Flushing residual butane from cylinder

[docbuild]

Hello! Not sure if this is the correct place to post this, please let me know if you recommend another subforum.

I want to completely empty a butane tank of residual butane fumes.

Butane tank details:
[ul]
[li]Small, cylindrical, clear plastic, holds about 50ml (around 1.7oz) liquid butane.[/li]
[li]Has a trigger-valve to release the butane at the "top" (one end of the cylinder), and that valve is connected to a "straw" that reaches down almost to the other end of the cylinder (which I will refer to as the "bottom").[/li]
[li]The bottom has a refill-inlet/valve that you can use to refill the cylinder (using a butane refill. To refill the tank, you press the refill against the tank).[/li]
[/ul]

So I want to empty the tank of residual butane fumes, BUT ALSO:
[ul]
[li]Without damaging the tank or the valve. I was going to try to forced compressed air through the bottom refill valve, but I'm worried the extreme cold from the compressed air may damage the valve.[/li]
[li]Without leaving unwanted OTHER residual liquids/gases in the tank (that may interfere with butane combustion when the tank is in use.)[/li]
[/ul]


Any suggestions?

 

[zdas04]

You really should have made both of your posts into a single post. Understanding why you want to do this is pretty important to the HOW to do it (i.e., if you need to know how much butane you removed it is a different problem than if you want to render the tank inert).

From the other thread I'm getting that you are trying to make this tank safe and benign for air travel. First, any vessel with any trapped pressure or vacuum will be unacceptable to the airlines or airport security. The only way that I can see that you can travel with this thing is to remove the inlet and outlet valves altogether. Even with that I would take the package to the TSA offices in the airport (make an appointment first) and show them what you have and the steps you've taken to make the tank unable to contain pressure or vacuum. Use a sniffer to ensure that no residual butane in present.

Don't worry about the "extreme cold" of compressed air (the JT effect has a velocity component and you control that, the slower you fill the tank the less cooling you'll see), worry instead about introducing air into a tank with residual butane in it, your really could create a bomb.

It seems like your last bullet is a half a thought, I can't tell what you were meaning to say.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[MortenA]

Steam is often used for larger tanks if you dont have N2

 

[zeusfaber]

You need to define "completely empty".

Atmospheric air has a real (although almost immeasurably small) butane content.

any vessel with any trapped pressure or vacuum will be unacceptable to the airlines or airport security.

That's actually not true. These things are ruled with a rod of iron by the IATA Dangerous Goods Regulations. For a container that size,there's an exemption that allows single containers charged with nonflammable/nonhazardous an pressures not exceeding 2 barg to be carried in hold or hand baggage.

We normally stick a declaration on the bottle to say what gas is inside it, that the pressure is less than 200kPa (2.0 bar) and therefore that under section 3.2.2.4 of the IATA Dangerous Goods Regulations it does not constitute Dangerous Air Cargo. That's enough to get them accepted. It doesn't always stop Customs from making you empty the bottles at the airport (but it doesn't sound like that would be a problem in your case).

A.

 

[docbuild]

Understanding why you want to do this is pretty important to the HOW to do it

Yes, I should had specified this in my post. Noted (for future posts)! Thank you.

It seems like your last bullet is a half a thought, I can't tell what you were meaning to say.

To "flush" the tank, requires a liquid or a gas as the flushing medium. It's likely that after the tank is flushed, some residual flushing medium will be left in the tank. What I was trying to say, is that I don't want to use a flushing medium that will damage the tank in any way. I also don't want the leftover flushing medium to interfere with the normal operation of the butane tank.

worry instead about introducing air into a tank with residual butane in it, your really could create a bomb.

... do you mean, due to the rapid compression of butane? Or something else?

 

[docbuild]

For a container that size,there's an exemption that allows single containers charged with nonflammable/nonhazardous an pressures not exceeding 2 barg to be carried in hold or hand baggage.

We normally stick a declaration on the bottle to say what gas is inside it, that the pressure is less than 200kPa (2.0 bar) and therefore that under section 3.2.2.4 of the IATA Dangerous Goods Regulations it does not constitute Dangerous Air Cargo. That's enough to get them accepted. It doesn't always stop Customs from making you empty the bottles at the airport (but it doesn't sound like that would be a problem in your case).

