Home » Volume 27, 2012 » Issue No. 5
Evaluation of furnishes for tissue manufacturing; wet pressing
Johan Kullander, Lars Nilsson and Christophe Barbier
Wet pressing is the last operation on the tissue machine in which water can be removed prior to the expensive evaporative drying of the web. An increase in dryness at this stage can lead to major savings during the manufacturing process. A higher solids content can be achieved by suitable selection of raw materials and by optimizing the treatment of the fibres in the furnish. In this work, wet pressing was evaluated with four pulps beaten to different levels in a PFI mill. Wet pressing was done in a dynamic press simulator and conditions representative of tissue machines with regard to nip pressures and dwell times were chosen. Water retention and thermoporosimetry were used to determine the pore structure of the fibres. Thickness measurements were made to determine the permanent deformation of the sheets after the pressure pulse.
Wet pressing in tissue manufacturing is shown to be affected by the choice of pulp, which can be explained by differences in pore structure of the fibres and consequently differences in ability to retain water. More water available before pressing leads to more water that can be removed. Beating has a negative impact on the solids contents reached after pressing, which is believed to be an effect of both internal and external fibrillation. These effects of beating seem mainly to affect the dryness after vacuum dewatering, which is also reflected after pressing. Beating delaminates macropores in the fibre wall but has a minor effect on micropores. Both water between the fibres and water in macropores are removed during pressing. These results give knowledge of how the furnish should be prepared in order to reduce energy consumption in the process.
Beating, Pore structure, Solids content, Thermoporosimetry, Tissue, Water removal, Water retention value, Wet pressing
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Evaluation of furnishes for tissue manufacturing; wet pressing (2012-27-05-p947-951-Kullander.pdf)