The results indicate that the new vacuum dewatering model for moisture can predict the dewatering behavior for several different experimental data series both from laboratory equipment and a pilot paper machine using the same set of fitting parameters. The aims of this study were to find new fitting parameters that allows the previous model to be used for vacuum dewatering instead of pressing, and to examine two extensions to the original model. A previ- ously published numerical model for wet pressing is used as the basis for this work. The work was mainly numerical and was based on, and compared with, previously published experimental results of vacuum dewatering from laboratory equipment and from a pilot paper machine. 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.Äewatering and air flow in high vacuum suction boxes was examined. 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. 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. A brief background of the papermaking process is presented, along with useful numerical models used previously in that particular context.
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. Aspects of how rewetting, the structure of the forming fabric and additives of cellulosic materials affect vacuum dewatering are discussed in detail throughout. 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. 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. Huge amounts of energy are used during paper manufacturing so there is a potential for making the processes more energy-efficient. 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. Ways to overcome such effects are also reviewed. Published findings support a hypothesis that dewatering rates can be decreased by densification of surface layers, plugging of drainage channels by fines, sealing effects, flocculation, and rewetting. The scope of this review includes all of the papermaking unit operations between the jet coming from the headbox and the final wet-press nip of an industrial-scale paper machine.
The goal of this article is to review published work dealing both with the concepts involved in water removal and evidence upon which existing and new theories can be based. In addition, energy can be saved, reducing environmental impacts. In principle, a fuller understanding of the controlling mechanisms, based on evidence, should permit progress in achieving both higher rates of production of paper and more reliable control of paper attributes. Because some of the critical events during the removal of water before the dryer section on a paper machine happen very rapidly within enclosed spaces-such as wet-press nips-there have been persistent challenges in understanding the governing mechanisms.