4 replies to this topic

[atn]

Hi,

For a binary distillation column with a single-feed, the optimal feed position (i.e. for which the number of trays is minimal) corresponds to the feed composition. In more precise terms, for a saturated liquid feed, the liquid coming from the plate directly above the feed plate should have the same composition as the feed of the column. Does the same conclusion hold for multicomponent mixtures ?

Thanks in advance for your replies (keep in mind I'm new to distillation).

[TroyH]

No stage in the column is likely to ever exactly match the conditions of the feed exactly. You need to make a judgement about where in the column is closest to the conditions of the feed, and locate the feed stage at that point.

I'm also new to multi component separations, but I hope that helps.


Edited for clarity.

[jairaj]

Hi,

For a binary distillation column with a single-feed, the optimal feed position (i.e. for which the number of trays is minimal) corresponds to the feed composition. In more precise terms, for a saturated liquid feed, the liquid coming from the plate directly above the feed plate should have the same composition as the feed of the column. Does the same conclusion hold for multicomponent mixtures ?

Thanks in advance for your replies (keep in mind I'm new to distillation).

hey there, im also new to distillation and what helped me gain a good theoretical understanding was a book, you should look into it. The multicompenent distillation section proves quite practical and usefull. I used it extensively in my course work. Heres the title and author,
Seader, Henley: Separation Process Principles, 2nd Edition
hope this provides some help,
cheers

[atn]

Thanks for your replies.

Let me change my question for a more realistic one.

Consider a single-feed distillation column separating a n-component mixture. Assume that the feed is a saturated liquid and let's denote by xF its composition vector. Let x_LK and x_HK be the molar fractions of the light key and heavy key components in the liquid coming from the tray above the feed tray. If we assume that the feed position is chosen as to minimize the number of trays, must the following equalities hold: xF_LK = x_LK and xF_HK = x_HK ?

[TroyH]

As I mentioned before, the feed stage composition is unlikely to match the feed composition in a MC separation. So I would have to say you equality does not have to hold true. You would however be aiming to have it hold approximately true (or as close as possible).

At least, that is the way I understand it.