Minimising the startup duration for mass- and heat-integrated two-column distillation systems: A conceptual approach

The startup of a chemical plant is a complex and highly dynamic process. The main source of complexity stems from the simultaneous variation of all process variables until the required operating point is reached. In previous studies, the startup of single columns for conventional and reactive distillation was considered. A two-column system was also analysed, but featuring only heat coupling without mass integration between the columns, which means with no positive feedbacks. In this work, a heat- and mass-integrated two-column system for continuous pressure-swing distillation (PSD) is investigated experimentally and theoretically on the example of the acetonitrile–water mixture. Rigorous models of the individual equipment units such as trays, condensers and heat exchangers have been formulated and integrated in an overall dynamic system model which has been validated against experimental data. Further, a simple qualitative model to guide the minimisation of the startup duration has been derived and applied to the considered distillation system. The results show that, following the derived criteria, it is possible to reduce the startup duration for the example in Case Study 1 by 78% compared to the duration of empirical startup procedure.