Application and evaluation of three methodologies for plantwide control of the styrene monomer plant

Abstract

Plantwide control (PWC) methodologies have gained significant importance given the high and increasing degree of integration in chemical processes due to material recycle, energy integration, and stringent product quality control, all of which though economically favorable, pose tough challenges to smooth plant operation. As part of the continuing search for more effective PWC system design methods, an integrated framework of heuristics and simulation was proposed [Konda et al. Ind. Eng. Chem. Res. 2005, 44, 8300-8313]. The basic idea behind this development is to make effective use of rigorous process simulators to aid in decisionmaking during the development of the heuristic-based PWC structure. Konda and co-workers have successfully applied the procedure to the toluene hydrodealkylation process. Though the integrated framework is promising, there is still a need to test its applicability to other complex industrial processes. The present contribution considers the development of a PWC structure for the styrene monomer plant using the integrated framework. In addition, in order to gauge its effectiveness in comparison to the other plantwide control methods, two more methods are considered in this study. First, the heuristics procedure of Luyben and co-workers [Luyben et al. Plant-Wide Process Control; McGraw-Hill: New York, 1998], which is a popular heuristics-based methodology, is also applied to the same flowsheet, and is considered as the base case for performance assessment. Second, the self-optimizing control procedure [Skogestad, S. Comput. Chem. Eng. 2004, 28, 219-234] is also used in order to have a more comprehensive analysis of the effectiveness of the integrated framework. An analysis of the results indicates that while all the procedures give stable control structures, the integrated framework and self-optimizing control procedures give more robust control structures than the heuristics procedure. This is the first study to develop simulation models and complete PWC structures for the styrene plant, together with a detailed analysis of the relative performance of the resulting structures in order to evaluate the different PWC methodologies. © 2009 American Chemical Society.