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Centrifugal Compressor Psv Setting


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#1 vr1

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Posted 08 December 2017 - 05:09 PM

Hello,
The centrifugal compressor curves show that, the discharge pressure will never reach the set pressure of the PSV at max rpm and max suction pressure. There is an anti surge valve also.
Compressor normal op press
Suction 50 barg
Discharge 80 barg
Design press 100 barg
PSV set @ 100 barg
My question is what is this PSV protecting?.

#2 fallah

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Posted 09 December 2017 - 01:30 AM

The centrifugal compressor curves show that, the discharge pressure will never reach the set pressure of the PSV at max rpm and max suction pressure. There is an anti surge valve also.
Compressor normal op press
Suction 50 barg
Discharge 80 barg
Design press 100 barg
PSV set @ 100 barg
My question is what is this PSV protecting?.

 

vr1,

 

If mentioned design pressure (100 barg) refers to discharge line design pressure, the PSV set pressure should be 100 barg; as it is.

It might protect the downstream facilities and compressor itself in blocked discharge line while anti surge valve won't open due to relevant control loop failure or something like this.
 



#3 vr1

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Posted 10 December 2017 - 11:36 AM

Thank you Fallah,

Yes I agree with you that it protects the system against high pressure. But where will that high pressure come from, there is a PSV upstream. The suction pressure cannot be more than its set pressure.

The curves provided by vendor are at normal suction pressure. How can we predict the max discharge pressure at max suction pressure. Going back to vendor is not one of the options.

Thank you for taking time to reply. Appreciate it.

#4 fallah

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Posted 10 December 2017 - 12:17 PM

Yes I agree with you that it protects the system against high pressure. But where will that high pressure come from, there is a PSV upstream. The suction pressure cannot be more than its set pressure.

The curves provided by vendor are at normal suction pressure. How can we predict the max discharge pressure at max suction pressure. Going back to vendor is not one of the options.
 

 

vr1,

 

Get compressor head versus capacity curve for maximum speed and find the maximum differential head from intersection of the line of the anti surge valve sizing (surge line plus a safety margin on the compressor curve) with maximum speed curve. Then find the maximum discharge head by subtracting the maximum suction head from maximum differential head from which you can calculate the maximum discharge pressure.



#5 vr1

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Posted 10 December 2017 - 12:47 PM

Vendor did not provide head curve. They provided discharge pressure vs flow and pressure ratio vs flow curves. I can calculate the max discharge press using the pressure ratio curve.

Will it be the same?.

#6 fallah

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Posted 10 December 2017 - 12:55 PM

Vendor did not provide head curve. They provided discharge pressure vs flow and pressure ratio vs flow curves. I can calculate the max discharge press using the pressure ratio curve.

Will it be the same?.

 

vr1,

 

Yes, it can be the same...



#7 vr1

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Posted 10 December 2017 - 01:36 PM

Thank you Fallah. I have used pressure ratio to determine the max discharge pressure. But wanted confirmation from someone that what I have assumed is right.
By assuming as above , I am also assuming that all other parameters that effect the relationship between pressure ratio and polytropic head are not changing.

#8 J_Leo

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Posted 10 December 2017 - 09:16 PM

Hello Vr1,

 

Is it possible for you to attach the compressor curves you have been referring to? I want to know how to calculate the max discharge pressure as well.

 

Thank you.

-Leo






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