Centrifugal Compressor Fast Stop Surge

How to design an anti-surge system for a centrifugal compressor.
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[@luisavila8350]

Thanks for sharing

[@Gavrick1965]

Excellent presentation Vern.

[@vernvanleuven3116]

Thank you!

[@mohammedalzahrani5071]

greetings, one question. In my plant, we never experienced a surge on fast stop and our design includes a gas blow-down to flare valve that would open upon compressor trip to depressurize the compressor casing up to a specific set pressure then it will close. Obviously before this valve opens, the discharge and suction valves will be closed to control the depressurization volume and the anti-surge valve will be fully opened. Is this something you have seen before and how reliable would you consider this set-up to be compared to your set-up?

[@vernvanleuven3116]

Hello and thanks for the question. Compressor surge typically occurs in the first few seconds after shutdown. It would be difficult to get the discharge valve closed that quickly. However, there is probably a check valve somewhere on the discharge header to reduce the discharge volume to be equalized to suction.
If the blow-down valve can achieve a very high flow, it would be possible to avoid surge with this strategy. The allowable flow rate to the flare would also need to be considered, especially in situations where the entire facility is blowing down, such as emergency shutdown.
I've not seen this design before. I think it could be just as reliable as a recycle anti-surge system, but it would not be my preferred strategy. With a recycle system the discharge gas is being moved to the suction header, which helps equalize pressure across the compressor. Also, the recycle approach avoids the concerns about high flow to the flare, which is not a trivial problem.