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Flow Field and Fibre Fractionation Studies in Hydrocyclones
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Hydrocyclones can be used to fractionate fibres according to their papermaking potential. The obtained fractions typically differ in fibre wall thickness and/or degree of fibre treatment. Despite a multitude of potential application scenarios, the process has so far had little commercial success. This is largely explained by the low fractionation efficiency and unfavourable operating characteristics of the process.

The fractionation efficiency of a hydrocyclone is closely related to its flow field. The influence of pulp concentration on the tangential velocity field was therefore studied, by using a self-cleaning pitometer. It was found that the pulp concentration had a strong influence on the tangential velocity. At a feed pulp concentration above 7.5 g/l, the suspension rotated almost as a solid body. As a consequence, the magnitude of radial acceleration and shear stresses decreased dramatically. It is suggested that this is detrimental to the fractionation efficiency.

The radial velocity field was measured using an Ultrasonic Velocity Profiler. The measurements showed that the rotational centre of the flow field did not correspond with the geometrical centre of the hydrocyclone. This displacement caused the tangential velocity component of the vortex to contribute substantially to the measurement result of the radial velocity component.

Based on the findings in respect to the flow field studies, a novel design for a fibre fractionation hydrocyclone was proposed. The flow field inside this hydrocyclone was compared to that in a conventional hydrocyclone. It was found, that high radial acceleration and shear stresses could be maintained in the novel design even at high fibre concentration. The fractionation efficiency of the novel hydrocyclone was characterised in terms of surface roughness difference between fine and coarse fraction. When operated with refined bleached softwood kraft pulp, the novel hydrocyclone could produce fractions with a substantial surface roughness difference without deteriorating the dewatering characteristics of the fine fraction. A low thickening of the reject is proposed to be the explanation for that. When fractionating TMP, the best efficiency occurred at a concentration of 10 g/l.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:40
Keyword [en]
Fibre suspension, fractionation, hydrocyclone, measurement technique, velocity measurement, shear forces
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-4175OAI: oai:DiVA.org:kth-4175DiVA: diva2:11075
Public defence
2006-12-01, STFI-salen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 10:10
Opponent
Supervisors
Note
QC 20100804Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
List of papers
1. Literature review of experimental hydrocyclone flow field studies
Open this publication in new window or tab >>Literature review of experimental hydrocyclone flow field studies
2007 (English)In: Separation and Purification Technology, ISSN 1383-5866, Vol. 53, no 1, 8-20 p.Article in journal (Refereed) Published
Abstract [en]

The complex flow field of hydrocyclones has been experimentally investigated on several occasions. Most studies present similar results for the tangential velocity component. In the inner part of the cyclone, it resembles a solid-body rotation, while it typically has a free-vortex-like behavior in the outer part. When looking at the axial velocity component, the results are more diversified. Most studies show a downward velocity close to the wall and an upward velocity in the center. However, some studies report a heavily varying axial velocity over short radii close to the centerline. The radial velocity component appears to be the most problematic one to measure. Dissimilarities in measurement results between the studies are often greater than similarities. However, later studies agree on an increasing inward radial velocity towards the hydrocyclone center. Despite the obvious relationship, extremely little experimental research work can be found in the literature where changes to the flow field are connected to changes in separation efficiency.

Keyword
Hydrocyclones; Measurement techniques; Fluid mechanics
National Category
Mathematics
Identifiers
urn:nbn:se:kth:diva-6374 (URN)10.1016/j.seppur.2006.09.019 (DOI)000243881600002 ()
Note
QC 20100701Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
2. Application of a pitometer to measure the tangential velocity in a cylindrical through-flow hydrocyclone operated with a fiber suspension
Open this publication in new window or tab >>Application of a pitometer to measure the tangential velocity in a cylindrical through-flow hydrocyclone operated with a fiber suspension
2005 (English)In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 20, no 1, 30-35 p.Article in journal (Refereed) Published
Abstract [en]

This investigation evaluates a novel fluid velocity measurement method to measure the tangential velocity in a hydrocyclone. The hydrocyclone was operated with an opaque fiber suspension in order to investigate the influence of fiber presence on the tangential velocity distribution. The tangential velocity was measured with a one-hole pitometer, 0.9 mm in diameter, that was equipped with a micro pressure transducer. The pitometer was kept clean with a continuous purge flow. The probe was tested in a cylindrical through-flow hydrocyclone operated with water and 0.4 g/l and 0.8 g/l (0 %, 0.04 % and 0.08 %) addition of a bleached softwood kraft pulp. The velocity profiles measured in pure water agreed qualitatively with velocity distributions that are found in the literature. The outer section had a free vortex-like distribution and the inner section had a solid body rotation. The addition of small amounts of fibers changed the tangential velocity profile significantly. The radius of solid body rotation increased, the maximum tangential velocity decreased and the transition from solid body rotation to free vortex rotation was smoothened.

