Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
On Suction Box Dewatering Mechanisms
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In previous studies on suction box dewatering, three mechanisms were identified that determine the dry content of a web, viz. web compression, displacement of water by air and rewetting. In the present work, the relative importance of the three mechanisms was investigated through direct measurement of the web deformation, the dry content changes during and after the suction pulse, the air flow through the fibre network and the saturation of the web after the suction pulse. Suction pressure, suction time and rewetting time were varied. The experiments were done with chemical and mechanical pulp webs of various grammages.

It was found that a large web deformation took place during the suction pulse, particularly at its beginning. Compression dewatering was found to be the most dominant dewatering mechanism. Displacement dewatering started after most of the web compression had occurred. Its contribution to the increase in dry content was most pronounced for higher suction pressures, longer suction times and for chemical pulp webs.

A surprisingly large expansion of the web was observed immediately after the suction pulse. This expansion was the effect of rewetting. This rewetting strongly reduced the dry content of the web if the web had not been immediately separated from the forming fabric at the end of the suction pulse. Under the conditions studied, the decrease in dry content amounted to the order of 3 to 6 %. Rewetting was smaller for longer suction times and higher suction pressures. A considerable air flow through the web occurred under these conditions. This air flow apparently moved water from the forming fabric into the suction box, thus making less water available for rewetting. Rewetting for mechanical pulp webs was more pronounced and took place faster than for chemical pulps.

The use of a membrane on top of the web during suction box dewatering proved to be advantageous for reducing the air flow through the web. However, under the conditions investigated, the dry content could not be improved. Although the web compression was increased when using a membrane, especially at a higher suction pressure, rewetting after the suction pulse had an even larger negative impact on the dry content, which, as a result, was lower.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , viii, 43 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:38
Keyword [en]
Suction box, vacuum, water removal, compressibility, displacement, rewetting, laboratory equipment
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-4780ISBN: 978-91-7178-974-7 (print)OAI: oai:DiVA.org:kth-4780DiVA: diva2:13918
Public defence
2008-06-04, STFI-salen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100924Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
List of papers
1. Dewatering mechanisms and their influence on suction box dewatering processes: A literature review
Open this publication in new window or tab >>Dewatering mechanisms and their influence on suction box dewatering processes: A literature review
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 4, 389-397 p.Article in journal (Refereed) Published
Abstract [en]

This review summarizes the present knowledge of suction box dewatering mechanisms. In addition, existing and novel suction box dewatering processes are described for applications in the pulp and paper industry.

Three mechanisms that determine the dry content of the web after suction box dewatering are identified, viz. web compression, displacement of water by air, and rewetting. Earlier work focused mainly on the influence of web properties and process parameters for the achievable dry content. That work did not give any information concerning the relative importance of the three mechanisms. There was no measurement of web compression or water displacement. Furthermore, the occurrence of rewetting was neglected by many researchers. A deeper knowledge and, above all, direct measurements are required to better describe suction box dewatering.

Some interesting modified suction box dewatering processes were presented in the literature, For example, the use of a membrane on top of the web during dewatering is believed to have the potential for an increase in dry content and energy savings. This increase in dry content is consequently believed to be a result of an increase in web compression.

Keyword
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8555 (URN)10.3183/NPPRJ-2008-23-04-p389-397 (DOI)000262102700006 ()
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
2. Method for studying the deformation of a fibre web during a suction pulse
Open this publication in new window or tab >>Method for studying the deformation of a fibre web during a suction pulse
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 4, 398-402 p.Article in journal (Refereed) Published
Abstract [en]

A laboratory suction box was built to study the dynamic thickness deformation of a fibre web during a suction pulse. Both the pressure in the suction box and the duration of the suction pulse are adjustable in ranges of 0 to -40 kPa and 50 ms to 10 s, respectively During and after the suction pulse, the web thickness and the suction pressures can be measured. Furthermore, the air flow through the web can be calculated after the experiment.

The first evaluation of the performance of the laboratory suction box shows that the web is considerably compressed, especially during the initial phase of the suction pulse. This indicates that web compression is an important dewatering mechanism. After the suction pulse, a rapid and significant web expansion was observed, implying that considerable rewetting probably occurs.

Keyword
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting, Laboratory apparatus
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8556 (URN)10.3183/NPPRJ-2008-23-04-p398-402 (DOI)000262102700007 ()
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
3. The deformation of chemical and mechanical pulp webs during suction box dewatering
Open this publication in new window or tab >>The deformation of chemical and mechanical pulp webs during suction box dewatering
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 4, 403-408 p.Article in journal (Refereed) Published
Abstract [en]

The deformation of the paper web during and after a suction pulse on initially saturated fibre web made of chemical and mechanical pulp was investigated. A laboratory suction box was used, where the suction time and pressure drop could be varied and controlled. During the experiments, the web thickness, the air flow through the web and the suction pressure were recorded and after the experiments, the dry content of the web was determined.

