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Margin In Stonewall Flow In Centrifugal Compressor

compressor stonewall margin

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#1 CSNK

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Posted 24 August 2018 - 01:25 AM

Hi all,

 

 

If centrifugal compressor is running at a load somewhat less by 2% than stonewall flow. Will there be any concern, if yes what?

What should be flow margin from stonewall that a centrifugal compressor should be allowed to run?

 

Thanks in advance.

 



#2 Technical Bard

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Posted 30 August 2018 - 11:03 PM

The challenge is that the stonewall LINE that is drawn on a compressor map isn't precise - it's a prediction.  I have seen someone run a centrifugal compressor to within 2% of the stonewall line without problem.  I have also seen someone stonewall a compressor before reaching the line on the map...  



#3 PingPong

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Posted 31 August 2018 - 01:12 PM

Stonewall occurs when the gas in the compressor reaches its sonic velocity (speed of sound).

 

The speed of sound in a gas depends on its actual specific heat ratio, its actual absolute temperature, its actual molecular weight and its actual compressibility factor.

 

The stonewall line on a compressor graph is therefor often not accurate for the actual operating conditions of the compressor.



#4 functionlake

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Posted 27 May 2021 - 11:44 PM

Hi CNSK,

 

I know this reply has been a long time since your post, but I want to put it here for others who are finding an experience operating a gas centrifugal compressor in choke, overload or stonewall region.

 

I've experienced a compressor had been running continuously within overload region for more than 2 months due to the unavailability of the parallel compressor. Overload region mentioned here means that the operating point of the compressor falls to the right of the stone wall line of the recommended operating map. The compressor delivered more than the design flow by 2MMscmd which was a significant increase in its capacity.

 

All compressor parameters including bearing vibration, lube oil temperature, bearing temperature were within their alarms. However, there was only a parameter, thrust bearing temperature, increased dramatically up to its alarm of over 100degC. The oil additives in lube oil has their limitation, and it is 90degC for our case. Normally, it is below 70degC. Consequently, the thrust bearing temperature was only the limit for our compressor at that time. Three years later, the compressor has been fine.

 

Of course, operating the compressor in overload region induces inaccurate aerodynamics prediction and impact on mechanical integrity. The tip Mach number of this condition shall be checked by the OEM, it was 0.45 for our case.

 

Hope it helps.






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