Compressor backflow 1

[JSalek]

I've observed backflow via antisurge valve on two trains centrifugal compressor. One compressor tripped and gas flow backwards from the other train via failed ESDV and single check valve through antisurge line into the suction scrubber. PSV lifted (sized for fire case), blowdown valve opened but the inlet pressure still exceeded design pressure of the scrubber by about 15% until operator commanded the antisurge valve to close. There was another check valve d/s compressor which hold so the compressor didn't experienced backflow.
The issue was fixed installing double check valve. The question is how sensitive is compresor and gas trubine to spinning in reverse direction? Is it worth to install check valve u/s of recycle line?

 

[Sam654]

Very sensitive. If the compressor is running backwards it most likely is shutdown and lubrication is minimal. It is also operating opposite of its normal thrust direction.

I had a 4000 HP compressor come apart after running backwards for several hours. The check valve failed (elastomer seat literally gone after 25 years of operation) and the two downstream isolation valves failed to fully shut to the extent that it was able to rotate the compressor with the blow off valve fully open.

The investigation uncovered numerous operation and mainteneance issues to say the least.

 

[atayto]

As i understood gas from tripped compressor discharge line flowed through antisurge valve to compressor suction scrubber. Why compressor should rotate bacwards? For case of overpressure of suction scrubber. You must install bigger PSV which can accomodated 10-15 % of discharge flow(assuming that both check valves are passing). fire case is is not appropriate. I never seen any compressor with PSV on its suction scrubber designed for fire case! usually it is for calm down condition when compressors stops inlet and outlet SDV are closed and flow from compressor discharge rushes to compresor suction and presure is equilized. Ususally it is higher than compressor suction line design pressure.
Anti surge valve should never be used!! I would suggest to revise/conduct HAZOP asessment for this compressor design. If this happened, something wrong with your compressor design. It looks very unsafe.

 

[dcasto]

OK, I have to put in my 2 cents. We shutdown a 10,000 HP centrifugal propane refrigeration compressor with a Westinghouse gas turbine drive and a 1200HP steam turbine all connected on 1 shaft. There was waste heat recovery systems on the exhaust and it had co-firing burners that were off (making steam for the helper turbine). The other unit was left running.

The discharge check valve failed and the 200 psig propane flooded back into the compressor. The gas turbine went from 5200 RPM forward spin to 5200 rpm backwards in under 40 seconds. The gas turbine sucked air through the exhaust and started blowing air through the intake.

the seal pumps ran backwards an blew seal oil out all over the engine.

no fire, but it took several mill to fix.

 

[psafety]

On centrifugal in paralell we use checks as safeties. This is air I'm referring.