Assessing Total Heat Load as a Proxy for Optimising Operating Specifications in Extractive Distillation

In this work, it is assessed whether the total heat load of the two-column extractive distillation system is a useful proxy for determining the optimal number of stages in systems that use cooling water in the condensers and steam in the reboilers. Thereafter, the optimal operating specifications of the extractive distillation column must be updated accordingly. The heuristic method features a straightforward, sequential, iterative optimisation approach for theoretical designs of a two-column extractive distillation sequence, developed using a process simulator. Four case studies are optimised to demonstrate the methodology’s suitability. The results were compared against simulated annealing, full total annual cost sweeps and data available in the literature. In all four cases, the proxy guided the choice of reflux ratio, and total annual cost determined the stage count. The operating specifications were then refined. Essentially, the proxy is utilised to identify the trend in total annual cost with the stage number of the extractive distillation column; therefore, the location or region where the optimal number of stages exists can be rapidly identified. Due to its efficiency, the proposed approach can theoretically be utilised to determine the optimal system specifications, using more complex modelling approaches, such as rate-based simulations.