engleski

Dimensioning packed dividing wall columns with multiple partitions

Detailed simulation studies have indicated that four and more products dividing wall column configurations could further enhance energy and capital savings potential associated with implementation of this utmost sustainable distillation technology. So far only one four product packed DWC has been installed in practice. This well operating column is designed as a single partition wall configuration, which means that from practical reasons certain concessions have been done with respect to energy saving potential. A detailed analysis of a similar four products case, from an actual aromatics plant, provided basis for comparison and evaluation of cost-effectiveness of a multiple partition wall configuration. It appeared that the relative gain in energy savings with respect to a single partition wall column is that large that a closer consideration of implementing a multiple partition wall becomes an interesting option. One should realize that well established non-welded partition wall technology allows arranging such a complex internal structure, however introducing multiple vapour splits along the partitioned part of the column represents a great challenge on dimensioning side. In order to ensure equal pressure drop in parallel sections wit fixed liquid loads the designer needs to be able to arrange the hardware related flow resistance to comply with vapour loads that will ensure spontaneous establishing and maintaining required liquid to vapour flow rate ratios. This implies certain flexibility with respect to adjusting the pressure drop, which, in case of columns equipped with structured packings, appears to be feasible to required extent by varying structures packing geometry and free area of liquid collecting and distributing devices accordingly. The objective of the present paper is to introduce and demonstrate a predictive model that accounts for variations in all pressure drop influencing structured packing and liquid collector/distributor geometry related parameters. This model is the heart of an overall design method that allows establishing the internal configuration of both single and multiple partition walls DWCs with sufficient accuracy. Realistic dimensions in conjunction with adopted capital costs estimation method allow proper assessment of alternative options. Base case evaluation results indicate that profitability of aromatics processing plants as encountered in complex refineries could greatly be improved by implementing four product DWCs, and that a multiple partition wall column is a highly attractive option in that respect. Three product dividing wall columns (DWC), as proven in industrial practice, can lead to significant reduction in both energy and capital costs when compared to equivalent conventional distillation sequences. 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. Screening and conceptual design by V-min diagram method showed that, depending on the choice and specification of products (pure components or fractions), a simplified four-product DWC and even a five-product DWC could be an interesting option for an aromatics processing plant. Rigorous simulations, using facilities available in a commercial software package, based on preliminary designs, provided optimum solutions with respect to stage and reflux requirements. Columns where then dimensioned as packed columns, and based on those results total annualized costs of studied configurations were calculated and compared. Results indicated a large potential for energy and capital saving by implementing DWCs in aromatics processing plants, as encountered in complex refineries.

Dividing wall column; dimensioning; energy saving

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