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Hierarchical synthesis of control systems at the conceptual design stage
Abstract
We have developed a systematic procedure for a limited class of chemical processes that includes control problems at the early stage of a flow sheet development. The procedure decomposes the control problem into a set of sub-problems. For the economic evaluations it is assumed that the raw-material and the recycle costs dominate the process economics, and therefore the variables which affect the input-output and the recycle material and energy flows are considered as the optimization variables (process-flow optimizations). The results obtained from this procedure will be helpful in the following areas: (1) Identifying potentially inoperable flow sheets due to the presence of trace component impurities in the feed streams or produced in the reactor, (2) Estimating the economically justified modifications (both in the flow sheet structure and the sizes of process units) to the optimum base-case design, (3) Generating alternative sets of process-flow, control structures (a set of controlled and manipulated variables, along with their pairing, that can drive the input-output and the recycle flows to their desired steady-states), (4) Estimating the magnitude of the overshoot of the manipulated variables during the transients, and changing the structure of the flow sheet, the equipment sizes, or the structure of the steady-state control structure to accommodate disturbances in an optimum way. Based on the process economics and the relative gain analysis, the optimum control structure is synthesized that would minimize the total operating cost in the face of disturbances. The optimum values of the sizes of the constrained unit designs (which restrict the process-flow optimization in the face of disturbances), and the optimum values of the process variables (i.e., the design variables and the process flows) are determined by solving a two-stage optimization problem. A method for developing approximate, dynamic models for the process flows for continuous chemical plants with recycle streams is described. (Abstract shortened with permission of author.)
Subject Area
Chemical engineering|Systems design
Recommended Citation
Joshi, Sanjay Kumar, "Hierarchical synthesis of control systems at the conceptual design stage" (1991). Doctoral Dissertations Available from Proquest. AAI9132871.
https://scholarworks.umass.edu/dissertations/AAI9132871