TABLE OF CONTENTS Modeling is a common activity in many engineering areas [AGU 99]. A model can be considered as a mapping of input variables into output variables. This chapter presents a set of problems related to some fundamental notions about the representation of dynamical systems in the form of models. The most serious difficulty in implementing control strategies is the lack of adequate models. A myriad of models can be developed for a given process. The models obtained are in general complex (non-linear, high-scale, etc.).
Observe that the complexity of a system is not correlated with its scale. It is, for example, easier to derive a control policy for an industrial phosphate-drying furnace 40 m long than for a rapid thermal system used in a semiconductor wafer fabrication process. Notice also that the complexity can be derived from multiple simple dynamic components that interact in varying and complex ways. For various reasons (improved conversion and selectivity, heat integration benefits, avoidance of azeotropes, etc.), chemical engineers are now concerned with process intensification [RAM 95], which generally leads to simple systems. For example, the manufacturing of methyl acetate is usually done in a plant consisting of a chemical reactor and nine distillation columns. This manufacturing can be done instead in a single reactive distillation. The resulting reactive distillation process is very simple and more economical, and it is easier to control it than to control a set consisting of a reactor, nine distillation columns, and many heat exchangers and pumps.
We can...
