I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

???

Steve

On 2012-06-17, Steve B wrote:
I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

I heard that Clorox works. I am sure that a good fire will also kill
that smell.

i

On Sun, 17 Jun 2012 13:15:46 -0700, Steve B wrote:

I have decided to make a bbq cooker out of a propane tank
[snip]

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

It might make no difference in smell removal, but according
to http://en.wikipedia.org/wiki/Liquefied_petroleum_gas the
odorant in use nowadays is ethanethiol.

Wikipedia says "In the United States, tetrahydrothiophene
(thiophane) or amyl mercaptan are also approved odorants,
although neither is currently being utilized." This doesn't
agree with http://www.msdshazcom.com/MSDS/E/exxon/wcd002fe.htm
or http://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html.
The former says "Exxon, like many other propane marketers, uses
ethyl mercaptan as the odorant, adding it in a ratio of 1.5 lb
per 10,000 gallons of propane..." and the latter says "In order
to detect presence and prevent an explosion from a buildup of
propane gas, odorant (almost always ethyl mercaptan) is added to
liquid LP-Gas. Ethyl mercaptan has a distinctive order and has a
high odor impact. To familiarize yourself with this type of odor
you can request €œScratch and Sniff€� leaflets from the National
Propane Gas Association..."

Does anyone here know for certain what's used now?

--
jiw

"Steve B" wrote in message
...
I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

???

Steve
Steaming for about 4 hours will get rid of about 80% of the smell.
The rest can be neutralised with a wash down with potassium
permanganate 10% solution, then steam again.

Its likely that the smell will recur as it really does get into the metal.

Steve B wrote:
I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

???

Steve



BEFORE you open it dump in a gallon of clorox and 10 gallons of water.
Roll it around and let it set a while. Then let it drain. Now cut it
open. Use a solution of 10% potassium permanganate and spray it down.

If you plan on splitting it and using hinges on parts of the top weld
angle strips around the cut areas before you cut. That way the cut areas
are reinforced and all you need to do add the hinges.

--
Steve W.

Steve B wrote:
...
I know to flush, fill with water, etc, to cut it.

TOTALLY unnecessary! Just cut it - there's no oxygen in the tank to
support combustion and no pressure to force anything but tiny amounts of
gas out. I have done it many times.

How about removing the mercaptan smell? ...

As others have said: bleach. Forget the potassium permanganate - you'll
have a devil of a time finding it and it's unnecessary (use a burn-in
fire to remove residual oil, etc & Bob's your uncle).

Not your uncle,
Bob

Bob Engelhardt fired this volley in
:

As others have said: bleach. Forget the potassium permanganate -
you'll
have a devil of a time finding it and it's unnecessary (use a burn-in
fire to remove residual oil, etc & Bob's your uncle).

Bleach converts mercaptans just fine, but Bob, you must be living wrong
if you have trouble finding potassium permanganate! It's _everywhere_ as
"green sand" recharging material for iron-removal water filters.

It's not cheap, and bleach is perfectly acceptable. Any strong oxidizer
will work -- even hydrogen peroxide, if you have enough money!

I differ with you on the idea of cutting into an "unknown" propane tank,
though. You can't know if someone has introduced air into it. If they
did, you have a bomb on your hands (and "bombs are us", since I'm in that
business).

It's a minor bit of safety practice to yank the valve and properly purge
the tank. It's certainly less expensive than a stay in the emergency
room.

Lloyd

Lloyd E. Sponenburgh wrote:
Bob Engelhardt fired this volley in
:

Bleach converts mercaptans just fine, but Bob, you must be living wrong
if you have trouble finding potassium permanganate! It's _everywhere_ as
"green sand" recharging material for iron-removal water filters. ...

Oh yeah, I remember using it for that. Easy enough to get, but awful to
work with - I also remember the indelible purple stains G.

