Multilevel Control of Continuous Digesters—Application and Results

Al-Shaikh, A.; Tu, Feng

doi:10.1016/s1474-6670(17)65948-2

Cited by 3 publications

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“…Whether the chip level should be controlled from the bottom of the digester (Fuchs and Smith 1971), from the top (Fuchs and Single, 1976), or by a combination of both methods (Al-Shaikh and Tu, 1978) is a matter of some controversy. In this study, the control is from the bottom, using either the blow flow or the outlet device (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Self‐tuning control of chip level in a Kamyr digester

Bélanger¹,

Rochon²,

Dumont³

et al. 1986

AIChE Journal

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A study is presented of the application of a self-tuning regulator to the control of the level of wood chips in a Kamyr digester, used in the production of wood pulp. Following an initial phase of experiments and model structure selection, two control schemes were studied, using respectively the blow flow and the outlet device speed as manipulated variables. The approach finally adopted uses the outlet device as the primary control. The control has been in operation for several months and has provided significantly improved control and a high degree of operator acceptance. G. A. DUMONT SCOPEThe objective of this study is to improve the control of the chip level in a Kamyr digester. Good level control is necessary for steady operation of the digester. It is difficult to achieve because chip level is not easily measured and because the dynamics change appreciably with different types of wood chips. It is not clear whether the chip level should be controlled by manipulating the blow flow or the outlet device (or scraper).Some attempts at adaptive control were made by Cegrell and Hedgvist (1974) and Sastry (1978). Very little information is available about the first; the second was finally abandoned. CONCLUSIONS AND SIGNIFICANCEThis paper describes a successful application of the self-tuning regulator (STR) to chip level control in a Kamyr digester. The development of the study is described, from parameter identification experiments and initial STR trials, through model and control algorithm refinements, to practical modifications and final implementation. Two different variables were tried as control inputs: the outlet device, which controls the outflow of solids, and the blow flow, which is the outflow of the diluted liquor carrying the solids. The two performed almost identically as control variables, but the use of the outlet device proved to have certain operational advantages. A reduction of 45 % was observed in the standard deviation of the chip level fluctuation. In practice, thii has meant much less frequent alarms and operator interventions. The new control has been in operation since May 1983.

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Section: Introductionmentioning

confidence: 99%