2 replies to this topic

[sharonlae]

Hi

 

I am designing a trayed column for separation of propylene glycol from water on HYSYS.

I have set the pressure drop across each tray to be approximately 0.1 psi per tray by heuristics, but after including the aeration factor in the internals tab, the calculated pressure drop across each tray drops to 0.02 psi, because of lower downcomer backup.

Is this feasible in the industry? Or should I modify my internals to increase the pressure drop?

 

Thank you.

 

Best regards,

Sharon Lam

 

[breizh]

Hi,

You may find hints reading this paper.

Hope this is helping you.

Breizh

[PingPong]

..... but after including the aeration factor in the internals tab, the calculated pressure drop across each tray drops to 0.02 psi, because of lower downcomer backup.

Downcomer backup is the result of tray pressure drop, not the cause of it.

 

I am not familiar with Hysys but I am sure that what Hysys calculates is the result of your input.

Total tray pressure drop depends not only on aeration factor but also on outlet weir height, liquid crest over outlet weir and dry tray pressure drop.

 

If you specified a very low outlet weir height (or none at all), a huge number of sieve holes or valves (depending on tray type specified), and a large number of liquid passes the resulting tray pressure drop could come out very low.

 

I suggest you simply specify the tray pressure drop that you know is normal in this service (separation of propylene glycol from water).

 

The option to let Hysys calculate the tray pressure drop only makes some sense if you are evaluating an existing column with trays of which all details are already known.

While doing a new design it makes no sense to let Hysys (or any other simulator) calculate the tray pressure drop.

 

The purpose of Hysys is to obtain a heat and material balance including tray loadings for all columns.

After that you use dedicated software to design the trays (using the tray loadings from Hysys).