| A chemical process control strategy is discussed within the scope of hierarchical multilevel theory. Its various elements are identified and their relations are clarified. In the chapters of this dissertation we also examine four elements associated with this strategy: (i) identification of low frequency disturbances, (ii) design of regulatory control structure, (iii) synthesis of steady-state optimizing control strategy, and (iv) operation procedures and control structures for process start-up.; Methodologies which deal with these problems are developed. For (i) we provide a structural and statistical approach to identify low frequency disturbances by checking for logical and numerical consistency between process data and equations. The algorithm is similar to a model testing scheme. For (ii) we develop a computer-aided method for synthesizing regulatory control loop structures by using singular value analysis. Dynamic measures of sensitivity and interaction are introduced as decision variables in designing the structure. In addition, a structural compensator is presented to further exploit the interaction within the system. The program functions interactively which allows the engineer to take practical considerations into account. For (iii) we again use singular value analysis to furnish insights into the internal structure of the system. This enables us to include control aspects as well as economical and heuristical considerations in synthesizing steady-state optimizing control strategy. The effects of scaling, i.e., the dimension of the physical variables, on the results of the analysis are examined. We find that empirical methods of scaling are adequate in characterizing the control behavior of the system. For (iv) we devise an algorithm for synthesizing start-up procedures of a chemical process. Initially the process is divided into subsections. Operational sequence trees are synthesized for these subsections. Screening rules are then used to select a start-up sequence for each subsection. The selected sequences are coordinated into a plant start-up sequence. Once the operating sequence is identified, the control system along the operating route can be designed. Consequently, the control system is of variable structure which lends increased flexibility to the system.; Chemical processing units such as gasoline polymerization plant, distillation columns and continuous stirred tank reactors are analyzed to demonstrate the applications of these methodologies. |
