This master thesis provides an overview of the paper machine with focus on the forming section. The forming section is the first part in the paper machine where the paper pulp is injected through a head box. The paper pulp contains about 99.5% of water and 0.5% fiber. The water as content is reduced by vacuum and gravity. The problem to be studied in this project is related to external rewetting. This is water going back to the paper web from the forming fabric after the dewatering zone. The dewatering is based on vacuum slots under the forming fabric. The vacuum slots absorb water from the soaked paper pulp through the forming fabric. External rewetting causes problem, hence the paper will have a higher dry content when leaving the forming section. The paper should have as low dry content as possible in the end of the forming section. Three different forming fabrics from Albany International were chosen for the project. The structures of the forming fabrics were two different double layers and one plain weave. The performance of the fabrics was studied by 4 different methods. The methods used were 2 different wicking tests, a vacuum dewatering trial and one foulard test. Also micro tomography was done to understand the structure of each design. The main test was a foulard test where the aim was to see in what way the rewetting got affected by different pores sizes. The results showed higher water content for the paper that was on top of the forming fabric with the larger pores.

Throughout recent years, computer based programs have been applied to solve and analyse industrial problems encountered global fields such as automobile design for reduction of CO2-gas, designing wind parks aimed at increasing power output etc. One of these developed programs is Computational Fluid Dynamics (CFD) which numerically solves complex flow behaviour based on computer power. As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides. Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand.  These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields. / As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides. Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand.  These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields.

We are provided countless products from the forest industry and has been through many years. Paper, paper board, packaging materials and furniture to mention a few. A special type of paper used in food packaging for example, is greaseproof paper. Many producers of greaseproof papers use the toxic and harmful group of chemicals called per- and polyfluorinated alkyl substances (PFAS) in coating since they possess grease resistance. Nordic Paper is a manufacturer of iamKraft® kraft paper and greaseproof paper with over a hundred years of experience without the use of PFAS. Without PFAS, they instead rely on excess refining to form a very dense paper. Nordic Paper has decided to introduce the addition of eucalyptus fibers to the softwood sulfate pulp to enhance the formation of the paper. This study aims to investigate the effects of ~20% addition of eucalyptus fibers to softwood sulfate pulp in regard to refiner energy expended, air permeance (as a measure of grease resistance) and formation. Laboratory work has been done on hand made sheets with a vacuum suction box in laboratory scale. Eight different pulps (four with addition of eucalyptus), provided from Nordic Paper Seffle AB, Säffle, with different refining degree was used in this study. The vacuum pressure used was 20 kPa through all tests, with dwell times 0, 1, 2.5, 5, 10, and 20 ms on sheets with a grammage of 50 g/m2. The study has shown that the pulp with ~20% addition of eucalyptus achieved 86°SR with only 82% expended energy relative to the softwood pulp, which had a refining degree of 87°SR. This small difference in refining degree led to a similar development in dewatering after 20 ms dwell time and 20 kPa, where the softwood pulp achieved a dryness of 9.2% and the pulp with addition of eucalyptus achieved 9.0% dryness. The formation of the softwood pulp was worse, which was the reason for the implementation of addition of eucalyptus. The air permeance on the other hand was not improved by the eucalyptus, but more data is needed to confirm since it is based on only one occasion. So, if the air permeance (grease resistance) allows, Nordic Paper Seffle AB may be able to save 20% in expended energy for refining of softwood sulfate pulp with addition of eucalyptus. / Vi tillhandahåller otaliga produkter från skogsindustrin och har gjort i många år. Papper, kartong, förpackningsmaterial och möbler för att nämna några. En speciell typ av papper som används i till exempel livsmedelsförpackningar är fettresistent papper. Många tillverkare av dessa papper använder den giftiga och skadliga gruppen av kemikalier som kallas per- och polyfluorerade alkylämnen (PFAS) i beläggning eftersom de har fettbeständiga egenskaper. Nordic Paper är en tillverkare av iamKraft® kraftpapper och ”greaseproofpapper” med över hundra års erfarenhet utan användning av PFAS. Utan PFAS förlitar de sig istället på extra malning av fibrer för att bilda ett mycket tätt papper. Nordic Paper har beslutat att införa tillsats av eukalyptusfibrer till sulfatmassa av barrved för att förbättra formationen på papperet. Denna studie syftar till att undersöka effekterna av ~20 % tillsats av eukalyptusfibrer till barrsvedssulfatmassan med avseende på förbrukad malningsenergi, luftpermeans (som ett mått på fettbeständighet) och formation. Laborationer har utförts på handgjorda ark med vakuumsuglåda i laboratorieskala. Åtta olika massor (fyra med tillsats av eukalyptus), tillhandahållna från Nordic Paper Seffle AB, Säffle, med olika malningsgrad användes i denna studie. Vakuumtrycket som användes var 20 kPa genom alla tester, med uppehållstider 0, 1, 2.5, 5, 10 och 20 ms på ark med en ytvikt på 50 g/m2. Studien har visat att massan med ~20% tillsats av eukalyptus uppnådde 86°SR med endast 82% förbrukad energi i förhållande till sulfatmassan, som hade en malningsgrad på 87°SR. Denna lilla skillnad i malningsgrad ledde till en liknande utveckling i avvattning efter 20 ms uppehållstid och 20 kPa, där sulfatmassan uppnådde en torrhalt på 9.2% och massan med tillsats av eukalyptus uppnådde 9.0% torrhalt. Formationen på sulfatmassan var sämre, vilket var anledningen till genomförandet av tillsats av eukalyptus. Luftpermeansen å andra sidan förbättrades inte av eukalyptusen, men mer data behövs för att bekräfta detta eftersom den enbart är baserad på ett enda tillfälle. Så om luftpermeansen (fettbeständigheten) tillåter kan Nordic Paper Seffle AB spara 20% i förbrukad energi för malning av barrvedssulfatmassa med tillsats av eukalyptus.

