From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Any experience with Suburban gas furnaces?
Date: Sun, 13 Feb 2005 01:17:13 -0500
Message-ID: <hjqt019fk8ofu29q4c752s20dfeufjv0nh@4ax.com>

On Sun, 13 Feb 2005 04:37:45 GMT, "Rich" <nospam@att.net> wrote:


>Do you consider it a problem even if the gas tanks have been turned off for
>several weeks as theirs have?

No, of course not.

>After a few weeks without pressure on the
>lines it always has taken me a long time, with several RVs, to get the the
>gas up to the stove burners.  I always do that first.  Then try to light the
>refrigerator and furnace.
>
>I would expect it is one of those furnaces that try three times and give up
>if they do not get a flame.

This seems to be a universal "problem".  I know that my rig's system will
hold 11" for as long as I care to watch the gauge and yet the pipes are
empty when I've had the gas off for awhile.  Same with my mom's rig.  Same
with the concession stand, etc.

I've casually wondered why this happens.  Tonight I've been sitting here
thinking about the situation, factoring in the observations I've made.
Here is a theory that fits all the observations:

I think that the gas slowly diffuses through the regulator diaphragm so as
to reduce the system pressure to zero.  This probably happens over a week
or more.  Supporting evidence is that a system will slowly zero even when
all the parts are known to be leak free, that my system will hold pressure
for a very long time if I close the downstream ball valve I installed, and
that one can almost always smell a little odorant at the regulator vent
port.

That would account for the pressure drop but not the "air" (actually
"non-flammable gases if my theory is correct) in the lines.  Here's where
some careful observations and some theorizing comes into play.

It is well known that both copper and the oxides of copper are powerful
catalysts.  It is also well known that propane is a pretty decent reducing
agent because the molecule is easily disassembled by influences like heat
and catalysts.  Invariably when I open a fitting on the propane system the
inside of the pipe is always dark, much darker than the outside of the
line which has been exposed to the atmosphere.  But when I open an
aluminum fitting such as on the stove or reefer, the inside is clean metal
(oxide).

Here's my theory.  The copper and oxide on the inside of the tubing
catalyzes the breakdown of the propane molecules, probably into carbon,
hydrogen, perhaps a little methane and ????  This would account for the
darkening of the inside of the tubing by the deposition of carbon
particles.  This breakdown would cause the system pressure to drop below
atmospheric pressure which causes the vent in the regulator to admit air.

Of the several regulators I have in my junk box, all would admit air if I
plug the high pressure side and suck on the outlet.

Once there is air in the system, the catalytic action becomes a redox one.
The oxygen and propane combine to make oh, probably CO2, CO, water vapor,
probably some hydrogen and maybe some carbon.  The atmosphere in the pipe
would become oxygen and propane depleted as the propane is consumed and
more air is drawn in.  Eventually one would end up with an oxygen
deficient, non-flammable mix of nitrogen, CO2, CO, simpler hydrocarbons
(methane, etc) and probably some moisture.  It is this mix that gets
discharged before the fresh propane arrives when the system is started up
again.

Further supporting evidence is the well known fact that copper will
catalyze the breakdown of the mercaptin odorant in propane which explains
why some small leaks are odor-free.  That was written up extensively in
the trade press back when I owned a propane filling station.

Confirmation of this theory would be the sampling and analysis of the dead
gas in a long-shutdown system.  Perhaps someone with ready access to the
proper instrument will do that someday.

Knowing that this always happens, I always purge the lines via stove
burners, then crack the inlet fitting on the reefer.  The little spur line
from the header to my furnace is short enough that about one or two
ignition cycles will purge it.  I would expect that to be the case on most
rigs, once the main header is purged.

So.  There's my theory.  Maybe someone can either shoot it down or confirm
it.

