Tranfilling (Decanting) Gas Cylinders

[ContractHome]

I have a one argon gas cylinder pressured at 2015psi with 80 cubic feet of argon. I want to transfer some of this argon into a small cylinder which is rated at will hold 40 cubic feet at 2015psi with a tranfill hose that has a bleed valve at the fill side of the hose.

I understand I have to vent to fill cylinder before transferring the gas, but won't air still remain at atmospheric pressure?

Given Argon is heavier than air, can open both cylinders and allow them to equalize and assume that by opening the bleed valve I would be removing all air leaving only argon to remain or will the air mix with the argon regardless of me bleeding?

In addition can I create a vacuum using heat or by opening the supply, bleed and fill valves in certain sequence which would insure I am displacing the air in the fill cylinder with air?

 

[zdas04]

Thinking that you get much gravity separation in gases is really wishful thinking.

I'm going to guess that the "cubic feet" you are mentioning is SCF. That would make your large tank about 1/2 ft^3 and the small one 1/4.

Now you have to ask yourself how pure the Argon needs to be? If the small one is full of air at atmospheric pressure and you just introduce the argon, you will get a significant dilution. Just connecting the two bottles would get you something like 1600 psig in both tanks which means that you'll have about a 20:1 dilution. If that isn't good enough you can pull a deep vacuum (do you have Food Saver?) or do a purge.

With a tank there is no way to do a clearing purge so you have to do a dilution purge. I haven't done the detailed calcs, but I would expect that if you pressure the small tank to about 6 psig and blow it down to 1 psig. Do that three times and you should be under 1 psia partial pressure of air.

David

 

[ContractHome]

I have a one argon gas cylinder pressured at 2015psi with 80 cubic feet of argon. I want to transfer some of this argon into a small cylinder which is rated at will hold 40 cubic feet at 2015psi with a tranfill hose that has a bleed valve at the fill side of the hose.

I understand I have to vent to fill cylinder before transferring the gas, but won't air still remain at atmospheric pressure?

Given Argon is heavier than air, can open both cylinders and allow them to equalize and assume that by opening the bleed valve I would be removing all air leaving only argon to remain or will the air mix with the argon regardless of me bleeding?

In addition can I create a vacuum using heat or by opening the supply, bleed and fill valves in certain sequence which would insure I am displacing the air in the fill cylinder with argon?

 

[ContractHome]

So I am assuming that the air and argon do not mix making them inseparable.

Would I get seperation if Argon liquidizes under the said pressures?

Do I pull the vacuum on the fill cylinder (with a food saver) and then close the cylinder before connecting the hose?

Is there a certain way I could create a vacuum repositioning the bleed valve after the fill cylinder? Or if I reposition the bleed valve after the cylinder can I purge?

Under these pressures can't I purge the air since the argon is liquidized allow the air (gas) to excape and argon (liquid) to remain?

What is meant by blow down? Please explain...

 

[BigInch]

Would I get seperation if Argon liquidizes liquifies under the said pressures? Probably, given that the N2 and O2 not liquifying.

I understand I have to vent to fill cylinder before transferring the gas, but won't air still remain at atmospheric pressure? yes

Given argon is heavier than air, can open both cylinders and allow them to equalize and assume that by opening the bleed valve I would be removing all air leaving only argon to remain or will the air mix with the argon regardless of me bleeding?No. It will mix.

In addition can I create a vacuum using heat or by opening the supply, bleed and fill valves in certain sequence which would insure I am displacing the air in the fill cylinder with argon? use a vacuum pump

the air and argon do not mix making them inseparable.

Do I pull the vacuum on the fill cylinder (with a food saver) and then close the cylinder before connecting the hose? yes

Is there a certain way I could create a vacuum repositioning the bleed valve after the fill cylinder? Or if I reposition the bleed valve after the cylinder can I purge? if you really need as much argon purity as you imply by thinking about so many ways to get it, the methods you propose are not going to give you that accuracy. Back to the vacuum pump.

