Industrial applications of system identification and control of processes with recycles

Lakshminarayanan, S.; Emoto, Genichi; Onodera, K.; Akamatsu, K.; Amano, Souichi; Ebara, S.

doi:10.1016/s1474-6670(17)33878-8

Cited by 6 publications

(4 citation statements)

References 6 publications

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“…Figure 2 shows the block diagram of a plant containing recycle dynamics. Such dynamics are typically seen in chemical process plants and are discussed in Lakshminarayanan et al, 2001b;Kwok et al, 2001. The step response dynamics of such plants are governed by the relative time constants of the forward and recycle dynamics.…”

Section: Comparison Of Pre-fi Lter Based Methodsmentioning

confidence: 99%

Analysis of Pre‐filter Based Closed‐loop Control‐relevant Identification Methodologies

Shreesha

Gudi

2004

Can J Chem Eng

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F rom the perspective of achieving an enhanced and superior closed-loop performance using a model based control scheme, accurate estimation of a plant model is the most important step. Towards this end, empirical model identifi cation methods, that use plant data, obtained after appropriate excitation of the plant, have been recommended. Typically, the excitation and model building has been proposed in open loop schemes. However, for open loop unstable plants as well as in situations involving time varying plant characteristics, excitation and model building are also proposed in closed-loop schemes. The added advantage of using closed-loop data for identifi cation is that the data in general, implicitly refl ects the intended operating condition of the plant, and may thus yield a better plant model than that obtained from open loop identifi cation. Irrespective of whether identifi cation is carried out in open loop or closed loop schemes, the infl uence of the model order on the model accuracy in terms of the bias and variance errors is an important consideration. This is particularly relevant when a parsimonious model and ease of controller structure and design is sought, subsequent to the identifi cation process. The task of obtaining a parsimonious yet accurate model requires a compromise between achieving a good match at certain control-relevant frequencies versus large mismatch at other frequencies and has generated considerable interest under the area of joint identifi cation and control or controlrelevant identifi cation.Often times, operating plants cannot afford the expensive task of open loop identifi cation as this violates the primary operating objective. Furthermore, in the presence of nonlinearities, time varying behaviour or changes in the operating regions, the model needs to be updated or adapted under closed-loop conditions. have proposed various approaches towards model identifi cation under closed-loop conditions. Vishwanathan and Rangaiah (2000) have proposed an optimizationbased approach to estimate a second order plus dead time model of the process using closed-loop response. Zang et al. (1992) have proposed an online refi nement methodology for controllers, for disturbance rejection using closed-loop modeling. Schrama and co-workers (1993,1992a, 1992b) have proposed an iterative identifi cation and control design scheme for adaptive performance enhancement using closed-loop identifi cation in the frequency domain with co-prime factor perturbations. Various other techniques have been proposed for closed-loop identifi cation from the point of view of bias and variance error minimization (Forssell and Ljung, 1999;Gevers et al., 2001;Gilson and Van den Hof, 2001). Another area of interest wherein closed-loop identifi cation is useful, is direct controller order reduction proposed by Landau et al. (2001) and Rivera and Morari (1992a). Wang et al. (2001) have proposed a robust closedloop identifi cation scheme with application to auto tuning. Lakshminarayanan et al. (2001a) have used the canoni...

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Section: Comparison Of Pre-fi Lter Based Methodsmentioning

confidence: 99%

Analysis of Pre‐filter Based Closed‐loop Control‐relevant Identification Methodologies

Shreesha

Gudi

2004

Can J Chem Eng

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“…Therefore, to overcome the inefficiencies of sequential arrangements, actual processes are designed to recycle mass and energy to previous stages of the plant, which aids in energy recovery or achieving better separation. Unfortunately, the effects on dynamic operability in the presence of recycles are often not considered, [17,25,26] where the resulting control effort affects previous and subsequent stages. Even if local control reaches the set point, studies have also reported that recycles cause an increase in the time constants of a system's dynamics, necessitating a tighter stability range.…”

Section: Introductionmentioning

confidence: 99%

“…Even if local control reaches the set point, studies have also reported that recycles cause an increase in the time constants of a system's dynamics, necessitating a tighter stability range. [5,25,[27][28][29] For example, in a reactor-separator-recycle system (R-S-R), [8,17] control strategies involve increasing the tank capacities to modify the time responses of their dynamic behaviour. [8,16,27,29] Consequently, a larger volume of devices improves the robustness of the plant in this way.…”

Section: Introductionmentioning

confidence: 99%

Plant‐wide control for processes with recycle and narrow feasible sets

Obando,

Muñoz

2023

Can J Chem Eng

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Recycling mass and energy is a feature in almost all plants and industries. It is reported as an inevitable characteristic in actual industries due to differences between the designed processes and implementation. When a process is set, engineers identify inefficiencies in the planned performance and utilize recycles to try to reduce this difference. However, although recycles help in improving a plant's overall performance compared with a serial arrangement, its effect on dynamic plant behaviour is seldom considered, and these changes begin to impact the features of processes like controllability and stability. Similarly, even though recycles affect the feasible region of individual equipment, its effect is not verified. Based on the aforementioned background, several studies have demonstrated that advanced control strategies allow for the improvement of the dynamic behaviour of complex plants. Different techniques, such as model‐based predictive control and plant‐wide control (PWC), also show that their implementation reduces the effects of recycles. However, there is no explicit methodology to design these controllers and address the impacts of recycles on dynamic behaviour and feasibility. Additionally, there is no tuning procedure to design controllers that optimize the dynamic performance of plants, including the control system. In this context, this work presents an analysis to characterize the effects of recycles on the dynamic behaviour of plants, including how they affect the feasible operating region. Based on the previous analysis, a control methodology is also proposed to design the PWC strategy, explicitly addressing the dynamical phenomena of recycles in processes.

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“…The forward-path and recycle-path models can be used to design recycle compensators to alleviate the harmful effects of the recycle (Scali and Ferrari). The issue of identification of process models from plant step response data and open-/closed-loop time series data was addressed very recently by Lakshminarayanan and Takada and Lakshminarayanan et al Once the forward-path and recycle-path models are available, the control engineer must quantify the strength of the recycle and determine whether an advanced control structure such as a recycle compensator is needed. If a recycle compensator is deemed important, then it can be implemented, and a feedback controller can be designed for the compensated plant.…”

Section: Introductionmentioning

confidence: 99%

Recycle Effect Index: A Measure to Aid in Control System Design for Recycle Processes

Lakshminarayanan

Onodera

Madhukar

2004

Ind. Eng. Chem. Res.

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Systems with material and/or energy recycles are quite common in the chemical industry. Modeling and DCS-level controller design are quite challenging for such processes because separation of the overall process response into a direct (forward-path) response and an indirect (recycle-path) response is often difficult. Even when this is possible, one needs to know whether a feedback-only control structure is sufficient or an advanced control structure that employs a recycle compensator is necessary. Using control loop performance assessment concepts, this paper proposes a quantitative measurethe recycle effect index (REI)to help determine whether a simple feedback control system can provide the desired quality of control.

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Industrial applications of system identification and control of processes with recycles

Cited by 6 publications

References 6 publications

Analysis of Pre‐filter Based Closed‐loop Control‐relevant Identification Methodologies

Analysis of Pre‐filter Based Closed‐loop Control‐relevant Identification Methodologies

Plant‐wide control for processes with recycle and narrow feasible sets

Recycle Effect Index: A Measure to Aid in Control System Design for Recycle Processes

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