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Dewatering mechanisms and their influence on suction box dewatering processes: A literature review
STFI-Packforsk AB.
STFI-Packforsk AB.
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.

Place, publisher, year, edition, pages
2008. Vol. 23, no 4, 389-397 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-8555DOI: 10.3183/NPPRJ-2008-23-04-p389-397ISI: 000262102700006OAI: oai:DiVA.org:kth-8555DiVA: diva2:13911
Note
QC 20100924. Uppdaterad från submitted till published (20100924).Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-24Bibliographically 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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