3 replies to this topic

[Zauberberg]

Rywo,

It's easy to visualize the concept you are speaking about. Let's look at it:

1. More feed at lower temperature = lower heat input to the column. What drives the process of fractionation? If you say "heat", you got the answer on your question about separation efficiency.

2. Distillation tower does not act as a storage tank, where liquid inflow and outflow affect system pressure. Vapors are generated in reboiler (together with vapors coming from the feed) and partially condensed by downflowing reflux. Reflux evaporates while condensing upflowing vapors, and is recondensed in overhead cooler/exchanger. Thus, reduced heat flow into the column will cause the reduction of pressure. Assuming all other things unchanged, in your case the pressure will remain the same because total heat input is not changed.

[ricky]

Assuming all other things unchanged, in your case the pressure will remain the same because total heat input is not changed.

In my quick thought,

1. Less feed temperature will cause less vapor fraction in feed

2. Case 1 will cause less vapor traffic in both rectifying and stripping section of the column

Note: Case 2 is true if cooling load at overhead condenser and heating load at reboiler is same at all time. This is, though, based on your control scheme. More liquid --> less bottom temperature --> fuel (or steam) control valve opening will be increased to meet temperature demand. However if the design of that control valve does not properly consider feed temperature drop (or minimum bottom temperature), the valve can not compensate the temperature drop, at some extent. At this point, the temperature at bottom section of column can not be maintained, and so cause less vapor traffic throughout the column.

3. If case 2 is true, column pressure will decrease.

Since designing distillation column is a complex matter, and simulating it is much more difficult, I can not consider all cases here. Those are up to your control design and scenario involved.

Any comment is welcomed

[Padmakar Katre]

Dear,As said by Zauberberg distillation column is is not the storage tank as it will have separation(mass transfer will take place) provided your column reboiler is designed for the cold feed condition. And the increase in feed flow is withing flooding limits of the resultant Vapor-Liquid traffic in your column.
As the query is related to the Student forum I like to ask to RYWO regarding the exposure to Distillation Column Operation whether he has it or no. Why the liquid level in column will increase? (Inflow= Outflow). The associated piping and all the related accesseries are designed so carfully that so any column could not have any issues as far as increased levels are concerned. You can have the increase in feed flow which within the design margin of the system so no column opertaional issue.