I differ with you on the idea of cutting into an "unknown" propane tank,
though. You can't know if someone has introduced air into it. If they
did, you have a bomb on your hands (and "bombs are us", since I'm in that
business).
....

Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added for
that.

Bob

Bob Engelhardt wrote:
....
Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added for
that.

Oh ... that reminds me of one caveat: do NOT cut open an unpurged tank
with oxy-fuel. That oxygen can create a problem.

Bob

Bob Engelhardt fired this volley in
:

Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added
for
that.

Bob, please take this from someone who knows something about explosive
mixtures -- Approximately any mixture of air and propane that would
create a good blue flame will constitute a mixture that will explode with
force sufficient to fragment the tank.

I'm not guessing or theorizing. I do this for a living -- making
explosives (and machines to make explosives) for stage and film. Propane
is one of our "staple" items. I have experience (deliberately) creating
both flame and explosion effects with propane. The lower and upper
explosive limits of propane/air mixtures are pretty broad. It doesn't
have to be stoichiometric mixture to explode. (acetone is worse... look
it up)

One machine I designed mixes pure oxygen and propane under PLC control to
create "tuned" explosions for noise-making, with differing mixtures for
differing noise levels. Another less expensive system (in terms of
expendables) does the same thing with compressed air. The difference is
one of total acoustic pressure -- oxygen being the more "efficient",
since the entire mass of mixture is explosive, where with air only about
30% of it is (the rest being nitrogen and trace gasses).

You seem to be working from the stance of "it hasn't killed me yet",
which is a fatal flaw in blasters, fireworkers, and stage
pyrotechnicians. We (who still survive) work from the posture of "what I
don't know will kill me."

You're welcome to cut into all the propane tanks you want, and I wish you
no harm when you do. Please don't recommend this practice to others who
might not end up as lucky as you.

LLoyd

Propane plus air, under pressure. That's explosive mix, if the proportions
are right. I'd not want to chance it. The risk of failure is too terrifying.

Christopher A. Young
Learn more about Jesus
www.lds.org
..

"Bob Engelhardt" wrote in message
...
Bob Engelhardt wrote:
....
Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added for
that.

Oh ... that reminds me of one caveat: do NOT cut open an unpurged tank
with oxy-fuel. That oxygen can create a problem.

Bob

Ethyl mercaptan is the old common name (along with mercaptoethanol) for the
more IUPAC-correct ethanethiol. Same compound, structurally CH3CH2SH,
ethanol with the oxygen replaced with sulfur. Never tried to wash it out
but I have to think that bleach followed by fire should do the trick :-).

-----
Regards,
Carl Ijames
"James Waldby" wrote in message ...

On Sun, 17 Jun 2012 13:15:46 -0700, Steve B wrote:

I have decided to make a bbq cooker out of a propane tank
[snip]

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

It might make no difference in smell removal, but according
to http://en.wikipedia.org/wiki/Liquefied_petroleum_gas the
odorant in use nowadays is ethanethiol.

Wikipedia says "In the United States, tetrahydrothiophene
(thiophane) or amyl mercaptan are also approved odorants,
although neither is currently being utilized." This doesn't
agree with http://www.msdshazcom.com/MSDS/E/exxon/wcd002fe.htm
or http://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html.
The former says "Exxon, like many other propane marketers, uses
ethyl mercaptan as the odorant, adding it in a ratio of 1.5 lb
per 10,000 gallons of propane..." and the latter says "In order
to detect presence and prevent an explosion from a buildup of
propane gas, odorant (almost always ethyl mercaptan) is added to
liquid LP-Gas. Ethyl mercaptan has a distinctive order and has a
high odor impact. To familiarize yourself with this type of odor
you can request "Scratch and Sniff" leaflets from the National
Propane Gas Association..."

Does anyone here know for certain what's used now?

--
jiw

Lloyd E. Sponenburgh wrote:
Bob Engelhardt wrote:

Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added
for that.

