SIS interlock issues for liquid ammonia storage tanks
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When the liquid ammonia storage tank level is too high, the SIS interlock shuts off the emergency shut-off valve at the feed point; is it also necessary for the interlock to stop the feed pump? The feed pump was originally interlocked with the DCS
It’s not up to anyone to decide this; the original design and logic diagrams must serve as a basis. You can’t rely on assumptions or what others say – when nothing goes wrong it’s fine, but once there are problems, you are the one held accountable
If closing the feed valve causes pressure buildup in the pump, the pump should be shut down via interlock
Signals entering the SIS still need to undergo HAZOP analysis and SIL rating. If these are not available, then try to route the interlock signals to the SIS as much as possible.
The design institute produces the chain diagram. If the pump is regulated via frequency conversion, it doesn’t matter whether it operates or not.
Is the feed pump a centrifugal pump or a reciprocating pump? The SIS interlocks are designed by the design institute; once they have done the design, we just need to implement it. If it hasn’t been designed, you need to submit a request to inquire about this matter. According to the production process, it’s incorrect to keep the pump running while the feed valves are closed. What is SIS? It’s a system that shuts everything down as soon as it’s activated, thereby minimizing risks. It is recommended to connect the SIS to the frequency converter of the pump, so that the SIS can directly reduce the pump’s frequency to 0
If you have a sis, just use it; it doesn’t matter if there’s one or two extra points
Check the HAZOP analysis results! Generally, the pump stops once the valve is closed!
Shut off the valves and stop the pump to prevent pressure buildup in the pump; ammonia is prone to vaporization, which can lead to overpressure and leaks. In my opinion, a interlocked shutdown of the pump is necessary!