A New Approach to Continuous Digester Control

Cegrell, Torsten; Hedqvist, Torbjörn

doi:10.1007/978-3-642-65796-2_25

Cited by 19 publications

(7 citation statements)

References 1 publication

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“…A binary sequence of blow flow set points was generated by flipping a coin. At every 2.5 min (half the sampling time used in Cegrell and Hedqvist, 1974) the blow flow setpint increased or decreased from a constant level by 2% of that level (about lZO/min). A 3 h experiment yielded 73 samples.…”

Section: Model Structurementioning

confidence: 98%

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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: Model Structurementioning

confidence: 98%

“…This is why a self-tuning regulator (STR) for chip level control has been proposed by Cegrell and Hedqvist (1974) and by Sastry (1978). Not much information is available about the first application; the second had to be abandoned due to lack of reliability of the STR.…”

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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show abstract

“…Despite these limitations, the standard self‐tuner was successfully used in a number of industrial applications, including digester control , moisture control in a paper machine , continuous cement raw material mixing , a titanium dioxide kiln and control of an ore crusher . In , the results obtained are evaluated by plotting on the space of parameters the evolution of the gains computed by the self‐tuners superimposed on the level curves of the minimum‐variance gain obtained with a plant model obtained independently.…”

Section: Background To Optimized Adaptive Controlmentioning

confidence: 99%

Survey of industrial optimized adaptive control

Martín‐Sánchez

Lemos

Rodellar³

2012

Adaptive Control & Signal

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This survey paper aims, to present in a systematic way, the 'state-of-the-art' of a class of so called optimized adaptive control methodologies, where adaptive systems theory is complemented by optimal control theory. It is based on literature published since 1958 and emphasizes results with proven industrial relevance. After recalling previous adaptive systems, results that had prepared the ground for the new ideas, the analysis departs from the work on adaptive predictive control in the mid 1970s, which provided the conceptual basis for the development of this kind of technique. Well-known design methods, both from the stability and optimization perspectives, along with their results, are interpreted in an intuitive way in order to understand how control law and the adaptive mechanism complement each other to produce mature controllers that can reliably solve the industrial process dynamic stabilization problem. Surveys of industrial applications from both design perspectives are presented and industrial products based on optimized adaptive control are cited.

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“…Therefore, this first impulse weight is deemed insignificant, indicating that the process has one complete sampling interval (5 min) of pure delay (f = 1). This delay may be attributed to the finite time required to accelerate the chip column because of its elastic characteristics (Cegrell and Hedqvist, 1974). The remaining impulse weights suggest one of several alternatives for the orders of the transfer function polynomials ~( z -' ) and 6(z-').…”

Section: Ui + Nlmentioning

confidence: 99%

“…Dumont (1986) reviewed adaptive control applications in the pulp and paper industry. Self-tuners have been applied to Kamyr digester chip level by Cegrell and Hedqvist (1974), Sastry (1978), and Btlanger et al (1986). Not much information is available about Cornspondenceconcerning this paper should k addressed to B. J. Allison.…”

Section: Introductionmentioning

confidence: 99%

Adaptive‐predictive control of kamyr digester chip level

Allison¹,

Dumont²,

Novak³

et al. 1990

AIChE Journal

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Kamyr digester chip level poses a difficult control problem, because the chip column dynamics are complex and it is difficult to measure the chip-liquor interface. Control of the chip level is required to smooth digester operation and to stabilize the residence time. Conventional methods rely largely on fixed parameter controllers which are unable to compensate for changes in the process dynamics. Manual controller retuning is often required.An adaptive chip level controller based on Generalized Predictive Control (GPC) is presented. Closed-loop time series identification methods were used to develop the process model and to design the controller. A significant reduction in chip level and P-number variability has been observed since commissioning the controller on an industrial digester in September 1988. The adaptive controller has eliminated the need for manual retuning, reduced the need for operator intervention, and demonstrated the potential to predict hang-ups.

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A New Approach to Continuous Digester Control

Cited by 19 publications

References 1 publication

Self‐tuning control of chip level in a Kamyr digester

Self‐tuning control of chip level in a Kamyr digester

Survey of industrial optimized adaptive control

Adaptive‐predictive control of kamyr digester chip level

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