Keyword
fiber suspension; hydrocyclone; measurement technique; velocity measurement
National Category
Mathematics
Identifiers
urn:nbn:se:kth:diva-6375 (URN)000228457000005 ()
Note
QC 20100701Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
3. Tangential velocity measurements in a conical hydrocyclone operated with a fibre suspension
Open this publication in new window or tab >>Tangential velocity measurements in a conical hydrocyclone operated with a fibre suspension
2007 (English)In: Minerals Engineering, ISSN 0892-6875, Vol. 20, no 4, 407-413 p.Article in journal (Refereed) Published
Abstract [en]

The tangential velocity flow field in a conical hydrocyclone was measured using a self-cleaning pitometer. The influence of pulp fibre concentration on the tangential velocity profile was of particular interest.

The measurement, showed that the pulp fibres had a strong influence on the tangential velocity profile. When operating the hydrocyclone with pure water, the velocity profile showed the typical combination of free-vortex-like rotation close to the hydrocyclone wall and solid-body-like rotation in the proximity of the hydrocyclone axis. This profile changed significantly when pulp fibres were added. At a low fibre concentration (1.2 g/l), the fibres smoothened the transition between the free-vortex-like and the solid-body-like region of the velocity profile. The location of the maximum tangential velocity moved to a larger radius. At higher fibre concentration (7.5 and 11 g/l), the free-vortex-like behaviour in the outer area was virtually suppressed. Due to networking, the fibre suspension in the entire hydrocyclone behaved as a solid body.

The radial acceleration profile and tangential rate-of-strain profile were determined. Based on these profiles, a hypothesis was proposed explaining the well-known observation that fractionation efficiency decreases significantly at higher fibre concentrations.

Keyword
hydrocyclones; shear forces
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6376 (URN)10.1016/j.mineng.2006.09.008 (DOI)000245938600013 ()
Note
QC 20100701Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
4. Measurement of the radial velocity in a cylindrical through-flow hydrocyclone
Open this publication in new window or tab >>Measurement of the radial velocity in a cylindrical through-flow hydrocyclone
2006 (English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6377 (URN)
Note
QS 20120316Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2012-03-16Bibliographically approved
5. Review of practical methods for the quantitative evaluation of fibre fractionation
Open this publication in new window or tab >>Review of practical methods for the quantitative evaluation of fibre fractionation
Show others...
2005 (English)In: Ecotarget Technical DeliverableArticle in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6378 (URN)
Note
QC 20100804Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
6. Method for fractionating an aqueous paper fibre suspension and hydrocyclone for carrying out said method
Open this publication in new window or tab >>Method for fractionating an aqueous paper fibre suspension and hydrocyclone for carrying out said method
Show others...
2008 (English)Patent (Other (popular science, discussion, etc.))
Abstract [en]

The invention relates to a method and to a device which is used to fraction aqueous paper fibre suspensions (S). Relatively large centrifugal forces are used, also in suspension components having essentially the same densities, in order to achieve good results. This is achieved by virtue of the fact that the paper fibre suspension (S) entering via the inlet (10) is guided initially in a first annular chamber (4) which narrows in an axial direction (4) and subsequently in a second annular chamber (5) which widens in an axial direction. As a result, good fractionating results can be obtained, in particular, when the fibre material consistency in the inlet area is approximately 0.5 - 2 % and also the necessary mass fluxes are maintained at a relatively low level. Said method can be used, for example, for fractionating fresh cellulose and/or wood pulp. It can also be used in the preparation of used paper, wherein said method is particularly economical.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6379 (URN)
Patent
EP 1799903B1 (2008-12-03)
Note

QC 20170615

Expired

Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2017-06-15Bibliographically approved
7. Evaluation of a novel fibre fractionation hydrocyclone
Open this publication in new window or tab >>Evaluation of a novel fibre fractionation hydrocyclone
2006 (English)Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6380 (URN)
Note
QS 20120316Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2012-03-16Bibliographically approved

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