The quest for more energy efficient technologies has made distillation processes a prime target for process intensification studies. In this respect, heat-integrated distillation is a promising technology that offers significant energy and capital savings over conventional distillation. In an internally heat-integrated distillation column (i-HIDiC), heat exchange takes place between the rectifying and the stripping sections of a distillation column. The generation of internal reflux and boil-up reduces the heat loads on external exchangers thus reducing the utility costs. On the other hand, in an externally heat-integrated double distillation column (EHIDDiC) system, the total feed to a conventional column is split-fed to two columns operating at different pressures, with heat exchange taking place between the condenser of high-pressure column and the reboiler of low-pressure column. This configuration reduces the overall process irreversibility and leads to lower energy consumption.

            In this study, three heat-integrated design alternatives (namely intercoupled iHIDiC, concentric iHIDiC, and EHIDDiC) for an industrial i-butane/n-butane fractionator have been explored using commercial process simulator Aspen Plus®. First, a base case model for the conventional column is developed and fine-tuned to match experimental data and reference cost analysis is performed. Then, for each heat-integrated configuration, optimization of key design variables and operational parameters is performed and thermal and hydraulic feasibility is checked. The simulation results show up to 40% savings in direct operating/energy costs and up to 15% savings in the net total annualized cost.