Interval Analysis in Automated Design for Bounded Solutions

Jacaranda is an automated process synthesis package. It can be used to aid an engineer in making decisions in the early stages of process plant design. In order to search the solution space, variables such as pressures and component flow rates are mapped to discrete levels. This discretisation means that optimal structures may be missed. In addition, the user may have no idea of how finely to discretise a given variable. This paper describes the use of intervals to bound the possible values of discretised variables. The method was applied to a five-component separation problem using distillation. The pressure of streams and distillation units were set to be intervals. Interval arithmetic was used to bound the possible costs of unit designs. The list of best solution structures was determined for capital, operating and annualised cost criteria. It is demonstrated that the use of interval analysis within Jacaranda enables the user to ensure that the global optimum is present within the solutions obtained.