7 replies to this topic

[Aelfarh]

I have read several threads on the forum about this and I'm still not sure what's the correct fail mode for the recycle valve of a reciprocating compressor.

If the valve FO then the suction piping, suction bottle and the first stage of the compressor itself needs to be sized to a "settle out" pressure, a value between the discharge and suction pressures (settle out in the recycle line, not the compressor itself since it's a recip machine). The suction PSV setting also needs to be taking this "settle out" pressure

If the valve is FC, then you can have a potential overpressure of the line and the compressor itself if for example you loose instrument air, but the compressor is still running.

In the FC case, how do you protect for this overpressure?

Also, do you need individual recycle valves for each stage or just one from the final stage to the suction, what are the pros and cons of each?

Edited by Aelfarh, 08 August 2023 - 04:10 PM.

[Bobby Strain]

All reciprocating compressors are protected by a cylinder discharge PSV.

 

Bobby

[Aelfarh]

Hi Bobby, I'm afraid I didn't explained myself correctly.   Let me rephrase it.    Is there a special sizing consideration for the discharge PSV that needs to be done (eg. full flow PSV) when the recycle line valve is FC?  also how do you prevent the compressor from sucking vacuum?  

 

Also how is the emergency shutdown or the loss of electric power shut down done with a FC valve?

[breizh]

Hi,

https://www.cheresou...ing-compressor/

 

Breizh

[Aelfarh]

Hi,

https://www.cheresou...ing-compressor/

 

Breizh

 

Hi Breizh

 

So the recommendation is always to have a FO one, as in that post?  However Bobby mentioned that he tends to have them FC?

[breizh]

Hi,

Not my expertise! You may have a chance to get the attention of Art Montemayor and others who have a lot of experience with this technology.

 

Breizh

[snickster]

 CompressorSeqOper.doc   42.5KB   12 downloads

 

I have worked on 2 design projects for high speed reciprocating gas compressors for gas compression stations for old Enron facilities.  Also  another project with smaller two stage receprocating compressor in process system.  In all cases the bypass/recycle valve was Fail Open (FO).  It been over 20 years now so I do not remember all of the reasoning in discussions with compressor supplier and operators.  However a reciprocating compressor must start up in unloaded condition (but with some initial pressure charge but equalized in suction and discharge) with the recycle valve open and all other valves into and out of the system closed closed until lube oil system is circulating and heated up, and all other system startup requirements taking place before loading the compressor (by closing recycle valve and opening suction and discharge valves).   I imagine at this time during startup if recycle valve should fail closed there could be issues.  Also possibly failure could have occured during previous operation and shutdown, and then startup is intiated with recycle valve unknowing failed closed.  After all systems and subsystems of the compressor system piping have been started and valves aligned, the recycle valve is closed simultaneoulsy with the discharge and suction valves opening.   Attached is one of the compressor station startup procedures which may be helpful to you.  You could talk to the compressor supplier as they have alot of experience in this.

Edited by snickster, 09 August 2023 - 08:58 PM.

[Bobby Strain]

One must know the complete system. There may be designs where there is no cooler on the compressor suction. Maybe there is a recycle cooler. Maybe there is a discharge cooler. In any case, two check valves are required on the discharge after the recycle split. So, the decision may rest on the particular installation. And I am certain Art has his preferences that will be worth due consideration. The compressor vendor or packager should always be consulted. Maybe Heinz Bloch may address these issues, too. Look for information from Ariel Corp.

 

Bobby