Guidelines/References for Clearing/Blowing Liquid out of a Line with Nitrogen

[Latexman]

We have a tank where one or more different chemicals are charged, mixed, and then fed to the reactors. After the last addition and before mixing, we currently flush the line to the tank with water to get all the active ingredients into the tank.

We want to stop using flush water and use nitrogen to blow the ingredients into the tank.

All the two phase flow information I have found so far deals with continuous flows of liquid and a continuous flow of gas, L/G is fixed. What we will have is a dynamic situation where the quantity of liquid decreases (full pipe to empty pipe) over time. I suspect the resistance to flow of the nitrogen will vary also, from liquid to two phase to gas flow.

I've done a little thinking on how to design this, but I figured someone else has probably done this before, maybe many times before, so . . . does anyone have a good reference, guidelines, or advice on this?

Thanking you in advance for any help you can give me!

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

I looked at a couple promising hits on gas well liquid unloading velocities:

Page 3 on

http://www3.epa.gov/gasstar/documents/ll_options.pdf

Several references in

http://www.netl.doe.gov/File Library/Research/Oil-Gas/2002ARI.pdf

Those would be for continuous "unloading" through a vertical pipe/tube using 5-10 ft/sec for HCs and 10-20 ft/sec for water. I wouldn't want to wait long (i.e. continuously) to clear my line, so 10 m/sec is sounding like a good starting point to look at.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[LittleInch]

Zdas04, I would have loved to see the look on the vendors face when you asked him why his material didn't transform into a pig like the video said it would - Ha. Really brought a smile to my face.

I was thinking because it is only a 1" pipe 25m long, it would survive long enough to prevent too much blow by and you could use slightly lower velocity.

Inserting the "pellet" - You can get 3 port valves? like this

http://www.nero.co.uk/Catalogue/Ball-Valves/Three-Way-Reduced-Bore-L-Port-Ball-Valve

With anything inserted, I wouldn't want to go much more than 5 m/sec


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MikeHalloran]

Forty years ago, I had a barrel of _a_ Freon (not a common one, but you could get it from Grainger) that was immiscible with water, liquid at room temperature, water clear, and so dense that you could just decant it from a trap to recover it from a water system. ... where, for example, you might use it as a liquid pig.

It was absolutely a CFC. Probably illegal now...


Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Using high pressure gas to blow-out small pipes is another safety department trigger, as it should be. This has caused plenty of injuries. When the gas reaches the end of the pipe you will have a pipe full of high pressure gas that will suddenly vent freely at high velocity. This can throw projectiles and over-pressure tanks.

There are a number of potential solutions. Pigging with proper design is one, but I've never found this to be practical. The usual approach is to always keep the line full, or let it drain back after every use.

 

[bimr]

Agree with Compositepro. You would have to have some type of knockout drum/receiver on the end to collect the projectiles that will spew out.

I don't believe that blowing out with compressed gas would clear the line of solids or other deposits in 10 sec, but it will produce fumes or particulates.

 

[Latexman]

We are pumping water-like liquids into a 300 gal, closed (i.e. not open), 150 psig MAWP mixing tank through 1", Sch. 10S, 150 psig class pipe and fittings. The vent valve on the tank is set for 2 psig. The tank normally runs at 0-2 psig. This small tank has a 3" RD with burst pressure 150 psig. Once we removed the water flush, there will be no solids in the line and tank. I'm just getting started on this, but I've seen enough to know less than 10 psig of nitrogen pressure will be needed to clear the line in 1-2 minutes. Our nitrogen header runs at 75 psig, so I'll need to regulate that down. I thought about putting a PSV after the regulator set at 15 or 20 PSV, but why? Full nitrogen pressure is only half the MAWP of the tank, pipe, and fittings. I realize [∫]PdV of a gas is a lot larger than a liquid, but I really don't see any excessive risk here. The tank has a pressure transmitter with indication and alarms. There is also a pressure transmitter with indication and alarms on the tanks transfer pump.

So, where are these projectiles going to come from and how are they going to hurt someone outside the tank? I don't see it.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.