The forest industry is efficient at transforming forest biomass to paper – but the manufacturing consumes a lot of electricity. A joint research project between business and academy aims to optimize processes and cut energy consumtion in half.

”Mill scale trials have shown that it is possibe to reduce electricity consumption by 25 percent compared to the best current technology used in paper mills. The study is very important for Swedish paper production”, says Per Engstrand, Professor in Mechanical Pulping Technology at Mid Sweden University.

”The pilot scale results for paper production are electricity savings of 30 percent for printing paper and 27 percent for paperboard. The smart process optimizations also contribute to lower carbon dioxide emissions and reduced climate impact from the pulp and paper industry”.

Collaboration with forest companies

The forest industry efficiently transforms forest biomass to paper products, but current process technology uses a lot of energy, says Per Engstrand, Professor at Mid Sweden University. Photo: FSCN.

”Mechanical and semi-chemical pulp come from manufacturing processes with a close to 100 percent wood yield. That means that almost all of the raw material is recovered in the final product. These kinds of pulp are essential to achieve high quality in the most important paper and paperboard products made in the Nordic countries. These products constitute half of the Swedish paper and paperboard production, and are highly developed. They are the foundation for the industry’s movement towards more refined products”, Per Engstrand says.

”Pulp production is energy-intensive, and our focus has been on developing energy efficiency improvements without compromising the product quality. The results stem from an initiative launched by the companies Holmen, Stora Enso, SCA and Norske Skog, called e2mp (Energy Efficiency in Mechanical Pulping). Three research projects, financed in different ways, have been started under the initiative. One of the intentions has been to achieve a significant reduction in energy consumption in the process from mechanical pulp to product”, Per Engstrand says.

”Besides the companies in the forest industry, other participants have contributed to the project as well – such as PFI (Norway), Chalmers University of Technology, Swedish University of Agricultural Sciences, ÅF, Luleå University of Technology and the companies Valmet and Andritz. The research has been cofinanced by The Knowledge Foundation, The Research Council of Norway and the Swedish authorities Vinnova and the Swedish Energy Agency”.

Aiming to cut energy consumption in half

Mechanical pulping is performed with one of two processes, TMP or CTMP. Both employ the same raw material: pulpwood and sawmill chips. In the TMP process, the chips are preheated and refined using pressurized steam, in order to soften the lignin and produce separated fibres. In the CTMP process, an additional chemical treatment is performed to produce even softer fibres. Mechanical pulp is used for thin, opaque, high quality printing paper (for newspapers, magazines and similar applications), while chemical-mechanical pulp is used for products where a higher bulk is preferred, such as multilayer paperboard and board packaging.

A conventional TMP process consumes 1.9 – 2.4 MWh per ton for newsprint, and 2.4 – 3.0 MWh per ton for magazine paper. The refiners consume between 80 and 90 percent of the total electricity. The refining uses some energy for defibering, but most is used for processing the separated fibres. The refining technology is important for the energy efficiency of the processes.

”Our aim is to be able to produce paper and paperboard by 2021 with half the energy consumption compared to 2011, when the project was launched. According to the studies we have performed so far, that is not an unreasonable goal. The companies would also be able to improve the pulp and product quality considerably”, Per Engstrand says.

Smart process optimization

Preserved paper quality, but significantly reduced energy consumption. The new process technology has been tested successfully at Holmen Paper’s mill in Norrköping. Photo: FSCN.

”The entire production process can be modified and improved once you gain a thorough understanding of the basic processes at work. One example is to soften the wood at a higher temperature with a small amount of sulphite as an additive, and increase the chip refining intensity; these measures improve the energy efficiency of the refining significantly, and also allows us to remove the subsequent process steps of screening and reject refining, which simplifies the entire process. Pilot scale testing of the modified process concept has been performed at Holmen Paper’s mill Braviken, in Norrköping”, Per Engstrand says.

”It is very interesting that several of the process steps could be eliminated without affecting the quality of the finished product. According to the test results, newsprint can be manufactured with a total energy consumption of approximately 1 500 kWh/ton, which is 900 kWh/ton lower than the reference value – a 40 percent improvement. The pulp produced had better properties in every aspect except tear strength. The printing properties (such as print through, dusting and smearing) were unaffected”, Per Engstrand concludes.

The article was published in September 2017.