3 replies to this topic

[SawsanAli311]

Dear All,, 

 

I would like to get your views on the requirement for performing surge test at site after having the surge test performed at the factory test. I believe that we need to validate the performance curves of the vendor at actual conditions considering the real constructed piping arrangements, system resistance and location of the anti-surge valve. Some OEMs refuse to do surge test on site after installation claiming that it has already been done during the factory performance tests!

I would also to know whether the result of the surge test is a ''new slope & new location of the surge limit line with the re-defined surge control margin'' or it is only adjusting the surge control margin between the surge limit line and surge control line. I have read that that during the test, the SLL is initially shifted towards the right while  Anti-surge valve is partially forced to close such that the operating point approaches both the adjusted SLL  (which is simultaneously having its slope increasing towards the left) and SCL and once the recycle back up line and safety on activates, the actual surge points are recorded and in this way we can validate the optimum surge control margin (between the SLL &SCL)). 

 

 

[fallah]

Sawsan:

 

Hi,

 

I think, basically the SLL cannot be so affected by ASV sizing and compressor's piping around design.  About the SCL, the relevant vendor which normally has the ASV sizing in his scope, should specify the conditions and limitations to approach the SCL for process and piping designer to consider them in relevant piping route, design and sizing.  Hence, if such pre-specified conditions and limitations would be met in compressor installation and relevant piping/process design and construction, it might there would be no need to test the compressor for SCL and the minor deviation can be removed by adjusting the set points and tuning the relevant controllers.

[SawsanAli311]

Thank you Fallah, 

 

For my own experience, I saw that tuning of the surge control margin based on dynamic simulations and FAT factory tests are really not sufficient due to the variations in the system's layout when compared to the reality. 

 

I have few points which I am seeking your valuable opinion:

 

 

1. I know that the surge control margin is greatly affected by the surge control loop volume, valve size and distance from compressor suction. Yet, if we find out that the antisurge control valve is undersized (not sufficient Cv selected) can we say that increasing the surge control margin may help to reduce the surge duration by having an earlier reaction of the controller. I understand that we should always avoid large surge control margin as operation would be inefficient with higher power consumption during recycle mode.
2.   I could see that in one of the performed dynamic simulations for one of the compressors, the value of the surge control margin was increased from 10% to 17% such that the surge duration is eliminated to zero. Hence, would really slightly increasing the surge margin help sometimes?

Thank you very much, 

 

 

 

[fallah]

 

1. I know that the surge control margin is greatly affected by the surge control loop volume, valve size and distance from compressor suction. Yet, if we find out that the antisurge control valve is undersized (not sufficient Cv selected) can we say that increasing the surge control margin may help to reduce the surge duration by having an earlier reaction of the controller. I understand that we should always avoid large surge control margin as operation would be inefficient with higher power consumption during recycle mode.
2.   I could see that in one of the performed dynamic simulations for one of the compressors, the value of the surge control margin was increased from 10% to 17% such that the surge duration is eliminated to zero. Hence, would really slightly increasing the surge margin help sometimes?

 

Hi, 

 

1- It's not common to increase the surge control margin to cope with undersized ASV, as it might help in short therm process upsets to avoid going to surge region but in long therm process upsets it really cannot help.

 

2- Considering the answer to your first question it might help in short therm process upsets but even in those cases reduce the operating range of the compressor.