A systematic analysis of the process model is proposed as a pre-solution step for integration of design and control problems. It is shown that the same set of process (control) variables and design (manipulative) variables is employed with different objectives in design and control. Analysis of the phenomena models representing the process model identify the relationships between the important process and design variables, which help to understand, define and address some of the issues related to integration of design and control issues. The model analysis is highlighted through examples involving processes with mass and/or energy recycle. (C) 2000 Elsevier Science Ltd. All rights reserved.