Deposit control in the pulp and paper industry-Part 3. Novel developments for soft water environments

摘要

Not surprisingly, most of the effort assigned to deposit control management has focused on overcoming the contamination problems, associated with the use of waste paper. But we cannot ignore the detrimental impact of pitch particles, which enter the paper-making process from virgin or high-yield pulps. Pitch constitutes less than 0.2% of virgin fibre but, due to its colloidal nature, generates millions of potentially tacky particles, per kilo of pulp. Surface tension in the paper machine water circuits plays an influential role in the assessment of potential deposition. In soft water locations, where conductivities are low, the surface tension approaches that of pure water (> 72 mN/m). In these circumstances, there is very little dispersing force between pitch particles, resulting in a strong tendency to agglomerate. Larger pitch agglomerates readily adhere to other hydrophobic surfaces, such as machine fabrics. Traditionally, the use of anionic surfactants has provided sufficient dispersing power to maintain the separation of pitch particles. This approach, however, is only valid if there is sufficient conductivity or water hardness in the system, to suppress repulsion from the electrical double layer. Ironically, the cleaner the water circuits, the higher the tendency for deposition. This paper reports on the progress of a development project, designed to manufacture a deposit control product with strong performance in soft water systems. Archroma has recently entered the trial phase of Cartaspers? PLH Liquid, with encouraging results. Targeted primarily at the pulping sector, the product is able to replace both inorganic absorbents and pitch dispersants, leading to significant cost savings. Many pulp mills are engaged in energy-saving initiatives, which may compromise the levels of extractives in the finished pulp. Enhancing the removal efficiency of pitch and associated contaminants, with the application of Cartaspers? PLH, facilitates lower energy consumption whilst maintaining pulp quality. New opportunities in paper mills are also being pursued. Blending virgin and recycled fibre creates a troublesome cocktail of pitch and stickies which, in soft water environments, increases the tendency for deposition.