(225b) Classification and Comparison of Dividing Wall Columns

Dividing wall columns (DWCs) are known to reduce capital cost of a distillation process by putting multiple columns into a single shell. However, in literature^1,2, DWCs are also said to reduce energy requirement, which is an incorrect statement since each DWC configuration requires same heat duty as its thermodynamically equivalent simple column configuration. For example, the well-known Wright's dividing wall column³ is thermodynamically equivalent to the 3-component fully thermally coupled (FTC) configuration⁴. FTC configuration always has the lowest heat duty when all the columns are operated at similar pressures. Thus comparing Wright's dividing wall column with other three column configurations can often result in incorrect conclusion regarding heat duties.

Medenoor Ramapriya et al^4,5 presented a simple rule that, for the first time, enabled exhaustive enumeration of DWCs corresponding to any given thermally coupled distillation column-configuration in 2017. This work has enabled the synthesis of all possible DWCs for a given separation. However, use of “dividing wall column” continues to refer to only some common DWC configurations while ignoring several potentially useful DWC options.

In this research, all possible dividing walls are classified into 5 types, each type of dividing wall has its unique structural characteristics, such as the position of the dividing wall in the column, the number of breaking points on the column, the number of transfer streams, the number of condensers and reboilers, etc. These characteristics indicate the capital cost to build such a DWC. This classification is expected to simplify choices of dividing wall columns and provide a common language regarding DWCs.

A ternary separation is used as an example to illustrate how the classification works. The heat duty requirement of each ternary separation configuration has been calculated from the Global Minimization Algorithm⁶ developed in the group. Combining energy consumption and capital cost, this research provides a guideline to choose the optimal DWC configuration for a ternary separation.

Literature Cited

1. Dividing-Wall Column for Fractionationof Natural Gas Liquids in Floating LiquefiedNatural Gas Plants. Chemical Engineering Technology. 2016;39(12):2348–2354.
2. Synthesis of dividing-wall columns (DWC) for multicomponent distillations—A systematic approach. Chemical Engineering Research and Design. 2011;89(8): 1281–1294.
3. Wright RO. Fractionation Apparatus. 1949. US Patent 2,471,134.
4. A Systematic Method to Synthesize All Dividing WallColumns forn-Component Separation—Part I. AIChE J. 2018;64(2):649-659.
5. Thermal Coupling Links to Liquid-Only TransferStreams: A Path for New Dividing Wall Columns. AIChE J. 2014;60(8):2949-2961.
6. Nallasivam, V.H. Shah, A.A. Shenvi, J. Huff, M. Tawarmalani, R. Agrawal, Global optimization of multicomponent distillation configurations: 2. Enumeration based global minimization algorithm, AIChE J. 62 (2016) 2071.