Well functioning wet-end starch : A prerequisite for capacity increase at Smurfit Kappa Piteå

Abstract: Cationic starch is a common wet-end additive in the paper industry which is mainly used to enhance retention and dry strength of the finished paper. At Smurfit Kappa Piteå, cationic starch is by far the most costly chemical used in the paper mill. It is therefore important that the added starch works efficiently, as poor adsorption of starch causes dissolved starch to circulate in the systems. This could cause slime deposits affecting the runnability of the paper machine and other equipment. In the planned production expansion at Smurfit Kappa Piteå during the nearest future, the demand on well-functioning wet-end starch will increase. Through mappings and laboratory studies, the purpose of the present project was to determine the efficiency of the current starch used in the paper mill and to identify any potential for improvements. A method to measure starch content in paper, pulp and white water was implemented to enable the above-mentioned activities to be carried out. As a tool for quality control of cooked starch, a microscopic method was implemented. The method was proven to be a simple and quick tool to verify whether the cooked starch was completely solubilized or not. Mappings at both paper machines were performed where adsorbed and dissolved starch content were analyzed according to the above-mentioned test method. The results showed the highest level of adsorption in the top ply system at PM2 while the base ply systems at both paper machines displayed lower levels. A significant difference of conductivity in pulps as well as furnishes is likely to explain the difference in adsorption efficiency between the systems. High levels of dissolved starch were observed in the top ply system at PM1 despite any use of cationic starch in this system. This is explained by dissolved starch in the white water that originates from other stock preparation systems is introduced via the shared dilution of pulp. A laboratory study was conducted to compare the adsorption of starches with different degree of substitution in pulp suspensions. The electrolyte concentration was adjusted to reflect the conditions in the base ply systems at PM1 and PM2.  Slightly higher adsorption was observed at higher levels of dosage for starch with a higher DS. Based on these values, the use of this product in the base ply systems at PM1 and PM2, could reduce the costs of starch through lowered dosages. A suggestion on how a rebuilding of the starch preparation system could be implemented has been made.