×
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

Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

(OP)
Hi all;

I am verifying the size of a two-phase separator (Gas/Liquid) vessel. There are two criteria which should be fulfilled. The terminal velocity in gas section and hold up time for liquid service.

I am struggling with the hold up time or height difference in liquid levels between each levels setting:
The criteria for liquid section; i have got here is as follow:

Description Symbol Requirement

High Level Shut Down HLSD 1-2 minutes with minimum 100 mm (from HLL to HLSD)
High Liquid Level HLL "liquid hold up time to be considered with 300 mm
min (from LLL to HLL)"
Low Liquid Level LLL 1-2 minutes with minimum 100 mm (from LLSD to LLL)
Low Level Shut Down LLSD 150 mm mini, but to becompatible with time required to close a
SDV

Now what my question is?:

Does anyone know what is the basis for 100 mm or 300 mm height differences in between the levels ? how about basis for time?

The vessel I am checking the size for, doesn't meet the above liquid criteria and I wanna to rationalize/ justify to ignoring these criteria. I mean not really ignoring, but changing a little bit in the height.

Any light in this shadow would be much appreciated.

Cheers;
Sinadi2003

RE: Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

the design depends from flows and properties of fluids so you may find separators of very different sizes with different operating conditions and levels,
it is difficult to answer without detailed information, however the "100 mm or 300 mm height differences" could depend from a specific process request or sensor type, for example a (magnetic) float level sensor, I have seen these spec's in petrochemical projects.

RE: Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

(OP)
Thanks apetri and 25362 for your replies.

RE: Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

I think that you focus a lot on the stated minimum distances - look more at the retention times.

Generally .- between HLSD and HL alarm you dont want that much time (hight difference) (it cost money) - but the accuracy of the instrument, waves etc should not trip your system. Also you would want some time for your operator to react.

- The volume between Nl and HL alarm(and NL and LL alarm) is where you would normally "absorb" you variations in flow. Here its important if your separator e.g. is an inlet separator where slugging from wells or pipelines may cause variation in liquid flow.

The level at NL is normally what you base your separation calculation on.

Best regards

Morten

RE: Two-Phase Separator Sizing - Hold up time criteria ....What's the concept behind it?

Those minimum guidelines are more for fabrication and control reasons.

The 150 mm minimum setting for the bottom LLSD is the distance above the lower tan line and is usually the minimum the mechanical engineers like to have nozzles and the resulting welds close to the circumferential weld for the bottom head.

100 mm minimum distance is only 4 inches. In terms of sizing your vessel and getting the total height it has a minimal impact. Depending on the instrumentation used, 4" isn't much of a margin to handle changing specific gravity and field calibration.

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