3 replies to this topic

[Neelrahs2006]

Is it possible to actually reduce the vented nitrogen gas (inert gas) used for blanketing?

The tank is firstly filled with nitrogen at 1.2bara. Then as the products (hydrocarbons) filled into the storage tank, the pressure inside the tank would increase to 3.8bara before it is vented (as the pressure control valve is set at 3.8bara).

I would need the vapour in the storage tank (hydrocarbon vapour with nitrogen gas) to be vented at atmospheric pressure (the venting pressure at 3.8bara just outside the storage tank would have to be remain, the pressure after the venting would hopefully be reduce) and there shouldn't have any mixing with air as this vented vapour would be treated before it is used for blanketing again.

Would a pressure regulating valve be suitable to reduce the pressure of the vented gas in this case? Can a pressure regulating valve actually be place in a venting line?

Or is there any suggestion to reduce the pressure of the vented vapour from the storage tank?

[proinwv]

Neelrahs2006

I understand part of your questions. PRV's can be used in a venting line, they are commonly called backpressure reducing/regulating valves, or BPRV's. There are some control issues with these, but that may be another issue.

However, I do not understand what you mean by, "(the venting pressure at 3.8bara just outside the storage tank would have to be remain"
so I believe that I am not understanding the remainder of your question(s). Possibly another explanation or a simple sketch would help me.

[Neelrahs2006]

Here's a sketch of it. The main problem here is actually i need to feed the vented gas which is released at 3.8bara into a VRU (vapour recovery unit) that is operating at atmospheric pressure. The whole thing would be a close system, where the inert gas is to be reused after removal of hydrocarbons in the VRU.

So, a PRV would be of use to reduce the pressure from 3.8bara to 1atm? Would the pressure build up just right before the PRV?

Attached Files

•  Sketch.doc   29KB   78 downloads

[proinwv]

Ok, I don't believe that you need the BPRV. The PCV will control by itself. Or, eliminate the PCV and just use the BPRV.

Better yet, use a piloted tank vent valve set at your pressure. The pressure at the VRU will be controlled at the VRU as long as it has the volumetric capacity to handle the flow. The outlet pressure of the piloted vent valve, or whatever you use, will be near atmospheric, controlled by the pressure loss in the piping between the vent and the VRU and the backpressure caused by the VRU.

I suggested a pilot op valve because it will have the least pressure build up in your tank after the vent cracks open, and will not be effected by any downstream pressure as a simple vent valve or BPRV would be. A PCV and control system would also be immune to backpressure effects.