8 replies to this topic

[xzell]

Hi guys, im new around here. Recently my lecturer gave me an assignment to size a column, and i need to decide the top liquid disengagement height and the bottom surge height for my column.

i know that the guidelines are bout 4 feet for the top and 6 feet for the bottom. However, my lecturers asked for justifications. I tried finding but to no avail, all of them just cite general figures as rule of thumbs. I'm wondering if anyone here could help me? Thanx

[breizh]

xzell ,
Let you read this document and consider the references .
http://www.cbu.edu/~...ll7.html#height

Perry is also a good reference

Hope it helps
Breizh

[xzell]

xzell ,
Let you read this document and consider the references .
http://www.cbu.edu/~...ll7.html#height

Perry is also a good reference

Hope it helps
Breizh

Hi bro, thanx for yr help, unfortunately, i was not able to access the link u gave me. it says access denied

[Zauberberg]

Refer to attached materials from GPSA Databook. The bottom sump dimensions (height) will depend on the residence time required for this particular application. Top section details will depend on feed/reflux arrangements so there is no universal answer.

Attached Files

•  Mech.Design.pdf   174.52KB   295 downloads

[abhi_agrawa]

If you have single pass trays, then the top height is usually governed by the requirement of a manhole at the top. In that case, you would need a 24 inch manhole and minimum 3.5 ft above the top tray for the manhole.

If you have a more complex arrangement like two or four pass trays, then you may need more than 3.5 ft above the top tray.

Hope this helps,
Abhishek

[xzell]

hi guys,

Thanks for all your help so far. Maybe I should phrase my questions this way:

Why must we have a liquid hold up at the bottom and a vapor space at the top?

[Zauberberg]

Liquid volume is required for two reasons: level control purpose, and provision of static head for reboiler circulation in case of thermosyphons. Different examples are given in the document I have attached in my previous post.

Vapor disengagement is required on top of the tower in order to maintain separation efficiency and avoid intensive liquid entrainment into the equipment downstream.

[Art Montemayor]

I will add this third reason to Zauberberg's good response:

An amount of liquid inventory is needed at the bottom sump due to the common sense need to create a SEAL between the liquid being evacuated and the vapor phase retained. This is typical engineering good, practical sense.

Think about it. How can one continuously evacuate liquid from the the bottom contents without allowing vapor blow-through? The answer is that you must create a phase barrier; and that phase barrier is a nominal level of liquid (either for thermosyphon reboiler purposes or for simply ensuring that you evacuate only liquid from the bottom sump. If you want to evacuate all liquid from the vessel as soon as it is introduced or formed, leaving only vapor in the vessel, you are trying something that is practically not possible or needed. Why would you seek to do such a thing?

[xzell]

Thanx alot for your help, really appreciate it