(442a) Fundamental Investigation of Divided Wall Distillation through Pilot Column

Roach, B., University of Texas at Austin; Eldridge, R. B., University of Texas at Austin;

In the United States, distillation accounts for approximately 5% of total energy consumption.  Dividing wall columns (DWC) offer an innovating approach to distillation, which can minimize energy usage and capital costs compared to traditional separation methods.  Despite the advantages of a DWC, the technology has not been widely implemented due to the lack of fundamental research available in open literature. 

A project has been initiated by the University of Texas’ Process Science and Technology Center (PSTC) with industry support to study and document the operation and control of DWCs.  A pilot scale dividing wall distillation column has been built and is fully operational.  The pilot column is investigating a variety of mixtures with a broad range of pressure and temperature ratings.  The column expands upon the work previously done by the Fieg group¹.  Their group studied an alcohol system at vacuum conditions with a 2.4” column diameter.  Their model’s utility in DWC operation and design has not been determined on its applicability to larger columns and other chemical systems.  The PSTC’s 6” pilot column will allow for a study of DWC scale-up from Fieg’s column studies.    

Preliminary results show the validation of process models and simulations.  The DWC was modeled with initial mass transfer and hydraulic coefficients, using AspenPlus and HYSYS.  Initial models show 30-50% energy savings for DWC versus traditional two column configurations. 

Both MPC and PID control are being employed in the pilot plant to determine optimal control strategies.  Since little is publically known about the DWC process the locations along the column that best reflect changes in composition must be identified.  The interactive nature of the DWC process presents challenges in composition control.  Stable divided wall column control has been achieved over a wide range of operation parameters.  Studies for various disturbances in the feed flow rate and composition as well as for start-up and shutdown have been performed to model industrial applications. 

1)     Niggemann, Gerit, Christoph Hiller, and Georg Fieg. "Experimental and Theoretical Studies of a Dividing-Wall Column Used for the Recovery of High-Purity Products." Industrial & Engineering Chemistry Research 49.14 (2010): 6566-577.