4 replies to this topic

[ma7ersi]

Hi,

 

The anti surge valve of a centrifugal gas compressor is clamped (Software clamp) at 65%. The output high clamp on the anti-surge controller is used for start-up purposes. The valve should not be open mortt than 65 % during start-up otherwise the motor trips on high motor current. But this clamp always remains activated and sometimes the compressor needs more opening during running operations with no fresh feed to the compressors (cool down process of the plant) or lack of inlet gas pressure or flow (in case of a backflow) . Therefore we need to disable this clamp after the start-up in order to reduce the effect of vibration.

Please advise if it is possible or not and when exactly we can disable the software clamp. Is it when the steady state flow is being reached?

 

Best Regards,

[breizh]

Hi ,

You should consult vendor or manufacturer , my view. It's abnormal to disable such equipment, consequences could be huge (safety first) .

You may need a turn around of the compressor , valves , sensors .

Good luck

Breizh  

[CHEMSTRONG]

Please understand that antisurge valve is not like any other level or pressure control valve in system. When it is going into surge , one will evaluate operating point on compressor characteristic curves . Antisurge valve should be fully open during startup and after shutdown always to protect the compressor from going into surge. Generally when there is gas turbine as a driver for compressor, there will be sequences like startup sequence, cooldown sequence like that.

So this logic will disable or enable the control valve. Even you are putting clamp on he valve to 65 percent during steady state operation, you should build logic in DCS such that if compressor is going into surge, this clamp will be disabled and valve will be open to 100 percent in just few seconds like 3 secs. Its gain will be very high generally.

 

Summary: There should be logic in place to enable or disable such a clamp like startup event or shutdown event will be sure candidates but also in case you have put clamp on it for 65 percent , put logic to disable that clmap when compressor goes in to surge during steady state operation always. otherwise it is highly risky.

 

Let me know if you have any more comments on this.

 

Regards,

Chetan Chavan 

 

 

 

 

Regards,

Chetan Chavan 

[fallah]

 

The anti surge valve of a centrifugal gas compressor is clamped (Software clamp) at 65%. The output high clamp on the anti-surge controller is used for start-up purposes. The valve should not be open mortt than 65 % during start-up otherwise the motor trips on high motor current. But this clamp always remains activated and sometimes the compressor needs more opening during running operations with no fresh feed to the compressors (cool down process of the plant) or lack of inlet gas pressure or flow (in case of a backflow) . Therefore we need to disable this clamp after the start-up in order to reduce the effect of vibration.

Please advise if it is possible or not and when exactly we can disable the software clamp. Is it when the steady state flow is being reached?

 

 

Hi,

 

Why did you consider such clamp on the anti surge valve of compressor?

 

Actually, the anti surge valve will act as a modulation control valve in normal operation and will be full open at very short time, typically 1 second, in emergency situations like when the compressor goes to surge condition. Hence, please clarify the need to considering such clamp.

[CHEMSTRONG]

Addition to earlier comments, Antisurge valve does not have finer control abilities like normal control valve. Aslo it should be put in auto at all times during normal operation. It should be driven by DCS logic for various events like startup, shutdown events. Even you want to put clamp on it, also configure additional logic which disables this clamp and opens the valve to 100 percent in very short time like 2 secs max. For doing this , you can configure gain scheduling logic also. DCS logic will evaluate distance to surge based on operating point of compressor on characteristic curves of compressor like surge line, backline and control line. When operating point is on control line, valve will be fully closed and in auto mode and when the point is on backline, it twill start slowly opening, when it is approaching surge line, as per gain scheduling, valve will open very fast like 1 sec to 100 percent from current position to get back to control line 

 

Let me know if you any more issues on this.

 

Regards,

Chetan Chavan