Check Valve and Compressor discharge

[ibrahim]

Can anyone share any practice, standard or need of check valve at centrifugal compressor discharge piping? If it is a must then kindly advise the location and precautions during its installations, if possible.

[alzuhd]

Dear Ibrahim

A check valve is not a must for a centrifugal compressor stage ...if your question is so open to all odds
however, if the medium being compressed is of a nature that is harmful or risky then u have to think of a check or a double check or even more valving

this should be associated with inerting, purging and blanketing

all this applies to particular application

then think of an application first

hope i was near to be correct

[dexter]

In general, on centrifugal compressors a check valve shall be installed to prevent reverse flow and to minimize surge. This check valve shall be located as close as possible downstream of the compressor to minimize inventory. Keep that in mind that the bypass offtake (for anti surge) must be before the check valves. That means that there must not be any other valves except ASCV in the anti surge loop.
alzuhd is right in a sense that in some processes there are other critical reasons also exist, that may mandate the requirement of NRV.

[ibrahim]

thanks guys for your comment. alzuhd, actually at my plant (its snamprogetti design) we have a check valve at the refrigeration compressor (ammonia compressor) discharge end. can you tell me in what circumstances check valve can be installed before antisurge loop take-off from compressor discharge.

[dexter]

I am quoting from a very renowned design engineering practices of an oil & gas EPC and operating company, as I remember;
"If the compressor bypass control line is taken downstream of the discharge cooler (after discharge check valve), an additional hot gas bypass line upstream of the discharge check valve is required to protect the compressor against surge during start-up, trip and normal operation."

I think this will give you an idea of what standards / best practices say about "installation of check valve at centrifugal compressor discharge". I think there will be a strong reason due to which your EPC company deviated from such standard. It would be better if you can ask the compressor vendor (OEM).

[alzuhd]

Dear Ibrahim

Dexter explained very well the locating of the ASCV and I support his view that the anti surge arrangement should be before the check valve you enquired about simply because if the case is not so you may very well end up without anti surge function
so, anti surge as a safety measure should not be interrupted and should be kept operational at all times
which means a check valve should be located further downstream of antisurge arrangement
moreover, dexter is right once more; may the best to ask is a compressor manufactutrer who would guide you better on how to keep inventory low, do proper purging and keep safe arrangement for opening up for maintenance

by the , ammonia and related things without could prove extremely unsafe
I knew of few fatalities due to inadvertent releases and improper purging