Improvement of energy efficiency in TMP refining by selective wood disintegration and targeted application of chemicals

A pilot refining trial on Loblolly pine (Pinus taeda) was conducted using a novel process configuration called ATMP (Advanced Thermomechanical Pulp). In this process, selective wood disintegration due to mechanical pre-treatment of chips and increased refining intensity is combined with targeted application of chemicals after defibration. Standard TMP was compared to ATMP where different chemical strategies were applied. These strategies employed active chemicals known to cause sulphonation, carboxylation/oxidation and degradation of fibre components in order to assist the refining process. Main goal of the study was to evaluate the potential of decreasing the energy demand in refining evaluated at equal tensile index compared to a TMP reference. Another goal was to produce pulp where the TMP character, i.e. good optical properties combined with good bulk and strength properties, was fully preserved. The objective was also to study other quality aspects of the pulp produced using the ATMP process and compare these to properties of conventional TMP. Energy demand in refining was decreased with at least 0.6 MWh/odt compared to TMP at tensile index 25 Nm/g when ATMP concept was used. Maximum achieved reduction in the refining energy demand was 1.1 MWh/odt (42%) compared to the TMP reference at tensile index 25 Nm/g. Statistical analysis showed that pulp, produced using the ATMP process, retained all its important properties such as light scattering, density and elongation on the same level as control TMP, i.e. it had the same character. All pulps produced using the ATMP process had very low shive content. Treatment with hydrogen peroxide and magnesium hydroxide was the most successful chemical strategy tested during the pilot trial. It was most successful both in respect to improved optical properties (14 ISO % increase in brightness could be achieved by adding 25 kg/odt hydrogen peroxide in the first stage refiner) and reduction of energy demand in refining.