High consistency refining of mechanical pulps during varying refining conditions : High consistency refiner conditions effect on pulp quality

Abstract:   The correlation between pulp properties and operating conditions in high consistency (HC) refiners at Holmen Paper AB were studied. Two types of HC refiners were investigated: the Andritz RTS refiner at the Hallstavik Mill and the Sprout-Bauer Twin 60 refiner at the Braviken Mill. The objective of the study was to clarify the relationship between the pulp properties and refining conditions such as electrical energy input, housing- and feed- pressure and plate wear in high consistency refining. The results of this project show that worn segments reduce the operating energy maximum input and the pulp and handsheet properties in negative aspects such as lower tensile- and tear index, and shorter average fibre length. Energy input is an important factor in the refining process and influence Canadian Standard Freeness and the tensile index as evident from the probability residuals. Housing pressure and feed pressure influence the pulp quality and should be adjusted in order to optimise the refining process, although the effect is not as great as for energy input or plate wear. The results of the study indicate that Braviken Mill is operating at its optimum for the parameters measured in this project. Hallstaviks goal, to avoid fibre shortening and to obtain better tensile index, can be reached by making slight changes in pressure condition.