4 replies to this topic

[garych]

Hi,

Which is a more typical scheme for a distillation column temperature control? Top of column or bottom of column? What is the considerations that can be accounted in?

 

If i wanted to have to have a temperature control at the bottom of the distillation column, should I have the control valve installed at the inlet of the reboiler (steam line) or the outlet of the reboiler (condensate line)?

Which is the typical scheme?

 

If the control valve is at the condensate line, in terms of size, control valve is smaller, isn't that better?

 

I read that having a control valve at the condensate line will has a poorer dynamic response, can anyone explain this in details?

 

Thank you.

 

[breizh]

Hi garych

 

Probably good to read .

 

Hope this helps

Breizh

[oscarsender]

It depends on which compositions you really want to control. If you want to control light components then control the top, otherwise control the heavy components at the bottom. In both cases it is important also to control the tower pressure at the set point.  

 

With regards to location of control valve for temperature control each has their advantages and disadvantage:

 

If the valve is in the condensate line: the size of control valve will be smaller,requires lesser reboiler area due to larger effective delta T, stable condensate return pressure. However it will have a delayed response and a seal height for control valve is required to prevent vaporization upstream of it.

Edited by oscarsender, 06 July 2014 - 02:15 PM.

[Bobby Strain]

Books by Kister are quite good for this subject. You must consider the whole system and your objectives to implement proper distillation control. The DCS suppliers also provide software for distillation control. Shinskey also is a good reference to own.

 

Bobby

[Babu Prasad]

Control tray temp at middle of columns will be right control in turn it will ensure the right bottom temp. Flow control valve at steam inlet by cascading with control tray temp will have good control but hammering of condensate pot needs to be taken care while feed load is more as steam gets fully condensed.  A small Equalization line with steam inlet to condensate pot will maintain enough pressure to push the condensate into header.

 

Whereas keeping control on condensate line (by level control) will not fetch good control as level in the condensate pot will fluctuate widely and makes difficult to control the steam flow.