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Recently we have 6 nos of recycle gas compressor trip incident, but even after 6 nos tripping we are not able to diagnose/analyse the reason for such trip. Tripping alarm in PLC for all occasion found to be same which is trip from compressor governor & trip from LCP (local control panel). Kindly suggest what may the probable reason for such a trip without any prior alarm? Compressor is steam driven.. RGC normal RPM ~11500 RPM. Is the trip incident caused by variations in gas molecular weight?
Is it possible that surge conditions occur due to comparative lighter gas handling than design operating which ultimately force the RGC to trip?
 
Answers
08/03/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Low molecular weight can cause surging that can trip the governor. Can you do any of the following?
(1) Increase separator temperature by shutting off air cooler fans
(2) Increase separator temperature by pinching cooling water outlet valve, but not so much that the cooling water outlet temperature is above 120 deg F
(3) Bleed in fuel gas or natural gas to the compressor suction far enough back to allow for mixing
If you use the gas injection, monitor the recycle gas specific gravity because the injected gas can possibly build up, depending on the flash conditions in the separator.