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

Centrifugal Compression Train with Lower MW Gas

Centrifugal Compression Train with Lower MW Gas

Centrifugal Compression Train with Lower MW Gas

We are running a centrifugal gas compressor train (x 3 compressors in series).

The compressors were designed for gas MW of 23. Due to a change in gas composition, we may need to periodically operate the compression train on gas with MW 17.5.

We have confirmed that the compressors can provide the required head based on the compressor curve (with flows in excess of surge line).

I’m not sure if the low MW can affect any other aspects of the compressor operation e.g. dry gas seals. Are there any other checks that we should be doing based on the lower gas MW before operating with the new gas?


RE: Centrifugal Compression Train with Lower MW Gas

Discharge temp on each stage will be higher with lower mol wt - check TSHH setpoint / margin to design temp for affected kit.

If you running at constant mmscfd for both cases, then heat rejection rate at interstage and final coolers may not be affected, since increase in feed temp to each cooler would be offset by lower mass rate - to be checked.

The operating point on each stage may be much closer to the surge line at design speed - check with antisurge controller supplier if they are comfortable working with the closer approach.

RE: Centrifugal Compression Train with Lower MW Gas

The compressor will also be running at higher speed to develop the higher head - check if you are approaching the high speed alarm limit at the required mmmscfd.

RE: Centrifugal Compression Train with Lower MW Gas

- Check new seal gas phase envelop vs. risk of condensation in dry gas seal
- Check gas composition versus current material selection (presence of CO2, H2S or chlorides etc.)
- Rotating speed shall be within 100% speed
- Thrust bearings might be sized considering limit points on map which you may be now operating on continuously, this to be verified.
- Check the seal gas system vs. new operating pressures - head being equal (flow to the seals, orifice sizing, utility consumptions, external seal gas etc.)
Other questions:
- How have you ensured the head-flow point is still in the operating envelop considering new MW with map shape having changed ? have you received revised maps including pressure vs. flow maps from OEM or have you approximated this yourself ? in the old map you may be fine (not surging) but with the map fitted for new MW you may be running at different distance from surge - I don't remember from top of my head if MW going down would play in your favor or not.
- What happens to the alternative cases - if this is applicable, is everything within the performance envelop or are you running one set of process conditions only ?
Best advice as usual is: contact the OEM and have the machine qualified for this new gas.

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