We have an application where the gas to the centrifugal compressor has a varying MW between 5 to 10. What impact, if any, does this have on the Surge protection of the compressor?

The CCC (Surge protection PLC) has surge test data for MW of 10. DO we need to perform surge tests again for the other MWs, or is there a scaling factor that we can use to shift the Surge lines to the left or to the right?

Regards

 

CCC normally uses an algorithm that is invariant to molecular weight changes. I would suspect that they used a reduced polytropic head versus reduced flow equation, especially if they knew that the MW was changing.

If this is the case, then you don't need to do anything to correct for the MW changes.

When they set up the controllers, they probably did a performance test at a few different MW's to verify that the surge line, margin, and tuning protected the machine.

If this was done, then you don't need to do anything else to protect the machine.

Byron Broussard
[email protected]

 

The controller A/S response depends on what fA mode is used to calulated deviation. During commission, certain assumptions are made, eg constant molecular weight etc. If your fA mode assumed constant MW and the MW changes I think you might consider talking to CCC about this. The Variable deviation is invariant to suction conditions of the compressor, not anything else.

 

I agree with Kerry Moodie.

There may more to it than just using one or another control mode.

If you are a CCC customer and if you have not resolved this issue yet with CCC or otherwise, I'd highly advise you to e-mail to [email protected] . They will take you from there, check with you the CCC project number,
determine how you can get info you may be missing and provide you with additional technical assistance. In the US you can also call 1-800-387-4657 to get support, or outside the US - (515)251-2736. If you face difficulties
going this route on any reason (which I doubt you will), contact me at [email protected] and I'll try to help further.

Regards,
Alex Benim
Compressor Controls Corporation