Routing PSV outlet to compressor suction header

[tgmcg]

Environmental regulations require than any new PSV's on our refinery hydrogen system be routed to a closed relief system.

We are planning modifications of our reciprocating booster compressor plant (46,000 HP total) which requires we install new PSV's on a few of the compressors. Existing hydrogen PSV's vent to atmosphere. A new dedicated relief/flare header is costly and difficult to accomplish since all local piperacks are at maximum structural load caacity.

A suggestion has been made that we might consider routing the PSV outlets to the compressor suction header, instead of into a relief header. The new PSV's are located on the compressor 3rd stage discharge operating at 3,000 psig and the main suction header operates at 350 psig. There is no risk of heat build-up as intercoolers are provided between compressor stages. The suction header is protected against overpressure by it's own PSV's.

I don't see any obvious faults with doing this provided all PSV's are sized for the correct flows and backpressures, and are of modulating design. An important advantage is that it removes a number of potential leak sources into what is already an overloaded relief/flare system, which presents it's own regulatory problems.

Thoughts/comments?

 

[dcasto]

You could do that, you will need PSV's on the suction header that goes somewhere like a flare or a built on purpose vapor recovery system, just like a relief header would. You will need to recalculate your capacities and makesure back preesure isn't a problem (recommend pilot operated for new PSV).

What you are doing is using existing low pressure gas system as a VRU, should be a nice project but will need a good PHA.

 

[tgmcg]

dcasto,

Thank you for your thoughts. The only resistance I'm running into is from the folks saying "we've not done that before". But it seems like a good solution and reduces the load on the flare system...and takes those new HP relief valves out of the environmental regulatory domain.