John

From: John De Armond
Subject: Re: Any experience with Suburban gas furnaces?
Date: Wed, 16 Feb 2005 20:49:42 -0500
X-Source: (private mail)

On Sun, 13 Feb 2005 22:03:10 -0500, "Norman Yarvin" <yarvin@snet.net>
wrote:

>In article <hjqt019fk8ofu29q4c752s20dfeufjv0nh@4ax.com> you write:
>
>>Here's my theory.  The copper and oxide on the inside of the tubing
>>catalyzes the breakdown of the propane molecules, probably into carbon,
>>hydrogen, perhaps a little methane and ????  This would account for the
>>darkening of the inside of the tubing by the deposition of carbon
>>particles.  This breakdown would cause the system pressure to drop below
>>atmospheric pressure which causes the vent in the regulator to admit air.
>
>Just a quick comment from a theoretical perspective.  (Your practical
>knowledge on this is much greater than mine.)  I don't see how you could
>have a reaction that would reduce the number of moles of gas, which is
>what it would take to lower the pressure.  Breaking down propane into
>carbon and hydrogen would increase the number of moles of gas and thus
>the pressure.  You'd need to catalyze it into a larger molecule, not a
>smaller one, to reduce the pressure.

I've been thinking about that a lot, trying to make theory agree with what
I see in experiments.  I know, for example, that if I fill a neon tube
with propane and excite it (a common method of reducing old oxidized
mercury back to its elemental form), the pressure drops rather rapidly and
carbon is deposited.  I had always assumed that the conventional wisdom
that the propane was "consumed", eg, broken down into its elements was
correct.  Now I'm not so sure what happens in either the neon tube or the
propane tubing.

>
>But I don't think you need this step at all.  If propane diffuses out
>through the regulator diaphragm, air will diffuse in, at least after the
>pressure is gone.

The problem with that theory is that it only accounts for the missing
propane in the vicinity of the regulator.  It would take "forever" for the
propane/air exchange to take place at the far end of a dozen or more feet
of tubing.  I think that the process (my theory is catalyzed breakdown
and/or oxidation) has to be distributed.

>Now there you'd get a reduction in the number of moles of gas: each O2
>eats a C, becoming the bigger molecule CO2, and the hydrogen goes to
>water, which condenses.  So all you'd need is a little air diffusing in,
>to start this process, after which it pulls more air in.

That could be true.  It would all depend on the rates.  Such a calculation
is far beyond my ability.  Hmm, maybe I feel an experiment coming on...

John

Date: Thu, 17 Feb 2005 00:39:02 -0500
From: Norman Yarvin <yarvin@snet.net>
Subject: Re: Any experience with Suburban gas furnaces?
X-Source: (private mail)

On Wed, Feb 16, 2005 at 08:49:42PM -0500, Neon John wrote:
>On Sun, 13 Feb 2005 22:03:10 -0500, "Norman Yarvin" <yarvin@snet.net>
>wrote:
>
>>In article <hjqt019fk8ofu29q4c752s20dfeufjv0nh@4ax.com> you write:
>>
>>>Here's my theory.  The copper and oxide on the inside of the tubing
>>>catalyzes the breakdown of the propane molecules, probably into carbon,
>>>hydrogen, perhaps a little methane and ????  This would account for the
>>>darkening of the inside of the tubing by the deposition of carbon
>>>particles.  This breakdown would cause the system pressure to drop below
>>>atmospheric pressure which causes the vent in the regulator to admit air.
>>
>>Just a quick comment from a theoretical perspective.  (Your practical
>>knowledge on this is much greater than mine.)  I don't see how you could
>>have a reaction that would reduce the number of moles of gas, which is
>>what it would take to lower the pressure.  Breaking down propane into
>>carbon and hydrogen would increase the number of moles of gas and thus
>>the pressure.  You'd need to catalyze it into a larger molecule, not a
>>smaller one, to reduce the pressure.
>
>I've been thinking about that a lot, trying to make theory agree with what
>I see in experiments.  I know, for example, that if I fill a neon tube
>with propane and excite it (a common method of reducing old oxidized
>mercury back to its elemental form), the pressure drops rather rapidly and
>carbon is deposited.  I had always assumed that the conventional wisdom
>that the propane was "consumed", eg, broken down into its elements was
>correct.  Now I'm not so sure what happens in either the neon tube or the
>propane tubing.

Well, certainly the propane that reduces the mercury would have to be
consumed.  But I guess the idea is that you put in a big surplus of
propane, and the pressure drops more than the mercury would explain?