Vacuum dewatering of paper is a heavily energy expensive process, even more so for greaseproof paper, which is one of the main products at Nordic Paper Seffle AB. Due to this being such an energy demanding process, improvements in the vacuum dewatering could save massive amounts of energy. The focus of this thesis is to investigate the effect of a triple vacuum suction box on the dewatering rate of greaseproof paper, using a tried and tested method of simulative triple vacuum suction box at a laboratory scale, with the difference of simulating a quadruple vacuum suction box, and how the grammage of the paper sheet affected this, using unbleached sulphate pulp consisting of soft wood with an addition of 20 % eucalyptus fibers. The results were as expected, showing the expected dryness curve behavior of diminishing returns of the dryness to dwell time ratio, and the method showed valid for improving the energy efficiency compared to a single vacuum suction box, in terms of both expended energy, and yielded dryness. The grammage had a significant effect on the dewatering, with the heavier paper at 100 gsm showing the need of higher dwell times and increased levels of vacuum pressure than the lighter paper at 50 gsm. An addition of a triple vacuum suction box could possibly replace multiple high vacuum suction boxes, leading to even greater savings. Further testing would be required for optimization of the vacuum levels and dwell times for the 100 gsm paper sheet, in order to reach the same dryness as the 50 gsm paper sheet. / Vakuumavvattning av papper är en mycket energikrävande process, ännu mer för greaseproofpapper, som är en av huvudprodukterna hos Nordic Paper Seffle AB. Eftersom detta är en så energikrävande process kan förbättringar av vakuumavvattningen spara enorma mängder energi. Fokus för denna avhandling är att undersöka effekten av en trippelvakuumsuglåda på avvattningseffektiviteten av greaseproofpapper, med hjälp av en beprövad metod för simulativ trippelvakuumsuglåda i laboratorieskala, med skillnaden att simulera en fyrdubbelvakuumsuglåda, och hur ytvikten på pappersarket påverkar detta; med oblekt sulfatmassa bestående av långfiber med tillsats av 20 % eukalyptusfibrer. Resultaten var som förväntat och visade den förväntade torrhaltskurvans beteende av avtagande förbättring av torrhalten, och metoden visade sig vara giltig för att förbättra energieffektiviteten jämfört med en enda vakuumsuglåda, både vad gäller förbrukad energi och torrhalt. Ytvikten hade en stor effekt på avvattningen, där det tyngre papperet på 100 gsm visade behov av längre uppehållstider och ökade nivåer av vakuumtryck än det lättare papperet vid 50 gsm. Ett tillägg av en trippelvakuumsuglåda kan troligen ersätta flera högvakuumsugslådor, vilket leder till ännu större besparingar. Ytterligare tester skulle krävas för optimering av vakuumnivåerna och uppehållstiderna för 100 gsm pappersarket, för att nå samma torrhet som 50 gsm pappersarket.

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.