Dynamic modeling of agitated pulp stock chests

TitleDynamic modeling of agitated pulp stock chests
Publication TypeJournal Article
Year of Publication2003
AuthorsEin-Mozaffari, F., L. C. Kammer, G. A. Dumont, and C. P. J. Bennington
JournalTAPPI Journal

The chief purpose of agitated pulp stock chests is to reduce high-frequency variability in mass concentration, freeness, and other quality factors. These chests behave as low-pass filters to complement the action of control loops, which only control low-frequency variability. Dynamic tests made on industrial and scale-model stock chests show non-ideal flows such as channeling, recirculation, and stagnant zones. These flows reduce the degree of upset attenuation at frequencies higher than the cut-off frequencies of paper machine control loops. We have developed a dynamic model of agitated pulp stock chests, incorporating these non-ideal flows. In this paper, we explore the excitation design required to estimate the model parameters and the effect of process variables on disturbance attenuation. The variables examined include the impeller speed, pulp feed and exit location, fiber mass concentration (consistency), and pulp flow rate through the chest. Test results show that the location of the input and output in the chest significantly affects the percentage of channeling and the degree of disturbance attenuation. We found that at higher pulp flow rates through the chest and fiber mass concentration greater than 3% the system is prone to a high percentage of channeling and a low degree of upset attenuation.

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