Simultaneous optimization of hybrid extraction-distillation process based on rigorous models considering the effect of operating pressure

Abstract

Hybrid extraction-distillation process has shown its strength in energy saving over pure distillation process; however, the widely used sequential iterative optimization method and the ignorance of optimizing distillation column operating pressure would miss a better optimal design. In this work, a rigorous pseudo-transient (PT) tray model and a steady-state optimization algorithm assisted by PT model were applied to realize the simultaneous optimization of column structural parameters and operating conditions. Two case studies were optimized to validate the correctness and the effectiveness of the proposed method. The optimal results revealed that it is more economically favorable to treat design specifications of product purity as inequality constraints to expand the search space of optimization. In the water/PM separation case study, the optimal operating pressures that facilitate separation in strippers help reduce the TAC by 14.64%, thanks to smaller reboiler duties per unit feed and smaller circulating stream flow rates. In addition, a heat integration design is feasible which reduces the TAC by 35.43%. This case study emphasizes the importance of optimizing operating pressures for such type of process.