Compressor Reverse Flow Relief Sizing - Additonal Info

[121202]

Gents, thanks for your replies. See additional info below.

Each train has three compression stages (LP,MP&HP). The trains are connected at the discharge of the LP and HP machines (there is a single Glycol Absorber between the LP and MP Compressors). There is no connection between the discharge of the MP Machines; they deliver directly to the suction coolers of the HP Compressors. At the discharge of each stage there is a check valve (non slam type) and a shutdown valve. The non slam check valves are mokveld type or equivalent and are relatively good quality. The system piping is fabricated in corrosion resistant alloy and therefore the system is likely to be relatively clean (i.e. corrosion products that could cause check valve malfunctions are not really an issue).

There is a scrubber on the suction side of each compressor. Each scrubber is fitted with a fire relief valve. The PSVs on the scrubbers can comfortably handle a flow equal to 10% of the design flowrate of the parallel train (each train can deliver 80000 kg/h and all scrubber PSVs can pass 35000 kg/h or more). Various upset and trip situations have been simulated using dynamic simulation to evaluate control responses. No overpressure situations were predicted on rapid opening of the compressor anti-surge valves, although as expected the suction pressure and electric motor load did increase.

Any additional comments most welcome

 

[25362]

I don't really know whether it is applicable to this case, but I remember having read once Trevor Kletz's opinion about the reliability of trips vs relief valves based on the likeliness of their failures.

He said, if I interpreted him correctly, that a trip (+ alarm), if tested and inspected regularly once a month, is doubly more reliable than a RV checked every two years. And a double trip would be 10 times more reliable if tested every month.

The trips' actuator could be thermally insulated to stand a fire situation for at least 15 minutes.

The right strategy would finally depend on the plant's philosophy and procedures for testing the safety equipment.

I recommend reading, at least, one of his books on safety issues.
One of them: Lessons from Disaster, "How organisations have no memory and accidents recur", ISBN 0 85295 307 0, is particularly interesting and has instructive value.