SYNTHESIS AND RETROFIT DESIGN OF OPERABLE HEAT-EXCHANGER NETWORKS .2.DYNAMICS AND CONTROL-STRUCTURE CONSIDERATIONS

Dynamic controllability of heat exchanger networks is considered in th is paper within a synthesis/retrofit framework to improve the operabil ity of HENs (flexibility and controllability). Based on a hyperstructu re network representation, where all structural and operational altern atives are included, a variable delay matrix and a variable gain matri x are introduced, to explore potential control structures simultaneous ly with network structures. Simple controllability criteria (diagonal dominance of the gain matrix, dynamic decoupling, time effective contr ol) are postulated employing graph theory concepts and included within the synthesis/retrofit model. A modified generalized Benders decompos ition is applied to solve the resulting mixed integer nonlinear progra mming synthesis/retrofit model and to derive a cost optimal network an d a favorable control scheme.