Bob, please take this from someone who knows something about explosive
mixtures -- Approximately any mixture of air and propane that would
create a good blue flame will constitute a mixture that will explode with
force sufficient to fragment the tank.

I'm not guessing or theorizing. I do this for a living -- making
explosives (and machines to make explosives) for stage and film. Propane
is one of our "staple" items. I have experience (deliberately) creating
both flame and explosion effects with propane. The lower and upper
explosive limits of propane/air mixtures are pretty broad. It doesn't
have to be stoichiometric mixture to explode. (acetone is worse... look
it up)

You don't say what your experience is regarding adding air to a propane
tank, so I assume that you are extrapolating and not speaking from
direct experience with tanks. I have added air to a propane tank,
attempting a stoichiometric mixture, and igniting it. I did get a good
whoosh.

I'm not saying the mixture won't "explode". I'm saying that the
explosion won't have much force. An empty tank just doesn't have enough
propane in it and a lot of it has to be displaced by air to get an
explosive mix.

...[oxygen] where with air only about 30% of it is ...

about 20%

You seem to be working from the stance of "it hasn't killed me yet",
which is a fatal flaw in blasters, fireworkers, and stage
pyrotechnicians. We (who still survive) work from the posture of "what I
don't know will kill me."

Let's turn to chemistry:
_Chemical analysis of propane combustion in a closed container_

Take the term "analysis" with a grain of salt - I'm no chemist and it's
been a long time since freshman chemistry. So, if the logic is wrong,
let me know. And if there are 2nd order effects that I haven't taken
into account (and are significant (10%)), those too.

The approach here is to determine the amount of heat generated/released
by ideal/stoichiometric propane-air combustion and then calculate the
effect of that heat on the temperature and pressure in a closed
container.

The propane combustion reaction:
C3H8 + 5O2 - 3CO2 + 4H2O

One mole of propane reacts with 5 moles of oxygen. After burning, the
reaction produces 3mol CO2 and 4mol H2O vapor (steam).

The heat produced: the (net) Heat of Combustion of propane is 2043
kJ/mole, i.e., the combustion of 1 mole of propane produces 2043kJ of heat.

How much will this heat raise the temperature of the gases? First, it's
just not propane and oxygen involved, but the nitrogen that's in the air
with the oxygen. Air is 21% oxygen and 78% nitrogen by volume, so for
each mole of oxygen (O2) in the air, there are 78/21 = 3.71mol nitrogen
(N2). And our mixture has 5mol O2, so there are also 18.6mol N2 in our
mixture. (I'll ignore the other 1% of atmospheric gases and any
atmospheric water vapor.)

Assume that all the heat of combustion goes to raising the temperature
of the gases in the container (none lost). The specific heat is the
heat it takes to raise a unit mass 1 degree (J/g-degree). For our
(resultant) gases the specific heats* (constant volume values) a
CO2: 0.63
steam: 1.76
N2: 0.71

Since mass = # moles * molecular weight, the contents have these masses:
CO2: 3mol * 44 = 132g
H2O vapor: 4mol * 18 = 72g
N2: 18.6mol * 28 = 520.8g

For a temperature raise of delT, the heat required would be:
delT * specific heat * mass

Then the total heat is:
(delT * 0.63 * 132) + (delT * 1.76 * 72) + (delT * 0.71 * 520.8) =
2043kJ
reduces to:
delT = 2,043,000/580 = 3,525K
and the final temperature, T is:
T = start + raise = 293 + 3525 = 3,818K

For a constant volume, pressure is proportional to temperatu
P2/P1 = T2/T1
P2 = P1 * T2/T1
= 14.7 psia * 3818 / 293
= 191 psia (176 psig)

So, the peak pressure in a closed container with a stoichiometric
mixture of propane and air would be (only) 191psi. Seems low? ...
consider that 64% of the heat went to raising the temperature of the
nitrogen in the air!

