Pressure profile in a distillation column

[naapranam]

I AM CONFUSED ABOUT THE CONDENSER AND REBOILER PRESSURE IN A DISTILLATION COLUMN..WHEN I AM SPECIFYING A DISTILLATION COLUMN IN HYSYS, WHEN I AM CONSIDERING THE Pcondenser>Preboiler, there is a message that "pressure reversal in the column"..but i feel that feed tray pressure is greater than the both condenser and reboiler...suppose at feed tray the pressure is 2kg/cm2....as it reaches the condenser there will be pressure drop in the trays and condenser and hence it should be less than the feed tray pressure (say 1.7 kg/cm2)...in the same way the reboiler pressure also should be less than the feed tray pressure....

but when i am specifying like this in hysy i am facing probelm that pressure reversal in the column...
can any body explain the pressure profile in a distillation column....and how my Pressure drop should be consider per tray ?

[sniperel]

hello my friend!
Please note some rules of thumbs when you simulate a distillation column:
1. The pressure in the condeser is dictated by the cooling medium. More often you have total condesation of the overhead product.
2. The top pressure is the pressure in the condenser plus approximatly 0.2 bar (pressure drop for the condenser)
3. The pressure drop per tray you can consider to be about 0.01 bar

Hope I helped you! Have a nice day!

[naapranam]

ok then what about the reboiler pressure? how to specify the pressures in the reboiler and condenser in hysys?

[marvalar]

Reboiler pressure is always higher than condenser pressure.
You take condenser pressure you add pressure drop in the column and you have reboiler pressure.

[naapranam]

let us assume that condenser pressure is 1.3 kg/cm2
when there is pressure drop then the reboiler pressure will be less than condenser pressure. say the pressure be 0.2 kg/cm2. then the reboiler pressure will decrease i.e 1.1 kg/cm2.then my doubt is how come the rebolier pressure will be greater than the condenser pressure????

[sniperel]

nooo!
You ad 0.2 kg/cm^2 so the pressure will be 1.5 kg/cm^2

[suresh72kumar]

Hi,
The vapour from the bottom flows up to the condenser through the trays. Hence the pressure at the bottoms will always be more than the top pressure.
suresh

[JelaniChem]

Hi friend, the vapor created in the reboiler flows up the column, because a pressure gradient exists in the column. The pressure is highest at the reboiler and lowest at the condenser. If the feed comes in at a higher pressure than the pressure at the feed stage, it will simply flash to the feed stage pressure. Note for dynamic simulations, you are required to specify the feed pressure equal to the feed stage pressure.

So if the pressure is highest at the bottom of the column, how does the liquid flows down the column? Simple, the liquid hydraulic head.

[naapranam]

thanks