Butane transfer to small bottle

[steveinnice]

Technical question : I have a full 15 kg bottle of butane that wont fit in the gas locker and an empty 7.5 one that will. If I connect them together to transfer the gas will I end up with a full 7,5 and 1/2 full 15 or what? I would of course disconnect them and put the 7,5 in the locker to use it. Discuss.

 

[[70521]]

This has been discussed many times and kits are available. The Forum search function is rubbish, but you can Google the topic, other search engines are available.
? ?

 

[footsoldier]

The search function will find a recent, lengthy thread on the subject where the views ranged from "perfectly logical, I often do it" to " highly dangerous, the world will end".

 

[sarabande]

Easy peasy provided you have the right kit, and do not fill the smaller bottle completely. No more than 90% to allow space at the top so that liquid propane can become gaseous.

 

[steveinnice]

Easy peasy provided you have the right kit, and do not fill the smaller bottle completely. No more than 90% to allow space at the top so that liquid propane can become gaseous.

thank you . I really only wanted to know the % left in each bottle when it reached equilibrium.

 

[Stork_III]

thank you . I really only wanted to know the % left in each bottle when it reached equilibrium.

You are not transferring gas, it is liquid. Done incorrectly you will fill the smaller with 100% liquid with no space for gasification, dangerous.
The larger bottle is inverted above the smaller to let liquid flow , stopping when the smaller is about 80% full of liquid. Please read up about the process, it can be dangerous.

 

[vyv_cox]

The safety dodge for a Camping Gaz 901 bottle is to float it in water. When it sinks it is about 80% full. Not sure this would work for a 7.5 kg bottle but of course bathroom scales are the answer. That way there seems no reason why you could not decant half your 15 kg bottle.

 

[LittleSister]

I'm interested in the general principles. Can someone explain whether the liquid is under pressure, or is the pressure only a function of the gas coming off the liquid?

 

[Little Dorrit]

If anyone knows of a good informative video on how to do this safely and what kit is required it would be helpful. I'll google later and report back if nobody else has already done this.

 

[steveinnice]

I'm interested in the general principles. Can someone explain whether the liquid is under pressure, or is the pressure only a function of the gas coming off the liquid?

My understanding would be that ( at a constant 25c) the butane would be a liquid while under pressure and as you release the pressure it would become gas. If you were decanting via a sealed system from a full( of liquid and gas) bottle to a empty at atmospheric pressure it would leave the full bottle as a gas and as the pressure in the "empty one increased it would return to liquid. My question to start this thread was at what stage does equilibrium occur between a full 15kg bottle and an empty 7.5kg bottle I would think it would be 66.6 % repeating for the 7.5 and 33.3 % repeating for the 15 one.

 

[steveinnice]

If anyone knows of a good informative video on how to do this safely and what kit is required it would be helpful. I'll google later and report back if nobody else has already done this.

Good luck. I spent ages doing that and as Footsolider said earlier "where the views ranged from "perfectly logical, I often do it" to " highly dangerous, the world will end". "

 

[steveinnice]

My understanding would be that ( at a constant 25c) the butane would be a liquid while under pressure and as you release the pressure it would become gas. If you were decanting via a sealed system from a full( of liquid and gas) bottle to a empty at atmospheric pressure it would leave the full bottle as a gas and as the pressure in the "empty one increased it would return to liquid. My question to start this thread was at what stage does equilibrium occur between a full 15kg bottle and an empty 7.5kg bottle I would think it would be 66.6 % repeating for the 7.5 and 33.3 % repeating for the 15 one.

upon reflection ( did the sums ) it would be 66.6% for both bottles. the 7.5 would have 4.995 kgs in it and the 15 would have 9.9 the difference is in the repeating bit. I think.

 

[vyv_cox]

My understanding would be that ( at a constant 25c) the butane would be a liquid while under pressure and as you release the pressure it would become gas. If you were decanting via a sealed system from a full( of liquid and gas) bottle to a empty at atmospheric pressure it would leave the full bottle as a gas and as the pressure in the "empty one increased it would return to liquid. My question to start this thread was at what stage does equilibrium occur between a full 15kg bottle and an empty 7.5kg bottle I would think it would be 66.6 % repeating for the 7.5 and 33.3 % repeating for the 15 one.

