3 replies to this topic

[maud]

Am designing a methanol distillallation plant. I have read that assumptions of pressure drops have to be made. If as an example my distillation column operates @ 101.3kPa then I assume pressure drop of 0.1.
Is the the following calculation accurate?

P=101.3*10^3 *0.1
=ANS

Pt=101.3*10^3 - ANS
=(this is then your pressure used to get the bubble & dew point temps.)

[Radionise]

maud,

I assume that the pressure you quoted in your post is an absolute pressure.

You can assume what ever pressure drop that you want. 0.1, 0.2, 0.3, 0.4, 0.5..... what ever it is, nobody can say you are wrong.

But my argument here is, atmospheric pressure = 101.31 kPa. So if you have a pressure drop on atmospheric pressure,
it means that you would have a pressure lower than 101.31 kPa. Now what does that tell you? A distillation tower operated at vacuum pressure? Would this make sense?

[joerd]

The common convention for operating pressure of a distillation column is to refer to its top pressure, if you don't explicitly specify otherwise (which would of course be the most accurate thing to do).
A pressure drop of 0.1 kPa (I assume, because you don't specify that) seems very low, 0.1 bar = 10 kPa seems more likely. However, as Radionise said, there is no way for me to tell what is right.
So a distillation column operating at 101.3 kPa with a pressure drop of 0.1 kPa has a top pressure of 101.3 kPa, and a bottoms pressure of 101.4 kPa.