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The deformation of chemical and mechanical pulp webs during suction box dewatering
STFI-Packforsk AB.
STFI-Packforsk AB.
STFI-Packforsk AB.
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, 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.

Place, publisher, year, edition, pages
2008. Vol. 23, no 4, 403-408 p.
Keyword [en]
Suction box, Vacuum, Water removal, Compression, Displacement, Rewetting
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-8557DOI: 10.3183/NPPRJ-2008-23-04-p403-408ISI: 000262102700008OAI: oai:DiVA.org:kth-8557DiVA: diva2:13913
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2017-12-14Bibliographically approved
In thesis
1. On Suction Box Dewatering Mechanisms
Open this publication in new window or tab >>On Suction Box Dewatering Mechanisms
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
Suction box, vacuum, water removal, compressibility, displacement, rewetting, laboratory equipment
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-4780 (URN)978-91-7178-974-7 (ISBN)
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

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Åslund, PeterVomhoff, HannesWaljanson, Alexander
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