Distillation, a ubiquitous method in the chemical industry, is often considered an energy-intensive separation method and accounts for about 2-3% of total U.S. energy consumption. For multicomponent mixtures, separation into multiple streams rich in one of the components requires a sequence of distillation columns and hence associated large capital cost. The dividing wall columns (DWCs) overcome these drawbacks due to the compact single-shell structure. A systematic framework for synthesizing the DWCs search space is present in the literature [1, 2]. Within this search space, DWCs with a single condenser at the lightest and a reboiler at the heaviest component product streams are especially attractive from the perspective of heat integration using a heat pump. Specifically, for four-component mixtures, three configurations are gaining renewed attention. These include Kaibel [3], Agrawal (satellite) [4], and Sargent [5] (fully thermally coupled) configurations.
The Kaibel DWC has a single partition, making it a preferred configuration in the industry due to its simple construction and control. The Sargent configuration is associated with the minimum heat duty but has the highest number of column sections and associated transfer streams. Also, controlling vapor flow distribution within the Sargent DWC presents the operational challenges limiting the industrial viability of this configuration. The Agrawal DWC presents a more practical scheme with fewer partitions. Multiple studies have focused on the design, hydraulics, and control within the intensified multi-partition columns [6, 7]. But there are no structured studies quantifying any potential energy penalty for Agrawal and Kaibel DWCs over the Sargent DWCs within the search space.
To bridge this literature gap, we examine the minimum vapor duty for the configurations with the help of a shortcut model based on the Underwood method. We systematically compare the vapor duty for the three DWCs configurations for a quaternary mixture over the feed composition and relative volatility space as suggested by Giridhar and Agrawal [8]. It is observed that the feed composition and relative volatility space where Kaibel DWC has similar heat duty as the Sargent column is much smaller than that of the Agrawal DWC. These results also indicate that the Agrawal DWC often has a heat duty similar to the more complex Sargent DWC.
Furthermore, for Sargent DWCs, we examine the variation in vapor duty when the side-draw transfer is constrained to be a liquid stream to alleviate the operational challenges. The existence of a flat optimality region allows the flexibility to operate the same configuration with redistributed material flows, enabling the practitioner to choose from viable solutions suitable from an operational and control point of view. We demonstrate the operational freedom through the V-min diagram and quantify the flexibility region for each partition/column. Further on, we extend the analysis to the five-component system and generalize the observed trends.
- Ramapriya, G., Tawarmalani, M., Agrawal, R. (2018). A Systematic Method to Synthesize All Dividing Wall Columns for n-Component Separation—Part I, AIChE Journal. 64, (2) 649-659.
- Ramapriya, G., Tawarmalani, M., Agrawal, R. (2018). A Systematic Method to Synthesize All Dividing Wall Columns for n-Component Separation—Part II, AIChE Journal. 64, (2) 660-672.
- Kaibel, G. (1987). Distillation Columns with Vertical Partitions, Chem. Eng. Technol. 10, 92-98.
- Agrawal, R. (1996). Synthesis of Distillation Column Configurations for a Multicomponent Separation, Ind. Eng. Chem. Res., 35, 1059-1071.
- Sargent, R., Gaminibandara, K. (1976). Optimum Design of Plate Distillation Columns, Academic Press, London, pp. 267–314.
- Uribe, C., Avila, J., Herrera, N., Gonzalez, R., Avila, S. (2021). Temperature control of a Kaibel, Agrawal, and Sargent dividing-wall distillation columns, Chemical Engineering & Processing: Process Intensification, 159, 108248.
- Guan, S., Li, Y., Li, G., Zhu, L., Pan, H., Ling, H. (2024). Design and hydraulic study of double-partition dividing-wall column, Asia-Pac J Chem Eng. 19(4):e3063.
- Giridhar, A., Agrawal, R. (2010). Synthesis of distillation configurations: I. Characteristics of a good search space. Computers and Chemical Engineering 34, 73-83.
