Model reduction and control in reactor-heat exchanger networks

This paper focuses on energetic aspects of the dynamics and control of process networks with high material recycle. Two prototype systems are analyzed, for which the large material recycle acts as an energy carrier, leading to a high energy throughput for the entire network. Using singular perturbation arguments, we show that the variables in the energy balance of these networks evolve in the fast time scale, while the terms in the material balance equations can exhibit both fast and slow transients. We present a procedure for deriving reduced-order, non-stiff models for the fast and slow dynamics, the latter typically of low order, and a framework for rational control system design, that accounts for the time scale separation exhibited by the system dynamics. The theoretical results are illustrated in a reactor-external heat exchanger network example.