Under these pressures can't I purge the air since the argon is liquidized allow the air (gas) to excape and argon (liquid) to remain? I didn't see where the liquid argon phase was established, or where the air (I assume you mean the O2 and N2) is also not liquified and I would imagine that you would probably have N2, O2 and Ar all in the same phase. I think the distillation, if it's even possible at the still unknown pressures and temperatures that you have, needs to be more controlled than what you will be able to do, given you only seem to have two tanks and a hose or two.

What is meant by blow down? Please explain... Vent to lower pressure.

 

[ContractHome]

at what pressure does argon liquify at room temperature?

Pressure in the supply cylinder is at 2015 psi...

 

[zdas04]

I don't know much about argon, so I looked in REFPROP.exe, and at 2150 psia and 80F it is all gas. I don't get any liquid at 2150 psia till -189F. Not sure where you are getting that it "liquifies", but unless your "room temperature" is a lot colder than an igloo you've got gas in your bottle.

David

 

[ContractHome]

Correct it is a gas I confused this with another gas but my question remains the same except for the liquidfing part. My mistake

 

[BigInch]

I thought it was pretty damn similar to "air" too. Thanks for looking that up zdas. I used to work for Big3 40 years ago, and all I saw there was liquids, liquids, liquids, with VERY cold temps.

The answer remains the same too, no separation will occur between gas phases.

 

[unclesyd]

Adding a little to the above posts
.
This from the days when we mixed our own calibration gases along with having to lower O2 in our process vessels.

As was posted you will have to have a booster pump to get 2150 psig in the small cylinder. We used a small oil-less pump made for filling Scuba Tanks.

We found that to get the O2 below 20 ppm in 6' dia. x 20' ft long vessel it took at least 7 fill and purge cycles to get the O2 to the required level due to the diffusibility of the O2. This is a good property in helping get rid of the O2 as it helps with the mixing.

An easy way to insure gas mixing in a cylinder is to use an infrared heat lamp on the side near the bottom of the cylinder. The cylinder doesn't have to get very hot to induce convection currents in the contents. We would use this method on most of our mixtures.

 

[BigInch]

At Big3 we found that rapidly filling the cylinders created too much heat, so we filled 100 of them at a time in a water bath. The water bath also doubled as a safety feature, since the water would supposedly also contain the schrapnal, if one of the tanks decided to let go, but to tell the truth I always had doubts about that.

 

[zdas04]

Unclesyd,
How much pressure were you putting into the vessels and how far down did you let them get? What kind of O2 spec did you have?

I've found that if I go to 1.5 times local atmospheric pressure (which is about 12 psia here, so if I go to 6 psig I'm at 1.5 times atm) and then blow down to about 1 psig that 3 cycles would get me less than 10 ppm O2 which was the spec I was working against. 7 times seems excessive.

David

 

[iainuts]

Argon has a critical temperature of -188 F at a critical pressure of 706 psia. That means it will NEVER be a liquid above that temperature.

As others have mentioned, the argon will mix with the air, so all you can do is purge it out by venting the air out of the container, pressurizing with argon, wait for it to mix, then vent out and repeat till you have the partial pressure of air down below the level you desire. You can generally assume the time for it to mix with air with this small a container is only on the order of minutes at the most.

The best way to do this is to evacuate the air from the cylinder to as low an absolute pressure as you can using a vacuum pump, then admit the argon. If the partial pressure of the air is still too high, you need to cycle purge it by evacuating each time with your vacuum pump.

 

[unclesyd]

zdas04[/],

We pressured up to 10 psig and vent to pressure of around 400 mm Hg. The vessel was limiting. We were doing less cycles until we got a better analyser. I believe it was a Teledyne.
At 7 cycles we always got the O2 below our limits normally down to 2-5 ppm O2. The number was set by some testing with He using a Mass Spectrophotometer. Cost didn't enter into the equation as we had an excess from an LN2 plant.

 

[zdas04]

Interesting, my experience was with methane, and we were usually below 5 ppm after 3 cycles and we didn't blow down nearly as far.

David