| Historically, plant design has been the precursor to control system design. Over the past several years it has been determined that much can be gained by simultaneously designing the plant with its control structure. Reduced capital costs, improved process dynamics, and tighter product specifications are advantages of considering process control during process design. In this thesis a generic methodology called the capacity-based economic approach is developed for considering both steady-state economics and dynamic controllability during process design. Variability in product quality is considered explicitly by determining the plant's capacity to make product within a desired specification range. The profitability of a given design may then be determined from its ability to make on-spec product in the presence of disturbances in addition to the costs associated with building and operating the plant. The method can be used to compare or screen alternative process flowsheets by quantifying tradeoffs between steady-state economic process design and dynamic controllability.; In order to demonstrate the method, detailed process design and control case studies of some typical chemical engineering processes are presented in order of increasing complexity. The following processes are considered: a nonisothermal continuous-stirred tank reactor; a binary reactor/separator system; a ternary system with two recycle streams; and a six component process involving two reaction steps, three distillation columns, two recycle streams, and one purge/makeup stream. The capacity-based economic approach is used to compare alternative conceptual flow sheets, alternative choices of design parameters, and alternative plantwide control structures. The most complex process examined is of industrial-scale and is described by approximately 750 ordinary differential equations, 18 design and control degrees of freedom, and two product quality specifications. |
