: Definitions of terms used within process flexibility design and controllability assessment are given and their relations discussed. Methods for controllability evaluation and methodologies for integrating these into the design process are reviewed for some modes of operation. Basically two types of evaluation and design methods prevail; One type is based upon linear model analysis, whereas another type is based upon physical chemical insight and thus provides nonlinear information. In process design practice the plant piping and instrumentation diagram evolves iteratively using mainly experience and process reasoning to address questions related to plant controllability. It would be desirable to be able to address such questions more quantitatively at different abstraction levels during process design such that controllability evaluation can be integrated into the design process. This paper is an unpublished internal report, which is produced within the EU CAPE.NET project (working...

this paper and need to be defined. Flexibility commonly refers to the range of operating conditions, normally steady state conditions, which a particular process design can achieve. Switchability refers to the ability of a plant to move from alternative steady state conditions. Controllability refers to the ability of a particular design, usually including TWG3/D Bogle/R&D SoA Review/Rev P/1998-01-12 3 the control system, to maintain safe and stable operating conditions following disturbances.

Process design is usually approached by considering the steady-state performance of the process based on an economic objective. Only after the process design is determined are the operability aspects of the process considered. This sequential treatment of the process design problem neglects the fact that the dynamic controllability of the process is an inherent property of its design. This work considers a systematic approach where the interaction between the steady-state design and the dynamic controllability is analyzed by simultaneously considering both economic and controllability criteria. This method follows a process synthesis approach where a process superstructure is used to represent the set of structural alternatives. This superstructure is modeled mathematically by a set of differential and algebraic equations which contains both continuous and integer variables. Two objectives representing the steady-state design and dynamic controllability of the process are considered. T...

Currently, chemical process design and process control are separate disciplines assisting process development at different stages. Design and control decisions are made separately despite the common objective of dissipating the impact of disturbances and uncertainty to ensure robust plant operations. Nowadays, it is broadly accepted that this is not a desirable situation since this approach can lead to processes that are difficult to control. As a consequence, different ways to take controllability issues into account in the process design stage have been developed and reported in the literature during past two decades. This paper presents the state-of-art review of: (i) methods which enable to screen alternative designs for controllability; and (ii) methods which integrate the design of the process and the control system. The paper first focuses on the methodologies available in the open literature to take controllability of process systems into account. The evaluation of open and closed-loop controllability indicator of different process designs allows the comparison and classification of alternatives in terms of operational characteristics. The controllability of alternatives that might have acceptable steady-state economics but poor control performance can be rejected in an early stage of the design. The controllability is quantified using indices like the Relative Gain Array