MECHANICAL PULPING.Effect of long fibre concentration on low consistency refining of mechanical pulp

Abstract The aim of this study was to investigate the influence of lang fibre concentration on Ioadability and pulp properties during LC refming of mechanical pulp. Lang fibre concentration was adjusted to three different Ievels by screen fractionation of the pulp. The three pulps were refined in a single disc pilot scale LC refiner at simi1ar process conditions. Increased lang fibre concentration suppmied a larger refiner gap and resulted in less fibre . cutting at a given specific energy consumption. The higher lang fibre concentration probably contributed to a stronger fibre network that maintained a !arger refining gap at certain specific energy consumption. Increased long fibre concentration also enabled a higher tensile index increase in the LC refmer at certain fibre length reduction. The study supports a process combining LC refining with screen fractionation, where the lang fibre fraction is recycled to the refiner feed. This enables a . higher Ioadability and a more effective utilisation of the LC refiner. By using this technology, overall specific energy consumption can be reduced if a !arger share of the refining is performed in LC rather than HC refining.