What to look for in a compressor ESD dynamic simulation analysis report

[JustSomeRoark]

Gents:

I am currently involved in the analysis of the results/findings of a dynamic simulation of the ESD of a gas compressor. This is a fairly large unit compressing some 300 MMSCFD of natural gas between 350 and 1000 psig. The results provided by the third party in charge of this simulation include the rhov2 in some points of the system (i.e. compressor discharge, inlet/outlet of antisurge valves and hot bypass valves etc.) Until I joined my current company I was involved in a couple experiencies similar to this, but no one paid much attention to the rhov2 parameter. However, in this project this is proving a challenge, as we are obtaining fairly large values (i.e. around 200000 Pa, but just for 2-3 seconds) and my Stress colleagues are worried since apparently they cannot support the lined adequately to withstand the loads caused by this scenario.

I am concerned that they may not be doing a proper analysis, since as I mentioned before, in my experience such attention was never paid to this parameter. Unfortunately my background is Process Eng so I cannot tell 100% sure whether they are missing something. Based on your experience as Process Engineers, how do you analyse the results of a dynamic simulation study of a compressor, focusing on the ESD scenario? What are the major parameters that you check? Do you pay special attention to rhov2 or do you assume that due to the small duration of the event (peaks velocities/rhov2 are only observed for 2-3 seconds) the piping system will be able to withstand the scenario of the rapid opening of a relatively large on/off valve upon the ESD of a compressor?

Thanks in advance for your feedback.

Regards.

 

[georgeverghese]

In my experience, rho-v2 of 200 e3 Pa is the permitted upper limit on momentum for supporting flare lines in continuous use, so you could use this limit for these recycle lines also.

Especially if you have a hot gas bypass (which may be the case for direct GT drive compressors - no gearbox), check that the correct values for the rotational moment of inertia are used for the drive train. Antisurge recycle valves and HGB valves are fail open - check for any hydraulic restrictions in the control valve exhaust line that may slow down valve opening. Also find out if there are controller interactions between capacity recycle and antisurge recycle controllers, and how they are dealt with.

Higher resolution dynamic simulations would cost more and involve more engg time compared to coarse simulations. I've yet to see or hear of any Operating Co trying to validate the results of dynamic simulation of a compressor ESD.