×
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

Purging gas flow rate design criterion

Purging gas flow rate design criterion

Purging gas flow rate design criterion

(OP)
S!
I have to estimate the flow rate of purging gas, air in this case, to keep some sighting glasses and instrumentation wells in a furnace. An older engineer told that is necessary to keep a superficial velocity (flow rate/internal area of the pipe) equals to 1 m/s, but he is not sure about this value. During my calculations I've found that the total amount is, im my opinion, too large. Just for example, in the smaller furnaces the flow rate for the purging gas is about half of the air needed for the combustion. The furnaces are specially sensitive to excess of air. It are sulfur recovery furnaces, so the air flow rate must be very well measured and controlled.
The smaller furnace, a in line reheater, has a total of five locations that need to be purged: 2 flame detectors (2 in), 2 sighting glasses (2 in) and 1 pilot/igniter well (3 in).
Does anybody knows a rule of thumb or a typical design value for purging gas velocity?

RE: Purging gas flow rate design criterion

sfacchin, I seem to recall instrument purge rates are typically 1-5 fps. If too much air is an issue, you can use nitrogen.  

RE: Purging gas flow rate design criterion

whatever velocity guarentees turbulent flow is what you need. depends on pipe diameter and roughness, but around 0.5 feet/second.  Just to make sure, use at a minimum 1 foot/second as pointed out earlier.  We always used the 1 foot/second as a minimum purge rate on a flare header.

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