Instrument air failure in low-temperature methanol washing process
Thread Content
There was a fault with the instrument air in the low-temperature methanol washing system, so all control valves were switched to manual mode for operation. . What are the main causes of abnormal operation in automatic valves? ? Learn about discussions on instruments.
It mainly depends on whether each self-regulating valve is a air-operated open valve or an air-operated closed valve: in the event of a failure in the instrument air supply, air-operated open valves will close automatically, while air-operated closed valves will open automatically! At this time, although the valve moves, no feedback signal is sent to the DCS system, so the DCS cannot detect the movement of the valve! But it can be determined from parameters such as system pressure and liquid level! Major accidents are likely to occur during normal production, so strict precautions must be taken to prevent failures in the instrument air supply!
Unstable instrument air can cause the indicator of the self-regulating valve to show incorrect values or be inaccurate; this has happened in our factory as well. Another time, there was a self-regulating valve that often responded slowly – sometimes the delay could be as long as 2 minutes; at other times, the overpressure levels were truly frightening!
In the low-temperature methanol washing system, with the exception of a few vent valves that are FO valves, almost all the valves are FC valves; when there is a failure in the instrument air supply, they automatically go into a closed state. If, as the original poster says, all control valves are in manual mode, I think it’s better to shut down the machine.
As long as the instrument air is cut off! There’s nothing to think about – it’s just parking! What if the gauge air is unstable? It is not possible to switch all control valves from automatic mode to manual mode for adjustment, so that the valve positions can be monitored on-site and at the control room; the main reason for this is that changes in instrument air pressure can cause distortion in valve regulation