ANALYSIS OF WEB BREAKS AND STICKIES IN A NEWSPRINT MILL USING RECOVERED PAPER

With the increasing utilisation of recycled fibre and the rising efficiency requirements, a better understanding on the factors contributing to web breaks on the paper machine is needed. Stickies are a common problem in paper mills using recycled paper and they are known to negatively affect both the runnability and the product quality. A follow-up study was conducted in a newsprint mill covering both the deinking plant and the newsprint paper machine. In this study, the effects of different factors on the occurrence of macro and THF-soluble stickies and their interrelationship with the number of dark spots in paper and web breaks on the paper machine were examined. Data containing 90 different factors were collected for a one-month period either on a shift or daily basis. A PLS (projection to latent structures) multivariate data analysis was carried out for the data collected from the fibre line. The results showed that most (57%) of the web breaks occurred at the press section and early part of the drying section. This means that wet web properties should be studied more closely when reducing the number of web breaks. The raw material composition was clearly related to the number of web breaks and the resulting shutdown time. The amount of THF-soluble stickies in the headbox furnish showed a clear correlation with the shutdown time caused by web breaks. However, although the amount of macro stickies is typically used for monitoring the efficiency of stickies reduction, they had no correlation with the total amount of THF-soluble stickies. In addition, the shutdown time caused by web breaks correlated with increasing air content in white water, ratio of different raw materials, temperature of pulp in DIP plant and strength of the paper. The number of black spots in the final paper did not correlate with the web breaks or with the amount of macro- or THF-soluble stickies but had a clear connection with the parameters used during flotation. Based on this, it was concluded that black spots are merely due to the residual ink and their agglomeration.