2 replies to this topic

[dylant]

A vessel has a pressure set point of 120 psig. It contains liquid naphtha has a level reading attached to it. At one period in the past, this level reading failed. The operator was not aware of that. He purged H2 gas into the vessel which was actually empty. The H2 flows through the pipeline and pressurized the storage tank.

What'd you recommend to prevent this from happening again? I was thinking of some kind of liquid trap (the opposite of steam trap) but I could not find that kind of instrument. Any suggestion?

[JoeWong]

A vessel has a pressure set point of 120 psig. It contains liquid naphtha has a level reading attached to it. At one period in the past, this level reading failed. The operator was not aware of that. He purged H2 gas into the vessel which was actually empty. The H2 flows through the pipeline and pressurized the storage tank.

What'd you recommend to prevent this from happening again? I was thinking of some kind of liquid trap (the opposite of steam trap) but I could not find that kind of instrument. Any suggestion?

dylant,
I am surprised that your tank does not have any LOW-LOW level trip and allowing explosive gas (H2) blowby. Has this system been HAZOPed ? Any redundant level transmitter in the tank ?

Liquid can be used however, it may not be reliable.

JoeWong.

[dylant]

Hey Joe, thanks for responding.

Yes, the unit has been HAZOPed last year. The procedure mentioned that H2 is not supposed to be added to that system but human makes mistake.

No, it was a vessel... an accumulator actually, not a tank. But this vessel is the last resort before the naphtha goes to the storage tank. The accumulator only have one level transmitter which failed last time therefore causing this "incident".

Why liquid trap may not be reliable?