×
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

Hi; For a reciprocating compresso

Hi; For a reciprocating compresso

Hi; For a reciprocating compresso

(OP)
Hi;
For a reciprocating compressor, the recycle valve failure is one of the suction PSV sizing scenarios. As during the reciprocating compressor start-up, the discharge Shutdown valve (SDV) should be kept open ( not same as centrifugal compressor which it should be closed), so failure of both recycle valve and SDV will be a double jeopardy. I just wanted to understand in which case this SDV can be closed so we can define the recycle valve failure scenario for PSV sizing?

thanks

RE: Hi; For a reciprocating compresso

The only time when a recycle valve failing open can lead to overpressure of the compressor suction components is when the suction side process - mechanical design pressure is not designed to handle worst case settle out pressure. This can also happen if the discharge SDV is wide open, since the discharge side check valve ( which would be downstream of the recycle valve piping takeoff) will act as a stop valve when the recycle valve goes fail open.
In my experience, there were many cases when compressor packages were not designed to handle worst case settle out pressure when there is loss of control of the recycle valve. It is not possible to set up a PSV to protect the suction side in this case. Engineering support to Operations end up having to provide half baked measures such as trip and blowdown of the compressor unit on detection of high pressure on compressor suction. Some folks may add a PSV on the suction side to handle some limited overpressure flows, but this cannot be called a protection measure.

RE: Hi; For a reciprocating compresso

At first, for the reciprocating compressor, the discharge shutdown valve is not common item. We normally use non-return valve at discharge side. Sometimes we need a blowdown valve to release the pressure at discharge side.
And your question is when the SDV can be closed. Of course the SDV can only be closed when the compressor stop.
For the suction PSV sizing, we generally consider the maximium flowrate of the compressor.

RE: Hi; For a reciprocating compresso

(OP)
Hi georgeverghese ;

You are right about settle out pressure and the PSV sizing is not for settle out condition. The settle out pressure is considered as design pressure of suction side to avoid PSV pop up during compressor trip which it could be happened frequently.

The PSV should be sized to protect the system from over-pressure during unexpected situation.

For the centrifugal compressors one of the relieving scenarios is :
“ Failure of the recycle valve during the compressor start up”.
In this scenario, the discharge valve is closed so PSV should be able to release the recycle valve fail open rate as compressor is still running .

My question is about reciprocating compressors, I found in some projects the same relieving rate was calculated for PSV sizing however I am not sure which case can lead to this scenario as discharge valve of the reciprocating compressor is not closed during start up.

RE: Hi; For a reciprocating compresso

(OP)
Hi KEVINZY;

The check valve reliability is very low so pending on the project , deletion of the SDV can be investigated. As per API 521:
1) In case of two dissimilar check valves if the check valves are maintained, 10% leakage needs to be considered for the check valves
2) Complete check valve failure is assumed for other cases ( check valves in series that are not inspected and maintained and for a single check valve regardless if it is inspected and maintained)

Maximum compressor throughput is one case for PSV relief rate calculation.
As reciprocating compressor has suction and discharge bottle so they can work as extra reservoir during recycle valve failure for extra relieving rate. But I think this scenario can be applicable if the compressor train discharge is blocked ( e.g. SDV closed). As I found in some projects the recycle valve failure scenario was considered for the PSV relieving rate calculation so I am not sure which case can lead to this scenario as discharge valve of the reciprocating compressor is not closed during start up.

RE: Hi; For a reciprocating compresso

The scenario is no different for a recip compressor, as long as you have a discharge check valve located downstream of the recycle line takeoff. This check valve behaves like a stop valve when the recycle CV fails open: it goes closed when the pressure upstream of the check valve becomes less than that downstream of the check valve.

RE: Hi; For a reciprocating compresso

Hi, AMXX,
As Georgeverghese said, the problem is the pressure downstream of the check valve or SDV.
If the downstream of the compressor is a storage for emergency condition, it means the downstream pressure is always nearly the rated discharge pressure of compressor.
In similar application(the downstream pressure is not ambient), if only SDV but no check valve, the SDV should be closed when the compressor start up.
However, we usually use check valve for this application.

RE: Hi; For a reciprocating compresso

(OP)
Dear georgeverghese
You are right. I missed this point.

Thanks for your kind respond.

RE: Hi; For a reciprocating compresso

(OP)
Dear KEVINZY;

The downstream of the compressor is high pressure system. However after recycle valve fail open, for a short period of time (before system reach to the steady state condition) the check valve can be closed so in this basis the recycle valve failure for the PSV relieving rate calculation can be justified.

As you mentioned, the SDV status always is checked before compressor start up so the discharge SDV closure during recycle valve failure will be a double jeopardy and I cannot address for it.

Thanks for your kind respond.

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


Resources

White Paper – Data Security and Know-How Protection
Our data is constantly exposed to the danger of being intercepted or stolen as it wends its way over global data networks. Data security measures and measures for protecting intellectual property should not, however, first be implemented when data is exchanged – companies must lay the foundation for these measures within their own organization. Download Now
White Paper – Collaboration in the PLM Context
The influence exerted by the Internet of Things (IoT) means that there is a steadily growing need for collaboration in industry. Partners from new industries and areas of application need to be integrated in cross-company business processes to ensure that the lifecycle of smart, connected products can be managed from end to end. 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