Increased energy-efficiency in mechanical pulping

Updated: 2015-12-07 | Print

Effective and optimized conversion technologies are a pre-requisite to fully utilize the potential of ligno-cellulosic fibres.

Forest-based lignocellulosic biopolymers are expected to play a major role in the transition from petroleum-based industries and products towards a resource–efficient and sustainable bio-economy. Effective and optimized conversion technologies are a pre-requisite to fully utilize the potential of ligno-cellulosic fibres. The disintegration and development of wood logs and chips into functional fibres by means of thermo-mechanical energy has undergone continuous process development, and has resulted in a versatile high-yield product: Mechanical pulp. Traditional applications range from coarse particleboard products to high-quality graphical paper grades. Mechanical pulps are also used in packaging materials, tissue, isolation products, and fibre-based composites. Innovative future perspectives involve fibre surface functionalization, nanofiber production and bio-refinery applications.

Sequential disintegration and development of solid wood into functional fibres (ATMP process). Images: Per Olav Johnsen, PFI


A major drawback of mechanical pulping has been its high energy consumption. Improving energy efficiency has been an ongoing effort in many mechanical pulp mills, supported by academic research. A major challenge is appropriate energy application, as wooden fibres - due to their structural heterogeneity - respond differently to applied refining forces. This may lead to both under-treated and over-treated fibres. PFI has for many years built up extensive experience and competence within fibre-process interactions in mechanical pulping. 

PFI has been actively involved in planning and management of the multinational Energy Effective Mechanical Pulping Initiative (e2mp-i) research program (2012-2015), which has united academia and industry in a unique research effort, aiming to reduce the specific energy consumption in mechanical pulping by 50%. The e2mp-i program has a total budget of 75 MSEK, whereof 30 MSEK are fundings by the Swedish Energy Agency. PFI has contributed to 5 of the 12 projects within the program, and managed 2 of these. Together with industrial partners (Stora Enso, Holmen Paper, SCA, Norske Skog, Valmet) and other research providers (Mid Sweden University, Swedish University of Agricultural Sciences, Chalmers University of Technology, QualTech, Capisco and InnovoCell), PFI has investigated energy-related aspects of chemical addition in high-consistency refining, high quality CTMP refining, fibre non-uniformity, and fibre property development in high-consistency and low consistency refining. In order to create a reference/baseline for a successive verification of implemented energy efficiency improvement measures, an extensive benchmarking study (BAT 2012) was conducted in Sweden, Norway and the UK. Sixteen TMP/CTMP lines for publication and board grades have been compared for energy efficiency in terms of pulp quality development. Results have shown that the pulp property profile and the process design differed substantially, even for similar product grades. A given level of a specific pulp property was reached over a wide range in specific energy.

During the period from 2002 to 2015, PFI has furthermore managed and executed extensive pilot scale research within the e2mp-ox projects, together with its partners Norske Skog and Andritz. The projects were partly funded by the Research Council of Norway, and have resulted in the development and industrial implementation of a new and energy-efficient refining concept (ATMP process), which has potential for 40-50% specific energy reduction at maintained or improved product quality. E2mp-ox research has resulted in 2 PhD degrees, 9 presentations at international conferences, 11 peer-reviewed publications, whereof one award-winning, and additional 4 articles submitted for publication.

Contact: Kathrin Mörseburg