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[MSalazar]

Hello all,

I'm a final year student doing my design project on Catalytic Reforming. I am currently designing a distillation column for the separation of C5+ reformate and LPG. In order to do this, I have been using Aspen HYSYS for liquid and vapour values, and Chemical Engineering Design by RK Sinnott, for design method. I have specified n-pentane as my Heavy Key and n-Butane as my Light key, and the column has 8 stages.

The problem I have encountered is that my feed contains a greater quantity of liquid and not much vapour, this causes the liquid-vapour flow factor, FLV, to be quite high (around 8.6). I am supposed to use FLV to work out a K1 constant (K1 is used to work out vapour flooding velocity) from figure 11.27 in Sinnott (pg. 568), however the graph in figure 11.27 has a maximum value for FLV of 5.0, hence I cannot obtain the necessary K1 value from the graph. I tried extrapolating the values however this is not valid since the graph is constructed from experimental data.

Is there any other way I could design this column? or are the sources where I can find the K1 constants with greater FLV values?

I'm attaching my design rationale spreadsheet and my catalytic reforming unit HYSYS simulation in .XML file extension.

Thank you for your time.

MS

Attached Files

•  CAT_REFORM_SIM REV 5.xml   2.04MB   94 downloads
•  Design Project Individual MS.xls   103.5KB   121 downloads

[joerd]

Your calc looks reasonable at first sight - I did a quick check against Hysys' built-in Tray Sizing utility, which gives about the same column diameter.
A few observations:
- your feed comes in cold, so it quenches a lot of the vapor going up. This is why the top of the column is much less loaded than the bottom.
- your condenser is rather cold, only 13 C. Make sure that this is feasible with the cooling medium you have available.
- what are the column specs? I suppose it is something like butane in the bottoms, or a recovery rate. Better set it as a spec, in place of using reflux ratio and vent rate.
- it looks like you have too many trays in the bottom section.
These are just a few thoughts, didn't spend too much time, but hopefully helps you thinking.