I think you are not appreciating how it is done. The donor bottle is hung upside-down. Liquid runs down the connecting hose into the receiving bottle. This takes time of course, as displaced gas has to pass back up the same hose. Ultimately there is no reason why the donor bottle could not become 100% full, which of course is not what is wanted.

 

[steveinnice]

Tell you what, does anybody want to swap a 15 kg full ( but maybe only 80% full) bottle of butane for a full (again at 80%) 7.5 kg bottle ? sounds the best way to go

 

[LittleSister]

But what is happening to pressure while the liquid is being decanted? Is it not reduced?

If one bottle is 80% full, at normal 'full' pressure (whatever that is), and connected to an empty bottle (lets assume same size for simplicity) which will presumably be near atmospheric pressure, the pressure will equalise between the two. If the liquid is compressible (is it?) then the pressure would presumably be halved, if the liquid is not compressible and only the gas is compressible, then there would presumably be a much greater reduction in pressure as the gas was only 20% of the volume of the 'full' bottle, but now 120% of the two.

And (some what related, perhaps) is it possible to transfer the entire contents of one bottle into another, or is there always some left in the original bottle, which is, say, halved each time another bottle is filled?

Yours in ignorance.

 

[VicS]

[

Yours in ignorance.

While there is liquid present the pressure in the bottle is dependent on the temperature ... not on how full the bottle is.
The pressure only falls if gas is vented/ used after all the liquid has vaporised.
The liquid is not compressible .... the gas is compressible.

If the donor bottle is smaller than the receiving bottle, or contains less gas than the capacity of the receiving bottle, all the liquid can be transferred leaving only gas in the donor bottle The final pressure in both bottles will be the same and depend on the temperature of the liquid in the receiving bottle.

The transfer process can be accelerated by very slightly warming the donor bottle and/ or cooling the receiving bottle because that will create a small pressure difference between the two.

 

[AngusMcDoon]

...if the liquid is not compressible and only the gas is compressible...

Yes. You can't compress liquids by any significant amount at gas bottle pressures, otherwise hydraulic lines on JCB's would not work, as this applies to all liquids. Similarly, if a liquid is heated the expansion will create enormous pressure if the volume is constrained, way beyond what a Calor gas bottle will hold. The bottle may spit and a BLEVE will result.

 

[vyv_cox]

But what is happening to pressure while the liquid is being decanted? Is it not reduced?

If one bottle is 80% full, at normal 'full' pressure (whatever that is), and connected to an empty bottle (lets assume same size for simplicity) which will presumably be near atmospheric pressure, the pressure will equalise between the two. If the liquid is compressible (is it?) then the pressure would presumably be halved, if the liquid is not compressible and only the gas is compressible, then there would presumably be a much greater reduction in pressure as the gas was only 20% of the volume of the 'full' bottle, but now 120% of the two.

And (some what related, perhaps) is it possible to transfer the entire contents of one bottle into another, or is there always some left in the original bottle, which is, say, halved each time another bottle is filled?

Yours in ignorance.

The pressure in the bottle is the vapour pressure of the hydrocarbon, about 35 psi for butane, a little more for propane at 20 C. Coincidentally today I disconnected an Autogas bottle from a bulkhead regulator. The temperature is only about 5 C and release was just a small puff of gas, very little pressure. I don't think the pressure is important, the liquid is simply running down the hose into an effectively empty bottle.

It is definitely possible to fill the receiver bottle 100%, I have seen this happen in Greece, where bottles are filled by all sorts of people in back yards.

 

[AngusMcDoon]

It is definitely possible to fill the receiver bottle 100%, I have seen this happen in Greece, where bottles are filled by all sorts of people in back yards.

That seems a bit careless when it's easy not to overfill using scales, and a possible unintended consequence from overfilling might annoy your neighbours. Do Calor and similar bottles have a PRV at least to release the excess pressure somewhat slowly?

 

[vyv_cox]

That seems a bit careless when it's easy not to overfill using scales, and a possible unintended consequence from overfilling might annoy your neighbours. Do Calor and similar bottles have a PRV at least to release the excess pressure somewhat slowly?

Greeks careless? Who could believe that?

Not sure that a BLEVE is the most likely consequence. I have heard of users of stoves experiencing liquid butane at their stove, Bad enough but not as bad as a bottle rupture.