Abstract
To improve the energy efficiency of distillation processes, various process intensification concepts have been proposed, including direct heat integration and thermal coupling. Identifying the most suitable alternative for a given separation task requires a rigorous and consistent techno-economic optimization. Superstructure models typically rely on isobaric operation and fixed HETP values, in order to avoid treating column hydraulics when solving the already challenging mixed-integer nonlinear optimization problems. In order to overcome this limitation and evaluate the effect of the simplification, the current work extends a rigorous equilibrium-stage superstructure model to account for tray-specific pressure drop and HETP values. A polylithic solution approach is implemented to improve the convergence for the resulting optimization problems. The proposed approach is demonstrated for the optimization of heat-integrated distillation sequences operated at close to atmospheric and vacuum conditions, enabling a closer investigation of the impact of the classically applied simplifications. As the results illustrate that the overall energy demand and total annualized costs are only marginally affected for the considered wide-boiling mixtures the evaluation of competing process configurations will not be affected by the simplifications. However, considerable changes in column height and heat exchanger areas are observed, particularly under vacuum operation, such that column hydraulics should be considered in design optimization, in case column size restrictions or other considerations require a more accurate equipment sizing.