Vacuum Dewatering of Cellulosic Materials : New insights into transport phenomena in the papermaking process

Sammanfattning: Working towards sustainable development within the forest industry, the dewatering of pulp and paper must be fully understood along with the dewatering of other cellulose-based materials. Huge amounts of energy are used during paper manufacturing so there is a potential for making the processes more energy-efficient. This thesis attempts to gain understanding of vacuum dewatering in the forming section of the conventional papermaking process and its connection with energy consumption in order to suggest actions that may be taken not only to improve energy efficiency but also facilitate the introduction of new materials into existing processes.  The main objective of this thesis is to develop a deeper understanding of the vacuum dewatering of forest-based cellulosic materials in existing paper manufacturing processes. Aspects of how rewetting, the structure of the forming fabric and additives of cellulosic materials affect vacuum dewatering are discussed in detail throughout. There is also a large section discussing the use of numerical models and software simulations of dewatering in the forming section of a papermaking machine. A brief background of the papermaking process is presented, along with useful numerical models used previously in that particular context. Three sets of experiments, including rewetting, forming fabrics and additions of cellulosic materials, compose the bulk of the thesis’ method along with two sets of simulations regarding fabrics and additives.   This thesis shows how rewetting is both rapid and substantial after high vacuum suction boxes, the way in which the structure of the forming fabrics affects vacuum dewatering and how additions of micro-fibrillated cellulose and dialcohol cellulose affect vacuum dewatering. The results of the simulations and numerical models show how they can be used to explore ways of saving energy in the process as well as to facilitate the introduction of cellulosic additives into existing papermaking processes.