×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Take credit for column condensing when reboiler is overboiling?

Take credit for column condensing when reboiler is overboiling?

Take credit for column condensing when reboiler is overboiling?

(OP)
Working on sizing a PSV for a column. I am considering the excessive reboiler heat input scenario. In a thermal-siphon reboiler, the process flow is heated in the tube side with steam on the shell side. The control vale on the steam supply senses the column temperature to control the steam flow. An overpressure scenario potentially can be created when the control valve fail-wide-open, passing excessive steam to the reboiler, generating excessive vapor in the column. Although it is likely the steam trap can not remove the consequent excessive steam condensate, eventually paralyze the reboiler operation, it is better to be conservative not to take credit for it. The column top pressure is controlled with reflux flow.
When calculating the relief rate, I assumed "steam control valve failure" with "reflux failure" is a double jeopardy. I checked the reboiler heat transfer capacity and determined the excessive heat input can exceed the condenser's capacity to condense or otherwise absorb the build-up of pressure. Therefore, I subtract the condensing duty from the reboiler duty at upset condition. Based on that heat input, I calculated the required relief rate.
Would you agree with my approach? Should I take more conservative way not to count on the condensing capacity? Please share your experiences and insights. Any comments are very welcome.  

RE: Take credit for column condensing when reboiler is overboiling?

carol2005, my view is you only have to relief the additional vaporization due to the control valve failing open, which seem similar to your approach.

The difficulty is deciding how much additional steam will condense in the reboiler. I would calculate it from the reboiler area, clean U value, and relieving temps, and not the change in control valve Cv.

  

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!


Resources