The underlying motives of the research undertaken here are twofold: to obtain a deeper understanding of the dewatering mechanisms at the forming section of a papermaking machine and to develop numerical models that describe the flow through forming fabrics. More comprehensive knowledge of dewatering in the forming section allows suggestions to be made for improvements that reduce the amount of energy used in the process without affecting the quality of the end product.

The objective of this thesis is to answer the following questions:

• How and why does rewetting occur at the high vacuum suction boxes?
• How does the structure of the forming fabric affect dewatering at the forming section?
• Is it possible to create accurate numerical models for forming fabrics, and can these be used to predict the dewatering behaviour of new types of fabrics?

Laboratory and pilot studies simulating high vacuum suction boxes were performed together with numerical modelling of the flow of air and water through both the forming fabric and the paper sheet.

The conclusion drawn from the pilot study is that rewetting significantly lowers the dryness of the paper sheet exiting the suction boxes. The phenomenon is extremely rapid and is most likely driven by capillary forces. The high speed at which this rewetting occurs makes it difficult to impede by placing the suction boxes closer to the couch pick-up: the solution is more likely to be the use of new and improved designs of the forming fabric. The structure of the forming fabric has been shown to affect the dewatering rate at certain conditions of vacuum dewatering, and can possibly be connected partly to the fact that fibres penetrate the surface of the fabric to varying degrees and partly to the flow resistance of the different fabric structures. Numerical models of high accuracy can be constructed and used to predetermine how new fabric designs would affect dewatering at the forming section.

This thesis quantifies aspects of dewatering such as rewetting and the influence of the forming fabric. Understanding these dewatering aspects further provides for the potential enhancement of energy efficiency in the forming section, and thereby the entire papermaking process. The forming fabric can play an important role in improving energy efficiency: rewetting after the high vacuum suction boxes occurs more rapidly than was previously known, so its design might be the only possible way of impeding it. The forming fabric can also improve the rate of dewatering: it is therefore likely that its design will be important in the next stage of developing energy efficiency and thereby play a part in achieving a more sustainable future.

This thesis quantifies aspects of dewatering such as rewetting and the influence of the forming fabric. Understanding these dewatering aspects further provides for the potential enhancement of energy efficiency in the forming section, and thereby the entire papermaking process. The forming fabric can play an important role in improving energy efficiency: rewetting after the high vacuum suction boxes occurs more rapidly than was previously known, so its design might be the only possible way of impeding it. The forming fabric can also improve the rate of dewatering: it is therefore likely that its design will be important in the next stage of developing energy efficiency and thereby play a part in achieving a more sustainable future.

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.

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. 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.