Mechanical Pulping: Peroxide-based ATMP refining of spruce: energy efficiency, fibre properties and pulp quality

Abstract

SUMMARY:Pilot scale refining of White spruce using a modified TMP refining process (ATMP -Advanced Thermomechanical Pulp) was studied. ATMP combines selective wood disintegration by mechanical pretreatment and refining at elevated intensity with chemical treatment after defibration (in this study hydrogen peroxide, alone and in combination with alkali).The electrical energy efficiency and pulp quality using ATMP were evaluated and compared to a conventional TMP process. One goal was to retain the combination of optical properties and strength of typical TMP. Fibre properties (structural dimensions, external and internal fibre development) as well as the amount of split fibres resulting from TMP and ATMP processes were compared.The results indicate an electrical energy efficiency improvement potential of 0.65 MWh/odt (34%) at tensile index 30 N.m/g of ATMP compared to reference TMP. All ATMP pulps retained their TMP character, i.e. the relationships between light scattering coefficient, density, elongation properties and strength that are important for printing paper. ATMP had a significantly lower content of shives and higher external and internal fibre development compared to TMP at equal energy application. The long fibre fraction of ATMP also contained significantly higher amount of split fibres. The brightness of ATMP produced with addition of hydrogen peroxide (28 kg/odt) and magnesium hydroxide (14 kg/odt) was 14 ISO % higher compared to TMP.

Mechanical Pulping: Role of equipment configuration and process chemicals in peroxide-based ATMP refining of spruce

“…Addition of chemicals to the refining process was shown to alter the character of TMP making it more "CTMP-like", i.e. the for printing papers very important light scattering coefficient was not maintained on the same level due to unfavourable defibration of chips caused by softening of the lignin in the middle lamellae (Franzén 1986;Cisneros et al 1992;Richardson 1998;Salmén et al 1999;Koljonen et al 2001), see Fig 1. The character of the ATMP and TMP was studied thoroughly using statistical methods to evaluate, whether the achieved reduction of the energy demand came with a change in the character of the produced pulp (Johansson et al 2011;Gorski et al 2011a). No difference in the character of ATMP and TMP was found in earlier studies, i.e.…”

“…A reduction of the electrical energy demand to reach a tensile index of 25 Nm/g was reported to be in the range of 1.1 MWh/odt for Loblolly pine (Johansson et al 2011) when an ATMP process was compared to a reference TMP process. The corresponding value for White spruce was 0.7 MWh/odt (Gorski et al 2011a) when a tensile index of 50 Nm/g was targeted. Energy reduction by at least 0.5 MWh/odt for pine and 0.3 MWh/odt for spruce was proposed to be caused by the action of chemicals added in the first stage refiner in the ATMP process and the rest (0.6 and 0.4 MWh/odt respectively) was proposed to be attributed to the process equipment configuration (Johansson et al 2011;Gorski et al 2011a).…”

“…The corresponding value for White spruce was 0.7 MWh/odt (Gorski et al 2011a) when a tensile index of 50 Nm/g was targeted. Energy reduction by at least 0.5 MWh/odt for pine and 0.3 MWh/odt for spruce was proposed to be caused by the action of chemicals added in the first stage refiner in the ATMP process and the rest (0.6 and 0.4 MWh/odt respectively) was proposed to be attributed to the process equipment configuration (Johansson et al 2011;Gorski et al 2011a). However, ATMP concept was compared only to a TMP reference in these studies.…”

“…It was earlier shown that the reduction of energy demand and change in pulp properties in the ATMP concept can be explained by more energy-efficient development of individual fibre properties (Gorski et al 2011a). External fibrillation, flexibility and cross-sectional characteristics were earlier shown to be suitable indicators for effects of refining process on fibres (Atack 1981;Koran 1981;Karnis 1994;Kure 1999;Reme 2000;Corson 2001).…”

“…The ATMP process was recently described in pilot and mill scale (Hill et al 2009;Hill et al 2010;Johansson et al 2011;Gorski et al 2011a;Gorski et al 2011b). One of the features of ATMP is the combination of mechanical pre-treatment (using Impressafiner and Fiberizer) and high-intensity first stage refining (achieved by feeding refiner segment pattern and/or elevated refiner speed).…”