On the dynamics of integrated plants - non-minimum phase behavior

Recycling of material and or energy in chemical plants imposes a feedback m echanism which is known to move the poles of the plant. In this paper the e ffect of recycling on the zero dynamics is considered, and it is shown that the feedback effect imposed by recycling also may move the zeros of contro l relevant transfer-functions. Sufficient conditions for the existence of n on-minimum phase transmission zeros caused by the presence of recycling are derived. The conditions may be evaluated based on steady-state information about the individual units only, and are hence particularly well suited fo r incorporation in a process design environ ment. The derived results are i llustrated through application to the design of a reactor-separator system. (C) 1999 Elsevier Science Ltd. All rights reserved.