Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Air separation

Air separation

Air separation

Any Smart comments!
Given that it takes 10 distillation trays to purify crude (or 40% purity)
oxygen into 95% oxygen at an air separation unit serving a chemical
complex.  The customer (owner of chemical complex), however, requires
99.9999% purity oxygen to feed a new oxidizer reactor in a pilot R&D

A new purification column is considered for purifying a side-stream of the
crude oxygen, to meet the oxygen purity demand in pilot facility. How many
trays should be designed into the new purification column ?  Assume that
the mass transfer efficiency per tray is constant (i.e. does not change
with composition and there is no pinch) and that tray gas-liquid flows will
be perfect.

RE: Air separation

Based upon the information you have given, if you assume that the tray efficiency is unchanged, the concentration of the impurities is multiplied by a factor of 0.78 across each tray.  At high purity levels, I have no idea if the assumption is valid.  If it is, you would need a total of 54 trays, or a second column with 44 trays in addition to your existing 10 tray column.

The math for the impurities is:

(0.6)*(0.78)^54 = 8.94*10^-7

Which gives a purity of:

1-8.94*10^-7 = 0.9999991

RE: Air separation

I want to ask about material of tray and thermosyphon type heat exchanger in bottom. 99.999% oxygen is likely to combust with aluminium metal. NASA has experienced that and lost lots of space pilots by implosion with oxygen and cloths made of aluminium.
In addition 99.999% oxygen means 1 ppm impurity. In air 50-100 ppm of hydrocarbons is normal. So it means that hydrocarbons accumulates in liquids in bottom when thermosyphon heat exchanger evaporates gas from liquids.
I am not sure of your process flow diagram. But you must change a lot and estimate cost & persuade customers.

Regards ;

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close