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Vacuum Dewatering of Cellulosic Materials: New insights into transport phenomena in the papermaking process
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [en]

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.

Place, publisher, year, edition, pages
Karlstads universitet, 2020. , p. 105
Series
Karlstad University Studies, ISSN 1403-8099 ; 2020:4
Keywords [en]
Vacuum dewatering, numerical model, water removal, air penetration, papermaking, microfibrillated cellulose, dialcohol cellulose, strength additives, retention aids, drainage, water retention value
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-75958ISBN: 978-91-7867-076-5 (print)ISBN: 978-91-7867-086-4 (electronic)OAI: oai:DiVA.org:kau-75958DiVA, id: diva2:1378560
Public defence
2020-02-07, 9C203, Nyquistsalen, 10:15 (English)
Opponent
Supervisors
Available from: 2020-01-16 Created: 2019-12-13 Last updated: 2020-01-16Bibliographically approved
List of papers
1. Rewetting after high vacuum suction boxes in a pilot paper machine
Open this publication in new window or tab >>Rewetting after high vacuum suction boxes in a pilot paper machine
2015 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 667-672Article in journal (Refereed) Published
Abstract [en]

Increased energy efficiency is a major concern for all companies today. Not only does the cost efficiency follow energy efficiency but also environmental and sustainability aspects motivate more energy efficient production lines. A study has been made on a pilot paper machine with the purpose to show the magnitude and time of rewetting after high vacuum suction box dewatering. The grammages used in this study were 20 and 100 g/m2 to cover both tissue and printing paper grades. Machine speed was varied from 400 to 1600 m/min and the maximum pressure drop in the suction box was 32 kPa. The pulp used was unbeaten, chemical, fully bleached softwood from Sweden. Rewetting is observed when the dewatering in the suction box is sufficiently high. No rewetting takes place when the dewatering in the suction box is limited due to insufficient pressure drop and dwell time. The time for the rewetting is in the range of 10-50 ms and in this study the maximum rewetting observed is 180 g/m2, or 6.1% decrease in dryness. The mechanisms behind the phenomenon are believed to be capillary forces caused by sufficiently low sheet moisture and expansion of the network. This study shows that rewetting is so fast that it would be difficult to prevent it without changing major machine parameters.

Place, publisher, year, edition, pages
AB SVENSK PAPPERSTIDNING, Sweden, 2015
Keywords
Energy efficiency, Forming fabric, High vacuum, Paper forming, Pilot study, Rewetting, Suction box dewatering
National Category
Paper, Pulp and Fiber Technology
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-46408 (URN)10.3183/NPPRJ-2015-30-04-p667-672 (DOI)000366040300015 ()
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2019-12-13Bibliographically approved
2. Modeling the influence of forming fabric structure influence on vacuum box dewatering
Open this publication in new window or tab >>Modeling the influence of forming fabric structure influence on vacuum box dewatering
2017 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 16, no 8, p. 477-483Article in journal (Refereed) Published
Abstract [en]

This investigation used numerical models to describe forming section sheet dewatering at the high vacuum suction boxes. Three different fabric structures were examined with numerical models for single-phase flow of air and for two-phase flow of air and water. This was done to evaluate how forming fabric structure influences sheet dewatering. The numerical models were compared with an experimental study of the same fabrics investigated on a laboratory suction box. The small differences in dewatering rate in the experimental study could be simulated with the models, which confirmed the validity of the models. This implies that these numerical models can be used to describe new fabrics and how they will respond in the papermaking process.

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-47598 (URN)000413824000005 ()
Available from: 2017-01-09 Created: 2017-01-09 Last updated: 2020-01-16Bibliographically approved
3. Dewatering properties of low grammage handsheets of softwood kraft pulps modified to minimize the need for refining
Open this publication in new window or tab >>Dewatering properties of low grammage handsheets of softwood kraft pulps modified to minimize the need for refining
2018 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 397-403Article in journal (Refereed) Published
Abstract [en]

Previous paper (Rahman et al. 2017) showed that the yield of softwood kraft pulp increased by the addition of either polysulfide or sodium borohydride because of higher hemicellulose retention. An increase in hemicellulose content can make dewatering more difficult as WRV of the pulp increases, but instead, an overall increase in pulp yield could improve dewatering as a sheet of a certain weight will contain fewer fibres, giving a more open sheet structure. It was therefore of interest to measure the dewatering properties of low grammage handsheets (20 g/m2) under conditions mimicking the tissue paper machine dewatering processes, and sheet strength properties, WRV, °SR and fibre dimensions were also studied. The results showed that the positive influence of overall yield increase dominated over the negative influence of an increase in hemicellulose content on the dewatering properties, particularly at lower refining energy levels. Moreover, higher yield and higher hemicellulose content pulps had a higher tensile index at the same dryness. A given tensile index was achieved with less refining energy. The results indicate that increased yield and hemicellulose content by modification of the kraft pulping process will result in a pulp with a potential to improve tissue paper quality.

Place, publisher, year, edition, pages
De Gruyter Open Ltd, 2018
Keywords
dwell time, hemicellulose, refining, solid content, suction box dewatering, tensile index, thermoporosimetry, water retention value, Cellulose, Dewatering, Kraft pulp, Paper products, Papermaking machinery, Sodium Borohydride, Softwoods, Tissue, Water content, Solid contents, Suction box, Pulp refining
National Category
Chemical Engineering Paper, Pulp and Fiber Technology
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-69226 (URN)10.1515/npprj-2018-3037 (DOI)000450923900005 ()2-s2.0-85052642839 (Scopus ID)
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2019-12-13Bibliographically approved
4. Dewatering of Softwood Kraft Pulp with Additives of Microfibrillated Cellulose and Dialcohol Cellulose
Open this publication in new window or tab >>Dewatering of Softwood Kraft Pulp with Additives of Microfibrillated Cellulose and Dialcohol Cellulose
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 3, p. 6370-6383Article in journal (Refereed) Published
Abstract [en]

The addition of nano-and micro-fibrillated cellulose to conventional softwood Kraft pulps can enhance the product performance by increasing the strength properties and enabling the use of less raw material for a given product performance. However, dewatering is a major problem when implementing these materials to conventional paper grades because of their high water retention capacity. This study investigated how vacuum dewatering is affected by different types of additives. The hypothesis was that different types of pulp additions behave differently during a process like vacuum suction, even when the different additions have the same water retention value. One reference pulp and three additives were used in a laboratory-scaled experimental study of high vacuum suction box dewatering. The results suggested that there was a linear relationship between the water retention value and how much water that could be removed with vacuum dewatering. However, the linear relationship was dependent upon the pulp type and the additives. Additions of micro-fibrillated cellulose and dialcohol cellulose to the stock led to dewatering behaviors that suggested their addition in existing full-scale production plants can be accomplished without a major redesign of the wire or high vacuum section.

Place, publisher, year, edition, pages
NORTH CAROLINA STATE UNIV DEPT WOOD & PAPER SCI, 2019
Keywords
Vacuum dewatering, Dewatering, Microfibrillated cellulose, Dialcohol cellulose, Papermaking, Strength additives, Retention aids, Drainage, Water retention value
National Category
Chemical Engineering
Research subject
Chemical Engineering; Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-74224 (URN)10.15376/biores.14.3.6370-6383 (DOI)000473204700100 ()
Available from: 2019-08-06 Created: 2019-08-06 Last updated: 2019-12-19Bibliographically approved
5. Numerical model of water removal and air penetration during vacuum dewatering
Open this publication in new window or tab >>Numerical model of water removal and air penetration during vacuum dewatering
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-75959 (URN)
Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2019-12-13

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