Discussion on the spontaneous opening phenomenon of the small flare valve at the inlet of the catalytic air compressor
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The small flare valve PC831B at the inlet of our company’s catalytic air compressor (with pressure readings taken from the compressor inlet pressure PI803) is normally under automatic control, with a set value of 0.27 Mpa and an alarm threshold of 0.26 Mpa. The normal pressure at the compressor inlet is around 0.25 Mpa. One day, the small flare valve suddenly opened automatically to 3.9% before closing on its own, lasting for 3 seconds. An examination of the historical pressure data revealed no significant fluctuations, with the highest pressure reaching 0.253 Mpa. The DCS issued a high-pressure sound alarm once due to a unit reaction. I would like to ask: if the pressure suddenly increases from 0.25 to 0.26 Mpa, but does not reach the set value of 0.27 Mpa, will the valve open automatically? Does the control system have a function for predictive adjustment in advance? Thank you!
Is it a control valve or a shut-off valve? Is the automatic control based on PID or some other control mechanism?
The concept of being ahead of schedule or anticipating something seems to refer to differential control. However, in the control system you described, if the measured value does not exceed the set value, then the deviation is definitely negative. Even if differential control is active, it will not change the direction of this deviation; in other words, it will not cause the valve to open. It’s possible that the actual measured value did exceed 0.27 MPa, but only for a short period of time. Due to the limitations in trend resolution, that period during which the value exceeded the set value may not have been recorded. Since no indication of exceeding the alarm threshold was seen on the trend chart, it’s possible that the value did not actually exceed the set value after all
Single-loop automatic control; the valve is a pneumatic butterfly valve, with proportional-integral control. The proportional gain K is 3.5, the integral time T1 is 1.5, and the derivative time T2 is 0
Thank you. It is possible that the pressure could momentarily exceed the set value of 0.27 Mpa, although no such trend was detected; the scanning interval for this valve is 1 minute
No trend can be detected; check the alarm records. An issue with the instrument cannot be ruled out
It may open if it exceeds the set value.