Mid Sweden University

Several combinations of high consistency (HC) and low consistency (LC) refiners were evaluated both in main line and reject line for production of pulp for printing papers. HC-LC processes were compared with processes with only HC refining. Processes with two different types of chip refiners were studied – single disc (SD) and double disc (DD). All process combinations were evaluated during continuous production in the Holmen Paper Braviken mill, Sweden. The purpose of this work was to evaluate energy efficiency and pulp quality for the processes.

LC refining was more energy efficient than HC refining for certain tensile index increase in all evaluated combinations. The highest energy efficiency was attained when LC refining was utilized in main line, but the difference was small compared to application on reject. Much higher specific energy was applied on reject pulp, but since the reject share was only around 30%, the LC refining specific energy, based on main line production, was around 80 kWh/air dry ton (adt) whereas up to 180 kWh/adt was applied in main line.

The combination of DD chip refining and LC refining had the highest energy efficiency (tensile index at certain specific energy consumption) and produced pulp with somewhat lower fibre length but higher light scattering and lower shives content compared to a line with only SD HC refining. Thus, for printing papers it seems beneficial to combine LC refining with high intensity HC chip refining. All processes with LC refining had lower light scattering and fibre length compared to the corresponding system with only HC refining.