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Analysis of instability in an industrial ammonia reactor
Author(s) -
Morud John C.,
Skogestad Sigurd
Publication year - 1998
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690440414
Subject(s) - instability , hopf bifurcation , steady state (chemistry) , mechanics , bifurcation , control theory (sociology) , continuous stirred tank reactor , extinction (optical mineralogy) , chemistry , thermodynamics , physics , nonlinear system , computer science , mineralogy , control (management) , quantum mechanics , artificial intelligence
The starting point for this study was an incident in an industrial plant, where the ammonia synthesis reactor became unstable with rapid temperature oscillations (limit‐cycles) in the range from about 300°C to 500°C. A simple dynamic model reproduces this behavior. In industry a steady‐state van Heerden analysis is often used to analyze the stability, but a more careful analysis for this reactor system reveals that instability occurs when there still is a positive steady‐state margin, namely as a pair of complex conjugate poles cross the imaginary axis (Hopf bifurcation). This is consistent with the obseruations where the instability manifests itself as oscillations rather than extinction of the reaction. This somewhat unusual behavior can be explained by the presence of an inverse response for the temperature response through the reactor beds combined with the positive feedback caused by the preheater.