Design of Heat-Integrated Distillation Processes Using Shortcut Methods and Rigorous Optimization

Abstract

The stepwise optimization based procedure for the design of heat-integrated distillation processes as presented by Harwardt et al. (2009) is extended to include complex column designs such as the divided wall column. In the first design step, the optimal flowsheet structure of simple columns is identified using a superstructure formulation and shortcut models based on rigorous thermodynamics. The column pressure is variable in this early design stage to allow for heat integration between the column and the network of heat exchangers. In the second design step, a rigorous MINLP optimization of the most promising flowsheet structure is performed for a thorough assessment of the cost savings potential of heat integration and to determine the optimal column tray numbers and feed stage location. The rigorous optimization can be solved with good robustness, efficiency and reliability due to a continuous reformulation of the MINLP. In a third design step, it is investigated via rigorous optimization whether the energy and capital costs can be further reduced by a fully heat-integrated complex column system such as a divided wall column setup. The design procedure is illustrated by a case study considering the complete separation of a quaternary azeotropic mixture.