Degassing propane tanks (for Grant)
 

Hi Grant,

I spent a while yesterday looking at people's project pages and came
across your propane tank degassing page. I've considered reusing propane
tanks on several occasions, but had a different method of degassing in
mind. Before I get to the details I should point out that our propane
tanks (in the UK) might be a little different from yours, and that I'm
talking about the largest (47 kg) variety.

I'm not thinking of trying this right now, so this post is just for your
interest really. These tanks appeal to me because, having built a few
high voltage machines, I want a source of large conductive metal spheres
(or near spheres) to use as discharge terminals. The custom made
aluminium spheres cost hundreds of pounds each, whereas as you've
already pointed out, these tanks are often free. Our tanks have a convex
top and bottom, and my idea was to remove two tank bases and stick weld
them together to made a large conductive dome. The base ring and
handle/valve protector could be removed from the cylinders easily. The
resulting terminal would be damn near indestructible, unlike the usual
spun aluminium spheres which are easily dented.

My plan was to take an "officially empty" cylinder out into our field
(we have no neighbours nearby) on a cool day, make sure it was away from
any sources of ignition and slowly open the valve to vent the propane to
the atmosphere. When the propane inside was at atmospheric pressure, I
intended to remove the valve and fill the tank with water from a hose to
expel the remaining propane. Not having removed a tank valve, I'm not
sure how easy it would be to fill the tank with water, but it seems like
a neat way to remove all the remaining propane. What do you think? I'd
be interested to hear your views.

Best wishes,

Chris

Christopher Tidy wrote:
My plan was to take an "officially empty" cylinder out into our field
(we have no neighbours nearby) on a cool day, make sure it was away from
any sources of ignition and slowly open the valve to vent the propane to
the atmosphere. When the propane inside was at atmospheric pressure, I
intended to remove the valve and fill the tank with water from a hose to
expel the remaining propane. Not having removed a tank valve, I'm not
sure how easy it would be to fill the tank with water, but it seems like
a neat way to remove all the remaining propane. What do you think? I'd
be interested to hear your views.

The bleeding off of the gas I did slowly i.e. I didn't open the valve fully, I
just cracked it and let it hiss slightly for several hours. When it stopped
hissing then I brought it inside to warm it up (I did it on a cold day) and then
repeated it. Then I opened the valve fully and turned it upside down and let it
get as aired out as it would (I'm not sure this actually does anything). Then I
pressurized the tank to about 140psi with compressed air and vented it again. I
repeated the pressurize/vent cycle 3 times. By that time I figure what was left
inside wouldn't burn, too diluted.

Then I clamped the tank, heated the neck to release the thread locker, and,
using a big wrench, I unscrewed the valve. No point at all in trying to get
water into one of those valves, gotta get it out fully. With the valve out, then
I ran it mostly full of hot water and poured in a cup or so of household bleach,
then plugged it and shook it all up (for a larger tank, I'd have rolled it
around for a couple of minutes) then drained out the solution. No more stink.

It isn't easy to remove the valve without a way to rigidly clamp the tank. With
the tank clamped, however, it's pretty easy as long as you use heat.

Grant

If you google in RCM, you will find some experiments someone did trying
to get more than a whoosh out of a propane tank when igniting a optimum
gas air mixture.


Dan

Christopher Tidy wrote:
Hi Grant,

I spent a while yesterday looking at people's project pages and came
across your propane tank degassing page. I've considered reusing propane
tanks on several occasions, but had a different method of degassing in
mind. Before I get to the details I should point out that our propane
tanks (in the UK) might be a little different from yours, and that I'm
talking about the largest (47 kg) variety.

Take the valve(s) out and turn it over for a day. The gas will run out,
it's considerably heavier than air. I've cut dozens of LP tanks, from
20lb to 1000gal. without problem, except for a couple that flashed
because I didn't let them drain long enough.

When cutting sealed containers I always make a point to start as far
from the hole as possible. If it does flash at least the fire isn't
between the not-yet burned mixture and the hole.

John

Christopher Tidy wrote:


My plan was to take an "officially empty" cylinder out into our field
(we have no neighbours nearby) on a cool day, make sure it was away from
any sources of ignition and slowly open the valve to vent the propane to
the atmosphere. When the propane inside was at atmospheric pressure, I
intended to remove the valve and fill the tank with water from a hose to
expel the remaining propane. Not having removed a tank valve, I'm not
sure how easy it would be to fill the tank with water, but it seems like
a neat way to remove all the remaining propane. What do you think? I'd
be interested to hear your views.



When I did this, I opened the fill vent, opened the main valve and
then held a running hose against the main valve fitting until water
came out the vent.
jk

Christopher Tidy wrote:
Hi Grant,

I spent a while yesterday looking at people's project pages and came
across your propane tank degassing page. I've considered reusing propane
tanks on several occasions, but had a different method of degassing in
mind. Before I get to the details I should point out that our propane
tanks (in the UK) might be a little different from yours, and that I'm
talking about the largest (47 kg) variety.

I'm not thinking of trying this right now, so this post is just for your
interest really. These tanks appeal to me because, having built a few
high voltage machines, I want a source of large conductive metal spheres
(or near spheres) to use as discharge terminals. The custom made
aluminium spheres cost hundreds of pounds each, whereas as you've
already pointed out, these tanks are often free. Our tanks have a convex
top and bottom, and my idea was to remove two tank bases and stick weld
them together to made a large conductive dome. The base ring and
handle/valve protector could be removed from the cylinders easily. The
resulting terminal would be damn near indestructible, unlike the usual
spun aluminium spheres which are easily dented.

My plan was to take an "officially empty" cylinder out into our field
(we have no neighbours nearby) on a cool day, make sure it was away from
any sources of ignition and slowly open the valve to vent the propane to
the atmosphere. When the propane inside was at atmospheric pressure, I
intended to remove the valve and fill the tank with water from a hose to
expel the remaining propane. Not having removed a tank valve, I'm not
sure how easy it would be to fill the tank with water, but it seems like
a neat way to remove all the remaining propane. What do you think? I'd
be interested to hear your views.

Just thought...I could use me recently-acquired vacuum pump to de-gas
the tanks and pipe the propane elsewhere.

Chris