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Technical problem of the control valve

Technical problem of the control valve

Technical problem of the control valve

(OP)
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

RE: Technical problem of the control valve

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

RE: Technical problem of the control valve

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

RE: Technical problem of the control valve

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

RE: Technical problem of the control valve

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.

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