Extractive Dividing-Wall Column Distillation with a Novel Control Structure Integrating Pressure Swing and Pressure Compensation
Cong Jing, Jiaxing Zhu, Leping Dang, Hongyuan Wei
Abstract
In this work, an energy-efficient extractive dividing-wall column process with heat integration (E-DWC-HI) is proposed for the first time to separate the dichloromethane (DCM)–methanol (MeOH) azeotrope, which is a widely existing waste effluent in the pharmaceutical industry. The result of economic evaluation shows that the E-DWC-HI process is a preferred choice for the separation of DCM–MeOH mixture. Designing a robust control strategy is essential for the E-DWC-HI process. Thus, four control structures are proposed and tested under the disturbances of ±20% feed flow rate and ±5% feed composition. The basic control structure (CS1) and the double temperature difference control structure (CS2) both have a fixed vapor split. The dynamic response shows that the required purity cannot be met due to the loss of an important control degree of freedom. In CS3, variable vapor split is carried out by adjusting the pressures on the two sides of the dividing wall, and all product purities are held close to their set points except for MeOH product purity with an obvious offset. The dynamic performance of CS4 has been significantly improved by integrating pressure swing and pressure compensation. The offset of MeOH product purity is significantly reduced from 2.05 to 0.03%.