Computers chem. Engng Vol.20, Suppl.. pp. $449-$454. 1996 Copyright© 1996ElsevierScience Ltd Pergamon S0098-1354(96)00085-3 Printed in Great Britain. All rightsreserved 0098-1354/96$15.00+0.~X) COMPUTER AIDED DESIGN OF POLYMER REACTORS A. PERTSINIDIS, E. PAPADOPOULOS, and C. KIPARISSIDES Chemical Engineering Department and Chemical Process Engineering Research Institute Aristotle University of Thessaloniki P.O. Box 472, Greece Abstract - This paper describes the development of CAD packages for high pressure polyethylene reactors. The overall goal of the software packages was to develop powerfull, flexible, adaptive design and predictive simulation tools that can follow and predict the operating conditions of a given high pressure polymer reactor in an accurate, prompt and comprehensive way. Their range of use includes the prediction in real time of the molecular properties of polymer produced in high pressure LDPE reactors, the estimation of control moves of key process variables as well as the prediction of the operational and product characteristics of alternative design options. Major points of consideration during the program development were the user friendliness of the input/output and the execution speed enabling its online use as a predictive tool. The functions of the packages have been built around a modular mathematical model of the reactor that includes the energy and material balances based on the leading moments of the Molecular Weight Distribution equations and supported by the physical and molecular properties evaluation equations. INTRODUCTION The development of computer-aided design (CAD) tools has advanced dramatically in the past fourty years. Furthermore, the perspectives for the near future developments are even more promising (Evans, 1994). The traditionally set path for the development of general purpose simulation packages requires a CAD expertise as an added value to the mathematical models of unit operations and physical properties evaluation, established in the literature. This modeling and problem solving expertise encompasses a wide variety of interdisciplinary fields such as numerical analysis for the solution of differential and algebraic equations, mathematical programming for the solution of the optimization problems, and computer science in order to keep up-to-date to the capabilities that the computer technology offers today. This latter includes issues that range from hardware, to languages (FORTRAN, C++) and operating systems, to programming approaches (mathematical modeling vs experts systems and artificial intelligence) and software structure (modular, equation oriented, object oriented programming). The challenge in the development of computer aided design tools for the chemical industry, compared with the design of other manufacturing processes, is that the exact properties of the system are often only imperfectly known and there is neither the money nor the time available to study them sufficiently in order to acquire a more accurate knowledge (Rippin 1989). On the other hand, there are considerable benefits when such tools are employed regarding both the operability and profitability of the processes (Boston, 1990). Regarding the polymer manufacturing industry both the challenges and the rewards are distinctively amplified (Schnler and Schmidt 1992, Ray 1989). In contrast though to the general status and perspectives of computer aided design, the polymer engineer can find little help in the established software packages either because the pertinent modules are lacking completely or they are quite simplistic. The fact that polymer reactors stand as the typical example for what the computer aided design tools should "ultimately" address in the near future (Evans, 1994), increases the scope for the urgent development of CAD packages for the polymer industry. Furthermore, what is vaguely called a "polymer reactor" is a label for a whole field of diverse technologies. The diversity of the field can be better appreciated in Ray (1989) where a CAD software package, Poly(mer)Re(actor)D(esign), is presented. The software package provides a unified framework for modeling and simulation of polymerization processes. The software package handles various types of polymerization mechanisms (e.g. free-radical, ionic), various polymerization techniques (e.g. bulk, suspension, emulsion), and can assemble various reactor configurations (e.g. tubular, stirred tanks). But despite the package's high degree of "specialization", it is not an on-line optimization tool for it does not address the specific peculiarities of a polymer process (e.g. presence of varying amounts of $449