(172c) Design of Vapor Recompressed Dividing-Wall Columns Processing a Light Component Dominant Mixture

When a dividing-wall column (DWC) processes a mixture with a dominant composition of the light component, there exists not only a relatively small temperature elevation from the overhead to the stripping section of its prefractionator but also a large amount of latent heat available in the overhead vapor. These provide opportunities for applying heat pump to the DWC and lead potentially to great improvement in system performance. In this paper, a DWC processing an N-pentane/N-hexane/N-heptane ternary mixture is chosen to examine the characteristics and effect of the applications of heat pumps. We use Stage-Enthalpy Deficit (S-H) profile and Temperature-Enthalpy Deficit (T-H) profile to guide the combinations of heat pumps with the DWC while taking the minimization of total annual cost (TAC) as an objective function. The obtained result shows that multiple heat pumps might be employed to use the compressed overhead vapor to heat the feed, the stripping section of the prefractionator, and the section above the intermediate product of the main column. The first heat pump is employed to preheat the feed, thereby allowing the adoption of feed splitting to strengthen the contact between vapor and liquid phase in the prefractionator. The second heat pump is installed to heat the stripping section of the prefractionator and the third heat pump is installed to heat the separating section above the intermediate product of the main column. The TAC decreases by 25.09% as compared with the DWC. The total utility consumption (TUC) decreases by 62.55% as compared with the DWC. These striking results highlight the great potential of applying heat pump to facilitate the DWC. Current work is underway to simplify the search process in process synthesis and design.