Suspension yield stress and the dynamic response of agitated pulp chests

TitleSuspension yield stress and the dynamic response of agitated pulp chests
Publication TypeJournal Article
Year of Publication2005
AuthorsEin-Mozaffari, F., C. P. J. Bennington, and G. A. Dumont
JournalChemical Engineering Science
Volume60
Pagination2399–2408
ISSN0009-2509
Abstract

Agitated pulp chests act as low-pass filters attenuating high-frequency variability and thus complimenting the action of control loops which attenuate slow disturbances. Dynamic tests made on industrial and scale-model chests show that non-ideal flows, including short-circuiting. recirculation, and dead zones, are common and significantly reduce the ability of the chest to attenuate fluctuations. In this paper, we explore the effect of suspension yield stress on the extent of non-ideal flow and upset attenuation by conducting dynamic tests using two different pulp suspensions: a long-fibred softwood pulp and a shorter-fibred hardwood pulp. Dynamic tests were also made as a function of the fibre mass concentration, with the yield stress used to characterize the dynamic behaviour observed in mixing. It was found that while the yield stress plays a significant role determining the mixing of pulp suspensions, the dynamic behaviour of pulp mixing could not be fully described by yield stress alone. Tests show that when the surface of the cavern created by the impeller approaches the pulp outlet, which was located on the impeller wall, the percentage of short-circuiting approached zero. (c) 2004 Elsevier Ltd. All rights reserved.

URLhttp://dx.doi.org/10.1016/j.ces.2004.11.019
DOI10.1016/j.ces.2004.11.019

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