Industrial continuous processes may have a large number of process variables and

Interaction among various oscillating inputs may result in significant modifications in the behavior of a system under forced periodic control.Forced oscillations in the input flow rate and input concentrations of an exothermic continuous stirred tank reactor enable the stabilized operation of the CSTR in the unstable steady state region. Reactor temperature oscillations under forced periodic control are similar to the oscillations resulting from proportional-integral feedback or nonlinear (push-pull) feedback control, and under some operating conditions the oscillation amplitude is significantly lower. Theoretical and experimental studies illustrate the effects of forcing frequency and phase shift on reactor behavior. Konstantinos Rigopoulos Xianshu Shu Ali CinarDepartments of Chemical and Electrical Engineering Illinois Institute of Technology Chicago, IL 60616 IntroductionForced periodic operation of chemical reactors has been used effectively for conversion improvement, selectivity, and yield enhancement in complex reactions and the stabilization of reactor operation. References to various review papers, different analysis techniques developed, and applications reported are given by Cinar et al. (1987a). Recently there has been a revival of interest in periodically forced systems. Promising experimental results on yield improvement in catalytic reactions have been reported (Cutlip, 1979, Jain et al., 1982Wilson and Rinker, 1982;Barshad and Gulari, 1985,1986;Silveston et al., 1986). A technique based on the Carleman linearization of nonlinear plant equations and the maximization of a time-averaged performance measure has been proposed (Lyberatos and Svoronos, 1987) for determining the optimal periodic operation and has been applied to an isothermal reactor model for the selection of the best forcing frequency, amplitude, and waveform. Common features of periodically forced reacting systems, particularly properties of spontaneously oscillating systems that are forced periodically, have been considered (Kevrekidis et al., 1986) and an algorithm using stroboscopic representation has been presented for the numerical computation and stability analysis of invariant tori. In stabilizing reactor operation by periodic forcing, the vibrational control approach has provided successful theoretical and experimental results (Cinar et al., 1987a, b).Vibrational control (Meerkov, 1982) is a method for modification of the dynamic properties of a system by introducing fast,

Model-based controllers for a bench scale autothermal tubular packed-bed reactor have been formulated using the Internal Model Control (IMC) approach. The Structural Dominance Analysis technique has been used in developing the reduced-order models. Controller performance at robust and sensitive steady states have been assessed through simulations and experiments. Both PI and model-based controllers can regulate reactor operation at robust steady states, but only third order IMC controllers are able to regulate reactor operation at the sensitive steady state.On a formulk a l'aide d'une mkthode de contrBle de modkle interne des contrbleurs basks sur des modbles pour un rkacteur a lit garni tubulaire autothermique a l'bchelle de laboratoire. La technique de I'analyse de dominance structurale a ktC utiliske pour dkvelopper les modbles d'ordre rbduit. La performance des contrBleurs 1 des ktats permanents robustes et sensibles a ktk kvaluCe par des simulations et des expkriences. Tant les contrBleurs PI que les contraleurs basks sur des modeles peuvent reguler le fonctionnement du reacteur a des ktats permanents robustes, mais seulement des contrbleurs de contrble de modble interne de troisibme ordre peuvent rkguler le fonctionnement du rkacteur a I'ktat permanent sensible.