Natural Gas Relief Valve Detection

[silvz71]

Hello,

I have an application where we are removing the sulfur from natural gas via carbon beds at less than 15psig. We have relief valves on the tank, and if they were to pop off, we would obviously want to automatically shut off the supply.

Is there some type of sensor that could be placed on the vent stack from the relief valve that would detect the presence of natural gas (potentially with little to no sulfur!) that we could use to communicate with the main supply valves?

I've explored the use of a standard flowmeter, but my concern is that it may get false readings, or be hard to maintain it's accuracy. Also, I'm afraid it may not function properly during a short pop off burst of the relief valve.

Additionally, this will be at an unmanned site, so reliability of the equipment is a must.

Any direction or suggestions would be welcomed.

Thanks,
David

 

[TD2K]

LEL detector near the nozzle outlet?

Some PSV manufacturers offer a 'lift' indication.

http://www.leser.pl/pdf/czujnik_ruchu.pdf

I'm sure I remember one of the PSV vendors talking about it, Farris, AGCO?

 

[Latexman]

I prefer prevention, like a pressure transmitter on tank with set point just below PSV set pressure. There's probably (plans to have) a PT on the tank anyway.

If you still need detection - how about a rupture disk under the PSV with a BDI?

Good luck,
Latexman

 

[DRWeig]

A differential pressure switch across the valve?

Best to you,

Goober Dave

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[silvz71]

I've discovered that Leser offers a prox switch on their valve to indicate when it has lifted. Seems a bit more reliable than flow meter/detectors. Might have to investigate if other manufacturers have similar options.

 

[don1980]

Silvz71 - yes, most other major manufacturers can supply that same switch. It's simple, cheap, and highly reliable. It fits onto the valve bonnet where the cap is installed, directly sensing movement of the valve stem.

US EPA is currently getting industry comments on new regulations that would require the owner to detect releases from PSVs in defined services. If this becomes law, these lift detectors will become common.

 

[MortenA]

Will the PSV often pop?

IF not then: Consider a bursting disc upstream your PSV. Pressurize the void space between the disc and the PSV (e.g. with N2) and then have a PALL at the SP of your PSV? Its a bit heavy on instrumentation but its a viable way? If your gas is sour you may also save someting on the PSV since now you can make it "non NACE".

Best regards

Morten

 

[maddocks]

You can actually buy a rupture disk holder with a sensor attached - it will alarm via a set of contacts.

 

[DRWeig]

How about a noise detector? I've only been around a few PSVs that opened unexpectedly, but each time I went for hours with no hearing afterward.

Best to you,

Goober Dave

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[maddocks]

Seems silly, but we actually witnessed a plant with a vibration switch clamped to the body of the PSV.....seemed to work but I didn't stamp the drawings.