Optimal Fibre Development and Energy Saving During Refining of High Kappa Softwood Chemical Pulp for Kraft Linerboard Products in a Fully Closed Mill

摘要

Optimization of pulp refining is recognized as a critical step in the paper making process. Final product quality can be greatly influenced by the treatment of the fibres during refining. Incorrect refining of stock can lead to either insufficient fibrillation or excessive fibre damage. Optimization of refining intensity can lead to power consumption saving and optimization of fibre quality. Refining results of low Kappa unbleached softwood kraft pulps are available in the literature based on investigation from laboratory PFI mills, pilot refiners and commercial refiners. Availability of such data for high yield unbleached softwood kraft pulps are rather limited. The refining response of such pulps is expected to be different from conventional low Kappa long fibre kraft pulps. A series of in-situ refining trials were undertaken to investigate the effect of refining intensity and mode of refining of such pulp, in view of establishing the optimal refining strategy, while refined using two refiners in series using commercial paper machine refiners in a modern kraft linerboard mill. Results of handsheet papers made from refined pulps from of in-situ trials showed that higher refining intensity in excess of 4.0 Ws/m is essential for better fibrillation and fibre development of such pulps. More than 30% improvement in key strength properties (tensile, burst, STFI and ring crush compression strength) was achieved when refining intensity increased from 3.0 Ws/m to 5.6 Ws/m at constant net specific energy of 160 kWh/t. For two refiners operating in series, the optimal mode of operation was found to be use of higher intensity plates on both the refiners with the first refiner operating at full motor load, while the specific energy application to the second refiner varied achieve the desired freeness level. When the optimal refining conditions established from the initial refining trials and handsheet test results implemented, the potential benefits were realized in terms of improvement in key strength properties of machine-made linerboard papers.