1 reply to this topic

[NoobMi]

Hi all

im using Fair's procedures for my distillation diameter calculations. i have attached my excel calculations on the below.
Some information: 24 in tray spacing, 75% flooding allowance, η=0.90
Max vapor flow at top = 11471.1 m3/hr
Max vapor flow at bot = 8137.7 m3/hr

Question:
1) my calculated diameter based on top and bottom was 6ft and 7ft respectively. so should i use 6ft, 7ft or an avg of 6.5ft?
2) if i was to use the highest diameter of 7ft and placing it back to the top diameter for re-calculation, my flooding % becomes 55%, which is below heuristics of 65-85% flooding operation. So is this ok?
I use (vapor vol/active area) to find the actual vapor velocity and compared to the flooding velocity
3) if i were to continue with the calculations for pressure heads should i then use the vapor/liquid flow rates at the top or bottom?

Thank you

Attached Files

•  Book1.xlsx   31.65KB   399 downloads

[S.AHMAD]

1. Technically speaking, you can use either 6ft or 7ft or 6.5 ft as long as the flooding is below the maximum limit. Since you are using 75% flooding, you can check the % flooding using 6ft diameter for the bottom section
2. Economically speaking, it is preferred to use the lower diameter, since the investment cost will be cheaper.
3. It is not unusual to have lower diameter at the top and bigger diameter at the bottom section. In crude distillation column, we normally encounter a tower that have smaller diameter at the top, bigger in the middle and smaller at the very bottom.
4. On the other hands, it is always a good idea to have bigger tower for future expansion program such as de-bottlenecking. This is normally a management decision
5. From project management point of view, try to save cost as much as possible.
6. The choice is yours and be ready to defend your decision

Edited by S.AHMAD, 14 March 2012 - 03:42 AM.