Abstract
Standard dividing wall columns (DWC) are state-of-the-art integrated fully thermally coupled (FTC) (or Petlyuk) distillation arrangements performing several separation tasks within one unit and with a lower energy consumption and capital costs than conventional column sequences. This may require careful design and control of the internal flow rates to achieve the potential energy savings, which typically are about 30%. In particular adjusting the internal vapor split is regarded to be challenging. The Liquid-only transfer (LOT) arrangements offer alternative internal flow rate adjustments that may mitigate this challenge. In addition, its use in retrofit may enable practical cost-effective solutions. The key result in this paper is to provide analytical minimum energy expressions for the LOT arrangement which are shown to be identical to the ones for the standard DWC. Furthermore, the optimal operating region and flexibility for the internal sub-columns in the arrangements are explored and are also found to be equivalent and the available adjustment margines for the LOT draw rates and other operational variables are clarified. The results give valuable insight in the characteristics of optimal operation and can also be used to provide good initialisation values for rigorous simulations.