Note that I didn't base the calculations on a particular tank size,
because the temperature and pressure results would be the same with any
volume (the amounts of gases would be proportional to the volume).

20# propane tanks are rated as follows:
Working pressu 240psi
Pressure relief: 375psi
Test pressu 480psi
Design burst pressu 960psi
Observed burst pressures: 1200 - 2000psi ( not a "rating", I know)

So our calculated peak pressure is 23% below the working pressure
and only 19% of the design burst pressure.

Also, this is worst case: it is a stoichiometric mixture in a sealed
container.

It's hard for me to see the risk.

* - Specific heats from Engineering Toolbox web site:
http://www.engineeringtoolbox.com/sp...ses-d_159.html
That for steam is for 150 psig, 360 - 600F, which is probably
conservative (increases with temperature and pressure).

You're welcome to cut into all the propane tanks you want, and I wish you
no harm when you do. Please don't recommend this practice to others who
might not end up as lucky as you.

I don't think that luck has anything to do with it.

Bob

Stormin Mormon wrote:
Propane plus air, under pressure. That's explosive mix, if the proportions
are right. I'd not want to chance it. The risk of failure is too terrifying.

But it's not under pressure - it's empty tanks that we're talking about.

"James Waldby" wrote in message
...
On Sun, 17 Jun 2012 13:15:46 -0700, Steve B wrote:

I have decided to make a bbq cooker out of a propane tank
[snip]

How about removing the mercaptan smell? Once I get it open, what should
I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

It might make no difference in smell removal, but according
to http://en.wikipedia.org/wiki/Liquefied_petroleum_gas the
odorant in use nowadays is ethanethiol.

Wikipedia says "In the United States, tetrahydrothiophene
(thiophane) or amyl mercaptan are also approved odorants,
although neither is currently being utilized." This doesn't
agree with http://www.msdshazcom.com/MSDS/E/exxon/wcd002fe.htm
or http://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html.
The former says "Exxon, like many other propane marketers, uses
ethyl mercaptan as the odorant, adding it in a ratio of 1.5 lb
per 10,000 gallons of propane..." and the latter says "In order
to detect presence and prevent an explosion from a buildup of
propane gas, odorant (almost always ethyl mercaptan) is added to
liquid LP-Gas. Ethyl mercaptan has a distinctive order and has a
high odor impact. To familiarize yourself with this type of odor
you can request "Scratch and Sniff" leaflets from the National
Propane Gas Association..."

Does anyone here know for certain what's used now?

--
jiw

Or how to remove it when it is undesirable?

Is there an echo in here, or is it just me?

Steve

On 6/17/2012 4:15 PM, Steve B wrote:
I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

???

Steve



YES, wirebrushing! THAT'S the ticket!

In article ,
"Steve B" wrote:

I have decided to make a bbq cooker out of a propane tank if I can find one
of the appropriate size. A friend of mine owns a supply house, and I
believe they will have a dead one or two I can cut up and use. I was going
to make a brick one in the back yard, and then a guy at my church wants me
to cook up some stuff for July 18th. One on wheels would do what I need,
and be available for others, too.

I know to flush, fill with water, etc, to cut it.

How about removing the mercaptan smell? Once I get it open, what should I
do to kill that smell, or will heating it up with charcoal for the first
time do the trick?

Electric wirebrushing? Scrubbing with some type of cleaner?

???

Steve

Bite the bullet and go buy yourself a Webber 22 1/2" [1] charcoal BBQ.
You'll never look back.

They work really well, and will put big smiles on your face till your a
little old man.

Had mine since the early 80's... probably used it once a week average,
and it's still going strong. Replacement parts are available (but I've
yet to need any).

http://www.weber.com/explore/grills/...ch-silver-22-1

http://www.amazon.com/Weber-741001-2...er/dp/B00004RA
LU/ref=sr_1_4?ie=UTF8&qid=1340000982&sr=8-4&keywords=webber+22.5+gold

Even used from Craigs list they're great, long as the porcelain isn't
chipped, there are no missing parts and corrosion/rust of legs and
grates is reasonable.