Hmmm... OK, I hope this applies to me. But in my situation:
[ul]
[li]The tank is "empty" (there is no liquid butane visible, though it's possible residual fumes remain, hence this post).[/li]
[li]The tank is a component of a prototype electrical appliance. The prototype, in a disassembled state, is what is being sent by air (along with the tank).[/li]
[li]I will not be travelling with the device. It will be sent overseas (Canada to the UK) by courier service.[/li]
[/ul]
Knowing these points, does section 3.2.2.4 still apply? RE: "We normally stick a declaration on the bottle to say what gas is inside it", should I specify the bottle is empty, but was used for butane? And should I put this note on the bottle, or somewhere on the shipping documentation, or both?

 

[berkshire]

Doc build
Check the rules and regulations for " inerting" used refrigerant containers . Without getting too much into the details , the standard practice is to pull a full vacuum on the tank, then allow air to enter the tank to normal atmospheric pressure, this removes any residual gas allowing for disposal of the cylinder.
If you can do this you will not have the residual butane problem.
B.E.

You are judged not by what you know, but by what you can do.

 

[zeusfaber]

Knowing these points, does section 3.2.2.4 still apply?

Being a component of something else: Can't see that being relevant unless the other components create a different hazard.

Shipping unaccompanied: Not an issue - that happens all the time (I should have included "Ordinary Cargo" alongside Hold and Cabin Baggage).

Unpressurised flammable vapour: The regulation 3.2.2.4 exemption applies to gases in Division 2.2 which are transported at a pressure of less than 200 kPa (2 bar) and are not liquefied or refrigerated liquefied gases. Liquid butane is both liquified and a Division 2.1 (ie flammable) gas. You've already dealt with the "liquified" bit of the problem, so it looks like you need to concentrate on getting yourself out of Div 2.1 and into Div 2.2. This means turning it from a gas with a lower flammable limit in air of 1.8% and a flammable range of 6.7% into one whose lower flammable limit is more than 13% and whose flammable range is less than 12%.

If your going to through-flush the tank, you need some way of knowing how far you've diluted the butane and to be sure that the flow is limited at the inlet rather than the outlet (to avoid overpressurising the tank).

The alternative is to drain to atmosphere, then charge with a diluent to a known pressure (2 barg seems appropriate for a butane cylinder), then repeat three or four times more. Provided you've eliminated all the liquid before you start, this method gives control over the final concentration.

Let me repeat an important point of David's:

worry instead about introducing air into a tank with residual butane in it, your really could create a bomb.

Find an inert diluent. One of the welding shield gases might be convenient. You may need to flush it out at the other end but, considering you'll be refilling with a liquified gas, that job will almost look after itself.

A.

 

[berkshire]

Doc Build,
I forgot about the filling aspect at the other end of the journey , So as Zeusfaber says instead of allowing air to enter after pulling a vacuum use nitrogen or argon.
B.E.

You are judged not by what you know, but by what you can do.

 

[docbuild]

Check the rules and regulations for " inerting" used refrigerant containers . Without getting too much into the details , the standard practice is to pull a full vacuum on the tank

Thanks for your post. I'll look into compressed gas companies to see if they can assist. But the butane tank is procured from a BBQ lighter, modified for use. It's made of plastic, small (50ml) and cylindrical. My knowledge of atmospheric stresses and material strength aren't good enough to determine if the cylinder can tolerate the stress of a full vacuum, but I know it wasn't designed with that in mind.

You've already dealt with the "liquified" bit of the problem, so it looks like you need to concentrate on getting yourself out of Div 2.1 and into Div 2.2. This means turning it from a gas with a lower flammable limit in air of 1.8% and a flammable range of 6.7% into one whose lower flammable limit is more than 13% and whose flammable range is less than 12%.

Thanks for your post. But how do I test for those target limits? Actually, how do they test for them, maybe I can use their testing process?


But let's say everything works out great, that I manage to inert (and not damage) the cylinder by pulling a vacuum and then using a inert diluent (process repeated 3-4 times). Will they simply take my word for it, that I did that?

I had an idea last night. What if I kept the release-valve open, and pumped regular air through the refill valve, using a compressor or hand-pump? It's not as good as inerting, but if this gets it into the acceptable range (of a lower flammable limit in air more than 13% and flammable range of less than 12%), then shouldn't it be fine?

 

[zeusfaber]

Somewhere in the middle of that process, the contents of your tank pass from above the upper explosive limit to below the lower explosive limit, via a pretty interesting concentration region. In a confined space. You'd need to be really sure you had no conceivable ignition sources (including static sparks and adiabatic heating - both if stuff goes according to plan and if anything goes wrong). Better not to go there in the first place.

A.