Thesis for the degree of LOW CONSISTENCY REFINING PROCESS CONDITIONS A Mid Sweden University, SE Mid Sweden University Licentiate of Technology, Sundsvall 20 OF MECHANICAL PULP ND ENERGY EFFICIENCY

The thesis is focussed on low consistency (LC) refining of mechanical pulp. The research included evaluations of energy efficiency, development of pulp properties, the influence of fibre concentration on LC refining and effects of rotor position in a two-zoned LC refiner. Trials were made in mill scale in a modern TMP line equipped with an MSD Impressafiner for chip pre-treatment, double disc (DD) first stage refining and a prototype 72-inch TwinFlo LC refiner in the second stage. Tensile index increased by 8 Nm/g and fibre length was reduced by 10 % in LC refining at 140 kWh/adt gross specific refining energy and specific edge load 1.0 J/m. Specific light scattering coefficient did not develop significantly over the LC refiner. The above mentioned TMP line was compared with a two stage single disc high consistency Twin 60 refiner line. The purpose was to evaluate specific energy consumption and pulp properties. The two different process solutions were tested in mill scale, running similar Norway spruce wood supply. At the same tensile index and freeness, the specific energy consumption was 400 kWh/adt lower in the DD-LC concept compared with the SD-SD system. Pulp characteristics of the two refining concepts were compared at tensile index 47 Nm/g. Fibre length was lower after DD-LC refining than after SD-SD refining. Specific light scattering coefficient was higher and shive content much lower for DD-LC pulp. The effects of sulphite chip pre-treatment on second stage LC refining were also evaluated. No apparent differences in fibre properties after LC refining were noticed between treated and untreated pulps. Sulphite chip pre-treatment in