They make other charcoal models with any bell/whistle imaginable... but
the basic ones are more than satisfactory.

Erik

[1] If just cooking for 2 or 3, go for the 18 1/2" model.

http://www.weber.com/explore/grills/...ch-silver-18-1

http://www.amazon.com/Weber-441001-1...dp/B00004RALW/
ref=sr_1_3?s=lawn-garden&ie=UTF8&qid=1340001070&sr=1-3&keywords=webber+18
..5

In article ,
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

Bob Engelhardt fired this volley in
:

As others have said: bleach. Forget the potassium permanganate -
you'll
have a devil of a time finding it and it's unnecessary (use a burn-in
fire to remove residual oil, etc & Bob's your uncle).

Bleach converts mercaptans just fine, but Bob, you must be living wrong
if you have trouble finding potassium permanganate! It's _everywhere_ as
"green sand" recharging material for iron-removal water filters.

It's not cheap, and bleach is perfectly acceptable. Any strong oxidizer
will work -- even hydrogen peroxide, if you have enough money!

I differ with you on the idea of cutting into an "unknown" propane tank,
though. You can't know if someone has introduced air into it. If they
did, you have a bomb on your hands (and "bombs are us", since I'm in that
business).

It's a minor bit of safety practice to yank the valve and properly purge
the tank. It's certainly less expensive than a stay in the emergency
room.

Lloyd

A little OT here, but just the other day I ran across a most interesting
YouTube video involving potassium permanganate and hydrogen peroxide...

http://www.youtube.com/watch?v=OLUyeCC-2Ko

Be patient, the cool part is the 'accidental' fast reaction towards the
end.

Erik

Bob Engelhardt fired this volley in
:

But it's not under pressure - it's empty tanks that we're talking about.

_I_ never said anything about pressure. The mixture will gladly provide
plenty of its own when ignited.

LLoyd

Bob Engelhardt fired this volley in
:

...[oxygen] where with air only about 30% of it is ...

about 20%

No, Bob. Air is 20% oxygen. About 30% of the mixture in the tank would be
explosive.

Read first, open mouth later.

LLoyd

Lloyd E. Sponenburgh wrote:
Bob Engelhardt fired this volley in
:

But it's not under pressure - it's empty tanks that we're talking about.

_I_ never said anything about pressure. The mixture will gladly provide
plenty of its own when ignited.

LLoyd

I was Reply'ing to Christopher A. Young

Lloyd E. Sponenburgh wrote:
Bob Engelhardt fired this volley in
:

...[oxygen] where with air only about 30% of it is ...
about 20%

No, Bob. Air is 20% oxygen. About 30% of the mixture in the tank would be
explosive.
[snip insult]

Right ... I was careless about what "it" was.

Erik wrote:
A little OT here, but just the other day I ran across a most interesting
YouTube video involving potassium permanganate and hydrogen peroxide...

http://www.youtube.com/watch?v=OLUyeCC-2Ko

Be patient, the cool part is the 'accidental' fast reaction towards the
end.

Skip down to 4:20 for the cool part.

On Sun, 17 Jun 2012 23:19:39 -0400, Bob Engelhardt
wrote:

Lloyd E. Sponenburgh wrote:
Bob Engelhardt wrote:

Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added
for that.

Bob, please take this from someone who knows something about explosive
mixtures -- Approximately any mixture of air and propane that would
create a good blue flame will constitute a mixture that will explode with
force sufficient to fragment the tank.

