(107a) Designing Packed Multi-Partition Wall Dividing Wall Columns

As proven in industrial practice, application of dividing wall columns (DWC), where appropriate, leads to approximately 30 per cent saving in both energy and capital, compared to equivalent conventional distillation sequences for obtaining three high purity products. Simulation studies performed with well defined, mainly hypothetical pure component systems, have indicated that designing four and more products DWCs could enhance potential energy and capital savings significantly. This implies that there is a strong incentive to consider implementing more complex designs of a DWC. These can certainly be assembled without great difficulties as structured packing columns, by utilizing well established non-welded, self-fixing partition wall technology that provides full flexibility in this respect. Nevertheless, the lack of experience and insight related to modeling and simulation of industrially relevant separations of multicomponent feeds, as well as suitable design procedures, accompanied often by a fear of unstable operation are main barriers in this respect.  

The design and control of four-product DWCs have been addressed and encouraging advancements made in previous efforts, indicating that a packed DWCs could be arranged as a practical, single partition wall column, or a thermodynamically optimal, but complex, three-partition walls column. These and other simulation studies performed using so called V_min-diagram method as a practical means to identify and quantify accordingly internal configuration of a DWC, providing reliable data for initialization and effective execution of detailed calculations performed using an appropriate rigorous model arranged for this purpose using facilities available in a commercial software package, indicated a large potential for energy and capital saving by implementing DWCs in aromatics processing plants as encountered in complex refineries.  Interestingly, it appeared that depending on the choice and specification of interesting products (components and/or fractions), a three-product, a four-product and even a five-product DWC could be an interesting option for aromatics processing plants.

Rigorous simulations provided optimum solutions with respect to stage and reflux requirements of alternative designs, and, most importantly imposed vapor splits that need to be realized in practice to enable proper operation of a complex DWC. The objective of this paper is to show how to dimension a multi-partition wall DWCs, i.e. how to arrange pressure drop in parallel sections, using available means (structured packings with different specific areas, corrugation inclination angles and corrugation designs in combination with state of the arts narrow trough distributors, and chevron and chimney tray type liquid collectors) in conjunction with appropriate predictive methods (available in public domain) to ensure achieving required vapor splits. The resulting column dimensions and related details in conjunction with adopted cost estimation methods allow a proper assessment of usability of a DWC. Our studies indicate clearly that a multi-partition wall DWC is an industrially viable option, which, if implemented, could contribute to a significant increase in profitability of aromatics processing plants.