As far as which way things would go: I'm looking at a table of heats of
formation.  Propane is listed as having a heat of formation of -24.8
calories/mole.  Some others:

	Methane		-17.9
	Acetylene	54.2
	Ethylene	12.5
	n-Butane	-29.8
	Isobutane	-31.4

	HgO		-21.7
	Hg2O		-21.8

	H2O(g)		-57.8
	CO2		-94.1
	CO		-26.4

So it looks like splitting up a propane molecule into two methanes, a
carbon, and a hydrogen is energetically favored.  But this isn't helpful
as regards reducing the pressure.  Hydrogen, as a small molecule, leaks
very well.  But then one still is left with two methanes.

If you hypothesize the hydrogen leaking very well indeed, then the
reaction doesn't have to be energetically favored: with hydrogen
continually exiting, the equilibrium gets pushed away from propane or
methane, and towards carbon and hydrogen.

(With the neon tube, by the way, what do you do with the carbon once the
mercury has been reduced?  Just leave it in the tube, or is there some
way of getting it out?)

>>But I don't think you need this step at all.  If propane diffuses out
>>through the regulator diaphragm, air will diffuse in, at least after the
>>pressure is gone.
>
>The problem with that theory is that it only accounts for the missing
>propane in the vicinity of the regulator.  It would take "forever" for the
>propane/air exchange to take place at the far end of a dozen or more feet
>of tubing.  I think that the process (my theory is catalyzed breakdown
>and/or oxidation) has to be distributed.

Yeah, the idea with that was mainly to start off the following process:

>>Now there you'd get a reduction in the number of moles of gas: each O2
>>eats a C, becoming the bigger molecule CO2, and the hydrogen goes to
>>water, which condenses.  So all you'd need is a little air diffusing in,
>>to start this process, after which it pulls more air in.
>
>That could be true.  It would all depend on the rates.  Such a calculation
>is far beyond my ability.  Hmm, maybe I feel an experiment coming on...

I can calculate diffusion rates inside a tube (after looking up the
appropriate data), but chemical kinetics pretty much just have to be
measured, as do diffusion rates through a membrane.

From: John De Armond
Subject: Re: Any experience with Suburban gas furnaces?
Date: Thu, 17 Feb 2005 01:46:54 -0500
X-Source: (private mail)

On Thu, 17 Feb 2005 00:39:02 -0500, Norman Yarvin <yarvin@snet.net> wrote:


>>I've been thinking about that a lot, trying to make theory agree with what
>>I see in experiments.  I know, for example, that if I fill a neon tube
>>with propane and excite it (a common method of reducing old oxidized
>>mercury back to its elemental form), the pressure drops rather rapidly and
>>carbon is deposited.  I had always assumed that the conventional wisdom
>>that the propane was "consumed", eg, broken down into its elements was
>>correct.  Now I'm not so sure what happens in either the neon tube or the
>>propane tubing.
>
>Well, certainly the propane that reduces the mercury would have to be
>consumed.  But I guess the idea is that you put in a big surplus of
>propane, and the pressure drops more than the mercury would explain?

Yes.


>So it looks like splitting up a propane molecule into two methanes, a
>carbon, and a hydrogen is energetically favored.  But this isn't helpful
>as regards reducing the pressure.  Hydrogen, as a small molecule, leaks
>very well.  But then one still is left with two methanes.
>
>If you hypothesize the hydrogen leaking very well indeed, then the
>reaction doesn't have to be energetically favored: with hydrogen
>continually exiting, the equilibrium gets pushed away from propane or
>methane, and towards carbon and hydrogen.

That could be.  My chemistry is much too rusty to pursue this much.

>
>(With the neon tube, by the way, what do you do with the carbon once the
>mercury has been reduced?  Just leave it in the tube, or is there some
>way of getting it out?)

After the tube is mercury-cleared, it is processed normally.  That is,
about 2 Torr abs of air is inserted and then a high current (1 amp or
more) discharge initiated.  The plasma cleaning is something to see.  Any
carbon is instantly oxidized.  I've had cases where some sort of critter
got in a tube and left a dark spot when heated for bending.  That spot
just evaporates under bombardment.

I use the propane technique to clear old tubes after repair in preparation
for bombarding.  If the mercury remains it will stain the phosphor plus it
will interfere with bombarding.  The ionization potential of Hg is so low
that the tube will not heat up, even with a couple of amps flowing through
it.

BTW, the transformer that supplies the high voltage for bombarding is a
20kva pole pig run in reverse - 240 in, 15kv out.  Makes for one hell of a
Jacob's Ladder :-)

John