I'm not guessing or theorizing. I do this for a living -- making
explosives (and machines to make explosives) for stage and film. Propane
is one of our "staple" items. I have experience (deliberately) creating
both flame and explosion effects with propane. The lower and upper
explosive limits of propane/air mixtures are pretty broad. It doesn't
have to be stoichiometric mixture to explode. (acetone is worse... look
it up)

You don't say what your experience is regarding adding air to a propane
tank, so I assume that you are extrapolating and not speaking from
direct experience with tanks. I have added air to a propane tank,
attempting a stoichiometric mixture, and igniting it. I did get a good
whoosh.

I'm not saying the mixture won't "explode". I'm saying that the
explosion won't have much force. An empty tank just doesn't have enough
propane in it and a lot of it has to be displaced by air to get an
explosive mix.

...[oxygen] where with air only about 30% of it is ...

about 20%

You seem to be working from the stance of "it hasn't killed me yet",
which is a fatal flaw in blasters, fireworkers, and stage
pyrotechnicians. We (who still survive) work from the posture of "what I
don't know will kill me."

Let's turn to chemistry:
_Chemical analysis of propane combustion in a closed container_

Take the term "analysis" with a grain of salt - I'm no chemist and it's
been a long time since freshman chemistry. So, if the logic is wrong,
let me know. And if there are 2nd order effects that I haven't taken
into account (and are significant (10%)), those too.

The approach here is to determine the amount of heat generated/released
by ideal/stoichiometric propane-air combustion and then calculate the
effect of that heat on the temperature and pressure in a closed
container.

The propane combustion reaction:
C3H8 + 5O2 - 3CO2 + 4H2O

One mole of propane reacts with 5 moles of oxygen. After burning, the
reaction produces 3mol CO2 and 4mol H2O vapor (steam).

The heat produced: the (net) Heat of Combustion of propane is 2043
kJ/mole, i.e., the combustion of 1 mole of propane produces 2043kJ of heat.

How much will this heat raise the temperature of the gases? First, it's
just not propane and oxygen involved, but the nitrogen that's in the air
with the oxygen. Air is 21% oxygen and 78% nitrogen by volume, so for
each mole of oxygen (O2) in the air, there are 78/21 = 3.71mol nitrogen
(N2). And our mixture has 5mol O2, so there are also 18.6mol N2 in our
mixture. (I'll ignore the other 1% of atmospheric gases and any
atmospheric water vapor.)

Assume that all the heat of combustion goes to raising the temperature
of the gases in the container (none lost). The specific heat is the
heat it takes to raise a unit mass 1 degree (J/g-degree). For our
(resultant) gases the specific heats* (constant volume values) a
CO2: 0.63
steam: 1.76
N2: 0.71

Since mass = # moles * molecular weight, the contents have these masses:
CO2: 3mol * 44 = 132g
H2O vapor: 4mol * 18 = 72g
N2: 18.6mol * 28 = 520.8g

For a temperature raise of delT, the heat required would be:
delT * specific heat * mass

Then the total heat is:
(delT * 0.63 * 132) + (delT * 1.76 * 72) + (delT * 0.71 * 520.8) =
2043kJ
reduces to:
delT = 2,043,000/580 = 3,525K
and the final temperature, T is:
T = start + raise = 293 + 3525 = 3,818K

For a constant volume, pressure is proportional to temperatu
P2/P1 = T2/T1
P2 = P1 * T2/T1
= 14.7 psia * 3818 / 293
= 191 psia (176 psig)

So, the peak pressure in a closed container with a stoichiometric
mixture of propane and air would be (only) 191psi. Seems low? ...
consider that 64% of the heat went to raising the temperature of the
nitrogen in the air!

Note that I didn't base the calculations on a particular tank size,
because the temperature and pressure results would be the same with any
volume (the amounts of gases would be proportional to the volume).

20# propane tanks are rated as follows:
Working pressu 240psi
Pressure relief: 375psi
Test pressu 480psi
Design burst pressu 960psi
Observed burst pressures: 1200 - 2000psi ( not a "rating", I know)

So our calculated peak pressure is 23% below the working pressure
and only 19% of the design burst pressure.

