Mill evaluation of an intensified mechanical pulping process

Mill-scale demonstration of a process concept inspired by Process Intensification (PI) principles was performed in Holmen Paper Braviken mill, Norrkoping, Sweden. The intensified process consists of wood softening by means of chip pretreatment with sodium sulphite, high intensity refining followed by low consistency refining. This process yields very low shives content and thus the unit operations screening and reject refining can be eliminated and the pulp is fed directly to the paper machine. Thorough evaluation of key paper-and print quality data showed that it is possible to produce pulp for newsprint at 1500 kWh/adt total specific energy (including auxiliary drives such as pumps, screw feeders, etc.). The total specific energy consumption was 900 kWh/adt lower compared to the normal process used for newsprint in Braviken, and 500 kWh/adt lower compared to today's best available technology. The auxiliary equipment energy demand was 120 kWh/adt, which was less than half of that of the reference TMP line. The PIinspired process reduces the number of machines drastically compared to a conventional TMP line, as well as the number of pumps, chests and other auxiliary equipment.