Flare stack solely for relief valve? What is common practice?
Flare stack solely for relief valve? What is common practice?
(OP)
Hello. I am doing some safety engineering work for an aerospace customer. They have a large high pressure gaseous hydrogen storage area that feeds other facilities. There is a large relief valve on the pipeline, as required by code. The RV dumps into a ~20 foot tall vent stack.
NASA Recommended practice is to flare when hydrogen venting flow rate exceeds 0.5 lb/s. If this RV went off it would flow about 2 lb/s. There is understandably some push back on installing a flare stack and propane system solely in case a relief valve goes off -- the facility is not commonly staffed but people do go there and there are no other flares or headers going to a flare anywhere nearby. So it would be an all new construction at considerable expense.
We decided that some benchmarking was in order. So I am trying to understand what other industries do in this kind of situation. Thanks in advance.
NASA Recommended practice is to flare when hydrogen venting flow rate exceeds 0.5 lb/s. If this RV went off it would flow about 2 lb/s. There is understandably some push back on installing a flare stack and propane system solely in case a relief valve goes off -- the facility is not commonly staffed but people do go there and there are no other flares or headers going to a flare anywhere nearby. So it would be an all new construction at considerable expense.
We decided that some benchmarking was in order. So I am trying to understand what other industries do in this kind of situation. Thanks in advance.
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RE: Flare stack solely for relief valve? What is common practice?
The refinery I'm currently working is has their main reformer LP flash drum PSVs going to atmosphere. The PSV sizing case is about 350,000 lb/hr so it's well over your 0.5 lb/sec. The gas isn't pure H2, it's about a 8 MW stream I believe, might be a bit less. The PSVs are located on top of the LP flash drum with relatively short tailpipes, maybe 6' length.
I worked in another refinery where we were doing an expansion. Another contractor was installing a NG reforming unit for H2 production. I thought those PSVs might relieve to atmosphere but they were routed to the Refinery flare when I checked my P&IDs. I've got another example but I need to check my files at work.
RE: Flare stack solely for relief valve? What is common practice?
Just redesign the outlet of the stack to be a burner/ flare?
Then there is no natural gas pilot light.
Would it work, I don't have any idea.
Usually when I mention these things there is already a design in place somewhere else.
ie. I thought that using exhaust gas blanketing was a novel idea until i googled around and saw you could buy units to scrub the exhaust gas etc.
So this is probably not novel either.
Regards
StoneCold