ChemCad Simulation of Divided Wall Column
Simulating a Divided Wall Column with various column configurations can be easily achieved when developed within ChemCad. Why would one consider a divided wall column in the first place? Divided wall columns offer savings in capital costs and operating costs but more specifically, energy costs!
Traditionally, if you have n components to separate by distillation then the number of columns required is n-1. For 3 components 2 columns are required and for 4 components 3 columns are required.
For example; separating benzene, toluene, and xylene there are three ways to do the ChemCad simulation:
Type 1 – Four-column setup (basic concept) SCDS
- Total 8 units, 12 interconnecting streams.
- Four (4) columns, two (2) mixers and two (2) splitters.
- Sequential calculation. Slow convergence.
Type 2 – Two-column setup (4 alternatives) SCDS
- Total 2 units, 4 interconnecting streams
- Two columns
- Sequential calculation
- Medium convergence
Type 3 – One-column setup
- Total 1 unit, no interconnecting streams
- One column
- Simultaneous calculation
- Fast convergence
Note that with this ChemCad simulation all three types of simulations lead to the design of one single divided wall column.
Some of the unique hardware for the design of these columns includes:
- The splitter that sends refluxed liquid down each side of the divided wall
- The divided wall itself
- The packing or structured packing sections that are half of a circle for that cross sectional area
- The packing or structured packing sections that are a full circle for that cross sectional area
- The length of the divided wall and its position inside the column
For this example, the feed and product streams shown here are for option three. They are the same for all three examples. (See below)
| Stream Name | A,B,C | A3 | C3 | B3 |
| – – Overall – – | ||||
| Temp °F | 215 | 176.2 | 291.7 | 231.2 |
| Pres mmHg | 760 | 760 | 760 | 760 |
| Enth MMBtu/h | 0.14088 | 0.094113 | -0.00022 | 0.0498 |
| Vapor mole fraction | 0.0395 | 0 | 0 | 0 |
| Molar flow lbmol/h | 11.0075 | 3.8403 | 2.826 | 4.3411 |
| Mass flow lb/h | 1000 | 300 | 300 | 400 |
| Std liq m3/h | 0.5158 | 0.1539 | 0.1538 | 0.2081 |
| Std vap 60F m3/h | 118.3 | 41.3 | 30.4 | 46.6 |
| Flow rates in lbmol/h | ||||
| Benzene | 3.8405 | 3.8389 | 0 | 0.0017 |
| Toluene | 4.3412 | 0.0014 | 0.0021 | 4.3377 |
| O-Xylene | 2.8257 | 0 | 2.8239 | 0.0018 |