A large deformation was observed when the suction pulse was applied. After the suction pulse, a considerable expansion of the web took place, probably an effect of rewetting. The compression of the web appeared to be the most important dewatering mechanism increasing the dry content of the web. However, if the web is not separated from the forming fabric, rewetting after the suction pulse will greatly reduce the dry content.

Keyword
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8557 (URN)10.3183/NPPRJ-2008-23-04-p403-408 (DOI)000262102700008 ()
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
4. External rewetting after suction box dewatering
Open this publication in new window or tab >>External rewetting after suction box dewatering
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 4, 409-414 p.Article in journal (Refereed) Published
Abstract [en]

A method has been developed to enable external rewetting to be measured during suction box dewatering. In a laboratory suction box, webs were instantaneously separated from the forming fabric at defined times, both during and after the suction pulse. External rewetting was measured for webs of mechanical (50, 100 g/m(2)) and chemical pulp (100, 200 g/m(2)). Suction pulses with a pressure drop of 10 and 40 kPa, and duration of 50 to 1000 ms were used. A considerable external rewetting was observed occurring primarily directly after the end of the suction pulse. Under the process conditions investigated, rewetting accounted for a dry content decrease of between 3 and 6%.

Keyword
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting, Forming fabric, Laboratory equipment
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8558 (URN)10.3183/NPPRJ-2008-23-04-p409-414 (DOI)000262102700009 ()
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
5. Evaluation of membrane-assisted dewatering on a pilot paper machine
Open this publication in new window or tab >>Evaluation of membrane-assisted dewatering on a pilot paper machine
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 2, 152-155 p.Article in journal (Refereed) Published
Abstract [en]

A membrane-assisted dewatering process was evaluated on a pilot paper machine. In this process, a membrane is located on top of the wet web when it passes over the suction box in the forming section. The intentions are twofold. Firstly, the dry content of the web should be increased by a more uniform compression, primarily in the thickness direction. Secondly, the airflow into the suction box should be reduced. The trials were performed using a specially designed membrane loop located at the end of the fourdrinier forming section of STFI-Packforsk's pilot paper machine EuroFEX. Two different membranes were tested. The use of a membrane resulted in a significant decrease in air consumption to achieve the same dry content of the web at the end of the wire section. To increase the dry content of the web, the structure of the membrane is important.

Keyword
suction box, vacuum, dewatering, compression, displacement, rewetting
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8559 (URN)10.3183/NPPRJ-2008-23-02-p152-155 (DOI)000258174600001 ()
Note
QC 20100924. Uppdaterad från accepted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
6. Web deformation during membrane-assisted dewatering
Open this publication in new window or tab >>Web deformation during membrane-assisted dewatering
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 4, 415-419 p.Article in journal (Refereed) Published
Abstract [en]

The potential of membrane-assisted dewatering was evaluated on a laboratory suction box. Different membranes, one impermeable and two permeable membranes were placed on top of the wet web, while a suction pulse was exerted underneath the web. The deformation of the wet web and the dry content of the web were determined approx. 30 seconds after the suction pulse. The results of these experiments were compared with results of those carried out without a membrane.

A significantly higher web compression was observed at the end of the suction pulse when a membrane was used. The increased web compression that occurred when using a membrane corresponded to a dry content of 3 to 4%. The highest dry content values were obtained, however, when no membrane was applied. This contradiction was interpreted as a higher rewetting after the suction pulse when a membrane was used. Here, due to the reduced air flow through both the web and the forming fabric, it is likely that more water was available in the forming fabric for rewetting. Apparently, the air flow removed water from the forming fabric that otherwise would have been rewetted by the web.

Keyword
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting, Laboratory apparatus
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8560 (URN)10.3183/NPPRJ-2008-23-04-p415-419 (DOI)000262102700010 ()
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved
7. Vorrichtung zur Entwässerung einer Faserstoffbahn
Open this publication in new window or tab >>Vorrichtung zur Entwässerung einer Faserstoffbahn
(English)Article in journal (Refereed) Submitted
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8561 (URN)
Note
QC 20100924. Patent application DE 10 2006 017 974 A1Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically approved

Open Access in DiVA

fulltext(925 kB)7111 downloads
File information
File name FULLTEXT01.pdfFile size 925 kBChecksum MD5
44cabac3a353c4d0aae43761c8a665a57f6af933cd4c19c0e6ccf948c7a616079a2ff5e3
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Åslund, Peter
By organisation
Fibre and Polymer Technology
Paper, Pulp and Fiber Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 7111 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 718 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf