Revamping a conventional naphtha splitter to a dividing wall column
Installation of new equipment, performance results, and final commissioning of a DWC and its ability to sharply fractionate three components in one single column
Giuseppe Mosca, Joshi Chandrakant, Andrei Cimpeanu and Brad Fleming Sulzer Chemtech
A dividing wall column 1 (DWC) is a distillation column combining the operation of two conventional col- umns in one shell. The separation of a three-compo- nent mixture into individual components is made possible by the installation of a vertical wall in the middle of the col- umn. The feed enters the column on one side of the wall, and on the other side of the wall, a high concentration of the middle boiling component is achieved. The result is that three components can be sharply fractionated in one single column. In the conventional setup, two columns, two reboilers, and two condensers are needed: the DWC needs only one vessel, one reboiler, and one condenser. The DWC has shown its advantages in many applications, typically for liquid mixtures of equal amounts of three volatile components and for cases where a high amount of middle boiling component must be separated from smaller amounts of light and heavier components. 2 Rule of thumb: The bigger the side-stream portion of the feed, the higher is the effectiveness of the dividing wall. DWCs have been implemented in a large variety of refinery,
petrochemical, and chemical applications. Recently, they have even been implemented for reactive distillation. More complex DWCs (Dual 3 DWCs) can be used for the separa- tion of a stream in four cuts. DWC: Benefits and limitations From a unit operation point of view, a DWC eliminates the thermodynamic inefficiency of the two-column setup,4 where the remixing of the middle and heavy boiling com- ponents at the bottom of Tower 1 cannot be avoided (see Figures 1 and 2 ). DWCs allows for several benefits5 compared to the two-column setup: • Up to 40% reduction of investment cost • Up to 40% reduction of operational cost • Up to 40% additional theoretical stages • Up to 50% energy savings • Up to 40% reduction of plot plan space and consistent reduction of greenhouse gas emissions. DWCs also have limitations compared to the two-column setup:
Qc1
Tower T1
Top
T1
A
A
Qc2
T2
B
Feed A, B, C
Qr1
B
C
B, C
Remixing
Qr2
Bottom
0
0.2
0.4
0.6
0.8
1
C
Composition mole fraction
Figure 1 Composition profile in Tower 1 for two-column setup
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PTQ Q2 2024
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