Systematic controllability analysis for chemical processes

Abstract

Modern chemical industrial processes are becoming more and more integrated and consist of multiple interconnected nonlinear process units. These strong interactions profoundly complicate a system's inherent properties and further alter the plant‐wide process dynamics. This may lead to a poor control performance and cause plant‐wide operability problems. To ensure entire processes run robustly and safely, with considerable profitability, it is crucial to recognize the inherent characteristics that can jeopardize controllability and process behavior at the early design stage. With a focus on inherently safer designs, from a plant‐wide perspective, a systematic method for chemical processes controllability analysis is addressed in this study. In the proposed framework, based on open‐loop stability/instability and minimum/nonminimum‐phase behavior, the entire operating zone of the process can be categorized into distinct subregions with different inherent properties. Variations in the inherent characteristics of a plant‐wide process with the operation and design conditions, over the feasible operation region, can be probed and analyzed. An attempt of this framework is made to illustrate how to clarify the roots of the poor controllability that arise in the design and operation of a large scale chemical process, and the results can provide guidance for both deciding the optimal operation conditions and selecting the most suitable control structure. Singularity theory is also applied in the framework to improve the computational efficiency. The framework is illustrated with two case studies. One involves a reactor‐external heat exchanger network and the other a more complex plant‐wide process, comprising a reactor, an extractor, and a distillation column. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3096–3109, 2012

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

“…Focusing on inherently safer designs, their study reveals how the essential properties of a process change with variations in its operating conditions. A systematic framework that includes multiplicity and phase behaviour together with open loop stability analysis over the entire feasible operation region of plantwide processes is presented in Yuan et al (2012b). Yuan et al (2009), address a strategy for classifying the process operating region into distinct zones at the early stage of process design, based on stability/instability and minimum/non-minimum phase behaviour analysis.…”

Process Design, Integration and Optimisation: Advantages, Challenges and Drivers

“…3.1 ). This is because, on the one hand, the degrees of freedom diminish severely, and, on the other, the number of multiple interconnections between non-linear processes increases, altering profoundly the time-scales (Morud and Skogestad, 1996) and thus the plantwide process dynamics (Yuan et al , 2012). According to Morud and Skogestad (1996), an interconnection, whether it be internal or external, can be classifi ed as either: (a) feedbackany secondary effect that modifi es the original dynamic, (b) feedforward (parallel paths) -any system where an input affects an output through several independent subsystems or mechanisms, and (c) series -the output of one subsystem is the input to the next (no feedback between subsystems).…”

Steady-state multiplicity analysis of two-stage-riser catalytic pyrolysis processes

“…Nonlinear analysis has been proved as an efficient approach to reveal potential operability problems at the stage of process design. During the past several decades, enormous contributions have been published to obtain a thorough understanding of the nonlinear characteristic of various chemical processes including relative simple continuous stirred tank reactors (Uppal and Ray, 1974;Russo and Bequette, 1995), adiabatic autothermal reactors (Lovo and Balakotaiah, 1992), polymerization reactors (Ray and Villa, 2000;Wells and Ray, 2005;Zavala-Tejeda et al, 2006), crystallization processes (Pathath and Kienle, 2002), toluene catalytic oxidation processes (Yuan et al, 2011b), fuel cells (Bavarian et al, 2013;Chen and Elnashaie, 2004), bioreactor systems (Namjoshi et al, 2003;Garhyan and Elnashaie, 2004), azeotropic distillations (Bekiaris et al, 1993(Bekiaris et al, , 1996, reactive distillations (Kumar and Kaistha, 2008), wastewater treatment processes (FloresTlacuahuac et al, 2009), and chemical networks (Wang et al, 2011;Yuan et al, 2012). Of course, a large number of valuable literature focusing on multiple steady states and nonlinear analysis of fluidized catalytic cracking (FCC) units have also been achieved.…”