Dynamics of plants with recycle

doi:10.1016/0300-9467(82)80050-6

The Chemical Engineering Journal

Volume 24, Issue 1, 1982, Pages 55-59

https://doi.org/10.1016/0300-9467(82)80050-6 Get rights and content

Abstract

The effect of recycle on plant dynamics is examined. The overall plant response will have a longer characteristic time and higher steady-state gain tha

References (3)

E.R. Gilliland et al.
Preprints 1970 Joint Automatic Control Conference, Stanford, CA
(1970)

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Open-loop dynamic analysis of the catalytic oxidation of vocs with heat recovery
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In this contribution, the open-loop dynamic behavior of the heat-integrated reactor for VOCs catalytic oxidation process is analyzed and the key variables that determine the stability of the system are studied. Systems with heat recovery often exhibit open-loop instability as a result of the positive heat feedback to the reactor. The results of the simulations demonstrate the existence of multiple steady states in the Reactor/FEHE/Furnace system, for the explored range of reactor inlet temperatures. There exists a close relation between the multiplicity of steady states and system stability for variables of interest such as feed fraction circulating through the FEHE and furnace duty. Under certain operating conditions, the system shows strong oscillations that can lead to physical damage to the catalyst (sintered) or undesired situations of light-off of the reactor. Particularly, sustained oscillations appear near the extinction point, an operating zone of practical interest to reduce the energy demand of the process and extend the catalyst life, since total conversion of VOCs is achieved at relatively low reactor inlet temperatures. The dynamic behavior of the reactor and heat exchanger in this steady state zones are analyzed. Finally, the effect of residence time and reactor time constant on system stability is discussed.
Application of Taiwo's Recycle Compensator to an Heat Integrated Ammonia Production Plant
2017, IFAC-PapersOnLine
Designing fixed-bed catalytic reactor to have heat integration is a common practice in the process industries. However, such design usually poses control challenges as a result of unusual dynamic behavior of the overall process, such as oscillations and instability. It is shown in this paper that the application of Taiwo’s recycle compensator eliminates the undesirable dynamics and leads to a better performance. Thus facilitating the design of more effective control system for heat integrated processes.
Effect of coolant flow rate on the dynamics of delayed recycle continuous stirred tank reactor
2017, Journal of the Taiwan Institute of Chemical Engineers
Numerical bifurcation analysis of delayed recycle stream in a continuous stirred tank reactor was studied using DDE-BIFTOOL. A first-order irreversible exothermic reaction $s_{1} \overset{k_{2, 1}}{\to} s_{2}$ was considered for analyzing effect of delay on the stability of the delayed recycle system. The non-isothermal CSTR was operated at both infinite and finite coolant inlet flowrates. A constant delay was considered in the recycle stream of CSTR for concentration of reactant, and temperature. DDE-BIFTOOL solver was used for finding dependency of delays on the bifurcation parameters, and its stability characteristics. The bifurcation parameters considered were: (i) fresh feed flowrate, (ii) coolant temperature, and (iii) coolant inlet flowrate. In the absence of delay, the system exhibits the region of dynamic instability for both infinite and finite coolant inlet flowrates. For infinite coolant flowrate, the region of dynamic instability on the reactor temperature was modified as a result of delay by varying either fresh feed flowrate or coolant temperature. The steady-state multiplicity was observed on the coolant temperature by varying fresh feed flowrate at finite coolant inlet flowrate. In the absence of delay, the fold and Hopf bifurcations were observed on the multiple steady-states of coolant temperature. The concentration and temperature delays do not alter substantially the dynamic characteristics of coolant temperature at T_c,in = 298 K. However, delays can alter the region of dynamic instability for coolant temperature when coolant inlet temperature is higher than 298 K. These are the main result of present work.
Integrated design and control of chemical processes - Part I: Revision and classification
2014, Computers and Chemical Engineering
Citation Excerpt :
Material and energy recycle affects process performance leading to complex dynamic behaviour, such as inverse response, open loop instability and chaotic behaviour. Several authors propose different strategies to quantify these effects (Denn and Lavie, 1982; Morud and Skogestad, 1994; McAvoy and Miller, 1999; Jacobsen, 1997; Dimian et al., 1997; Semino and Giuliani, 1997; Bildea and Dimian, 2003; Lakshminarayanan, 2004; Bildea et al., 2004). Luyben and coworkers present a series of papers devoted to the study of dynamics and control of recycle systems in chemical processes (Luyben, 1993a, 1993b, 1993c, 1994, 1999; Tyreus and Luyben, 1993).
This work presents a comprehensive classification of the different methods and procedures for integrated synthesis, design and control of chemical processes, based on a wide revision of recent literature. This classification fundamentally differentiates between “projecting methods”, where controllability is monitored during the process design to predict the trade-offs between design and control, and the “integrated-optimization methods” which solve the process design and the control-systems design at once within an optimization framework. The latter are revised categorizing them according to the methods to evaluate controllability and other related properties, the scope of the design problem, the treatment of uncertainties and perturbations, and finally, the type the optimization problem formulation and the methods for its resolution.
Dynamics and control of benzene hydrogenation via reactive distillation
2014, Journal of Process Control
Citation Excerpt :
Sloley [33] has extensively reviewed control strategies that can be used for columns based on the type of condenser. Recycle loops in chemical plants are known to significantly alter the control and dynamics of process networks [34–36]. Recycle streams increase the overall time constants, thus “slowing down” its overall response [34].
This work develops a dynamic, first principles-based model of a reactive distillation column used for benzene hydrogenation of a reformate stream and investigates different control structures for this process. The model is used initially to develop and evaluate a feedback control strategy which provides good regulatory performance for small disturbances, however, it tends to be sluggish for significant disturbances in the feed composition. In order to address this point, adding a feedforward controller to the feedback structure has also been investigated. However, the feedforward controller can only be implemented if composition measurements of the feed are taken. As online composition measurements are expensive in practice, several different scenarios have been investigated where samples of the feed are taken and subsequently analyzed in a lab, as represented by measurement time delays. Simulation results show that adding feedforward control to the feedback scheme can be very beneficial for this process, however, this is only the case if the composition disturbance measurements do not involve a significant time delay.
On robust control system design for plants with recycle
2014, IFAC Proceedings Volumes (IFAC-PapersOnline)
A direct procedure for deriving the component transfer functions in plants with recycle when mechanistic procedure is used in the mathematical modeling is demonstrated. Multi-loop feedback controllers are then designed for the plants with recycle incorporating recycle compensator and without recycle compensator using internal model control (IMC) parameterization. In general, it is found that controllers parameterized using the recycle compensated plant model result in closed-loop systems with better nominal and robust performance characteristics when implemented on the uncompensated plant model than when its controller is parameterized using the uncompensated plant model. Furthermore, recycle compensated plants result in overall best closed-loop systems when their feedback controllers are parameterized using the compensated plant model.

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¹: Present address: Department of Chemical Engineering, University of California, Berkeley, CA 94720, U.S.A.

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Dynamics of plants with recycle

Abstract

Preprints 1970 Joint Automatic Control Conference, Stanford, CA