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A reliable control for the ammonia loop facing limit-cycle and snowball effects

Authors

  • Maurizio Rovaglio,

    Corresponding author
    1. Dipartimento di Chimica, Materiali ed Ingegneria Chimica “G. Natta” Politecnico di Milano, P.zza Leonardo da Vinci 32, 20133 Milano, Italy
    • Dipartimento di Chimica, Materiali ed Ingegneria Chimica “G. Natta” Politecnico di Milano, P.zza Leonardo da Vinci 32, 20133 Milano, Italy
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  • Davide Manca,

    1. Dipartimento di Chimica, Materiali ed Ingegneria Chimica “G. Natta” Politecnico di Milano, P.zza Leonardo da Vinci 32, 20133 Milano, Italy
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  • Francesco Cortese

    1. Dipartimento di Chimica, Materiali ed Ingegneria Chimica “G. Natta” Politecnico di Milano, P.zza Leonardo da Vinci 32, 20133 Milano, Italy
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Abstract

Autothermal catalytic reactors may show limit cycle behavior because of the simultaneous presence of inverse response and thermal feedback actions. In this study, a classical ammonia reactor (two beds, radial flow) was considered, and simulated together with the overall synthesis loop. Oscillations, caused by feed gas temperature disturbances, have been confirmed, whereas a pressure dependent hysteresis pattern appeared when the temperature is reset to the original design value. A more sensitive dynamic behavior is highlighted for the synthesis loop compared with the reactor alone, because of energy and material recycles. Finally, a control strategy extended to the overall synthesis loop has been tested in order to avoid dangerous dynamics and undesired reactor shutdown. The proposed control configuration, applied to the overall synthesis loop, is able to face and avoid both “snowball” effects and dangerous limit cycle conditions. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1229–1241, 2004

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