain generally accepted perception postulated in the 1970s.

Dissertation

Last updated: 16.5.2019