The diameter given by Aspen Plus can be checked by using the approximate heuristic that the F factor should be equal to 1 (in English engineering units)
F = VmaxyTV
where Vmax is the maximum vapor velocity in units of ft/s and pV is the vapor density in units of lb/ft3.
All the detailed information about the vapor and liquid flows throughout the column can be accessed by clicking the subitem Report under the C1 block and under Property Options checking the box in front of Include hydraulic parameters. Then, after the program is run, click the subitem Profiles and click the Hydraulics page tab. The window that opens gives lots of information about liquid and vapor rates and properties, as shown in Figure 3.54.
The maximum vapor volumetric flowrate is 9.23 ft3/s and occurs on stage 32. The vapor density on this stage is 2.82 lb/ft3. Using an F factor of 1, the maximum velocity is 0.595 ft/s, which give a cross-sectional area of 155 ft2. This corresponds to a diameter of 14.0 ft or 4.28 m, which is somewhat lower than the Aspen Plus result (5.91 m).
In either case, this is a very large distillation column, and, as we will see in the next chapter, it is very expensive to buy.
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