FLOWSHEET OPTIMIZATION AND OPTIMAL SENSITIVITY ANALYSIS USING ANALYTICAL DERIVATIVES

Over the past decade, flowsheet optimization has become an important t ool for process design. However, for flowsheet optimization the most t ime consuming step is devoted to the evaluation of the first derivativ es, especially for modular process simulators. To overcome this proble m, the ProSim simulator has been modified in order to generate exact g radient information automatically. Based on the modular input-output s ensitivities and a chain-ruling procedure, this strategy allows signif icant time savings during the optimization. Several optimization metho ds are implemented (a Reduced Gradient and two Successive Quadratic Pr ogramming strategies) and their results are compared in combination wi th the analytical derivatives. Furthermore, it is often useful to asse ss the sensitivity of the optimum flowsheet to design parameters (e.g. feed flowrates, constants in kinetic and transport equations) that ma y be subject to variation and uncertainty. With the calculation of exa ct derivatives, post-optimality analyses, which were considered too ex pensive before, can now be implemented with very inexpensive computati onal costs. The optimal flowsheet sensitivity analysis thus allows us to estimate easily the changes in the optimal process under parametric variations and other process uncertainties.