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

Recycling of material and or energy in chemical plants imposes a feedback mechanism which is known to move the poles of the plant. In this paper the e€ect of recycling on the zero dynamics is considered, and it is shown that the feedback e€ect imposed by recycling also may move the zeros of control relevant transfer-functions. Sucient conditions for the existence of non-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 for incorporation in a process design environ- ment. The derived results are illustrated through application to the design of a reactor-separator system.