8 replies to this topic

[Ceng]

Hi dear friends

 

We have a two stage compressor in our project.

Our designer considered fire case for first and second stage KO drums and blocked outlet for PSVs before air coolers.

I want to know that isn't blocked outlet a probable scenario for KO drums too?

a simple sketch is attached.

 

thanks a lot.

Attached Files

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Edited by Ceng, 05 February 2013 - 02:29 AM.

[fallah]

Ceng,

 

As per your sketch blocked outlet, due to downstream SDV malfunction to close, could be a credible overpressure scenario for KO drums. But it might the KO drums were already rated for maximum upstream pressure, then no need to be protected against such overpressure scenario.

Edited by fallah, 05 February 2013 - 03:30 AM.

[Ceng]

Thanks fallah

 

kheili mamnoon

[Bobby Strain]

It may be possible that the low pressure drum could reach 2nd stage discharge pressure should both machines trip. Need to know all the details to assess, though. One usually develops all the scenarios that are possible. Then decide.

 

Bobby

[thorium90]

yes, when the compressor trip and if the recycle valve is fail open, the gas at the discharge will get dumped into its suction and overpressure the suction

[Tsquare09]

Hi Ceng,

 

Blocked outlet may be a credible scenario but not necessarily the worst case and the governing case. You need to do your engineering analysis to determine which of your credible scenarios gives the highest relief load and this becomes your PSV sizing governing case.

 

In this case as confirmed from your drawing, your engineers have chosen fire case as the governing case for the PSVs on KODs and blocked outlet for compressor discharge.

 

 

Tunde, SolaX-PI

[chemsac2]

Ceng,

 

I think, pressures and temperatures marked in your sketch are operating conditions. Design pressure of the system would be same i.e. settle-out pressure for the loop. In such a scenario, PSV at compressor discharge would be sized for blocked outlet. PSV on KOD is generally sized only for fire case.

 

In event of blocked outlet, PSV on compressor discharge would relieve as source of pressure is compressor and all PSVs in the loop are set at settle-out pressure i.e. at same value. PSV at compressor discharge would relieve before KOD PSV can respond.

 

Regards,

 

Sachin

Edited by chemsac2, 27 March 2013 - 12:08 PM.

[maryam]

Hi,

Anti-surge valve failure can cause overpressure in suction drum or not?

please be noted that suction drum has already been designed for settle-out pressure.

[fallah]

 

Anti-surge valve failure can cause overpressure in suction drum or not?

please be noted that suction drum has already been designed for settle-out pressure.

 

Maryam,

 

Considering flow forward to the normal destination is continued, while ASV is failed to open. Then the system control and piping configuration specify if the suction drum will be overpresssured. It may a dynamic simulation specify the possibility...

But if there would be the possibility of overpressure in suction piping/drum, the high pressure trip on suction line or the PSV on suction drum are the normal safeguards for such consequence.