Dynamics of process networks with recycle and purge: Time scale separation and model decomposition

Process networks with recycle are well-known to exhibit complex dynamics and to present significant control challenges, due to the feedback interactions induced by the recycle streams. In this paper, we address the dynamic analysis and control of process networks with recycle and small purge streams used for removal of light inert components (feed impurities and/or reaction byproducts) from the recycle loop. We establish, through a singular perturbation analysis, that such networks exhibit a time scale separation in their dynamics, with the slow dynamics induced by the small amount of inert purged from the recycle loop. We also present a model reduction method for deriving a nonlinear low-order model of this slow dynamics which can be used to rationally address the control of the level of inerts in the network.