Production of high quality and low energy chemithermomechanical pulp

Chemithermomechanical pulps (CTMP) were produced from Eastern black spruce chips in a two-stage pilot plant using different conditions of chemical pretreatment and refining intensity. The conventional CTMP was produced by impregnating chips with sulfite liquor at a pH of approximately 10 and the conducting the first-stage refining in a double disc refiner at 1,200 rpm. The distribution of specific energy and refining intensity was about the same in the two stages. The experiments showed that, by decreasing the impregnating liquor pH to approximately 4.5 and conducting the first-stage refining at a relatively low specific energy and high refining intensity (by operating the refiner at 1,800 rpm), an energy saving of up to 33% could be achieved without any adverse effect on the pulp quality.