3 replies to this topic

[Siraj]

Recent trip of our refrigerant compressor is baffling me. When plant was on 30% load and all 4 antisurge valves are open 30% , in a fraction of second first stage suction flow reduced by 40% and the antisurge opening scaled from 30 to 45 and 60 and RTL occured followed by safety on and the end..now the reason for first stage flow decrease....unknown but still curious to know if any coincidence elsewhere..
No reason for flow reduction from users or antisurge flow even...everything normal before. All occured in 6 seconds

Edited by Siraj, 19 December 2017 - 05:22 AM.

[Bobby Strain]

Maybe you have an instrument problem. Or the PLC programming is not quite right.

 

Bobby

[Saml]

It looks like a surge event.

 

It may be that the antisurge control line is set too close to the actual surge line so any minor variation can send the compressor into surge.

 

I would suggest the following. If your trending software allow (or do it offline in Excel) plot an X-Y of the flow to first stage vs polytropic head.

 

Compare it with the compressor curves to see if there is anything serously off.

 

If it is flat near the point where the event occurred it is because you are close to surge, and the event was just a matter of chance.

 

But it may be many things like a faulty intrument (flow, pressure, temperature or compressor speed), a slugish control valve, or a positioner with offset, or....you name it.

[Siraj]

On further investigation, it was the third stage antisurge valve that has opened first  and caused the first stage flow to reduce.... now... y did the third stage antisurge valve open?..

 

In the CCC configurations, 1st and 2nd stage Antisurge valves are coupled in one control group n likewise 3rd and 4th .

when will the third stage A/S valve open?? .. when 3rd stg flow reduces... and any variation in 4th stage parameters..as I guess...

 

3rd stage flow at first instance gradually reduced at marginal 3-5% that caused antisurge to open by 10%.. Actual theoretical reason behind antisurge opening in this kind of system...if described would be helpful...