Tight energy integration: Dynamic impact and control advantages

Process integration is a key enabler to increasing efficiency in the process and energy generation industries. Efficiency improvements are obtained, however, at the cost of an increasingly complex dynamic behavior. As a result, tightly integrated designs continue to be regarded with caution owing to the dynamics and control difficulties that they pose. The present work introduces a generic class of integrated networks where significant energy flows (either arising from energy recycling or of external origin) result in dynamic models with a multi-time-scale structure. Such networks feature a clear distinction between the fast dynamics of individual units and the slow dynamics of the entire network. We draw a connection between specific (steady-state) design features and structural properties that afford the development of a framework for the derivation of low-order, non-stiff, nonlinear models of the core network dynamics. Furthermore, we demonstrate that tight energy integration and the presence of significant energy flows can facilitate, rather than hinder, control structure design and performance, and propose a cadre for hierarchical control predicated on the use of fast, distributed control for the individual units and nonlinear supervisory control for the entire network. The developed concepts are illustrated with examples. (C) 2010 Elsevier Ltd. All rights reserved.