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

Abstract

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.

Integrated design and control of chemical processes – Part I: Revision and classification

“…Material and energy recycle affects process performance leading to complex dynamic behavior, such as inverse response, open loop instability and chaotic behavior. Several authors propose different strategies to quantify these effects (Denn and Lavie, 1982;Morud and Skogestad, 1994;MacAvoy andMiller, 1999, Jacobsen, 1997;Dimian et al, 1997;Semino and Giuliani, 1997;Bildea and Dimian, 2003;Lakshminarayanan et al, 2004;Bildea et al, 2004).…”

Control of a Process with Recycle: Robustness of a Recycle Compensator

“…For instance, Luyben 3 has shown that the poles of the transfer functions are changed with K r . More recently, Lakshminararayanan et al 13 have shown that the "recycle effect index", a measure of the recycle effect, was directly related to the product of K r and K p .…”

Nonlinear model predictive control of energy-integrated process systems

“…Intuitively, integration creates physical connections between process units that are not part of the main flux and can thus give rise to feedback interactions which increase the complexity of the dynamic behavior of the process. These effects (including inverse response and open-loop instabilities) are by now well-documented in the literature [2][3][4][5][6] and make the control of integrated process systems especially challenging. Furthermore, in the recent past, market conditions have become increasingly dynamic, dictating that the control of integrated chemical processes go beyond simple regulation at a steady state, and towards efficient transient operation within a broader operating envelope.…”