Also, this is worst case: it is a stoichiometric mixture in a sealed
container.

It's hard for me to see the risk.

* - Specific heats from Engineering Toolbox web site:
http://www.engineeringtoolbox.com/sp...ses-d_159.html
That for steam is for 150 psig, 360 - 600F, which is probably
conservative (increases with temperature and pressure).

You're welcome to cut into all the propane tanks you want, and I wish you
no harm when you do. Please don't recommend this practice to others who
might not end up as lucky as you.

I don't think that luck has anything to do with it.

Bob
You do need to take into account that by cutting into the tank you
are adversely affecting the structural integrity of ther tank,
reducing the burst pressure by a significant amount. Not saying it
WILL cause harm if it goes off - but the possibility is definitely
higher than your detailed analysis would indicate.

wrote:
You do need to take into account that by cutting into the tank you
are adversely affecting the structural integrity of ther tank,
reducing the burst pressure by a significant amount. Not saying it
WILL cause harm if it goes off - but the possibility is definitely
higher than your detailed analysis would indicate.

You're right and I hadn't considered that. Still, with only 175 psig in
the tank it's not likely "..." to burst.

The 13 year old in me is dying to do some experiments. I don't know how
much longer I can restrain him G.

Gunner Asch wrote:

Not to mention any short duration/ high pressure Jet effect which
launches that bottle some score of yards from where the torch ignited
the contents.......hopefully..in a clear direction....

Well, with 4-5 gal of gas at 175 psig, the impulse is going to be pretty
low. And applied to a tank weighting 18(?)lbs, its resultant velocity
is going to be insignificant. Not that I could actually calculate it.
Even approximately. But I'd stand behind it, no hesitation.

There's another experiment to do!

Bob

On Tue, 19 Jun 2012 20:11:34 -0400, Bob Engelhardt
wrote:

Gunner Asch wrote:

Not to mention any short duration/ high pressure Jet effect which
launches that bottle some score of yards from where the torch ignited
the contents.......hopefully..in a clear direction....

Well, with 4-5 gal of gas at 175 psig, the impulse is going to be pretty
low. And applied to a tank weighting 18(?)lbs, its resultant velocity
is going to be insignificant. Not that I could actually calculate it.
Even approximately. But I'd stand behind it, no hesitation.

There's another experiment to do!

Bob
Wear your body armour.

An "empty" gas tank, filled with water, pinned a highschool classmate
of mine up against the garage wall when he tried to braze a patch on
it. Some small amount of captured gasoline vapour ignited, blowing the
water out the filler or gas guage hole and the tank came up and nailed
him to the wall. Scared the crap out of him, because he KNEW it was
safe to weld a tank if it was full of water. Found out real quick how
much he did NOT know.

On 6/19/2012 9:59 PM, wrote:
On Tue, 19 Jun 2012 20:11:34 -0400, Bob Engelhardt
wrote:

Gunner Asch wrote:

Not to mention any short duration/ high pressure Jet effect which
launches that bottle some score of yards from where the torch ignited
the contents.......hopefully..in a clear direction....

Well, with 4-5 gal of gas at 175 psig, the impulse is going to be pretty
low. And applied to a tank weighting 18(?)lbs, its resultant velocity
is going to be insignificant. Not that I could actually calculate it.
Even approximately. But I'd stand behind it, no hesitation.

There's another experiment to do!

Bob
Wear your body armour.

An "empty" gas tank, filled with water, pinned a highschool classmate
of mine up against the garage wall when he tried to braze a patch on
it. Some small amount of captured gasoline vapour ignited, blowing the
water out the filler or gas guage hole and the tank came up and nailed
him to the wall. Scared the crap out of him, because he KNEW it was
safe to weld a tank if it was full of water. Found out real quick how
much he did NOT know.


There is what you know you know,
what you don't know you know,
what you now you don't know
and what you don't know you don't know.

That last one can be tough sometimes.