Public defence, Natural Fiber Products, MSc (Tech) Antti Fredrikson

Title of the thesis: Refining phenomena of the chips at the high-consistency refiner plate gap – new insights to load distribution paradigms

Thesis defender: Antti Fredrikson
Opponent: Professor Per Engstrand, Mid Sweden University, Sweden 
Custos: Professor Jouni Paltakari, Aalto University School of Chemical Engineering

What really happens inside a high-consistency refiner? New findings could help reduce energy consumption

Producing thermomechanical pulp (TMP) for paper and packaging materials from wood requires considerable amounts of energy. TMP is a highly resource-efficient process that converts more than 90% of wood into well-developed fibre material, but its high electricity consumption remains a major challenge. Improving the energy efficiency of this process could reduce manufacturing costs and further support the transition towards renewable, fibre-based materials.

In his doctoral thesis at Aalto University, Antti Fredrikson, M.Sc., investigated what happens inside the narrow gap between the rotating and stationary plates of a high-consistency TMP refiner, known as the refining zone. The research aimed to understand how mechanical forces and energy are distributed, how wood fibres are distributed within the refining zone, and what temperature measurements reveal about the process.

Using specially developed sensors, the study measured mechanical forces and temperatures directly inside an operating refiner. The results showed that fibres do not continuously occupy the entire refining zone. Instead, mechanical forces occur as irregular, short-duration events, and energy dissipation varies considerably across the refining zone.

A particularly important finding was that temperature profiles do not reliably describe the spatial distribution of mechanical refining load. However, local temperature peaks can reveal unfavourable conditions in which fibres are damaged rather than effectively developed.

These findings challenge traditional assumptions about refining and provide new information for designing more energy-efficient refiner plates and improving process control. By better understanding and controlling the mechanical and thermodynamic phenomena within the refiner plate gap, manufacturers may reduce energy consumption while maintaining or improving pulp quality.

Keywords: thermomechanical pulp, shear force, high-consistency

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.

Contact information: 
antti.fredrikson@gmail.com
+358405061857
https://www.linkedin.com/in/anttifredrikson/