Technical problem of the control valve 1

[Jack Nicholson]

Hi.
Would you please help us about technical problem we encountered?

In attached PFD, during normal compressor shut-down operator increases opening of 05-330-FV-015 and 016 (1st and 2nd stage compressor anti-surge valves) and at the same time decreases compressor speed.
When anti-surge controller output signal ("valve demand" as illustrated in attached graph) goes above 70%, 05-330-FV-015 won't open above 70%. Although right after 3 seconds when operator trigger STOP button of compressor and speed decreases more rapidly (which is controlled by compressor logic), 05-330-FV-015 open to 100%.
What is the root cause? Based on the fact that the maximum flow of the control valve is on 80% opening, the Instrument division of our company claimed that restriction on flow causes valve opening limitation, which I think is not reasonable. What do you think?
Thank in advance

 

[pierreick]

Hi,
Let you check the SOP and Manual supplied by the manufacturer of the compressor; the shutdown procedure should be well described.
Take a look at the safety matrix (thresholds), you may find the answer.
Good luck
Pierre

 

[Jack Nicholson]

Dear pierreick
Hi.
the safety matrix (thresholds)??? Could u please explain it?

 

[pierreick]

Hi,
You may have interlocks (safety matrix) which affect the opening of the valve during operation.
Pierre

 

[georgeverghese]

There may be some process controls logics in the antisurge controller for either FCV 15 or 16 that limit the opening of FV 15 to 70% during normal operation - this is most likely part of the controls decoupling logics for the 2 antisurge controllers. You may see a controls link between the 2 controllers. This is done on multistage compressors to prevent controls instability during normal operation. Read up the detailed controls logics for the 2 controllers - some of these logics may not be disclosed by the AS controls vendor.