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

Vapor recirculation line

Vapor recirculation line

Vapor recirculation line

We are pumping MeOH from a railcar to a storage tank, and venting the vapors from the tank back to the rail car. I have run flow calculations from the tank to the rail car to determine the maximum vapor rate through the OH line - to not overpressure the tank. Then I back calculated the liquid flow rate that matches the maximum allowed vapor rate (then limiting the pump in rate). I am second guessing myself.. Since the vapor back to the RC matches the displacement of the MeOH being pumped out of the RC, should I not be limiting the pump out rate?

RE: Vapor recirculation line

I think you want to limit the backpressure in the tank, so as to not lift/crack the vent unit with the lowest set pressure. Say, limit the backpressure to at least half the lowest set pressure vent unit. Tell us what those pressures are, because I’ve made some assumptions, but I doubt that will limit the pumps liquid flow appreciably.

Good Luck,

RE: Vapor recirculation line

Vapor recirc. line must be free draining, else local liquid pools within the line may invalidate pressure drop calcs. Use a generous roughness value for dp calc since carbon steel corrodes with methanol vapor. API650 tank PSV usually is set at 80% of tank upper design pressure - ask PSV manufacturer what the simmer / crack open pressure is. Say 80-90% of PSV simmer pressure would be the permissible upper limit of operating backpressure on the tank during RC pump out operations.

RE: Vapor recirculation line

Thanks for the input!

RE: Vapor recirculation line

I don't fully understand your question or what yu are doing?

You say you're pumping methanol into the tank and getting a vapour return line back into the railcar. So far so good, though normally the pressure available for the vapour is very low as atmospheric tank design pressure is usually inches of water.

But then you mention pump out rate? From the storage tank?? Is this always going to happen or how does it fit into the process.

Also you need to be very carefully about the negative pressure in the rail car. They really don't like it and can collapse very easily.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Vapor recirculation line

Thanks for the comments. We are pumping from the RC to the tank, and running the vapors back to the RC.

Regarding the vacuum problem you are correct - RCs don't like vacuum. These are vacuum protected.


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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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