Process factors affecting colloid stability and deposit formation in manufacture of newsprint from TMP and recycled fibre

摘要

Formation of pitch and sticky deposits through the destabilisation of colloidal material present in paper manufacture continues to be a challenge in improving machine efficiency in newsprint manufacture from a furnish comprising 60% thermo-mechanical pulp (TMP) and 40% recycled fibre (RCF), and in an environment where water usage efficiency is at best practice. Findings from laboratory studies that have investigated colloid structure, impact of multiple and multi-valent cations, pH, temperature, shear and dissolved organic matter on Pinus radiata extractive colloid stability have been applied to process conditions in Norske Skog's Albury mill to determine which properties are most important in maintaining colloid stability. Through analysis of process data, we demonstrate that all of these factors are relevant in the Norske Skog Albury mill process, thus making the management of deposits a significant challenge. However, initiatives such as minimising soluble calcium formation through management of pH and pulp storage levels, minimising temperature shocks by reducing freshwater make-up at machine start-up and avoiding pH shocks through mixing of neutral and acid pH process streams, are practical steps that contribute to reducing deposit formation and therefore paper breaks and paper machine downtime.