Deposit control in the paper industry : Results from Skogn mill

To evaluate the formation of deposits in a full-scale papermaking system, metal coupons can be placed in the system and later evaluated with advanced microscopic methods, e.g. SEM with EDX or CSLM. The information gained can be used to evaluate the efficiency of the various wet-end additives, e.g. biocides, dispersants, fixatives or antiscalants. Results from Norske Skog Skogn show that : it is possible to maintain high efficiency in the papermaking process without the use of biocides. The deposits cannot be considered uniform throughout the circulating system. The deposits vary at different levels within tanks giving rise to variations in the system. The concentration of microbes in different streams can be affected by their physical size and the PM equipment used. There is a range of chemicals to control the different types of deposition found in most systems. Steel coupons inserted in the system can be used to evaluate deposit formation. Biocides do not prevent formation of deposits ; they only reduce the total concentration of bacteria. A multi-functional dispersant can provide stability in a system prone to variations. Deposit Control Systems have to be designed taking a holistic view of the paper making process.