Optimal design and effective control of Kaibel column with liquid-only transfer streams for quaternary distillation

Abstract

The Kaibel column (KC) is considered to be energy effective and capital economical replacement of conventional distillation sequences for quaternary distillation. However, the industrialization of such a structure is still hesitant due to increased complexity and related uncertainties. Compared to the highly integrated KC, distillation configurations with liquid-only transfer streams (LTS) are more easily understandable and acceptable to the industrial community. A KC-LTS configuration is therefore investigated through an optimal design and controllability comparison to the conventional direct sequence (DS). When separation of aromatics is proposed as a case study, the results demonstrate the economic superiority of KC-LTS to DS in terms of the total annual cost. Considering the controllability using composition controllers, the former structure performs as favorable as the latter when tackling a ±20% step changes in throughput and feed composition. An inferential temperature control strategy is also established for KC-LTS. Good controllability is generally realized in most cases at handling relatively small (10%) throughput and feed composition disturbances, except for large product offsets when resisting large (20%) feed perturbations. To further improve its dynamic control effectiveness, an intensified control option with three composition control loops is successfully proposed to handle 20% step feed disturbances. Overall, this work expands LTS to quaternary distillation, suggesting a competitive substitute of the well-known KC for both academic and industrial purposes.